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EVIDENC E FO R A SOLAR COM PANION STAR

Ric h a r d A . Mu l le rD e p a r t m e n t o f P h y s i c sandL a w r e n c e B e r k e l e y L a b o r a t o r y

Un iv e r s i ty o f Ca l i f o r n iaBe r k e le y , Ca l i f o r n ia 9 4 7 20

DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United SlatesGovernment. Neith er the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsibility for thf* accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United Slates Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.

T he s u b m i t t e d m a n u s c r i p t h a s b e e n a u t h o r e d b y a c o n t r a c t o r o f t h e U . S .government under contrac t No. DEACO3-76SFOO098,

, t ^ b e ^ b ! i c t h e d i n : h e P r o c e e d i n g s o f ih e I n te r n a t io n a l As t r o n o m ic a l Un io n Sy mp o s iu m1 1 2 , T h e S e a r c h f or E x t r a t e r r e s t r i a l L i f e : R e c e n t D e v e l o p m e n t s " , J u n e 1 8 - 2 1 1 9 84Bos ton M ass . (D. Re ide i Pu b . Co , D ord rec t Hol land) ' *

m U M \ OF MIS ESC'JHEHT IS IMIMTCD ^ . < K


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EVIDENCE FOR A SOLAR COMPANION STAR

Richard A. MullerDepartment of Phys ics andLawrence Berkeley LaboratoryUniversity of Cal i forniaBerkeley , Cal i fornia 94720

ABSTRA CT. Per iod ic i ty seen in both the mass ext inct ion s and largeimpact cratering on earth can be explained i f one postulates that thesun has a companion star, orbit ing in a moderately eccentric orbitwith a major axis of 2.8 l igh t- yea rs. No other expla nation s thathave been suggested are compatible with known facts of physics andastronom y. If the companion is a red dwarf star, the mo st com m onkind in the galaxy, then no previous astrono m ical obse rvation s w ouldhav e found i t . A search for red obje cts with large paral lax is nowunderway at Berk eley, and has a good cha nce of ide ntifying the starin the near future.

INTRODUCTIONIn the last few years there have been several major discoveries that haveupset th e standard mo del of gradual evolu tion. The f irst was the discover y byAlv arez et al . that a large extrater restria l obje ct , a co m et or an astero id, had hitthe earth at the t im e of the ma ss ext i nct ion s at the end of the C ret ac eou s. Theim pa ct would throw a large amou nt of dust into the upper atm osph ere for severa lmonths, and species would be ki l led by the lack of sunl ight and the result ingcessat ion of photosynthes i s and sub- freez ing tem peratu res . Desp i te in i tia lskept ic i sm by som e paleon tologi s t s and geo logi s t s , m any of the predict ions of theAlv are z m odel hav e turned out to be true. Th ese, includ e the discovery of theworld-w ide nature of the extraterr es tr ia l mater ia l {marked by the presen ce ofiridium), the s imultaneous ext inct ion of microscopic plant l i fe , and recentlyconclus ive ev iden ce that the mater ia l in the boundary layer had been subjected toa shock wave . Ne ver the le ss , some paleon tologi s t s mainta ined that i t was s t i l lnot possib le for an im pac t to hav e caused the ext in ct io ns. The y argued that theext inct ions had been gradual, and took place over a per iod of 1 0 - 1 0 years . As Ihope to show , I be l iev e that w e can now reco nci le the concep t of gradualext inct ions wi th the impact theory .

The second discovery that shook the standard theory of evolution was madeby D . Raup and J. Sepkoski , paleo nto logists at the Un ivers ity of Ch icago . Theyhad com piled the m ost com ple te record of marine ext inct ion s ever assem bled. In


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this record they found strong evidence that mass ext inct ions were not rareindividual events , but that they occured on a regular schedule: every 26 mil l ionyears . The last ext inct ion took place about 13 mil l ion years ago, so we are halfway betw een c atas trop hies . Their paper also m et with init ial skeptic ism , in part (Ibel iev e) be cau se th eir results were so revolutionar y, and they were socon serv ative in their claim s. I too wa s init ial ly skeptic al , unti l I studied theirmathemat ics and methods , and dupl icated many of the ir ca lculat ions myself. I amnow convinced that their discovery wil l eventual ly be accepted as one of thestandard facts on which evolutionary models must be based.

