Asteroids in Cometary Orbits (ACOs)

It has been longed assumed that comets and asteroids form two distinct classes of small objects of the Solar System. Comets, together with TNOs and Centarus, constitute the most pristine observable objects formed during the early ages of the Solar System. In particular, comets are planetesimals generated in the region of the giant planets and slightly beyond the limits of the solar nebula. Asteroids, on the other hand, are the most direct remnants of the building blocks that formed the planets, and so they mainly concentrate between the orbit of Mars and Jupiter. Due to their different formation places, comets and asteroids volatile contents are consequently different, and this has been the key to separate the two populations: comets produce a coma when approaching the Sun due to the "evaporation" of those volatiles, while asteroids do not. But the discovery of cometary-like objects that never develop a coma, or comets that look like asteroids when the evaporation process is stopped, has questioned this simple criteria to distinguish between the two populations.

If one cannot use the presence or not of a coma to separate between asteroids and comets, it is necessary to find another criteria. Dynamically, the Tisserand parameter (Kresàk 1979) has been widely used to see if an object is a comet or an asteroid. The Tisserand parameter (or invariant) is defined as:

T = aJ / a + 2 cos I ( a / aJ )1/2 (1- e)1/2

 where a, e, I, are the orbital parameters of the object and aJ is the semi-major axes of the orbits of Jupiter. With this definition, objects with T < 3 are comets (or have cometary-like orbits) and objects with T > 3 are asteroids. Consequently, asteroids that have T < 3 are called Asteroids in Cometary Orbits (ACOs). Hildas and Trojans, which also have T < 3 due to their resonant orbits are not included in this category.

 

List of observed objects

Here is a table with the observed asteroids in cometary orbits (ACO), Hildas, Trojans and main belt asteroids (MB) included in Licandro et al. (2008). We show the asteroid name, the spectral range of the data, the dynamical group, the absolute visual magnitude (H) and the Tisserand parameter (T ). To see a plot of the object's spectrum click on its name. To download the corresponding ASCII file click on data.

 

Asteroid Data Group H T
 (225) Henrietta    ACO 8.72 3.001
 (1036) Ganymed VIS  ACO-NEO 3.50 3.032
 (1345) Potomac    Hilda 9.73 2.993
 (1362) Griqua    ACO 11.18 2.962
 (1529) Oterma    Hilda 10.05 2.999
 (1542) Schalen    MB 10.30 3.211
 (1754) Cunningham    Hilda 9.77 2.997
 (1922) Zulu    ACO 12.20 2.752
 (2246) Bowell    Hilda 10.56 3.040
 (2363) Cebriones    Trojan  9.11 2.693
 (2569) Madeline    MB 11.20 3.147
 (2938) Hopi    ACO 11.50 2.775
 (3248) Farinella    MB 10.70 3.145
 (3688) Navajo    ACO 14.90 2.996
 (4744) 1988 RF5    MB 11.10 3.034
 (4837) Bickerton    ACO 11.60 3.012
 (6144) 1994 EQ3    ACO 11.50 2.871
 (6909) Levison    ACO 14.10 2.935
 (8373) Stephengould    ACO 13.80 2.606
 (10739) Lowman    ACO 14.50 3.006
 (14409) 1991 RM1    ACO 11.60 2.996
 (18898) 2000 JX    ACO 12.50 2.982
 (19748) 2000 BD5    ACO 11.50 3.010
 (20898) Fountainhills    ACO 11.00 2.374
 (22653) 1998 QW2    ACO 13.60 2.912
 (22714) 1998 SR2    ACO 12.60 3.008
 (23186) 2000 PO8    Hilda 11.10 2.994
 (24689) 1990 OH1    ACO 12.80 2.999
 (44566) 1999 CK103    ACO 11.60 2.989
 (65996) 1998 MX5    ACO-NEO 18.50 2.955
 (102528) 1999 US3    ACO 13.70 2.986
 (137427) 1999 TF211    ACO-NEO 15.00 2.966
 (172678) 2003 YM137    ACO-NEO 18.70 3.027
 1992 UB    ACO-NEO 15.98 2.903
 2004 JR1    ACO-NEO 17.56 2.866

 

Citation

Researchers using these data are kindly requested to reference the following paper:

Licandro, J., Alvarez-Candal, A., de León, J., Pinilla-Alonso, N., Lazzaro, D. and Campins, H. (2008). "Spectral properties of asteroids in cometary orbits", A&A, 481, 861