The Centaurs are a set of solar system objects whose orbits are confined between those of Jupiter and Neptune. The current belief is that Centaurs are objects scattered from the Kuiper Belt that may eventually end up in the inner solar system as short-period comets. There are some 167 centaur/scattered-disk objects clasiffied as such by the mpc as of april 2006.
Cometary activity has been found in some of these centaurs, including two objects numbered and named as asteroids, 2060 Chiron and 60558 Echeclus.
List maintained by Yanga Fernandez
|165P/LINEAR||6.830||0.621||15.9||76.4||3.095||(= C/2000 B4)|
|166P/NEAT||8.564||0.384||15.4||51.9||3.285||(= C/2001 T4)|
|167P/CINEOS||11.788||0.269||19.1||64.8||3.527||(= C/2004 PY42) MPEC2005-M12|
|174P/Echeclus||5.826||0.457||4.3||35.1||3.032||(= (60558) = P/2000 EC98) orbit solution JPL#8|
|C/2001 M10 NEAT||5.303||0.801||28.1||138||2.586|
|C/2004 A1 LONEOS||5.463||0.308||10.6||22.2||2.963||MPC51184|
|P/2005 S2 Skiff||6.398||0.197||3.1||22.5||3.076||MPEC2005-T76|
|P/2005 T3 Read||6.202||0.174||6.3||20.6||3.045||MPEC2005-W81|
The first discovered and brightest known Centaur, 2060 Chiron, is relatively well studied. The object is firmly established as a comet, with a weak but persistent coma.
60558 Echeclus was discovered by Spacewatch in 2000 and initially classified as a centaur with provisional designation 2000 EC98. A detection of cometary coma on images taken on 2005 Dec 30.5 with the Palomar 5-m reflector by Y.-J. Choi and P. R. Weissman, Jet Propulsion Laboratory, was published in IAUC 8656 issued on 2006 January 6th.
On 11 April 2006, IAUC8701, S. Tegler, Northern Arizona University; G. Consolmagno, Vatican Observatory; and W. Romanishin, University of Oklahoma, obtained R-band CCD images on Apr. 2.3 UT with the Vatican Advanced Technology 1.8-m telescope at Mt. Graham, the coma previously reported around this object (IAUCs 8656, 8660, 8677) had developed a complex structure. A low-surface-brightness coma of diameter 2' is centered 1' east of the nuclear condensation. A higher-surface-brightness condensation about 12" in diameter was centered about 7" west of the nuclear condensation, which itself was of mag R about 20.1 and clearly offset from the center of the higher-surface-brightness structure, suggesting a detached coma produced by a transient event.
The origin of the coma seems to be the sublimation of carbon monoxide at temperatures about 80K, however no spectral data is available as yet.
Echeclus was the subject of 120 CCD images 30 seconds exposure each that were obtained the night of 2006 April the 7th through the 0.3m LX200 at J87 La Caņada. Below is the image result of stacking on the comet's motion, a jet-like structure, some 26 arc seconds long in position angle 23 degrees is seen
An enlargment to better show the structure(s)
An animation demonstrates how the jet structure moves together with the nucleus as a whole.
Next night's images do not show the possible jet (more moonlight, worse seeing)
As a comparison, here follows a stack of images of comet 29P/Schwassmann-Wachmann 1, also a centaur, displaying a coma and ject activity, this time the heliocentric distance was just about that of jupiter.
Further observation was required to confirm/roule out the possible jet
John Farrell (MPC H02) Sulphur Flats Observatory, La Cueva, using a 0.41m telescope, confirmed the existence of jets using a rotational gradient on his images dated 17, 18 and 19 April reproduced here with his permission
These observations, showing collimated jets escaping from the nucleus, seem to support the idea that activity for these centaurs is generated by localized sources (vents/jets)