The da ta of Raup and Sepkoski is shown in Figure 1 . The ordinate shows th epercentage of fami l ies present in the preceding geologic s tage that Lavedisappeared in the subsequent sta ge . Only sp eci es that did not survive to thepresent are analyzed; thus the ext in ct ion s look a l i t t le m ore sever e than theyactu al ly w ere. We ha ve used a l inear ordinate inste ad of the logarithm ic one usedby Raup and Sepkoski . The arrows are drawn with 26 m il l ion- year inter vals , andthey appear to l ine up with the larger ex t inc t ion s. Their careful m ath em atica lanalysis showed that th e a priori probab il i ty of such agre em ent i f ther e was noreal effect was about one in a thousand.

R. P. Feynman once said that the "glory" of physics was that i f somethingwere true, there would be a way of presenting i t such that i ts truth would beobvious. Although I don't claim to have suc cee ded at pre sentin g the Ch icago da tain such a way that the e ffe ct is "obvious", I would like to show m y version anyw ayin Figur e 2 . I ha ve take n the data from the Raup and Sepkosk i plot (Fig. 1) but foreach ex t inct ion I have plotte d a Gaussian curve, and then superimposed theGaussians. The area of each Gaussian repr esen ts the inte nsit y of the ex t inct io n(and is equal to the ordinate for Fig. 1); the width (rms) of each Gaussian is theunc ertain ty in when the ex t inct io n took p lac e, wh ich I took as the grea ter of. thefol lowing: unce rtainty in the geo logic t im e scal e (e st im ated by Harland et al . ) orhalf th e duration of the sta ge . I think this plot shows the corr esp ond enc e found bythe mathematical analysis in a way that is more evident .

COMPANION STAR MODELA t the t im e we rec eive d th e preprint of Raup and Sepkoski (Novem ber 1 983)we knew that at least two of the mass ext inct ions in their cycle were associatedwith i r id ium layers , the Cre taceou s /Te- t iary and the Eo cen e/O l igoce ne . I t tooknearly tw o mo nths for us to f ind a plausible hyp othesis that could explain the da taand that was consistent with everything else we knew about astronomy andphy sics . During this period we reje cted many theo ries , including one thatattribu ted the ext in ct ion s to osci l lat ions in the galac t ic plane. (Til return to thistheor y short ly.) Final ly, with the help of Marc Da vis and P iet Hut, we had amo del that worked. Simultaneou sly, D . Whitmire and A. Jackso n deve loped anesse ntia l ly equivalent theory, that arrived at Na ture mag azin e on the sam e day asours .Our model postulates that the sun has a companion star that orbits i t with a26 mil l ion- year period. By Kepler's law , this dete rm ines the sem i-m ajor axis ofthe el l ipse to be (?6,000,000) ' = 88,000 A. U. Changing units and mult iplying by


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tw o, we find that th e major axis of the orbit is 2 .8 l igh t- ye ar s. During pe rih el ion ,the companion perturbs the denser regions of the comet c loud, sending a shower ofa bil l ion com ets towards the inner so lar system (which i s usual ly kept re lat ive lyclean of co m et s by the pertu rbative ef fe ct s of Jupiter and Saturn) . We ex pe ctthat about t w o dozen would hit the earth. The dinosaurs had survived many suchimpacts before they were destroyed by .he very large one at the end of thec r e t a c e o u s .From the fa ct that this companion star has not been identi f ied, we canconclude i t must be dimmer than 7th magnitude ( i .e . not in the Yale bright s tatca talo g). To be on the m ain seq ue nc e, th e star must then be les s than about 0.3so lar mas ses . To have perturbed the co m ets the star must be grea ter than about

0 .05 solar m ass es . In order to com e suf f ic ien tly c lo se to the sun to aff ec t theco m ets , the orbit must have ec ce nt r ic i ty bet w een 0 .6 and 1 .0 . (Whitmire andJackson assumed a lower mass in order to make the star invisible; this forcedthem to an ec ce n tr ic i ty c los e to 1 .0 . We saw no reason to assume the starinvisible, s ince most of the stars in the sky have never had their distance from usmeasured. ) These are very comm on ecc en tr i c i t i e s in mu l t ip le s tar sys tem s; oneex pe cts , for orbi ts distr ibuted randomly in phase sp ace , that half o f them wouldhave ecce nt r ic i ty gr eate r than 0 .7 . The m ass range su gge sts the star i s a reddwarf, which i s the m ost com mo n ste l lar typ e in the G alaxy. Thus there was noneed to postulate anything new or exotic .

