Cometa 2P/Encke em Abril

Luis França

23 Mai 2006
APPROACHING PUZZLE: Comet 2P/Encke is approaching Earth and it's bringing a puzzle.
On Feb. 22nd, veteran comet observer Mike Holloway of Van Buren, Arkansas,
photographed 2P/Encke. See below. The comet is the fuzzy blob in the middle--but what are those strange "spikes" sticking out either side?


"It does not resemble any comet tail I've ever seen," says Holloway. Instead of a tail, he suggests, maybe it's a trail. Encke is a prodigious source of dust, which litters the comet's orbit. So much dust reflects sunlight, and that should make the comet's orbit--or "trail"--shine faintly in the night sky. Indeed, the spikes in Holloway's photo do seem well-aligned with Encke's orbit.

It all makes sense except for one thing: The trail should be too faint for Holloway's 5-inch telescope. The last time Encke's trail was seen, in 2002, astronomers needed a 16-hour exposure on Kitt Peak's 2.3-meter telecope to find it: report. A 7-minute exposure on a backyard telescope should not be adequate--yet there it is.

Soon we'll get a closer look. Encke, currently 14th magnitude and 1.9 AU away, is approaching the inner solar system for a mid-April flyby of the Sun. In early April, Encke's distance to Earth will shrink to less than 1.3 AU and the comet will become an easy 6th or 7th magnitude target for backyard telescopes.

Skilled observers should start watching now. Encke is located in the constellation Pisces to the right of Venus at sunset. More photos may solve the puzzle before the comet arrives.