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https://ntrs.nasa.gov/search.jsp?R=19750024914 2018-10-18T10:08:03+00:00Z

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UnG1av Astroph y si cal oLsprvatory) CSC& r3L' G3/91 X1136

THE STUDY OF THE PIMICS OF COMETARY NUCLEI

u

Grant NSG 7052

Semiannual Progress Report No. 21 March 1975 to 31 August 1975

Principal Investigators

Dr. Fred L. WhippleDr. Brian G. MarsdenDr. Zdenelc Selmnina

Prepared forNational Aeronautics and Space Administration

Washington, D.C. 20546^i

September 1975

Smithsonian InstitutionAstrophysical Observatory

Cambridge, Massachusetts 02135

The Smithsonian Astrophysical Observatoryand the Harvard College Observatory

are members of theCenter for Astrophysics

OCT 1975 i7j—

RECEIVEDsAn to Flow "'g

NM wool

The NASA Technical Officer for this grant is Stephen E. Dwornik, SL/PlanetaryPrograms, NASA, Washington, D.C. 20546.

it ..

'HE STUDY OF TUE PHYSICS OF COMETARY NUCLEI

Grath NSG 7082

Semiannual Progress Report No. 2

1 March 1975 to 31 August 1975

Principal Investigators

Dr. Fred L. WhippleDr. Brian G. MarsdenDr. 7.dcnek Sekanina

Prepared for

National Aeronautics and Space AchiiinistrationWashington, D.C. 20546

September 1975

Smithsonian lnsiitutionAstrophysical Ohservatory

Camhridge, Massachusetts 02138

The Smithsonian Astroph 'N'sical Observatoryand the Harvard College Observatory

are members of theCenter for Astrophysics

The NASA Technical Officer for this grant is Stephen E. Pwornik, SL/PlanetaryPrograms, NASA, Washington, D.C. 20546.

509-057

,a

THE STUDY OF THE PHYSICS OF COMETARY NUCLEI

Semiannual Progress Report No. 2

Individual reports on the progress of reseexch by F. L. Whipplep B. G. Marsden,

and Z. Sekanina follow. The Catalogue of Cometary Orbits (1975) by B. G. Marsdenhas been used as a basis for a detailed computer search for comet groups.

.N

SPLIT AND IIYPERBOLIC- (?) COMETS

Whipple's paper "Do Comets Play a Role in Galactic Chemistry and y-Ray Bursts?"was published In the Astronomical Journal, vol. 80, no. 7, July 1975. His paper "A

Speculation About Comets and the Earth" was presented at the Twentieth 'Liege Inter-national Astrophysical Colloquium at Liege, Belgium on 19 June 1975, and will soonappear as a Center for Astrophysics Preprint. It will eventually be published in theLiege Colloquium volume. An abstract is attached (see Addendum I). Work on thisintriguing subject is postponed because of other research and writing commitments,

some mentioned below.

i

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With W. F. Huebner, Whipple is completing a chapter entitled "The Physics ofCcmets" for Reviews of Astronomy and Astrophysics (1976), which will appear as aPreprint from the Center for Astrophysics.

His earlier reported paper on "Criteria for the Identity of Comet Orbits" withM. Lecar is under preparation and will first appear as a Preprint of the Center forAstrophysics.

Whipple's research on split comets continues and will soul, be presented in a

three-part series of papers that will feature:

a) A report on the study of the phenomena of split comets, showing that gravi-tationally double comets are an unlikely cause for those not tidally disrupted and that

jet-action "spin-up" appears to be the most likely of the intrinsic splitting mechanisms.

b) A report on the study of split-comet criteria among the orbits of parabolic

and very long-period comets with inclinations in the range 79° to 100%

c) An analysis of E. J. Opik's comprehensive study "Comet Families andTransneptunian Planets" (Irish Astronomical Journal, vol. 10, pp. 35-92, 1971).

G By statistical methods, Opik proves to his satisfaction that most very-long periodcoquets occur in a number of orbitally associated groups that must have involved

2d

^8

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ii

either multiple comet splitting or large original cohesive groups in the Opik—Oortcloud. Whipple is finding by the Monte-Carlo method of statistics and by probability

theory that much of apik's statistical evidence is untrustworthy.