QP iet Hut wa s able t o show that su ch an orbit would be sta ble for about 1 0 7yea rs against breakup by pass ing stars and m olecu lar c louds. G alac t ic t ides tendto increas e the eff ec t iv e binding of the star to the sun in the d irect ionperpendicular to the gala ct i c plane; they g ive a resto ring force . Hut deduced thatif the osci l lations of the star are in this direction, then the major axis must besl ightly larger than Z.8 l ight years (to keep the period at 26 Myr) and so the orbiti s s l ightly less s table to perturb ations of pass ing sta rs . The stab i l i ty of the orbi t issuf f ic ien tly long to accoun t for the regu lari ty in th e ext inc t ion s , but i t a l soimpl ies that the companion star could not have been in this orbi t s ince theform ation of the earth. Sinc e capture is very improb able , the most l ike ly scenariois that the companion was once more t ightly bound, and i s s lowly being evaporatedby pass ing star s . I t i s con ceiva ble that cra ter reco rds wi l l prov e this specu lat ion,s ince th ey hold the record of the per iodic i ty and int en si ty of past co m et sho wers .It i s poss ible , for example , that the end of the late great bombardment of themoon that ended 3.9 bi l l ion years ago came about when the companion star wassc at ter ed from a c lose - in orbit to one mu ch further out . I t i s inter est in g to not ethat the f irst ev id enc e for l i fe on earth in i soto pic record s occurs just after theend of this bombardment.Another sugges t ion has been m ade , tha t the ex t in c t io ns were tr iggered by

the pas sages of the so lar syst em through the ga lac t ic plane . . . T h e t im es ofthe ga lac t ic plane cross ings , as pre sen ted by Ram pino and Stoth ers , are plo ttedagainst the mas s ext inc t ion s in Figu re 3 . N ot only i s the re no obvious correlat ion,


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250 Myr ago; 46% of the se random sets had a smaller RMS deviat ion from theext inc t ion da tes than had the gala ct ic plane crossings. In con trast an ex ac t 26Myr period f i ts the ext in ct ion s bet ter than 99-5% of th e random data se ts .Rampino and Stothers mistakenly claim in their paper that the probabil i ty ofrandom data doing as w el l as the g ala ct ic plane crossing is not 46% as we found,but 0.4%! Their inco rrec t number is due to a s imple m ath em atica l m istake: incalc ulat ing the a priori probabil i ty of agreem ent, they used the value one wouldget for agreement between two sets of unordered numbers, but the sets theycom pared (dates of ext in ct ion s and date s of gala ct ic plane crossings) we re bothordered ( i .e . they both increase monotonical ly) .

EARTH CRATERING PERIODICITYAf ter our companion mod el was subm itted to Na tur e, Walter Alvar ezreal ized that the comet shower model made another impl ic i t predict ionconcern ing the date s of imp act craters on the earth. Although the proba bil i ty off inding a crater from an earth imp act m ay be 10% - 25% (since man y imp actregions, such as the ocean f loors, ha ve not yet been studied ) , the com et sho wermodel im plied mult iple im pa cts , so that the probab il i ty of f inding at leas t onecra ter from a given show er should be high. To our de ligh t, in a com pclation ofcrater ages- we found that they had an apparent 28 Myr per iodic ity ag reein g(within errors) with the frequen cy and phase of the ext inc t ion s. Most of theeffect was coming from the larger craters (greater than 10 km diameter); the agesof these craters are plotted in Figure 4, along with arrows indicat ing the 28 Myrper iodicity . Fourier analysis and Mo nte- Ca rlo s imu lat ions showe d that the errorasso ciate d with the period was about 1 Myr, and the error associa ted with the

t im e of the mo st recen t ev ent w as about + 2 Myr. The period when a nominal 26Myr and a 28 Myr period would get out of phase, 150-200 Myr ago, is the t imewhen the paleontological data is weakest (see Fig. 1) and when the ages of thegeo logic al stag es are mo st unce rtain. The analysis proved to be rather robustagainst changes in the data set , including the addit ion or el imination of a fewcraters , or changes in the minimum crater diameter included.PREDICTIONS

