Extrasolar Planets The Search for the Extrasolar Planets: A Brief History of the Search, the Findings and theFuture Implications Table of Contents PREFACE SECTION 1: INTRODUCTION SECTION 2: BARNARD'S STAR AND VAN DE KAMP'SPLANETS: THE BEGINNING SECTION 3: A GENERAL DESCRIPTION OF THEEXTRASOLAR PLANETARY WORK RECENTLY IN PROGRESS BETA PICTORIS CM-DRACONIS 16 CYGNI B EPSILON ERIDANI GAMMA CEPHEI HD3346 HD 114762 LALANDE 21185 PEG 51 POSSIBLE PLANETARY BODIES AROUND PULSARS PSR0329+54 PSR1257+12 PSR1620-26 PSR1829-10 RHO 1 CANCERI RHO CORONAE BOREALIS TAU BOOTIS T-TAURI STARS UPSILON ANDROMEDAE 47 URSAE MAJORIS 70 VIRGINIS SECTION 4: FUTURE CONSIDERATIONS SECTION 5: CONCLUSIONS APPENDIX PREFACE This web page is an attempt to provide a review of humankind's quest for the discoveryof planets outside our Solar System. In addition, a series of major web sites dealing with thesearch for extrasolar planets are listed. They are as follows: Discoveryof Extrasolar Planets Extrasolar Planetary Systems Exoplanets The Extrasolar Planets Encyclopedia New Planets Known PlanetarySystems Other SolarSystems Other Worlds, Distant StarsIn addition to the above sites, NASA's OriginsProgram is attempting to answer an important question (among others), Are there worldslike the Earth around nearby stars? If so, are they habitable, and is life as we know it presentthere? SECTION 1: INTRODUCTION Our solar system exists. This is an irrefutablefact. Because of our solar systems existence, the question that begets itself time and time again iswhether or not planets exist around stars other than our own. Based on the size of our universeand the laws of probability, the odds are excellent that our solarsystem is not unique in the universe. To better appreciate the odds, it is useful to consider thesize of the universe .At the present time it is estimated that 50 billion galaxies , the largest of which containthousands of billions of stars, are visible to modern telescopes including theHubble Space Telescope . (1) . Thenotion of planetary worlds orbiting stars other than our Sun is not new. Throughout history,beginning with the Greeks, humans have been pondering over the possibility of other solarsystems beyond our own. From mere speculation to the astronomical amassing of data, as in thecase of Barnard's Star, and others, our speculations and searches for these extrasolar planets have spanned well over 2,000 years. Although it is beyond the scope of this paper to provide achronology of all these speculations, an excellent book published in 1996 provides thebackground for this interesting history. (2) In order to determine the existence of extrasolar planets it is important to consider one minor and one major premise. The minor premise, and to alarge degree a philosophical one, is to consider the existence of additional solar systems based onthe probability factor. As stated above, with the number of galaxies and the number of starscontained within each of the galaxies, the probability of another solar system existing is excellent. The speculation based on probabilities is not new. Two very important books on the search forextraterrestrial life, written in the 1960's attest to this thesis. "With 10 to the 11th stars in our galaxy and 10 to the 9th other galaxies, there are at least 10to the 20th stars in the universe. Most of them may be accompanied by solar systems. If thereare 10 to the 20th solar systems in the universe, and the universe is 10 to the 10th years old -- andif, further, solar systems have formed roughly uniformly in time -- then one solar system is formedevery 10 to the negative 10 yr = 3 x 10 to the negative 3 seconds. On the average, a million solarsystems are formed in the universe each hour." (3) "The implication is that solar systems are common, but the argument will be greatlystrengthened if there is real agreement on how our solar system came about. The spaceexploration of the next decade should enable us to narrow down the theories to a great extent. We will have samples of the Moon and direct knowledge as to the nature of its interior. We willlearn the precise compositions of other planets and their atmospheres to compare with those ofour Earth. However, study of our own solar system is not the only way to learn if it is unique. Another approach is to search for clues among the other stars of our galaxy. Such observations,carried out originally without reference to the question of whether or not there are planetselsewhere, led to surprising discoveries..." (4) The first of these quotes can be found in a monograph co-authored by Carl Sagan who needs nointroduction, while the second was quoted by Walter Sullivan, who at that time was ScienceEditor of The New York Times . These two monographs, although concentrating onthe possibilities of intelligent life, needed to make a strong statement regarding the probability ofthe existence of extrasolar planets. If indeed the probability of intelligent life is a strongpossibility, then the existence of extrasolar planets is a definite. On the other hand, the major premise, and certainly the most important, is to ascertain theexistence of extrasolar planets by direct astronomical observations. Speculation is easy, scientificendeavors are not. During the past several years the astronomical techniques used forobservations have become more and more sophisticated leading to precise indirect methods ofdetecting planetary bodies orbiting stars other than our Sun. Although the evidence is compellingfor the existence of extrasolar bodies, there has been no direct observation of an extrasolar planet;i.e., a viewing of a planetary body via a telescope and/or a photograph. A number of theseastronomical techniques are discussed in Section 2 and 3 of this paper. It is, therefore, the purpose of this paper to consider a brief history on the work that has beendone on planetary bodies outside of our solar system during the past decade or so, beginning withthe controversy surrounding the search for companions around Barnard's Star. New astronomicalmethodologies and future programs and missions will also be considered. Because the discoveriesand/or confirmations of said planets have been ascertained within the last several years, the mainthrust of this writing will be confined to information accrued during the 1990's. 1. Gribbin, John. Companion to the Cosmos . London: Weidenfed & Nicolson, 1996. Pgs. 156-157. 2. Anonymous. Book Review: Mammana, Dennis L., and Donald W. McCarthy, Jr. OtherSuns. Other Worlds?: The Search for Extrasolar Planetary Systems . New York: St.Martin's Press, 1996. 225p. Astronomy 24(11):100, November 1996. 3. Shklovskii, I.S. and Carl Sagan. Intelligent Life in the Universe . New York: DellPublishing, 1966. 509p. Pg. 130. 4. Sullivan, Walter. We Are Not Alone: The Search for Intelligent Life on Other Worlds. New York: McGraw-Hill, 1964. 325p. Pg. 43. SECTION 2: BARNARD'S STAR AND VAN DE KAMP'S PLANETS: THEBEGINNING In the September 15, 1916 issue of The Astronomical Journal (1) and the September 7, 1916 issue of Nature , (2) an articleappeared that dealt with the discovery of a rather small, insignificant star that demonstrated alarge proper motion. The purpose of the article was to alert the astronomical world that indeed,E.E. Barnard detected a unique find, that is a star with a proper motion larger than any star thathad been studied previously. The large proper motion was calculated by Barnard to beapproximately 10.3 arcseconds per year. (3) The proper motion is definedas "the apparent angular motion per year of a star on the celestial sphere, i.e., in a directionperpendicular to the line of sight" . (4) Proper motion is attributed to two basic premises; the star can move of its own accord and the star's galaxycan also move. Because of the vast distances between us and stars, the stars appear to be glued inthe night sky and that the only apparent movement of stars that we see is due to the rotation ofthe Earth about its axis. If you look at a constellation, such as Orion this year, you will note thatit will look exactly the same next year, and the year after that, and so on. It takes thousands ofyears to see that the stars have moved by seeing a change in the position of the stars with respectto one another. For example, the stars in the Big Dipper did not have the same positions 2,000years ago, and hence, did not look like the Big Dipper. Because of the large proper motion of Barnard's Star, astronomers felt the need to determineadditional information regarding this amazing star. It was found to be a red dwarf, and itsdistance from the Earth to be 1.82 parsecs (5.95 light years); practically a next door neighbor inastronomical terms. Not only was the distance determined but the star was found to be movingcloser to us. By 11,800 AD it will be as close as 1.16 parsecs (3.8 light years) from us. (5) Because Barnard's Star is a red dwarf (common in our galaxy), its closeproximity to us, and its large proper motion, this star was a prime candidate for further studyregarding the search for extrasolar planets. It should be noted, however, that it was the largeproper motion of the star that encouraged astronomers to determine its other physical parameters.Before the story of Barnard's Star continues it would be best to consider a few astronomicalterms that will play a large role in the supposed confirmation of planets revolving around the star. These terms are astrometry and perturbation. Astrometry is that part of astronomy that measures the proper motion ofstars as a function of time. In the case of Barnard's Star, photographic plates were examined overmany decades in order to determine its motion. Perturbation, on the other hand, is a way ofdescribing any abnormalities in the stars motion. Does the star move in a straight line or does itexhibit some wobble (or sinusoidal) motion? If so, this wobble could be explained bygravitational forces between the star and an unseen body or bodies revolving around the star.With the above in mind, the story of this star continues with the photographic plates of Peter vande Kamp. Working at theSproul Observatory of Swarthmore College, van de Kamp devoted most of his life over2,000 plates of Barnard's Star that he and his students had taken from 1938 