Icarus 141, 354–366 (1999) Article ID icar.1999.6177, available online at http://www.idealibrary.com on Cometary Evidence of a Massive Body in the Outer Oort Cloud J. J. Matese,1 P. G. Whitman, and D. P. Whitmire Department of Physics, University of Louisiana at Lafayette, Lafayette, Louisiana, 70504-4210 E-mail: [email protected] Received September 9, 1998; revised March 11, 1999 been shown that the vast majority of these comets are first-time Approximately 25% of the 82 new class I Oort cloud comets have entrants into the inner planetary region (Fernandez 1981) and are an anomalous distribution of orbital elements that can best be un- therefore commonly refered to as new. We denote the original derstood if there exists a bound perturber in the outer Oort cloud. value of semimajor axis, prior to perturbation by the planets, as Statistically significant correlated anomalies include aphelia direc- A. More conveniently we discuss scaled original orbital energies tions, energies, perihelion distances, and signatures of the angu- x 106 AU/ A so that the range of interest is x 100. Accurate lar momentum change due to the Galaxy. The perturber, acting in determination of the original energies of near-parabolic comets concert with the galactic tide, causes these comets to enter the loss is made more difficult by observational uncertainties and out- cylinder—an interval of Oort cloud comet perihelion distances in the gassing. However, these effects do not substantively influence planetary region which is emptied by interactions with Saturn and Jupiter.More concisely, the impulse serves to smear the loss cylinder the determination of other orbital elements. The data we con- boundary inward along the track of the perturber. Thus it is eas- sider consists of those 82 new comets whose original energies ier for the galactic tide to make these comets observable. A smaller have been calculated with sufficient accuracy to be deemed class number of comets are directly injected by the impulsive mechanism. I by Marsden and Williams (1996). Young comets with x > 100 We estimate that the perturber–comet interactions take place at a provide only indirect evidence about the outer Oort cloud. New mean distance of 25,000 AU. The putative brown dwarf would comets with less accurately known energies (class II) are less have a mass of 3 2MJupiter and an orbit whose normal direction is likely to be truly first-time entrants from the outer Oort cloud within 5 of the galactic midplane. This object would not have been and are omitted since they could bias the analysis. detected in the IRAS database, but will be detectable in the next Our analysis is based on the data listed in Table I. It contains generation of planet/brown dwarf searches, including SIRTF. It is the relevant orbital elements of all 82 new class I comets. All also possible that its radio emissions would make it distinguishable angles refer to the galactic coordinate system and include the lat- in sensitive radio telescopes such as the VLA. c 1999 Academic Press itude, B, and longitude, L, of aphelia as well as an orientation co- Key Words: comets, dynamics; celestial mechanics; infrared ob- servations; jovian planets. ordinate of the angular momentum vector discussed below. They were obtained by us using standard transformations from eclip- tic coordinates (Marsden and Williams 1996) to galactic coordi- nates. The scaled energy and perihelion distance are also listed. 1. INTRODUCTION In Fig. 1 we show the scatter in aphelia directions. We identify an anomalously abundant “great circle” of comet aphelia cen- Dominance of the galactic tide in making Oort cloud comets tered on galactic longitude 135(315) 15. A histogram sum- observable has been firmly established. Beginning with the work marizing the galactic longitude distribution is shown in Fig. 2. of Byl (1983), a succession of studies (see Matese and Whitman The fundamental question to be addressed is whether it is pos- (1992) for a review of early contributions) has demonstrated that sible to identify dynamical signatures from the data. the distribution of orbital elements correlates well with the pre- Mechanisms considered include impulsive events from Oort- dictions of a theory that the adiabatic galactic disk tide is predom- cloud-penetrating