This new model of the mass ext inct ion s m ake s seve ral new pred ict ions. Theobvious one is the exis ten ce of the companion star. (If i t i s found, we sug geste d i tbe cal led "Nemesis".) I wi l l discuss our ongoing search for this star later. An otherimportan t pred ict ion is that al l the ext in ct io ns se en by Raup and Sepkoski areasso ciate d w ith come t imp act s , and should have asso ciated iridium layer s.Subsequent to our work, such an iridium layer was found at one of the se layer s,the Pe i 'm ian /T iias sic We also predict that som e, i f not al l , of the m assext inc t ions w i ll be assoc iated wi th mul t ip le imp acts . This sugg ests that we lookfor mu lt iple ir idium la yer s. The bes t that one can say now is that ther e is no goodevid enc e against mu lt iple ir idium layers; the published data are consisten t withthe exis ten ce of sever al pea ks. A new iridium d etec t ion apparatus now undercons truction in the Alva rez group, based on coincident 317 keV and 468 keVgamma rays from the decay of Ir -192 , vnl l be capable of measuring the l eve l s aslow as S xlO without prior chem ical purif icat ion , and should be able to testboth predict ions .


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EXTENDED EXTINCTIONSThe durat ion of the comet shower depends on the eccentr ic i ty of thecompanion's orbit . A rough es tim at e of the duration of the show er can be mad e bycalc ula ting t he stre ng th of the perturb ation (proportional to 1/r ) as a fun ction oftim e; this is show n in Figu re 5 for ec ce nt ric it i es of 0.6 to 0.8. If w e arbitrari lydefine the duration of the shower to be the width of the peaks in the curve(FWHM), then the duration of the shower is pl ot ted in Fig . 6. For reaso nab leranges of eccentric ity, 0.6 to 0.9, the duration of the shower (ful l -width at half-max) is 1 00,000 yea rs to 2,000 ,000 ye ars . Very high (and rela tiv ely unstable)ecc en tr ic i t ie s are required to have very short show ers . Thus we expec t a typicalshower , w i th perhaps 1 0 imp acts spread over 1 Myr , wi th an intervals averaging

50 , 000 ye ar s be twe e n im pac ts .An interest ing consequence of the comet shower model i s that we would notneces sar i ly ex pe ct a l l sp ec i es to d ie out s imultan eously during a shower . Som espec ies could be destroyed by an ear ly comet impact , whi le others make i tthrough, only to be ki lled by a lat er and larger im pa ct. The claim of so m epa leon tolo gist s tha t th e exti nc tio ns w ere not sudden but spread over 1 Myr ormore i s no longer in obvious contra dic t ion to the imp act mo del . The shower m odeldoes predic t that , g iven suff ic ient t ime resolut ion , each catastrophe could beresolved into a short ser ies of abrupt e ve nts .

EVOLUTIONIf al l this is r ight, then evolution on the earth has proceeded through a vastlydi f ferent h is tory than we had previous ly supposed. S ince Darw in, we haveassumed that the m ain dr iv ing for ce of evolu t ion i s com peti t io n betw een sp ec ies .Our new model says that such evolut ion takes p lace only dur ing the re lat ive lyquie t per iod be tw een co m et show ers . Every 26 mi l l ion years or so a newmechanism com es into p lay; the earth i s h i t by a wor ld- wide d isaster . Withoutsuch a catastrophe , mammals might never have wrested the earth from thedinosaurs. We don't know how impor tant this m echan ism is for evo lution as w eknow it , but i t is pos sible that i t is essen tia l . It may pre ven t spec ies "stagnation"by ki l ling most of th e dominant spec ies and opening new ec olog ical n iches forprevio usly suppressed spe cie s to occup y. It m ay play a role in evo lution similar tothat played by "death" in our everyday l ives, making possible the introduction of"young blood". W ithout dea th to open so m e new nic he s, for exa m ple, I could neverhave obtained tenure at my univers i ty .Sinc e I am a ph ysic ist , I hav e no cre de nt ials to lose in the theory ofevolut io n . So I have been able to spe cula te free ly . Future speculat ion onevolut ion I should lea ve t o the real exper ts . Le t m e return to phy s ics .