through 1962. According to van de Kamp, a wobble in the movement of Barnard's Star was detected which hedetermined was the result of a body revolving around the star. The body, according to van deKamp, was 1.6 times the mass of Jupiter and that its rate of revolution was 24 years. He alsosuggested that the orbit was elongated. (6) Over the years Peter van de Kamp published a series of papers refining his initial results of thecompanion planet revolving around Barnard's Star. In the March 1969 issue of the Astronomical Journal (7) he reconsidered a number of physicalparameters regarding the companion. From photographic plates from 1916-1919 and a largenumber of plates from 1938-1967 he determined that the planet (van de Kamp sometimes referredto it as "his" planet) revolved around Barnard's Star every 25 years and that it was extremelylarge, i.e., 1.7 times the mass of Jupiter. In August of the same year another article was publishedby van de Kamp in the Astronomical Journal (8) stating thatwhile reconsidering the photographic plates in his possession, there were not one but two planetsrevolving around Barnard's Star. Not only were there two planets but instead of an elongatedorbit, the orbits of both companions were found to be circular. In addition, by reconsidering hiscalculations, he ascertained that one of the planets revolved around the star every 26 years whilethe other 12 years. Likewise, the previous mass he had given the first companion at 1.7 times themass of Jupiter was incorrect. At this point in time the companions seemed to have masses 1.1and 0.8 the mass of Jupiter. In 1975, van de Kamp published yet another article (9) analyzing astrometric data from 1950 to 1974. According to this paperthe masses of the two planets were determined to be 0.4 Jupiter masses and 1.0 Jupiter masses. In addition, the number of years that the planets revolved around the star were recalculated to 22years and 11.5 years. The 0.4 Jovian mass planet was determined to be the body that revolvedaround the Star every 22 years while the 1.0 Jovian mass planet was thought to revolve aroundBarnard's Star every 11.5 years.However, van de Kamp did not stop there. He continued to amass more photographic plates onBarnard's Star. In 1982, with measurements of photographic plates from 1938 through 1981, hepublished yet another paper with slightly different results of the planetary companions that hadbeen published previously. In his 1982 paper (10) , he reconfirmed thefact that both orbits were circular. However, he reconsidered their periods of revolution aroundBarnard's Star as well as the planets' masses. In re-examining his data, he reconciled the planetsrevolutions around the star to be 12 and 20 years with masses of 0.7 and 0.5 the size of Jupiter. According to van de Kamp the reason for the changes in the physical parameters of the twoplanets had to do in part with the reference stars he was using when examining the photographicplates. In additon, he now had more years of photographic plates to work with than what he hadwhen publishing his earlier papers.While van de Kamp was honing his measurements on the two companions revolving aroundBarnard's Star, a few papers in 1973 were published that questioned his claims either directly orindirectly. Astrometrists Gatewood and Eichhorn (11) examinedphotographic plates taken with a 20-inch refractor at the Van Vleck Observatory located at Wesleyan University and the 30-inch Thaw refractor of the Allegheny Observatory inPittsburg. They were unable to detect any wobble in the proper motion of Barnard's Star. Inshort, if there was no wobble, then no planetary companions existed. In the same year, John L.Hershey, while working at the Sproul Observatory (12) , analyzed thesame photographic plates as van de Kamp. He made a systematic study of not only Barnard's Starbut a number of other stars found on the plates. A total of twelve stars were considered in thestudy. It should be noted that these plates were a result of the use of the telescope at the SproulObservatory. To Hershey's amazement, not only did he detect a wobble in the proper motion ofBarnard's Star, but wobbles in all the stars compiled in the study. A number of inferences couldbe made with these results. One possibility is that all the stars had planetary companions, or onthe other hand, there were problems with the Sproul telescope that had been used to photographthe stars in question. Indeed, if it were the latter case, then van de Kamp, who based hisconclusions on the photographs was using incorrect data, as was Hershey. It was found that thereseemed to be a large discrepancy in the results of star movement on the plates in 1949 through1956 and then again in 1957. In 1949 a new cell for the 24 inch lens was installed and in 1957 theobjective lens was adjusted. (13) Could the readjustment of thetelescope be the reason for the big jump in star positions?Years later, Robert Harrington, using a 61-inch reflector of the United StatesObservatory at Flagstaff, compiled over 400 plates of Barnard's Star. Unfortunately, instudying these plates Harrington could not detect a wobble. Laurence Fredrick, working with a26-inch refractor at the McCormickObservatory of the University of Virginia, also recorded no detectable wobble. NeitherHarrington or Fredrick are willing to toally discount the existence of planetary bodies, but on theother hand, are extremely pessimistic. (14) Harrington, however, is quickto add that in 1977 there was some wobble detected in the North-South direction. 15 In 1985, a few years after van de Kamp published his definitiveand last paper on the subject 10 , a Govert Schilling from Utrecht, TheNetherlands 16 published the account of an interview with van de Kamp. In essence van de Kamp admonished his critics by stating this his study of Barnard's Star waslonger (over 40 years), the number of photographic plates he studied was larger (tens ofthousands of plates), he did everything he could to eliminate errors, and yes, he is still under theopinion from his observations that there are indeed two planetary companions revolving aroundBarnard's Star and that the masses of these planets are 0.7 and 0.5 times Jupiter's mass. To hiscritics van de Kamp suggests that they (present researchers) spend the same amount of time withthe same amount of plates and then, after that, he (van de Kamp) would be happy to talk withthem. (Peter van de Kamp died in 1995. I do not know whether he and his critics ever gottogether to discuss his life's work.)As a footnote to the above account, it should be noted that Gatewood, using astronometrictechniques is trying to ascertain what planetary bodies would be most unlikely to be revolvingaround Barnard's Star. In a 1995 paper Gatewood suggested that brown dwarfs (more massivethan Jupiter by greater than 10 masses, but not massive enough to glow as a star) could not existaround Barnard's Star. In addition, he feels that planets having a mass smaller than Jupiter's maypossibly be present. 17 Although work on Barnard's Star has spanned well over a half century, the jury still seems to beout. No definitive confirmation by the astronomical community as a whole has been established. Only time will tell as to whether a planetary body or bodies orbit Barnard's Star as suggested byvan de Kamp. 1. Barnard, E.E. "A small star with large proper-motion." The Astronomical Journal 24(3):181, September 15, 1916. 2. Barnard, E.E. "Faint star with large proper motion." Nature 98:22, September 7,1916. 3. Croswell, Ken. "Does Barnard's Star have planets." Astronomy 16(3):6-17, March1988. Pg. 13. 4. Illingworth, Valerie, Ed. The Facts on File Dictionary of Astronomy , 3rd ed. NewYork: Facts on File, Inc., 1994. Pg. 354. 5. Harrington, Robert S. "Barnard's Star: A status report on an intriguing neighbor." Mercury 16:77-79 & 87, May/June 1987. Pg. 77. 6. Croswell, Ken. "Does Barnard's Star have planets." Astronomy 16(3):6-17, March1988. Pg. 13. 7. van de Kamp, P. "Parallax, proper motion acceleration, and orbital motion of Barnard's Star." Astronomical Journal 74(2):238-240, March 1969. 8. van de Kamp, P. "Alternate dynamical analysis of Barnard's Star." Astronomical Journal 74(6):757-9, August 1969. 9. van de Kamp, P. "Astrometric study of Barnard's Star from plates taken with the Sproul61-cm refractor." Astronomical Journal 80(8):658-61, August 1975. 10. van de Kamp, P. "The planetary system of Barnard's Star." Vistas in Astronomy 26:141-157, 1982. 11. Gatewood, George, and Heinrich Eichhorn. "An unsuccessful search for a planetarycompanion of Barnard's Star (BD + 4 degree3561)." Astronomical Journal 78(8):769-776, October 1973. 12. Hershey, John L. "Astrometric analysis of the field of AC +65degrees6955 from plates takenwith the Sproul 24-inch refractor." Astronomical Journal 78(5):421-425, June 1973. 13. Croswell, Ken. "Does Barnard's Star have Planets." Astronomy 16(3):6-17, March1988. Pgs. 15-17. 14. Ibid 15. Ibid 16. Schilling. Govert. "Peter van de Kamp and his "lovely Barnard's Star"." Astronomy 13:26 & 28, December 1985. 