Borrelly, Comet (19P/Borrelly)
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The nucleus of Comet Borrelly seen by
Deep Space 1
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A short-period comet discovered by the
French astronomer Alphonse Borelly (1842–1926). It became only the
second comet to have its nucleus photographed by a space probe when Deep
Space 1 flew passed it at a distance of only 2,170 km on September 22,
2001. Images showed the 8-km-long by 4-km-wide nucleus to be shaped like
a bowling pin and to be spraying material into space along a handful of
tightly collimated jets. Scientists were surprised when the probe revealed
that, though the solar wind flows symmetrically
around the coma of Comet Borrelly, the nucleus
lies to one side, shooting out a great jet of material that forms the cloud
that makes the comet visible from Earth. Around the most active regions
are a series of flat-topped, steep-sided hills, or mesas, that probably
formed much like terrestrial mesas. The top of each mesa has a thick insulating
layer of dust, but the steep sides expose the underlying ice-rich comet
material. Ices sublimate from the sides, undercutting the thick, insulating
layer and causing sections of it to collapse on the valley floor. Borrelly
seems to be broken into two pieces, canted at about 15°, that appear
to chaff against each other, raising what look like compressional ridges
at the boundary of the two sections.
| semimajor axis |
3.61 AU |
| perihelion |
1.358 AU |
| eccentricity |
0.624 |
| inclination |
30.3° |
| period |
6.86 years |
Related category
• COMETS
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