OTHER PHYSICS AND ASTROPHYSICS


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by a sma ll orbit for the compan ion? Did this bom bardm ent prev en t life fromforming, or just obl it era te i ts record? Could the com et show ers help explain otherphenomena in the solar system such as the existence of the Apollo objects andplanetary rings (especial ly the short- l ived rings, such as those on Jupiter)?Perhaps th e prese nce of a companion star will help us to understand the ex ist en ceof the co m ets the m selves . Did the showers p lay any ro le on earth geo logy , e .g .triggering volcan os or earthquakes? Did the showers contrib ute s ign if icantm ater ial to planetary a tmosph eres? If mater ial is thrown into solar orbit after anearth imp act , there m ay be a recurrent shower ev ery year as the orb its of th eearth and the debris intersect at the same place; could this mechanism del iver aniridium layer without b lackening the sky and causing extinct ions ? Or would i t justcause multiple-Tunguska type disasters for many decades.THE BERKELEY SEARCH FOR THE COMPANION STAR

We know a lot about the hypo thesize d com panion star. I t must be be tw ee n2.5 and 2 .8 l igh t-y ear s away (depending on ec ce nt ric ity ) . I ts mass is les s than 0 .3and probably more than 0.05 solar masses, so it is vety likely a red dwarf. I tsproper motion and radial ly velocity are virtual ly zero, so i t never would have beendetected by o ther searches that have been made for nearby s tars .Un fortun ately , we don't know what direction to look. Pertu rbation s fromthis star now should be smaller than those from alpha-centauri and the galacticgravitational grad ient. For tun ately , my group at Ber kele y over the past fouryears has been developing an instrument that turned out to be ideal ly suited to asear ch for the companion. Using a small autom ated te les co pe (either the 30" atLeuschner or the 36" a t the Monterey Ins t i tute for Research in Astronomy) we cansurvey a large number of ob jects in a short period, and obtain ele ctr on icphotographies wi th a CCD (charge-cou pled dev ice) cam era . We are present lytaking such photographs of 5000 red stars in the northern hem isphe re. We willreturn in 3 to 6 months to take a secon d set of photograp hs. In eac h photographwe measure ( in a computer) the distance between the red star and other "fiducial"star s in the sam e field. I f the apparent posit ion of the star cha nge s, then t hedistances in the second set of photographs wil l be different.The 30" Leuschner te lescope i s operated remote ly by our PDP-11 /44com pute r, l inked via telephone l ine to an IBM-PC at the observato ry. An observerat the te lescope monitors the operat ion , but v irtua l ly everything (movement o ftel es co pe and dome, opening of a shu tter, recording of ima ge, and readout t o avide o tape recorder) is auto m ated . We ave rag e about 75 star f ields per hour inthis m ode. Our survey of th e 5000 red stars should be com pl ete by the end of1 9 8 4 . A survey of the southern sky could be done with an automated telescope, orwith emulsions and a Schmidt camera, and we are currently investigating both ofthese poss ib i l i t i es .If the star is not found among the red stars, then it is possibly a brown

dwarf, a dim star with mass probably less than 0 .0? solar mas ses . Good cand idates


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- 9 -The submitted manuscript has been authored by a contractor of theU.S. Government under contract No. DEAC03-76SF00098.

R E F E R E N C E S

1 . L. W. Alva rez , W. Alva rez , F . Asaro , H. Michel , Sc ience 208 , 1C95-1 108(1980) .2. L.W. Alvarez , Proc . Nat l . Acad. Sc i . USA, 80 , pp.627-642 (January 1983) .3 . C.J. Orth, J. S. Gilmore, J.D. Knight , C.L. Pi l lmore, R.H. Tschudy, J.E.Fas s e t t , Sc i e nc e 21 4 , 1 341 - 1 343 ( 1 981 ) .4 . B. F. Bohor, E. E. Foord, P. J. Modreski , D. M. Triplehorn, Science 224, 867-

869 (1984) .5. S. M. Stan ley, "Mass Ex tinct ion s in the Oceans", Sc ien ti f ic Am erica n 250, p.