17. Gatewood, George D. "A study of the astrometric motion of Barnard's Star." Astrophysics and Space Science 223(1-2):91-101, 1995. SECTION 3: A GENERAL DESCRIPTION OF THE EXTRASOLAR PLANETARYWORK RECENTLY IN PROGRESS Within the last several years a great deal of study has been focused on the search for extrasolar planets, with a number of confirmations. The basic techniques, according to J. Schneider,used in the search for extrasolar worlds are astrometric detection , direct imaging , radial velocity, ground based photometry, andoccultation. (1) Of the various techniques used in determining the existenceof a planetary body, the measurement of the radial velocity of a star, using doppler shiftmethods , has been used to a greater degree than any of the aforementioned. This can readilybe seen in examining the Appendix, which can be found at the end of this paper. It may beinteresting to note that Bruce T.E. Campbell has developed a rather sensitive technique formeasuring velocity perturbations using doppler shifts. He compares the spectrum of stars byusing a reference spectrum involving hydrogen fluoride. (2) Astrometry, which was mentioned in Section 2, is used to determine theproper motion of a star, using other stars as reference points. If a body is revolving around a star then thebody will affect the circular motion of the star. As one measures the stars linear motion, it will befound that the motion is not in a straight line, but rather in a wobbly line due to the presence of aplanet or planets revolving around the star. This situation is similar to observing a personspinning a shotput around his or her body. The person shows a wobbling type motion due to theheavy load that is being rotated about his or her body. The person represents the star while theshotput represents a planet. In addition, the person can move from point A to point B while theshotput is revolving. Therefore, there are two motions, the wobbly motion caused by the rotationof the shotput, and the linear motion caused by the movement of the person. (3)If the person was not rotating a shotput and simply walking, then the only motion observedwould be the distance from point A to point B, and no wobble in the motion would occur. This,of course, presupposes that the person is sober. In like manner, if one were to observe the propermotion of a star without any planets revolving about it, then the distance the star moves frompoint A to point B would not reflect a wobbling motion, the motion would be in a straight line.Radial velocity, which is measured by the doppler effect (lines in the stars spectrum) takes intoaccount the line-of-sight velocity; i.e. the velocity of which a star is moving towards or away fromus. If the light from the star is moving towards us then the spectrum of the star will be shifted tothe blue portion of the spectrum (blueshift) and the velocity would be negative. If, on the otherhand, the star is moving away from us then the spectrum of the star will be shifted to the redportion of the spectrum (redshift) and the velocity will be positive. By observing the spectral shiftone can determine the rate at which the star is moving.How does this relate to the detection of planetary bodies revolving around stars? If a planet orplanets revolve around a star then the motion of the star will be affected. According to AlanBoss, writing in Physics Today (4) , if a star is orbitingaround the center mass of a system, then it suggests a planetary body or bodies revolving about it. More to the point, if the above is true then there would be a periodic shift in the doppler velocity. This is the star's spectrum would exhibit a shift to the red and then to the blue, and then to thered, periodically. In other words, the effect of planetary bodies around a star will affect the radialvelocity of the star so that it would be moving towards us and then away from us, and continue torepeat that pattern. It should be noted that the perturbation or doppler velocity shift is very small,and therefore, extremely difficult to detect.Many of the ensuing discoveries rely heavily upon radial velocity techniques. Highly specializedspectrographs, that can detect tiny doppler-induced wavelength shifts in a star's spectra are usedto calculate the radial velocities. However, it will be of no surprise to note that the planets thatwere discovered using this technique are large and/or are in tight orbits, because this techniquedisposes itself to that type of finding. (5) The direct imaging method is based on the fact that planets reflect the stars' light. Planets do notgive off any light of their own. For example, the various planets we see in the night sky are aresult of the sun's light reflecting from them. Likewise, planets around other suns would alsoreflect the light of their suns. This method is used in order to determine reflected light from anextrasolar planet. It is obvious that only extremely large planets may be detected using thismethod. The major problem with this technique is that the star is much brighter than the planet itilluminates, and can tend to obfuscate it. (6) Photometry can be used to detect a change in the brightness of a star, as in the case when a planetoccults a star. On Earth we can observe this during a solar eclipse. That is, our Earth occults ourSun during an eclipse. As an extrasolar planet revolves about its star, it will pass between its starand the line of sight as seen from the Earth. A change in the brightness of the star due to thistransit would then suggest a planetary body. (7) What follows is a series of reports that deal with the history and ongoing research in the searchfor extrasolar planets. These reports are not to suggest that every researched star listed haveplanets orbiting them. Many of the planetary bodies detected by astronomers and theirco-workers have not been confirmed or established as fact in the astronomical community atlarge.For the sake of clarity, the following section is arranged alphabetically by the name of the star inquestion. At the present time no specific names have been given to the planetary bodies. However, some of the newly discovered planets are named after the name of the star, and are setapart from the star name by an additional letter. For example, one of the stars in question is Peg51. The planetary companion discovered around it has been labeled Peg 51 B.In addition to the ensuing reports, the Appendix, which can be found at the end of this paper,provides in tabular format a summary of the physical parameters of the stars and their supposedplanetary bodies. If more than one planetary body has been detected, then the star, in a number ofcases, is listed as many times as there are companions, with the planet closest to its star listed first. From this table it is clear that many of the findings have not yet been confirmed. In fact, in a fewcases retractions were made by the researcher. On further examination of the Appendix it is alsoclear that the majority of detected planets are of Jupiter mass or larger, most have circular orbits, most have been detected by radial velocity measurements using doppler shifts, the majority ofthem are less than 1 astronomical unit from their star, and except for the pulsars, the majority ofthe planets discovered are orbiting stars that are similiar to our Sun.1. Schneider, Jean and Laurance R. Doyle. "Ground-Based detection of terrestrial extrasolarplanets by photometry: the case for CM Draconis." Earth, Moon and Planets 71(1-2):153-173, 1995. Pg 154-155.2. Black, D.C. "Worlds around other stars." Scientific American264(1):76-82, January, 1991. Pg. 79.3. NOVA: Hunt for Alien Worlds . Presented on PBS (Channel 8):8:00 PM -9:00 PM, February 16, 1997.4. Boss, Alan P. "Extrasolar planets." Physics Today 49(9):32-8, 1996. Pg.33.5. MacRobert, Alan M., and Joshua Roth. "The planet of 51 Pegasi." Sky andTelescope 91(1):38-40, January 1996.6. Black, D.C. "Worlds around other stars." Scientific American264(1):76-82, January 1991. Pg. 78.7. Schneider, Jean and Laurance R. Doyle. "Ground-based detection of terrestrial extrasolarplanets by photometry: the case for CM Draconis." Earth, Moon and Planets 71:153-173, 1995. Pg. 155. BETA PICTORIS Beta Pictoris is a starbelonging to A5V spectral class, it has a visual magnitude of 3.85, and is approximately 17.17parsecs (58.68 light years) from Earth. In addition, it has a dust ring revolving about it. The dust ring, according to Fridman and Gor'kavyi has a radius of 100 to 500 astronomical units. (1) However, Roques, et al, report (2) that, in 1987,Smith and Terrile used coronographic images to find that the radius of the disk measures over1,000 AU's. Smith and Terrile (3) actually suggest that the disc extendsmore than 1,100 AU's from the star. They go on to say that after examining over 100 nearbystars, no other circumstellar disk is comparable in visible optical properties as those of Beta Pictoris. In anyevent, the presence of a dust ring around the star and the observations of absorption spectra ofcomets revolving around the star are leading astronomers to conclude that a planetary body existsaround Beta Pictoris.In so far as the dust ring is concerned, researchers have observed a void in the dust ring; i.e., adepletion of dust. This finding encourages the idea is that a planet is making a path in the dust asit orbits the star. Levison and his team suggest that this void in the ring is between 10 and 30astronomical units from Beta Pictoris, and further suggest that not one but two planets arecausing the dust depletion zone. (4) Levison is not the only researcher to suggest that a planet is revolving around Beta Pictoris. Writing in Icarus , Roques (5) and Lazzaro (6) present evidence that suggests that the planetary body hypothesis holdstrue. Their premise is based on numerical, and analytical hypothetical models, respectively. Theysuggest that the planet is 20 astronomical units from Beta Pictoris, has an orbital eccentricity of0.01; a nearly circular orbit, and a mass five times that of the Earth. In addition to the modelscreated by Roques and Lazzaro, other researchers (7) present a modelbased on an analysis of physical processes that occur in disks. According to the model, theastronomers are confident that indeed a planet can create the type of path that has been suggestedin the disk (dust void). As they state, "Now, we can confirm that, in spite of the collisionaldestruction process, a planet can effectively create asymmetry of about 10 or 20% in the dust diskof B Pictoris." (8) As with the dust disk models, the comet evidence is compelling. Because of the short-livedabsorptions that have been found while monitoring Beta Pictoris, scientists conclude that theymay be caused by comets revolving in eccentric orbits around the star. Based on a model usingour own Solar System, they feel that the comets orbits may be due to the presence of two ormore planets revolving around Beta-Pictoris. (9) It should be noted, however, that although both the dust disk model and the short-livedabsorption spectra of the star are compelling evidence of a planet or planets revolving aboutBeta-Pictoris, the existence of said planets have not been confirmed. 1. Fridman, A.M. and N.N. Gor'Kavyi. "On the possibility of detection of massive planets inprotoplanetary disks." Astronomical and Astrophysical Transactions 5(3):249-51, 1994. 2. Roques, Francois, et al. "Is there a planet around beta Pictoris? Perturbations of a planet on acircumstellar dust disk. 1. The numerical model." Icarus 108(1):37-58,1994. Pg. 38. 