F. L. Whipple

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ORBITAL CALCULATIONS

Further calculations have been made on the nongravitational forces affectingshort-period comets, notably P/Westphai, a comet having a period of some 62 years

dN !; that was observed in 1852 qnd 1013 and that should now be about to retim. Since the

r comet faded out before reaching perihelion in 1913 there is some doubt as to whether

i it will now in fact be observed. Considerable difficulty has been experienced inlinking the 1852 and 1913 observations, both without and with recourse to nongravita-tional terms in the equations of motion. It is not yet clear whether this difficulty ispeculiar to this comet (perhaps because of its fade-out) or a potential problem with the

other periodic comets (e. g. , P/IIailey) that have periods of 60 years and more. Theavailability of recently measured positions of P/Pons-Winnecke, P-Grigg-Skjellerup,and P/Honda-Mrkos-Pajdusakova has made it possible for us to extend the earliercalculations of the nongravitational forces on these comets.

Together with Z. Selmnina, B. G. Marsden has continued the determinations ofimproved orbits for long-period comets. During the six months ending 13 August1975, they derived orbits for comets 1844 III, 1895 IV, 1937 IV, 1948 I, 1955 V,1960 II, 1967 11 1 1972 VIII, 1972 IX, 1972 XII, 1973 11 1 1973 VII, 1073 X, and 1974b.

B. G. Marsden

4

4

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INTERSTELLAR COMETS

Z. Selamina completed his work on the probability theory of encounters withInterstellar comets (Sekanina, 1975a) and submitted the paper for publication in Icarus.The results of the investigation were presented at the 146th meeting of the AmericanAstronomical Society, held at San Diego, California,, in August 1975 (Sekanina, 1975b;see Addendum II).

NUCLEAR PROPERTIES FROM ANOMALOUS TAILS AND BAND STRUCTURESIN DUST TAILS

Sekanina has further advanced his study of the emission processes of large dustparticles from comets. The preliminary results of his statistical investigation ofanomalous tails (antitails), which are composed of the large particles, were presentedat the IAU Colloquium No. 31 on Interplanetary Dust and Zodiacal Light, held at

Heidelberg, Germany, in June 1975. Also part of this research was 5ekanina's Augusttrip (connected with his travel to the American Astronomical Society meeting at SanDiego) to the Lunar and Planetary Laboratory of the University of Arizona at Tucson,Arizona, where images of a number of comets from Dr. E. Roemer's collection ofphotographic plates were examined for potential displays of antitaiis. The results ofthe inspection in regard to periodic Comet Encke were incorporated in the writtenversion of the Heidelberg paper and will appear in the Colloquium's Proceedings(Sekanina, 1975c; see Addendum III). Work on this whole subject is still continuingand is expected to result in a number of papers.

While dust tails are usually structureless, a few comets did display temporary,nearly parallel bands of light in their dust tails. These structures may retainimportant information on the material they are composed of and thus an the solid com-ponent of the cometary nucleus. Unfortunately, comet photographs showing such forma-tions in the dust tails are extremely rare. Through a good deal of correspondence andpersonal contacts, however, Sekanina gathered sequences of photographs of two comets,where the development of the band structures was observed most completely: Comet

5

Mrkos 1957 V (1957d) and the Great January Comet 1910 I (1910a). It is fudged thatthe essential information can be derived from the study of the motions of the bandsthrough the tail. Since none of the photographs was photometrically calibrated, theintensity distribution in the bands cannot be determined. The available photographicmaterial consists in part of loaned originals, in part of copies, some of them gained,some on loan. The photographs of Comet Mrkos come from the following observers:John A. Farrell, now at the Los Alamos Scientific Laboratory, Los Alamos, NowMexico, who photographed the bands at Port Worth, Texas, on 1957 August 14. 1 1 15.1216. 1, and 17.1 (UT) with a 19-cm f/1. 5 Schmidt camera using a Royal Pan film;Alan McClure, Hollywood, California, observing from Frazier Mountain, near FrazierPark, California, on August 10. 2 t 11. 2 1 12. 2, and 14.2 with a 10-cm f/5 camera andusing 103a-E plates and a filter; and Henry L. Giclas, Lowell Observatory, Flagstaff,Arizona, who used the Observatory's 33-cm f/5. 1 astrograph and an 103a-0 plate onAugust 16. 2. The photographs of Comet 1910 I (not calibrated, either) were obtained