64-72 (June 1984) .6. D. Raup and J. J. Sepkoski , Pro c. N at . A cad . Sci . _81j 801 -8 05 (1 984) .7. W. B. Harland, et al . , A G eolo gic Tim e Sc ale , (Cam bridge Un iversity Pres s ,

1982) .8. M. Da vis , P. H"t, and R. A. Muller, Na ture 308 , 71 5- 71 7 (1984) .9 . D. Whitmire , A. Jackson, Natu re 308 , 71 3-7 1 5 (1984) .1 0. M. R. Rampino and R. B. Stothers , Nature 3 08 , 709- 71 2 (1984).1 1 . R. D. Schwartz and P. B. Jam es , Natu re J508, 71 2 -71 3 ( 1 984 ) .1 2. R. A. F . Grieve , Geol . Soc . Am. Spec . Pap. 190 , 25 -37 (1982) .1 3. W. Alvarez and R. A. Mul ler, Na ture 308 , 71 8-7 20 (1984) .1 4. X. Dao-Yi , M. Shu-Lan, C. Zhi -Fang, M. Xuo-Ying, S . Yi -Ying, Z. Oin-Wen,Y. Z heng-Z hong, "Abundance Variat ion of Iridium and Tr ace Ele m ents at thePermian-Triassic Boundary at Shangsi , Guangyuan, Srchuan, China", to bepublished; also, S. yi -Ying et al . , "The Discovery of Iridium Anomaly in thePermian-Triassic Boundary Clay in Changxing, Zhejiang, China and i ts

s ignif icance", to be published.1 5. J. T. Kare, C. R. Pennypacker, R. A. Muller, T. S. Mast , F. S. Crawford, andM. S . Burns , Lawrence Berkeley Laboratory report LBL-13317 , a l so in"Supernovae: A Survey of Current R esearch ", M. J. Re es and R. J.Stoneham, eds , p . 325- 339 (D. Reid e l , Dordrect 1 981 ) .


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2 5 0

Million years before presentF ig .l . Fam ily extinctions in the oceans, adapted from Raup and Sepkoski . Thepercentage of families present in a preceding stage and extinct in thefollowing is plo tted at the sta ge boundary. The ver tica l scale is linear, notloga rithm ic as in the original pap er. Species still alive at the pre sen t w ereexcluded from the data set. The arrows indic ate the 26 Myr perio dicity.

uGoOe

arrows indicate26 UJT period

5 I i

2 5 0 2 0 0 1 5 0 1 0 0 5 0Million years before present

i g 2 . Familiy e xtinctions versus t ime; same data as Figure 1 but plotteddiffe ren tly. A t eac h boundary a Gaussian curv e was plotte d, with widthequal to the uncertainty in the time of the extinction, and area equal to thepercen tage of famil ies that became ext inct . The Ga ussan s were added tog*'s* the cu rr e shown. The arrow s ind ica te the 26 Myr periodicity.


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- 1 1 -^ arrows Indicate t imes ofgalact ic plan* crossings

Millioii years before presentGa lactic plane crossings: sam e curve as Figure 2 but now the arrows ind icatethe times when the solar system passed through th e gal actic plane. Thecorrelation between the extinctions and the crossings is no better than fortotally random data.

. ,,J v J v V / v y \ / v A2 S 5 0 7 5 & 0 1 2 5 6 0 C 5 2 0 Q 2 2 5 2 5 0Age (trillion years)

t ! J \ i f \ tLarge impact erasers en the ear th , Iron* A lare i and M n ii er 1 3 . The arrowsindicate a 28.4 Myr periodicity.


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Inte nsity of Comet Sh ow ers v s. time

- 0 . &

13 59Time before present (Myr)

65

F i g . 5 . ^J5JS t2rstar p e r t u r b a t i o n 1 / r 3 " t i n j e ' f- * *

0.2 0.4 0.6Eccentricity 0.5 1.0

F ig . 6 . Durat ion of com et showers , as a funct ion of ecc ent ric i ty . The fu l l -w idth-hal f -max of the perturbat ion curve (Figure 5) i s p lot ted vs . eccentric i ty .