3. Smith, B.A. and R.J. Terrile. "The Beta Pictoris disk: recent optical observations." Bulletin of the American Astronomical Society . 19(3):829, 1987. 4. Anonymous. Sky and Telescope 89(2):10-11, February 1995. 5. Roques, Francois, et al. "Is there a planet around beta Pictoris? Perturbations of a planet on acircumstellar dust disk. 1. The numerical model." Icarus 108(1):37-58,March 1994. 6. Lazzaro, D., et al. "Is there a planet around beta Pictoris? Perturbations of a planet on acircumstellar dust disk. 2. The analytical model." Icarus 108(1):59-80,March 1994. 7. Lecavelier des Etangs, A., et al. "Perturbations of a planet on the B Pictoris circumstellar dustdisk. 3. Time scale of collisional destruction versus resonance time scale." Icarus 123(1):168-179, September 1, 1996. 8. Ibid Pg. 178. 9. Anonymous. "More evidence for extrasolar planets." Sky and Telescope 89(2):10-11, February 1995. CM-DRACONIS Although no planetary bodies have been detected orbiting CM-Draconis , it is worthconsidering, because of the research program focused on this star and the use of the astronomicaltechnique known as occultation. At the present time very few star systems that are being studiedmake use of photometry in order to detect occultations. In short, Doyle (1) and Schneider (2) feel that because this star is a small eclipsing binary , not only willthey be able to ascertain the existence of terrestrial planets, but Jupiter-mass planets as well. Bystudying CM Draconis, which is a small eclipsing binary, the use of photometry can be improved. Inessence, the researchers feel that it will be easy to detect an occultation of the two stars by aplanetary body, whether that body is small or large. When a body orbiting the star passes in frontof it in relation to our line of sight there will be a change in the brightness of the star. Becausethere are two stars it is felt that the other star will also be occulted by a planet, thereby exhibitinga change in brightness as well. Because these two stars are very close to one another (about 15.4CM Draconis radii) one occultation should follow the other, therefore suggesting some type ofplanetary orb.According to Schneider and Doyle, using photometric techniques should allow one to detect largeJupiter-mass planets as well as those that are similiar in size to the Earth. "Terrestrial-sized(Earth-Neptune-radii) extrasolar planets may be detectable in the CM Draconis system and severalothers using a ground-based network of 1-meter-class telescopes performing CCD photometryover several months. The small size of the system, and the orbital plane being edge-on, enhanceboth the probability as well as the sensitivity of detection." (3) Thesedetections are based on the transits of short-period planets. This work is currently in progress. No planets have been detected as of this writing. 1. Doyle, Laurance R., et al. "Ground-based detectability of terrestrial and Jovian extrasolarplanets: Observations of CM Draconis at Lick Observatory." Journal of GeophysicalResearch 101(No. E6):14823-14829, June 25, 1996. 2. Schneider, Jean, and Laurance R. Doyle. "Ground-based detection of terrestrial extrasolarplanets by photometry: The case for CM Draconis." Earth, Moon and Planets 71(1-2):153-173, 1995. 3. Ibid Pg. 170. 16 CYGNI B 16 Cygni B isone of two stars in a wide binary system, which is known as 16 Cygni AB. Because the planetdetected has been found orbiting 16 Cygni B, the thrust of this report will be concentrated on thisstar.By means of radial velocity observations, researchers suggest that a planet orbits around the star16 Cygni B, a star similiar to our Sun. According to measurements by Cochran and others (1) the planet revolves around the starevery 800.8 days, with a velocity amplitude of 43.9 m/s, and an extremely large eccentricity of0.63. It is felt that this is the largest eccentricity of any of the extrasolar planets discovered up tothis point in time.According to Mazeh and others (2) , the reason for the high eccentricity isdue to the binary system, Cygni AB. They suggest that the distance between the two stars isapproximately 1,100 AU. By means of numerical simulations they feel that at one time the planetin question had a small eccentricity of about 0.15, and that over a ten million year period theeccentricity changed due to the tidal forces of 16 Cygni A. They also go on to state that in aprivate communication with Marcy it is possible that other stars mentioned in this reportare also part of a wide binary system. These stars are Rho 1 Canceri, Upsilon Andromedae,and Tau Bootis. The planets detected orbiting these stars, however, show a low eccentricity, which the researchersfeel is due to a small orbital period, unlike the orbital period of the planet orbiting 16 Cygni B.In addition, Cochran and his colleagues further suggest that the planet's mass is about five timesthe mass of Jupiter. Astronomers feel that this planet could, indeed, be an extremely low massbrown dwarf. (1) The planet liesapproximately 1.8 AU from 16 Cygni B. (3) 1. Cochran, W.D., et al. Astrophysical Journal (in press ). 2. Mazeh, Tsevi, Yuval Krymolowski, and Gady Rosenfeld. "The high eccentricity of the planetorbiting 16 Cygni B." Astrophysical Journal 477(2, Pt. 2):L103-L106, March10, 1997.3. Extrasolar Planet Search (3) EPSILON ERIDANI (HD22049)Epsilon Eridani is considered to be a star very similiar to our sun. It is a main dwarf sequence starwith a temperature of approximately 5,000 K. It has been found to be 3.23 parsecs (10.7 lightyears) from the Earth. Van de Kamp uncovered information that indicates a wobble in the star'sproper motion. Because of its similarity to our sun, its close proximity to us, and the strometricinformation compiled by van de Kamp, this star has been examined for possible planetary bodies.Based on the research, two speculative conclusions arise. One is that Epsilon Eridani'scompanion is nothing more than a dwarf star making this a binary star system. The other train ofthought is that based on astrometric measurements, radial velocity measurements, and theexistence of a dust cloud, a planetary body exists. This planetary body has been calculated tohave a mass twice that of Jupiter, an orbital period of approximately 5 years, and a distance of 5AU from Epsilon Eridani. (1) At the present time no definitive conclusionscan be drawn as to whether there is indeed a planet revolving around this star.1. Lawton, A.T., and P. Wright. "The search for companions to epsilon Eridani."Journal of the British Interplanetary Society . 43(2):556-8, December, 1990.GAMMA CEPHEIThe possibility of a planet orbiting this star is rather speculative, unconfirmed, and probably isnon-existent. In fact, the original team that suggested a planet recanted their findings in 1992. Since that retraction no information has been forthcoming. Gamma Cephei, a star having adiameter of six times that of our Sun, and producing a brightness equivalent to 11.5 times that ofour Sun, has been studied for the possibility of a companion using radial velocity measurements. It lies approximately 15.4 parsecs (51 light years) from our Solar System. Lawton and Wright,citing Campbell, Walker and Yang's brief discussion in Astrophysics of Brown Dwarfs, 1986 state that Campbell and associates feel they have discovered a planet orbitingGamma Cephei with a mass of 1.5 to 2.0 times the mass of Jupiter lying at a distance from the starat approximately 4.5-5.0 astronomical units; similiar to Jupiters distance from our Sun. (1) In 1992, Walker and his colleagues (2) retractedtheir previous statement. After 11 years of radial velocity measurements, they conclude that whatthey were describing previously was the star's period of rotation.1. Lawton, A.T., and P. Wright. "A planetary system for Gamma Cephei?" Journal ofthe British Interplanetary Society 47(7):335-336, July 1, 1989.2. Walker, G.A.H., et al. "Gamma Cephei: rotation or planetary companion?" Astrophysical Journal 396(2, Pt. 2):L91-4, September 10, 1992. HD3346 (HR152) In 1996, Noyes, et al. (1) discussed the possibility of two planets revolvingabout HD3346. Their evidence was based on short-term radial velocity variations. Whenmeasuring the radial velocity of the star they noted that the velocity variations were larger thanwould be expected. They attributed these large variations to the possibility of two planetarybodies revolving about the star. They further suggest that the masses of the two planets areapproximately sixty times the mass of Jupiter and approximately ten times Jupiter's massrespectively.1. Noyes, R., et al. "HD 3346." International Astronomical Union Circular . Issue 6316, February 16, 1996:1p. HD 114762 This star, found inComa Bernices, is approximately 27.27 parsecs (90 light years) from Earth. Because of periodicvariations in its proper motion, this star has become yet another candidate for the existence of aplanetary body or bodies revolving about it. (1) In the early 1990's two papers were published discussing research on this star and its possiblecompanion. The first of these was involved in the search for eclipses of the star caused by acompanion, while the second paper concentrated on radial velocity measurements.Robinson and his colleagues (2) , who worked on the eclipse problem, felt itwas necessary to tabulate eclipse information in order to ascertain the inclination of the stars orbitto the line of sight. The inclination needed to be ascertained in order to identify the companion. The researchers go on to speculate that if the inclination of the orbit is head on from our line ofsight then they may be dealing with a companion with a size greater than the mass of thirteenJupiters. Based on the above speculation the companion could be a brown dwarf or another star. Their research on the eclipse suggests that because the inclination of the orbit was found to be 89degrees (an inclination far from 90 degrees is needed), their results on the mass of the companionis inconclusive. On the other hand, they do feel that using the occultation method is a way ofdetermining information about a companion, whether it be a star or a planet.Cochran and his colleagues (3) on the other hand provided research resultsusing