.1

by C. O. Lampland, Lowell Observatory, with the Observatory's Voigtlander 3.7-cmf/5.4 camera on two different emulsions, and copies of the plates from 1910 January27.1, 28. 1 2 29. 1, and 30. 1 (UT), showing the bands, were acquired courtesy ofMr. Giclas during Sekaniaa's stay at the Observatory in August (after the meeting atSan Diego). Also available are copies of other plates of Comet 1910 I, taken with aBrashear doublet 12.7-cm f/7 camera between January 27 and 30, and showing an

antitail. It is expected that a significant fraction of Sekanina's next research periodwould be spent on the photographic material of the two comets.

REFERENCES

Sekanina, Z. (1975x). A probability of Encounter with interstellar comets and thelikelihood of their existence. Center for Astrophys. Preprint Series No. 297;to be published in Icarus.

Sekanina, Z. (1975b). On the existence of interstellar comets and the probability oftheir encounter with the sun. Presented at the 146th meeting of the !AmericanAstronomical Society, San Diego, California, August 1975; abstract in Bull. Amer.

Astron. Sec., vol. 7j p. 467.

6

._ _ _

Sekanina, Z. (1975c). Predicted favorable visibility conditions for anomalous Wigof comets. Presented at the IAU Colloquium No. 31, Interplanetary Dust and

Zodiacal Light, Heidelberg, Germany, June 1075; to be published in theProceedings, from the Colloquium.

Z. Sekanina

ADDENDUM

i^ l

4

1

,, i

DO COMETS PLAY A ROU IN GALACTIC C111.111STRY

l AND y-RAY BURSTS?

E

Fred L. Whipple

Center for AstrohhvsicsHarvard College Observatory and Smithsonian Astroplivslcal Observatory

t Cambrldl e, A lass achiisetts 02138

This paper explores the plausibility of the assumption that enough mate-

rial from Interstellar space is locked up in comets to reduce significantly the

apparent growth rate of 'heavy" elements (mass greater than Ile) and, there-

fore, the present abundance of heavy olemonts in the interstellar medium and

in the disk stars. A related suggestion concerns the influx of comets on

neutron stars as a source of y-ray bursts. Although no interstellar comets

have been observed, reasonable upper limits to the observed numbers and

masses do not rule out the first suggestion. The y-ray-burst suggestion

appears unlikely. A sui-prisingly large total mass of comets could he gravi-

tationally bound to the Sun and, of course, to other stars, but remain undetected.

The nature of the 1908 Tunguska explosion is discussed briefly. It was prob-

ably not an encounter with an active comet.

VA

1

ADDENDUM II

lLL

A

BULLETINOF THE

AMERICAN ASTRONOMICAL . SOCIETYPUBLISHED BY Tim.,AMERICAN INSTITUTE OF PHYSICS INC.

e VOL UHL 7, A''UNUrl? 3, PART / 1975

THE 146TIl MEETING OF THE AMERICAN ASTRONOMICAL SOCIETYHELD I8-21 AUGUST 1975 AT SAN DIEGO, CALIFORNIA

" Abstracts of Papers Presented

} (Numbers preceding abstract titles indicate: session, sequence of presentation, and category,)