stars, tidal impulses from Oort-cloud-grazing inantly responsible for changing comet perihelia and bringing molecular clouds, the adiabatic galactic interaction (both disk them into the observable zone. This is true during the present and core tides), and impulses from a putative bound perturber. In epoch and is likely to be true when averaged over long time contrast to these dynamical options there is the chance that small- scales (Heisler 1990). number statistics and observational selection effects preclude the The outer Oort cloud is formally defined as the interval of possibility of identifying dynamical effects. Aphelia directional original cometary semimajor axes 104 AU (Oort 1950). It has distributions in ecliptic, equatorial, and galactic coordinates have been studied (Matese et al. 1998), and it was concluded there that asymmetries in the observed distributions are unlikely to be 1 To whom correspondence should be addressed. Fax: (318) 482-6699. entirely attributable to nondynamical explanations. 354 0019-1035/99 $30.00 Copyright c 1999 by Academic Press All rights of reproduction in any form reserved. EVIDENCE OF A MASSIVE BODY IN THE OUTER OORT CLOUD 355 TABLE I New Class I Comets Out of the great circle In the great circle Comet q (AU) x () L () B () H˙ Comet q (AU) x () L () B () H˙ C/1890 F1 1.91 89 167.3 235.8 23.7 C/1958 R1 1.63 76 134.0 307.7 18.8 C/1955 G1 4.50 82 169.0 233.3 29.4 C/1959 X1 1.25 69 66.4 124.3 78.5 + C/1941 K1 0.87 78 80.8 271.9 35.1 + C/1898 L1 1.70 68 314.9 143.9 28.8 C/1973 W1 3.84 71 63.3 32.7 48.2 C/1987 F1 3.62 59 185.8 130.4 26.2 C/1972 L1 4.28 69 67.2 235.3 39.9 + C/1976 D2 6.88 59 315.0 121.8 44.2 + C/1937 C1 1.73 62 354.6 214.7 38.7 + C/1900 B1 1.33 57 264.6 305.5 42.1 + C/1993 F1 5.90 59 214.2 330.2 45.5 C/1989 Y1 1.57 49 96.5 329.2 6.6 C/1973 A1 2.51 49 219.9 107.3 50.6 C/1983 O1 3.32 48 356.1 325.3 54.7 C/1886 T1 0.66 46 314.4 288.7 24.5 + C/1888 R1 1.81 48 290.0 314.9 59.2 C/1987 H1 5.46 46 161.5 191.2 17.0 C/1932 M2 2.31 45 171.7 146.9 14.1 C/1912 R1 0.72 45 121.0 225.8 13.0 + C/1946 P1 1.14 44 108.2 127.2 19.7 C/1954 O2 3.87 42 53.6 336.6 18.9 + C/1954 Y1 4.08 39 232.9 314.2 23.9 C/1979 M3 4.69 42 126.8 207.4 14.6 + C/1950 K1 2.57 37 269.3 138.5 43.4 C/1960 M1 4.27 40 164.0 221.2 12.3 C/1976 U1 5.86 37 90.2 310.0 30.8 C/1925 G1 1.11 40 151.7 238.7 10.9 + C/1974 F1 3.01 36 10.2 140.5 22.1 C/1990 M1 2.68 40 164.5 172.0 48.4 C/1948 T1 3.26 34 307.4 324.5 17.4 C/1925 F1 4.18 35 327.1 66.4 41.2 + C/1903 M1 0.33 33 92.8 320.7 34.5 C/1948 E1 2.11 34 83.9 250.1 38.3 + C/1978 A1 5.61 33 167.3 142.9 31.0 C/1987 W3 3.33 29 63.2 334.5 64.1 C/1993 K1 4.85 33 346.9 131.2 2.6 C/1913 Y1 1.10 29 238.4 282.6 52.5 C/1989 X1 0.35 32 218.5 325.6 41.4 C/1947 Y1 1.50 28 37.3 245.1 49.1 + C/1992 J1 3.01 28 0.9 316.8 44.2 + C/1906 E1 3.34 28 133.6 38.1 44.9 C/1978 H1 1.14 24 29.6 124.9 20.4 + C/1914 M1 3.75 27 101.0 201.2 0.8 C/1925 W1 1.57 24 140.7 323.9 21.6 C/1902 R1 0.40 27 229.5 189.0 16.9 C/1944 K2 2.23 18 158.6 125.0 31.5 C/1980 E1 3.36 27 29.8 177.3 17.6 + C/1988 B1 5.03 13 122.8 316.1 48.0 C/1902 X1 2.77 26 191.1 20.8 31.0 C/1974 V1 6.02 11 63.7 309.5 27.6 C/1907 E1 2.05 25 280.6 53.4 20.4 + C/1946 C1 1.72 13 277.7 312.6 60.7 + C/1962 C1 0.03 25 106.3 218.6 27.5 + C/1983 O2 2.25 18 178.4 134.2 27.6 C/1947 S1 0.75 24 170.2 185.8 11.5 + C/1978 G2 6.28 23 260.2 126.9 33.9 C/1975 E1 1.22 23 178.2 55.1 42.0 + C/1899 E1 0.33 109 264.1 308.5 50.5 + C/1922 U1 2.26 21 53.0 271.2 16.4 C/1984 W2 4.00 20 100.3 79.5 32.9 + C/1973 E1 0.14 20 46.6 207.8 17.6 C/1935 Q1 4.04 19 115.9 248.5 12.1 + C/1921 E1 1.01 18 143.1 219.3 59.0 C/1956 F1 4.45 17 62.1 180.3 24.8 + C/1916 G1 1.69 17 30.5 226.4 18.4 C/1991 F2 1.52 16 344.4 90.0 29.6 C/1942 C1 1.45 16 22.1 89.8 17.3 + C/1978 R3 1.77 15 18.5 31.0 24.3 C/1853 L1 0.31 12 344.5 223.6 34.9 C/1896 V1 1.06 5 243.7 192.5 2.2 + C/1993 Q1 0.97 3 173.8 112.5 41.4 + C/1940 R2 0.37 1 88.5 42.1 24.4 + C/1946 U1 2.41 1 255.3 347.7 48.4 + C/1892 Q1 0.98 27 105.1 72.1 32.5 C/1942 C2 4.11 34 335.0 19.2 25.1 + C/1932 M1 1.65 56 76.7 250.7 25.1 + C/1898 V1 2.28 71 172.4 11.0 11.5 C/1991 Y1 0.64 94 102.7 16.9 9.0 + C/1952 W1 0.78 125 10.2 84.9 15.6 C/1895 W1 0.19 172 354.5 31.9 48.8 356 MATESE, WHITMAN, AND WHITMIRE bution in aphelia directions will be nearly isotropic.