high-precision radial velocity. Again the results of their research are inconclusive, becausethey cannot ascertain whether the companion is a star or a planet. According to Cochran and hisgroup "the determination of the mass of the companion object thus depends on two quantitieswhich remain unknown: the stellar equatorial velocity and the relative orientation of the orbitalaxis and the rotational axis". (4) They feel that it is imperative tocontinue to study the star in order to ascertain the star's radial velocity.In 1995, Alan Hale writing in Publications of the Astronomical Society of the Pacific (5) , continued the study of the star based on the previous resultsof the early 1990 papers discussed above. Based on measurements taken from spectra at Kitt Peak , it was found that the equatorialinclination of the companion is low, which would also suggest that its orbital inclination as wellwould be low. Based on the evidence Hale suggests that the companion is probably a low massM star. He further goes on to say, as Cochran suggested, that the stars radial velocity needs to beascertained.At present neither the stars radial velocity has been ascertained nor has there been anyconfirmation regarding the companion.1. Anonymous. "Extrasolar planets: A definite "maybe." Sky and Telescope 83(8):8,January 1992.2. Robinson, Edward L., et al. "A search for eclipses of HD 114762 by a low-mass companion." Astronomical Journal 99(2):672-674, February 1990.3. Cochran, William D., Hatzes, Artie P., and Terry J. Hancock. "Constraints on the companionobject to HD 114762." Astronomical Journal 380(1, Pt 2):L35-L38, October10, 1991.4. Ibid Pg. L38.5. Hale, Alan. "On the nature of the companion to HD 114762." Publications of theAstronomical Society of the Pacific 107(707):22-26, January 1, 1995.LALANDE 21185 Using photoelectric astrometry Lalande 21185 was studied over a four-year time period for perturbations in the propermotion of the star. Fifty-four observations were made from 1988 through 1991. In 1992Gatewood and others writing in the Astronomical Journal (1) stated that they were not able to detect any significant perturbation in the star's propermotion. Lalande 21185 was studied because it is very much like our own sun, is relatively closeto us (approximately 2.5 parsecs or 8.25 light years), and has a fast proper motion (4.78arcseconds/year).Gatewood, in examining 50 years of radial velocity data of Lalande 21185, as well as using amore sophisticated set of observations, contend that, indeed the velocity of the star has beenchanging over time, thereby suggesting a planetary companion. Gatewood suggests that thecompanion is between 0.5 to twice the size of Jupiter, revolves around Lalande 21185 between 35and 50 years, and is approximately 9.5 astronomical units from its sun. (2) A month later writing in Astronomy , Gatewood revised his conclusion toinclude not one but possibly two planetary companions revolving about Lalande 21185. Gatewood suggests that the second body may be less massive than Jupiter, and orbiting the star ata distance of approximately 3.5 astronomical units. (3) At the present time no confirmations have been made on either of the two planets.1. Gatewood, George, et al. "Multichannel astrometric photometer and photographic astrometricstudies in the regions of Lalande 21185, BD 56degrees2966, and HR 4784." Astronomical Journal 104(3):1237-1247.2. Anonymous. "A nearby extrasolar planet?" Astronomy 24(8):22, August1996.3. Anonymous. "Extrasolar planet update." Astronomy 24(9):26 & 28,September, 1996. Peg51 Mayor and Queloz, using radial velocity measurements, announced to the world in 1995 that theyindeed had discovered an extremely large planet (Peg 51 B) orbiting the star Peg 51 , which is a star similiar to our sun;spectral type G2.3. Peg 51 is considered to be approximately 13.7 parsecs in distance from theEarth (45 light years). Their official announcements were made in the October 25, 1995 International Astronomical Union Circular (1) as well as a moreformal article that appeared in the November 23, 1995 issue of Nature . (2) The radial velocity measurements were obtained by concentrating theirefforts on the doppler shifts of the star over a one year period (1994-1995). The ELODIE spectrograph of the Haute-ProvenceObservatory in France was used in the study. Although theradial velocity measurements could indicate other possibilities (spot rotation and pulsation),Mayor and Queloz are confident that these alternative possibilities can be ruled out.By compiling the data, they determined that the planetary body has a minimum mass of half thesize of Jupiter, with a mass no more than twice Jupiter's. Lin and others (3) suggest that the mass is probably that of one Jupiter. Other information gathered by Mayorand Queloz (2) suggest that the planet lies about 0.05 astronomical unitsfrom Peg 51, with a temperature of 1,300 K, and an orbit having an eccentricity of approximately0.09, indicating a circular orbit. In addition, the orbital period was calculated to be 4.23 days. Itshould be noted that Mercury lies between 0.3 and 0.4 astronomical units from the sun, makingPeg 51 B much closer to Peg 51 than Mercury is to our Sun. In addition, Mayor and Quelozspeculate from their data that perhaps a second low mass planet is revolving about Peg 51 muchfurther out in space than Peg 51 B. They base this speculation on Peg 51's long periodperturbation.One of the burning questions (no pun intended) that begets itself from the above parameters ishow could a planet as large as Jupiter form so close to its sun? Based upon current knowledgethis does not seem possible. Lin and others (3) feel that Peg 51 B did notform at its current location. Rather, it formed from an amassing of solids and gases at about 5astronomical units from Peg 51. They feel that it began to approach the star, stopping at itspresent location due to the result of tidal interactions (inward and outward forces on the planetsorbit). Another point to take into account regarding the above parameters is whether indeed Mayor andQueloz had discovered a planet or another type of body. According to the discoverers theyspeculate that due to the high temperature of the planet this body could possibly be a low massbrown dwarf. Guillot and others (4) also speculate that Peg 51 B mayindeed be a tidally stripped brown dwarf or other star. However, it should be realized that theyalso consider within the realm of possibility that Peg 51 B may be a giant terrestrial planet.Marcy and Butler has confirmed Mayor and Queloz's findings. (5) As afootnote, Mayor and Queloz recognize and thank other teams of researchers for confirming theirresults that indeed a planetary body is orbiting Peg 51. They write at the end of their article thefollowing: "After the announcement of this discovery at a meeting held in Florence,independent confirmations of the 4.2 day period radial-velocity variation were obtained inmid-October by a team at Lick Observatory, as well as by a joint team from the High AltitudeObservatory and the Harvard-Smithsonian Center for Astrophysics. We are deeply grateful to G.Marcy, P. Butler, R. Noyes, T. Kennelly and T. Brown for having immediately communicatedtheir results to us." (2) In addition to the discovery of the planet orbiting Peg 51, Gehman and others (6) suggest that it is very possible for an Earth-like planet to orbit Peg 51. In fact, theyextend their premise beyond Peg 51 to further suggest that stars such as Rho 1 Canceri, 47 UrsaeMajoris, and 70 Virginis (to some degree) are also strong candidates to have at least oneEarth-like planet as part of their solar system family. Further information on Rho 1 Canceri, 47Ursae Majoris, and 70 Virginis can be found elsewhere in this Section.Gehman and his colleagues feel that in order for a habitable planet to orbit a star, the orbit of theplanet must be dynamically stable, and the planet's temperature must be suitable for liquid water. They base the orbital stability of these systems by applying the circular form of the restrictedthree-body formulation, and noting the temperature of the planet by obtaining probable values ofthe incident stellar radiation flux, and the atmospheric and surface properties of the planet. Venuswas used as a reference point for the probability study. By applying these two techniquesmentioned above, Gehman and associates feel that all four of these star systems could possiblyhave Earth-like planets, with the possibility of habitability. The results found in 70 Virginis'ssystem is not quite as strong as in the other three. It should be noted that this work was basedtotally on the fact that a planet had been discovered around each of the four stars underdiscussion, and that the physical characteristics of these planets were used to determine theprobability of other planets in the system; in this case, Earth-like planets.1. Mayor, M., et al. "51 Pegasi." International Astronomical Union Circular no. 6251:1p.2. Mayor, M., and D. Queloz. "A Jupiter-mass companion to a solar-type star". Nature 378(6555):355-9, November 23, 1995.3. Lin, D.N.C., Bodenheimer, P., and D.C. Richardson. "Orbital migration of the planetarycompanion of 51 Pegasi to its present location." Nature 380(6575):606-7,April 18, 1996.4. Guillot, T., et al. "Giant planets at small orbital distances." Astrophysical Journal459(1, Pt. 2):L35-8, March 1, 1996.5. Glanz, James. "Is first extrasolar planet a lost world?" Science 275(5304):1257-1258, February 28, 1997.6. Gehman, Curtis, Fred C. Adams, and Gregory Laughlin. "The prospects for Earth-like planetswithin known extrasolar planetary systems." Publications of the Astonomical Society ofthe Pacific 108(729):1018-1023, November 1996. POSSIBLE PLANETARY BODIES AROUND PULSARS Because the following four stars are pulsars, and are ratherdifferent than any of the other stars mentioned, it would be best to consider some generalinformation about pulsars, and how it may be possible for planets to have evolved about them.The discovery of pulsars portrays a rather recent history. Pulsars, by means of a radio telescope,were first identified as such in 1967 by Jocelyn Bell Burnell. Pulsars, which develop from asupernova, are considered to be neutron stars that spin(or pulse); pulsating stars