WEDNESDAY, 20 AUGUST

Session 34: Rooms KLNIN, 0915-1215

74.06,02 On the Cxlntenae,—_ofIntorntnllnr Camaraand the probability oftheir 1,eount,a r with thaSun.Z. Sekbnlea, Center fur. A5'ra hvole x. - A generaldreary is formulated extabllnh lag tlm relation mmtingthe opatu denulty of interstellar covats, their Influxrate to the observable region of thn solar syntax, thedegree of dlaperalon III the MaxVelltnn distribution ofcomet velocities In the interstellar cloud, and thecloud'n nydtematle velocity relative to the akin. Thetheoretical expronsLon for the probability of encounterof Cho tun with an interstellar tnmet. is then combinedwith the observed absence of strongly hyperbolic cometorbits to determine An upper limit of 6 x 10-4 solarmanes per cubic parsec, or 4 x 10-24 g UM-3, for theSpace density of interstellar comets. 'file distributionof nemlmajor axes among the orbits of Interstellar com-eta. ralntive to Cho nun,. calculated from Cho. model,indicates that a strong hyperbolic excess must be typi-cal for nn overwhelming, mijorlty of Interstellar cometsragardleas of the dynamical behavior of the cane Corycloud, except when the cloud follows the motion of thesun and the. aloperslon of Individual velocities is verylaw.. Thio • cass, however. beeooes rile problem of anCart-type cloud, since It implies a possibility of cap-ture by the sun. This research was supported by front.NSC 7082 from the National Aeronautics and Space.Administration.

ADDENDUM Hl

I

To appear inInterplanetary Dust and Zodiacal LightProceedings from IAU Colloquium No. 31Heidelberg, Germany, 10-13 June 1975

PREDICTED FAVORABLE VISIBILITY CONDITIONS FOR ANOMALOUS TAILS OF COMETS

Zdenek Sekanina

Center for AstrophysicsHarvard College Observatory and Smithsonian Astrophysical Observatory

Cambridge, Massachusetts 02135, U.S.A.

It was shown elsewhere (Sekanina, 1974) that the observability

from the earth of an anomalous tail (antitail) of a comet can be rather

straightforwardly predicted from the dynamical and geometric conditions.

The physical presence or absence of the antitail at a precalculated time

-d is then a measure of the comet's production rate, at the relevant emis-

sion times, of relatively heavy dust particles (mostly of submillimeter

size) that constitute such an antitail. Because the large grains are e-

mitted from the nucleus at very low vulocities (typically meters or tens .

of meters per second), an antitail is essentially a two-dimensional for-

;l oration in the orbit plane of the comet and can be recognized best when

( projected edge-on, i.e., when the earth crosses the nodal line of the`t comet's orbit. In general, however, this condition is not essential for

the recognition of antitails (cf., e.g., Comet Kohoutek 1973 XII).

Since the emission rate of heavy dust particles is a potentially

significant parameter for a physical classification of comets, we made

use of the visibility conditions to list the comets that should have dis-

played a sunward tail around the time of the earth's pasaages through the

orbit plane. This type of the antitail observability will be termed the

nodal appearance. A computer program executing the conditions for a no-

dal appearance was applied to the Catalogue of Cometary Orbits (Marsden,

1975), starting with the comets of 1737. However, we excluded all comets

that were at the critical times located near the antisolar point in the

sky (elongations exceeding 135°), where the definition of the sunward di-

rection becomes meaningless. We also excluded all cases at heliocentric

distances larger than 2 AU in order not to confuse the antitails with the

icy tails (Sekanina, 1973, 1975) that are observed far from the sun and

point fairly frequently in the general direction of the sun.

A

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2

The statistics of the nodal appoarances of antitails of comets,1

whose co:ditions were satisfied within, or not more than 5 days outside,

the period of observation, arc listed in.Table I, separately for nearly-

Parabolic comets (revolution periods more than 200 years) and for short-

period comets. The calculations were done for dust particles with a ra-x do 1-p of radiation pressure to solar gravity of 0.01 (known to be com-

men in observed antitails) and for two different starting emission times.

Whereas the choice of 1-p is not crucial, Tabled shows that the time of

onset of dust production affects the statistics substantially. The com-

ets with a sunward tail reported to have been detected near the predicted

time are listed in Table II, where columns 2 to 4 give, respectively, the

perihelion distance, the reciprocal value of the original semimajor axis

(for P/Encko the revolution period), derived from Marsden (1975) and from

Everhart and Raghavan (1970), and the absolute magnitude (VsLkhsvyatsky,

1958). We remark that with the exception of 1937 IV the comets have per-

ihelia well inside the earth's orbit, and that apart from the controver-

sial case of P/Encke (see details below) the comets' revolution periods

` are longer than 7000 years and their absolute magnitudes brighter than a.

