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 = a_J / a + 2 cos I ( a / a_J )^1/2 (1- e)^1/2

where a, e, I, are the orbital parameters of the object and a_J 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

Minor Bodies of the Solar System

Asteroids in Cometary Orbits (ACOs)