emitting radio waves. These pulses are due to the fact that the magneticand spin axes of pulsars are not aligned. (1) As of this writing over 650pulsars are known to exist within our galaxy. (2) Millisecond pulsars is thename given to those pulsars that spin incredibly fast; i.e. faster than 0.01 seconds. Many of thesemillisecond pulsars are part of a binary star system . (3) This fact is important to keep in mind because in the ensuing entries thecompanion to a pulsar may be a star as part of the binary system or may be a planet constituting atertiary system.There are two main theories regarding the formation of planetary bodies around pulsars. One,which is known as the Salamander Scenario, (4) is that the planet existedaround the star before it went supernova and somehow survived, while the other theory known asthe Memnonides Scenario (5) and which seems to be more plausible, isthat the planet formed after the star went supernova and became a pulsar. The MemnonidesScenario would also imply that some type of a dust disk formed prior to planet formation.Livio, and others (6) consider a different type of model. They suggest thata pulsar could form from the collision of two white dwarfs and that the planets formed from thedebris, which was produced as a result of the collision.Stevens, and others (7) on the other hand, speculate on planet formationfrom a binary star system in which one of the stars is a neutron star (pulsar). They argue that thecompanion star to the pulsar expands and goes over its Roche limit. They feel that due to thedisruption of the companion star, a large disc develops around the pulsar, eventually leading tothe formation of planets.In any event, no matter what theory one wishes to consider, it is important that we have a soundfooting in the fact that the possibility exists that planets could have formed around a pulsar. Ifastronomers feel that it is virtually impossible for planets to have formed around a neutron starthen the basis of the planetary discoveries that ensue will seem superfluous.1. Phillips, J.A., and S.E. Thorsett. "Planets around pulsars: a review." Astrophysicsand Space Science 212(1-2):91-106, February, 1994.2. Gribbin, John. Companion to the Cosmos. London: Weidenfeld &Nicolson, 1996. 504 p. Pgs. 325-329.3. Rankin, Joanna M. Pulsars, Observed Properties. In: The Astronomy andAstrophysics Encyclopedia . New York: Van Nostrand Reinhold, 1991. Pp.567-568.4. Phillips, J.A. and S.E. Thorsett. "Planets around pulsars: a review." Astrophysicsand Space Science 212(1-2):91-106, February, 1994. Pg. 100.5. Ibid . Pg 100-101. 6. Livio, M., J.E. Pringle, and R.A. Saffer. "Planets around massive white dwarfs." Monthly Notices of the Royal Astronomical Society 257(1):15p-16p, July 1, 1992.7. Stevens, I.R., M.J. Rees, and P. Podsiadlowski. "Neutron stars and planet-mass companions." Monthly Notices of the Royal Astronomical Society . 254(3):19p-22p,February 1, 1992.PSR0329+54In 1994, Dagkesamanky and others (1) suggested, by means of pulsartiming techniques and over a 25 year period, that a planetary body may be orbiting an extremelybright pulsar known as PSR 0329+54 . They suggest that the planet revolves about the pulsar every 6,140 days. Inaddition, they continue to speculate that a second planet with an orbital period of 1,110 days mayalso exist. No information since their original announcement in 1994 has been forthcoming. In allpracticality these discoveries have not been confirmed.1. Dagkesamansky, R.D., Shitov, Y.P., and T.V. Shabanova. "PSR 0329+54." International Astronomical Union Circular no. 5930:1p., February 7, 1994. PSR 1257+12One week before Bailes and Lyne published their retraction of the existence of a planetary bodyrevolving about PSR 1829-10, (1) Wolszczan and Frail (2) were announcing the fact they had discovered a planetary system around PSR 1257+12 ,a millisecond pulsar about 500 parsecs from our Solar System (1,630 light years). In Wolszczan's1992 paper, they suggest that two, and possibly three, planets may be part of the planetarysystem. Using a radiotelescope and recording timing measurements from the pulsar, they feel thatthese two planets have a mass of 2.8 times, and 3.4 times the mass of the Earth. The planethaving the 2.8 mass is considered to be 0.47 astronomical units from the pulsar with a nearlycircular orbit. The planet has been estimated to revolve about the pulsar in about 98.2 days. The3.4 mass planet is considered to be 0.36 astronomical units from the pulsar with a nearly circularorbit. This planet has been estimated to revolve about the pulsar in about 66.6 days. Theperturbations of the pulse arrival times of this pulsar were independently confirmed by Sallmenand Foster, (3) thereby offering more credence to the existence of theplanets mentioned above. Sallmen and Foster felt that this independent confirmation wasnecessary due to the problems with PSR 1829-10.Another paper that attempts to verify the existence of planetary systems, deals with the formationof the system around a pulsar. Chakrabarti and Swamy (4) argue that dueto the way a planetary system was formed around a pulsar, a series of planetismals should also bepresent. These planetismals can be verified from spectroscopic analysis of OH, CN and C2. Thistype of experiment can be used to suggest the possibility of planetary systems around pulsars ingeneral. In addition, they also consider the fact that a third planet may also be part of the systemdue to the angular momentum and the mass of the cloud circling the pulsar. They go on to saythat the planet is approximately 1.1 astronomical units from the pulsar with an orbital period ofabout a year.Bisnovatyi-Kogan (5) also supports the fact that this pulsarhas more than two planets. In fact according to the above researcher a whole family of planetsmay exist around PSR 1257+12. He bases his statement that due to the thickness of the disk (thedisk must exist because of the fact that planets have already been detected), the size of the diskwould be large enough to create outer planets in this system.Since Wolszcan's initial report suggesting at least two planetary bodies orbiting the pulsar, anumber of papers confirming these findings were published. In 1993 (6) and then again in 1994 (7) S.J. Peale, studying the variations(perturbations) in the times of arrival of the pulses produced by PSR 1257+12 suggest that thetwo planet hypothesis offers the best conclusion of the perturbations. In addition, Wolszcan,himself, (8) also reports confirmation of three planets by measuring thegravitational perturbations of the planets orbits over a three year period by means of timingobservations using the Arecibo (305 meter) radiotelescope. A good summary of the planetarysystem located around PSR 1257+12 can be found in a paper presented by Wolszczan (9) and published as part of the Astronomical Society of the PacificConference.Wolszczan reports that three planets are orbiting the pulsar. The latest parameters of theplanetary system are as follows: Planet 1 has a mass of 2.8 times that of Earth, is 0.47 AUaway from its star, an orbital period of 98.22 days, and an orbital eccentricity of 0.0264. Planet 2has a mass of 3.4 times that of the Earth, is 0.36 AU away from its star, an orbital period of 66.54days, and an orbital eccentricity of 0.0182. Planet 3 has a mass of 0.015 times that of the Earth, is0.19 AU from its star, an orbital period of 25.34 days, and an orbital eccentricity of 0.0. It shouldbe noted that there have been discrepencies in the parameters in much of the preceeding literature. At the present time it would be best to consider the above parameters to be the definitive word. With more experimentation and confirmation, it is likely that these numbers may change. An interesting side line regarding the findings of this newly discovered planetary system are thesimilarities it shows to our own Solar System when the masses and orbital radii of the three newlydiscovered planets are compared to our three innermost planets. The planet with the smallestmass of the three is located closest to the pulsar. Mercury has the smallest mass when comparedwith Venus and the Earth and is closest to the Sun. Venus and Earth masses are nearly identical,with Venus being somewhat less massive than Earth. The outer two planets of the pulsar systemare also similiar in mass having a distance ratio from the pulsar similiar to the distance ratio forVenus and the Earth. On the basis of this information it would be foolish to base these similaritieson all solar systems discovered. Nevertheless, the fact that these planetary systems, in alllikelihood, evolved differently (protoplanetary solar accretion disk in the case of our Solar Systemvs. debris from binary companion in the case of PSR 1257+12's solar system), the similarities areworth noting. (10) Although the majority of the astronomical community feels confident of this three planetarysystem, Gil and his associates (11) suggest alternative conclusions for theperturbations of the pulses. Although they do not rule out that the perturbations (tugging of thestar back and forth) are due to planetary masses, they do suggest that the "combination ofeffects involving precession and/or nutation of the spin axis and/or migration of the magnetic axisaround the spin axis is responsible for the observed residuals in PSR 1257+12." (11) Basically, what Gil was alluding to was, like the Earth, the pulsarwobbles as it spins thereby causing a precession. On Earth this precession is evidenced by thechange in date and time for when a season commences. That is, the date and time varies fromyear to year. Therefore the perturbations of the timing data may be caused by precession and notby planetary bodies.It seems safe to say, with the exception of Gil, that the discovery of three planets around thepulsar PSR 1257+12 has been confirmed by the astronomical community at large.ADDENDUM TO THE ABOVE PARAGRAPHS REGARDING STATEMENTSMADE BY GILL AND HIS ASSOCIATESThis paper was written in May of 1997. Many changes have occured since then. On April 4,2001, I received an e-mail from Axel Jessner, one of Gil's colleagues. This e-mail states thatprecession is no longer a good alternative. I wish to quote the statement sent to me by AxelJessner regarding this