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a v a i l a b l e , w e c a n s t u d y t h e p a r a l l a x i n t h e v is i b le u s i n g o u r a u t o m a t e d t e l e s c o p e .If t h e r e i s no v i s i b l e c om pon e n t , t he n we ma y ha ve t o a t t e m p t pa ra l l a x i n t hein f ra re d f rom the g round , oz wa i t un t i l t he S pa c e Te l e sc ope i s a va i l a b l e .

S U M M A R YI wi l l t ry t o d i s ti ngu i sh he ro b e tw e e n t hos e fa c t s wh ic h I f e e l ha ve b e e ne s t a b l i sh e d , a nd t hose t he o r i e s wh ic h a re sp e c u l a t i v e . I f e e l t h a t t h e fo l l owingfa c t s ha ve be e n e s t a b l i sh e d by t he da t a :

e s t a b l i s h e d1 . Th e re i s a pe r iod i c i t y i n e vo lu t i on on t he e a r th ; m a ss e x t i n c t i o ns oc c u r wi tha re gu l a r 26 Myr pe r iod .2 . A t l e a s t t h r e e of t h e s e e x t i n c t i o n s o c c u r e d s i m u l t a n e o u s l y w i t h t h e i m p a c to f a c ome t o r a s t e ro id on t he e a r th .3 . L a r g e i m p a c t w a t e r i n g o n t h e e a r t h o c c u r s w i t h a 2 8 + 1 M y r p e r i o d , e q u a lwi th in e r ro r s t o t he pe r iod s e e n i n t he ma ss e x t i nc t i ons , w i th t he s a mep h a s e .The fo l lowing c onc lus io ns , wh i l e no t a s f i rmly e s t a b l i s he d a s t he a bove fa c t s ,fo l lowly re l a t i v e ly d i r e c t l y from the m wi th ou t ne e d fo r a m ode l . The y do no t , fo re xa m ple , de pe nd on t he e x i s t e nc e of a so l a r c omp a n ion s t a r .

ve ry l i ke ly t rue1 . Al l of t he pe r iod i c e x t i n c t i o ns s e e n by Ra up a nd S e pkosk i a re c a use d byshow e rs o f c o m e t s o r a s t e ro id s . (Tha t " show e rs " a re r e qu i re d i s ac onse que nc e o f P o i s son s t a t i s t i c s , a nd t he sma l l l i ke l i hood t ha t i nd iv idua lob jec t s wil l h i t the ea r th . )2 . The ne x t showe r i s due i n a bou t 13 mi l l i on ye a r s .3 . The se showe rs ha ve p l a ye d a n impor t a n t ro l e i n e vo lu t i on t ha t ha d no tp r e v i o u s ly b e e n r e c o g n i z e d .

The fo l lowing con c lus io ns a re no t a s f i rm ly es tab l i sh ed as the two abov e , anda re ba se d p r ima r i l y on t he a bse nc e o f c ompe t ing mode l s t ha t a re c ons i s t e n t wi tht h e kn o w n a s t r o p h y s i c a l a n d p a l e o n t o l o g i e s ! d a t a .s p e c u l a t i v e1 . Th e sun ha s a c om pa n ion s t a r , o rb i t i n g wi th a m od e ra t e ly e c c e n t r i c o rb i twi th a ma jo r a x i s of 2. 8 l i g h t - ye a r s .2. The du ra t i on o f a c ome t showe r shou ld be be twe e n a f e w hundre d t housa ndye a rs a nd a f e w mi l l i on ye a r s .

I f t he c om pa n ion s t a r doe s e x i s t and i s no t a n e xo t i c ob j e c t , t he n de d i c a t e dsearches such as ours a re l ike ly to f ind i t in the next few years .


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This report was done with support from theDepartment of Energy. Any conclusions or opinionsexpressed in this report represent solely those of theau tho rs) and not necessarily those of The Regents ofthe University of California, the Lawrence BerkeleyLaboratory or the Department of Energy.Reference to a company or product name doesnot imply approval or recommendation of theproduct by the University of California or the U.S.Department of Energy to the exclusion of others thatmay be suitable.

evidence for a solar companion star (1984)

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