Table I points consistently to a conclusion that only about 20 to

30£ of the nearly-parabolic comets that should have displayed an antitail

at the node were actually observed to do so.- Indeed, if we count only

".he comets with nearly-ideal - observing conditions, the figure is 222 for

the onset of emission at 4 AU and increases to 302, if the condition is

relaxed to 2 AU. If we count all comets that were observed near the

node, the fraction of positive observations is lower, as can be expected,

but not very substantially: we find 19% for 4 AU emissions and 23% for

2 AU emissions.

The results are dramatically different for short-period comets.

Although there were numerous opportunities for observing a nodal appear-

ance of an antitail, we do not yet have a single clearly positive obser-

vation. The only promising case so far is that of P/Encke in 1964, for

which Roemer (Roemer and Lloyd, 1966) secured a pair of plates only 2.5

days after the earth's nodal passage; the comet was 88 days after peri-

helion. A close inspection of the plates by Dr. Roemer and the writer

revealed two extensions emanating from the weak; nearly-stellar image ofY

the comet in the opposite directions, one of them pointing right toward

the sun. Although this sunward tail does not, in the writer's opinion,

resemble the gas jets, frequently observed in P/L•'ncke before perihelion, i

there is still no more than a 50% chance that it is a true antitail.

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The general ab*ance of .antitails among the short--perioJ com,2t:i ap-pears to be incompatible with the existence of meteor streams known to :De

associated with many of these comets. Unfortunately, at their observed

return, the parent comets; of the three spectacular-storm producing me-

teor streams - P/Iliela, P /Giacobini- 'l.inner arid . P/Tempel-Tuttle -- werenever placed favorably enough for a nodal appearance of an antitail.

And, of all the other comets known to he related to meteor streams, only

-wo had such very favorabl y apparitions. P/E:nckce in 1878, 1888 and 1964,and P/Pons-tr'innocke in 1909, although P/Pons-Ilinnecke is not apparently

associated with a permanent stream (Cook, 1973). The other comets with

favorable condAtions were P/Tempel 1 in 1867, P/Finlay in 1919, P/Kopff

in 1945, P/Grigg-Skjellerup in 1947, and P/Schaumasse in 1952 and 1960.

Streams that could be associated with P/Finlay or P/Grigg-Skjellerup have

never been reported; the other come,- ,.: have perihelia well beyond 1 AU.

With one doubtful an, two negative results in the three nearly-

ideal returns, I'/Encke presents probably the most solid evidence to date

against the positive correlation between the antitails and the meteor

streams. In order to obtain more data, positive or negative, on the oc-

currence of the antitails, %.e investigated their visibility conditions in

the future returns of the: short-period comets. Among 166 returns of 60

cornets with perihelia within 2 AU between 1976 and 1999 (orbital elements

courtesy of Dr. Marsden), the following instances - most of them outside

=lal areas - are considered as most significant: P/d'Arrest in 1976/77,

P/Encke in 1977 and 1987, P/Schwassmann-t •tachmann 3 in 1979, P/Honda-Mrkos-Pajd lrikova in 1980, P/Grigg-Skjellerup in 1982 and 1987, P/Cr.ommelin iru1984, P/Pans-Winnecke in 1989/90, and P/Giacobini-Z inner in 1999.

This work war; supported by grants NGft 09 - 015 - 159 and NSG 7082 from

the National Aeronautics and Space Administration.

References

Cook, A. F. (1.973), in "Evolutionary and Physical Properties of Meteor-^;ds", Ifemnnway, C. h., V.iIIman, P. M., and Cook, A. F.. Eds. , NA',A SP-319, 11ashir.gton, D.C., p. 183.

l.vorhart, E., an:] Raghavdn, N. (1970), Astron. J. 75, 258.Marsden, B. G. (1975) , Catalogue of Cometary Orbits. (2nd edition.) IAUCentral Bureau for Astrono;;ical Telegrams, Smithsonian Astrophys. Obs.

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