[meteorite-list] Scientists Watch for a 'Hartley-id' Meteor Shower

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 27 Oct 2010 12:15:39 -0700 (PDT)
Message-ID: <201010271915.o9RJFdmU006427_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2010/27oct_hartleyids/

Scientists Watch for a "Hartley-id" Meteor Shower
NASA Science News

Oct. 27, 2010: This month, Comet Hartley 2 has put on a good show for
backyard astronomers. The comet's vivid green atmosphere and auburn tail
of dust look great through small telescopes, and NASA's Deep
Impact/EPOXI probe is about to return even more dramatic pictures when
it flies past the comet's nucleus on Nov. 4th.

Another kind of show might be in the offing as well. Could this comet
produce a meteor shower?

"Probably not," says Bill Cooke of NASA's Meteoroid Environment Office,
"but the other night we saw something that makes me wonder."

On Oct 16th, a pair of NASA all-sky cameras caught an unusual fireball
streaking across the night sky over Alabama and Georgia. It was bright,
slow, and--here's what made it unusual--strangely similar to a fireball
that passed over eastern Canada less than five hours earlier. The
Canadian fireball was recorded by another set of all-sky cameras
operated by the University of Western Ontario (UWO). Because the
fireballs were recorded by multiple cameras, it was possible to
triangulate their positions and backtrack their orbits before they hit
Earth. This led to a remarkable conclusion:

"The orbits of the two fireballs were very similar," Cooke says. "It's
as if they came from a common parent."

There's a candidate only 11 million miles away: Small but active Comet
Hartley 2 is making one of the closest approaches to Earth of any comet
in centuries. It turns out that the orbits of the two fireballs were not
only similar to one another, but also roughly similar to the orbit of
the comet. Moreover, meteoroids from Comet Hartley would be expected to
hit Earth's atmosphere at a relatively slow speed--just like the two
fireballs did.

Cooke stresses that this could be a coincidence. "Thousands of
meteoroids hit Earth's atmosphere every night. Some of them are bound to
look like 'Hartley-ids' just by pure chance."

Even so, he plans to keep an eye out for more in the nights ahead,
especially on Nov. 2nd and 3rd. That's when a potential Hartley-id
meteor shower would be most intense, according to calculations by meteor
expert Peter Brown of UWO.

The comet was closest to Earth on Oct. 20th, but that's not necessarily
the shower's peak-time. Cooke explains: "The comet has been sputtering
space dust for thousands of years, making a cloud that is much bigger
than the comet itself. Solar radiation pressure and planetary encounters
cause the comet and the dust cloud to diverge???not a lot, but enough to
make the date of the shower different from the date of the comet's
closest approach."

If there is a Hartley-id shower???"that's a big IF," notes Cooke--it would
emanate from the constellation Cygnus the Swan, visible to observers in
the northern hemisphere almost directly overhead after sunset in early
November. Lunar interference should not be a problem. On Nov. 2nd and
3rd, the Moon will be a slender crescent, providing dark skies for a
meteor watch.

"I'll definitely have our cameras turned on," says Cooke. "It's probably
going to be a non-event. On the other hand," he points out, "we might
discover a whole new meteor shower."


Author: Dr. Tony Phillips
Credit: Science at NASA
Received on Wed 27 Oct 2010 03:15:39 PM PDT