issue.I like to point out, that these ideas represented an alternative, just in case Malhotra'sconfirmation using secular variations should fail or be inconclusive. They were published beforeenough data were available for such an analysis. But because of the really striking verification ofWolszcan's interpretation by Malhotra, I do not think that precession is a good alternative toexplain the TOA's of PSR 1257+12. I am certain that this view is also shared by my colleagueJanusz Gil.1. Lyne, A.G., and M. Bailes. "No planet orbiting PSR 1829-10." Nature355(6357):213, January 16, 1992.2. Wolszczan, A., and D.A. Frail. "A planetary system around the millisecond pulsar PSR1257+12." Nature 355(6356):145-7, January 9, 1992.3. Sallmen, S., and R. Foster. "Pulsar's double period confirmed." Nature 358(6381):24-5, July 2, 1992.4. Chakrabarti, S.K., and K.S. Krishna Swamy. "Is there a comet cloud around PSR 1257+12?" Astronomy and Astrophysics 263(1-2):L1-2, September, 1992.5. Bisnovatyi-Kogan, G.S. "Planetary system around the pulsar PSR 1257+12." Astronomy and Astrophysics 275(1):161-2, August, 1993.6. Peale, S.J. "On the verification of the planetary system around PSR 1257+12." Astronomical Journal 105(4):1562-70, April, 1993.7. Peale, S.J. "On the detection of mutual perturbations as proof of planets around PSR1257+12." Astrophysics and Space Science 212(1-2):77-89, February, 1994.8. Wolszczan, A. "Confirmation of Earth-mass planets orbiting the millisecond pulsar PSRB1257+12." Science 264(5158):538-42, April 22, 1994.9. Wolszczan, A. "Pulsar Planets." In: A.S. Fruchter, M. Tavani, and D.C. Backer (Eds.), Millisecond pulsars: a decade of surprise (pp.377-386). San Francisco:Astronomical Society of the Pacific, 1995. (Astronomical Society of the Pacific ConferenceSeries; 72).10. Mazeh, Tsevi, and Itzhak Goldman. "Similarities between the inner solar system and theplanetary system of PSR B1257+12." Publications of the Astronomical Society of thePacific 107(709):250, March 1995.11. Gil, J.A., and A. Jessner. "Are there really planets around PSR 1257+12?" In: J.A. Phillips,J.E. Thorsett, and S.R. Kulkarni (Eds.), Planets around Pulsars (pp.71-79). San Francisco: Astronomical Society of the Pacific, 1993. (Astronomical Society of the Pacific;36). PSR1620-26 (PSR B1620-26) During the past several years (1993-present) a series of papers have been published suggestingthat a planetary companion may be orbiting the binary pulsar PSR 1620-26 , which is located in theglobular cluster Messier 4. What is being considered then is a triple system composed of thebinary and a companion. The first series of papers discussing this possibility came out in 1993. Backer (1) , Thorsett (2) , and Sigurdsson (3) all seem to agree that because of the anomalous spin period secondderivative of PSR 1620-26, suggesting an additional source of acceleration, a third companionmust exist. The nature of this third companion, however, differs from one researcher's findings toanother.Backer and others interpret the data to suggest that the third companion has a mass of 5-10Jupiters and a circular orbital period of 100-120 years. Thorsett and others suggest either a planetten astronomical units from the binary system or a star approximately fifty astronomical units fromthe binary system would reflect the data. Thorsett goes on to consider that much work still needsto be done, and that observations may need to be carried out during a ten-year period. Sigurdssoninterprets the data to reveal a somewhat eccentric orbit for the third companion orbitingapproximately seven astronomical units from the binary system. Sigurdsson feels that additionalmonitoring of the binary is necessary in order to ascertain whether the spin period secondderivative suggests the existence of a planetary companion.Rasio (4) reporting in 1994, seems to be more conservative in his findingsthan what had been mentioned previously. Considering the large eccentricity of the binary system,Rasio contends that a third member of this triple system could not produce this type ofeccentricity. He goes on to suggest that a few more years of timing data will be necessary inorder to ascertain whether the third companion in question is a planetary body or a star.In 1994, the Astronomical Society of the Pacific, devoted their entire conference to millisecondpulsars. It was at this conference, that was held January 3-7 in Aspen, Colorado, that PSR1620-26 was discussed by Backer and Thorsett (5) , Sigurdsson (6) , and Michel (7) . The thrust of these talks onceagain centered on how the anomalous spin period second derivative could be interpreted. Backerand Thorsett feel that the best interpretation to make is that there is a third body within the systemwith a limiting mass of between 0.02 and 0.05 that of our sun, thereby suggesting a Jupiter type ofbody. Sigurdsson suggests two possible scenarios. Either the results indicate a planetary bodysimiliar to the mass of Jupiter with an orbital distance greater than ten astronomical units, and aneccentricity of 0.3-0.5 or a star in a highly eccentric orbit with an orbital distance ofapproximately fifty astronomical units.Michel's talk centered on the orbital elements for the companion by means of differentialequations. He suggests that a longer period of time is necessary in order to ascertain these orbitalelements. In addition, he feels that the companion in question could have any mass. It seemsclear from the published articles as well as the published proceedings of the conference that noconfirmation has been made regarding the third companion. More work will need to be done inorder to determine whether the companion is a star, a brown dwarf, or a planet.1. Backer, D.C., R.S. Foster, and S. Sallmen. "A second companion of the millisecond pulsar1620-26." Nature 365(6449):817-18, October 23, 1993.2. Thorsett, S.E., Z. Arzoumanian, and J.H. Taylor. "PSR B1620-26: a binary radio pulsar witha planetary companion?" Astrophysical Journal 412(1, pt. 2):L33-6, July 20,1993. 3. Sigurdsson, S. "Genesis of a planet in Messier 4." Astrophysical Journal 415(1, pt. 2):L43-6, September 20, 1993.4. Rasio, Frederic A. "Is there a planet in the PSR 1620-26 triple system?"Astrophysical Journal 427(2, pt.2):L107-10, June 1, 1994.5. Backer, D.C., and S.E. Thorsett. "PSR 1620-26--A triple system?" In: A.S. Fruchter, M.Tavani, and D.C. Backer (Eds.), Millisecond pulsars: a decade of surprise (pp. 387-390). San Francisco: Astronomical Society of the Pacific, 1995. (Astronomical Societyof the Pacific Conference Series; 72).6. Sigurdsson, Steinn. "The companion of M4A: a planet or a star?" In: A.S. Fruchter, M.Tavani, and D.C. Backer (Eds.), Millisecond pulsars: a decade of surprise (pp.429-431). San Francisco: Astronomical Society of the Pacific, 1995. (Astronomical Societyof the Pacific Conference Series; 72).7. Michel, F. Curtis. "Orbital elements of PSR 1620-26." In: A.S. Fruchter, M. Tavani, andD.C. Backer (Eds.), Millisecond pulsars: a decade of surprise (pp.421-423). SanFrancisco: Astronomical Society of the Pacific, 1995. (Astronomical Society of the PacificConference Series; 72). PSR1829-10 Based on the Doppler shift of light emanating from the pulsar PSR 1829-10, Bailes and others (1) suggest that a planet has been found orbiting it. The planet has beencalculated to be in an almost circular orbit with an eccentricity of 0.1, and having a mass ten timesthat of the Earth. The time it takes the planet to make one revolution about the pulsar is about sixmonths. The planet is considered to be 0.7 astronomical units from the star. The pulsar itself, hasbeen calculated to be approximately 10 kpc (about 30,000 light years) from our Sun.One of the major aspects of this finding is how could a planet form around a pulsar. Because ofthe importance of this aspect several papers have been published following the announcement byBailes. Both Lin (2) and Nakamura (3) concedethat there is no way the planet could have been present before the star exhibited a supernova andbecame a pulsar. Therefore, they both suggest that a possible solution is that the planet formed asa result of the supernova. Lin suggests that during the supernova, large amounts of star materialwere thrown out into space. Some of this material found its way back towards the star. Theseparticles coagulated into plantesimals which in turn accreted into a planetary body over a periodof about one million years. Nakamura, on the other hand, considers that this was initially a binarysystem with a neutron star and a companion with mass of approximately 1.5 times that of theSun. This companion formed a disk around the neutron star. When the star went supernova thecompanion star escaped, and the planet was formed from the remnants of the disk.Podsiadlowski, and others (4) consider two possible explanations for theformation of the planet, which are somewhat similiar to those mentioned above. One possibility isthat PSR 1829-10 formed from the merger of two white dwarfs. From this merger some materialwas left behind thereby forming the planet. The other scenario is that there was a collisionbetween a neutron star and a solar type star that had planets around it. Because of this collisionthe inner planets of the solar type star, which orginally exhibited an eccentric orbit, became morecircular by drag forces.In considering the above scenarios, the most important point to keep in mind is that the possibilityof a planet forming around a pulsar is good, thereby adding more credence to the fact that aplanet can possibly exist around PSR 1829-10.Unfortunately the best laid plans of mice and men do not always come to fruition. In 1992 Lyneand Bailes (5) announced to the world that they were retracting their initialconclusion that a planet exists around PSR 1829-10. They attributed the retraction to the factthat there was an error in the pulsar's original position, thereby creating faulty results in theprocessing of the information. As of this writing no further information has been forthcoming onthe existence of a planetary body revolving about PSR 1829-10.1. Bailes, M., A.G. Lyne, and S.L. Shemar. "A planet orbiting the neutron star PSR 1829-10." Nature 352(6333):311-13, July 25, 1991.2. Lin, N.C., S.E. Woosley, and P.H. Bodenheimer. "Formation of a planet orbiting pulsar1829-10 from the debris of a supernova explosion." Nature 353(6347):827-9,October 31, 1991.3. Nakamura, T., and T. Piran. "The origin of the planet around PSR 1829-10." Astrophysical Journal 382(2, pt. 2):L81-4, December 1, 1991.4. Podsiadlowsky, Ph., J.E. Pringle, and M.J. Rees. "The origin of the planet orbitingPSR1829-10." Nature 352(6338):783-4, August 29, 1991.5. Lyne, A.G., and M. Bailes. "No planet orbiting PSR 1829-10." Nature 355(6357):213, January 16, 1992. Rho 1 Canceri (HR 3522) By measuring the doppler shifts in the spectrum of Rho 1 Canceri, a starsimiliar to our sun; spectral type G8, Marcy and Butler (1) announced thata planetary companion is indeed revolving about the star. The doppler shifts suggested a wobblein the star as seen from the Earth. Therefore, a gravitation pull on the star seems to exist. As aresult of this observation, the conclusion is that there may be a planet exerting the gravitationalpull. It was also determined by the wobble's characteristics that the planet lies approximately 18million kilometers (0.11 AU) from the star, and has a mass similiar to that of Jupiter (i.e., 87%Jupiter's mass).Baliunas, et al, writing in the Astrophysical Journal , (2) verify Marcy and Butler's claim by suggesting that the possibility of a planet revolving aboutRho 1 Cancri cannot be ruled out. Their statement was primarily based on analyzing the spectraof the star. The researchers go on to suggest that the planet is probably orbiting the star at0.1117 astronomical units.Butler, Marcy, and associates (3) writing in the AstrophysicalJournal state that after amassing 41 measured doppler velocities of the star, they inferthat a companion does exist. The companion has been calculated to revolve about its star every14.65 days with an orbital eccentricity of 0.05. In addition, its mass is 0.84 times the mass ofJupiter, and it lies approximately 0.11 astronomical units from its star. The planetary body hasalso been calculated to have a radius of 1.2 that of Jupiter, and a derived temperature ofapproximately 700 K. They also go on to suggest that because of the velocity perturbationsmeasured, a second companion may be in the offing. They feel that this second companion has amass of five Jupiters, and an orbital period of eight years. In addition, the planetary companion isconsidered to have a minimum mass of 0.84 the mass of Jupiter, with a distance from the star at0.11 AU, an orbital period of 14.7 days with an orbital eccentricity of 0.05. This planet seems tobe acknowledged by the astronomical community.1. Anonymous. "Another extrasolar planet." Sky & Telescope 92(1):13,July 1996.2. Baliunas, Sallie, et al. "Properties of sun-like stars with planets: Rho 1 Cancri, Tau Bootis,and Upsilon Andromedae." Astrophysical Journal 474:L119-122, January 10,1997.3. Butler, R. Paul, et al. "Three new "51 Pegasi-type" planets." Astrophysical Journal 474:L115-118, January 10, 1997. Rho Coronae Borealis On Thursday, April 24, 1997, a month after this paper was written, Robert Noyes of theHarvard-Smithsonian Astrophysical Observatory announced to the world that another planet hadbeen discovered; in this case, around the star Rho Coronae Borealis. In addition, a press release(SAO Release 97-13) issued by three institutions the following day related the result of thefindings. The institutions are the SmithsonianAstrophysical Observatory, the National Center for Atmospheric Research , and the Pennsylvania State University. Namerecognition for the discovery was awarded to Noyes, Jha, Korsennik, Brown, Kennelly, andHorner. A paper on the discovery is soon to be published in Astrophysical Journal,Letters . For a pre-publication version of the paper click here . The star, Rho Coronae Borealis can be found in the constellation known as the Northern Crown. This star can be seen with the naked eye. It is approximately 15.15 parsecs (50 light years) fromEarth. According to the SAO Press Release (1) the radial velocity measurements for Rho CoronaeBorealis were taken with the Advanced Fiber Optic Echelle spectrograph located at the1.5-meter Tillinghast Reflector of the Fred Lawrence Whipple Observatory on Mt. Hopkins,Arizona. Based on the perturbations of the star, the planet has been determined to be 0.23astronomical units from its sun, with a mass of 1.3 Jupiters. It revolves around its star every 39.6days, and has a very small eccentric orbit. The eccentricity has been calculated to be about 0.028,an almost circular orbit. In addition, it has also been determined that the planets temperature isabout 300 degrees Centigrade or 500 degrees Fahrenheit. What we have here is similiar to thefindings elsewhere in this paper; i.e. a Jupiter sized planet close to its sun with an eccentricitydefining an almost circular orbit. As of this time thereseems to be strong evidence to indicate that this discovery will be confirmed by the astronomicalcommunity as a whole.1. SAO Press Release No: 97-13 Tau Bootis Tau Bootis,which is a star similiar to our sun, has been observed 19 times for doppler velocity perturbations. The time span for these measurements extend from 1995 through February 1996. Based uponthese observations it has been determined that Tau Bootis has a planetary companion. Calculations seem to imply a companion with a mass of 3.87 times the mass of Jupiter orbiting itsstar at a distance of 0.0462 astronomical units. Its orbital period around Tau Bootis seems to beevery 3.312 days. In addition, the radius of the companion is considered to be about 1.2 times theradius of Jupiter with a derived temperature of 1,400 K. (1) Baliunas and her associates (2) feel that the velocity perturbations stronglysuggest a planetary companion that is 0.046 astronomical units from Tau Bootis. Based on thestar's radial velocity variations, it has been determined that it lies approximately 0.046astronomical units from its star, Tau Bootis. The velocity variations strongly suggest a planet. (2) It is worth noting that based on the observations and calculations it seems reasonable to assumethat indeed a planetary companion is orbiting Tau Bootis.1. Butler, R. Paul, et al. "Three new "51 Pegasi-type" planets." Astrophysical Journal 474:L115-118, January 10, 1997.2. Baliunas, Sallie L., et al. "Properties of sun-like stars with planets: Rho 1 Cancri, Tau Bootis,and Upsilon Andromedae." Astrophysical Journal 474:L119-122, January 10,1997. T-Tauri Stars Marsh and Mahoney (1) , (2) in a series of papershave suggested gaps in the interstellar dust clouds (circumstellar disks) that may infer thepossibility of a planetary body. This work was carried out by observing the spectral energydistributions of a number of T-Tauri stars in Taurus the Bull. At the present time no conclusions can be drawn regarding what is causingthe gaps. Faint stars, brown dwarfs, groups of planets, and planetesimals are all possibilities. Theidea of gaps within the interstellar dust clouds was explored more fully in the section on Beta Pictoris .1. Marsh, K.A., and M.J. Mahoney. "Evidence for unseen companions around T Tauri stars." Astrophysical Journal 395(2, pt.2):L115-18.2. Marsh, K.A., and M.J. Mahoney. "Do the spectral energy distributions of GK Tauri and HKTauri indicate the presence of planetary companions?" Astrophysical Journal 405(2, pt.2):L71-4, March 10, 1993.Upsilon Andromedae After a total of 18 Doppler measurements, the velocity variations suggest that a planetarycompanion may be orbiting Upsilon Andromedae, a star very similiar to our Sun. It has beencalculated that the companion revolves about itsstar in about 4.611 days, and has a mass of 0.68 Jupiters. It lies at a distance of 0.057astronomical units from Upsilon Andromedae. Furthermore, it has been suggested that thecompanion has a radius of 1.2 times the radius of Jupiter, and a derived temperature of about1,300 K. (1) Although there is no photometric data, researchers feel that velocity perturbations caused byconvection may be large, thus suggesting a planetary companion. It may be useful to note thatalthough this star is considered to be a spectroscopic binary in many star catalogs, Morbey andGriffin, two research astronomers, feel this is not so. (2) With the evidence amassed within the last 6 months it seems reasonable to assume that indeed aplanetary companion orbits Upsilon Andromedae.1. Butler, R. Paul, et al. "Three new "51 Pegasi-type" planets." Astrophysical Journal 474:L115-118, January 10, 1997.2. Baliunas, Sallie L. "Properties of sun-like stars with planets: Rho 1 Cancri, Tau Bootis, andUpsilon Andromedae." Astrophysical Journal 474:L119-122, January 10,1997. 47 Ursae Majoris Using doppler shifts to measure the radial velocities, Marcy and Butler (1) strongly suggest that a planet is revolving about 47 Ursae Majoris, which is a star similiar to ourSun. Iodine lines were used as a base reference point tomeasure the doppler shifts. A total of 34 observations were made spanning an 8.7 year period(1987-1996). According to the velocity curves amassed, Marcy and Butler feel that the planet inquestion has a minimum mass of 2.39 Jupiter masses, not to exceed 4.8 Jupiter masses, an orbitalperiod of 2.98 years (amount of time it takes for the planet to revolve around its sun), aneccentricity of 0.03, which suggests an almost circular orbit, and an effective temperature ofapproximately 180 degrees Kelvin. In addition, the authors suggest that the planet isapproximately 2.1 astronomical units from its sun. This star is 47 light years from Earth. (2) What we have here is an extremely large planet, revolving about its star at a distance of 44.5million miles more than Mars is to our Sun. According to Marcy (3) theeffective temperature would be 90 degrees Centigrade, and that its atmosphere could containliquid water. Unlike the planetary body found revolving about 70 Virginis, there is little doubtthat due to its mass, this is more a planet-like body than a brown dwarf.1. Butler, R. Paul, and Geoffrey W. Marcy. "A planet orbiting 47 Ursae Majoris." Astrophysical Journal 464(2, pt 2):L153-6, June 20, 1996.2. Anonymous. "More extrasolar planets." Sky & Telescope 91(4):11, April1996.3. Cowen, Ron. "Two extrasolar planets may hold water." Science News |
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