[meteorite-list] Sunset Comet C/2011 L4 (PANSTARRS)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 15 Mar 2013 13:50:31 -0700 (PDT)
Message-ID: <201303152050.r2FKoV2C001410_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2013/15mar_sunsetcomet/

Sunset Comet
NASA Science News
March 15, 2013

For a comet, visiting the sun is risky business. Fierce solar heat
vaporizes gases long frozen in the fragile nucleus, breaking up some
comets and completely destroying others.

That's why astronomers weren't sure what would happen in early March
when Comet Pan-STARRS, a first-time visitor to the inner solar system,
dipped inside the orbit of Mercury. On March 10th , NASA's STEREO-B
spacecraft watched as the comet made its closest approach to the sun
only 28 million miles away. At that distance, the sun loomed 3 times
wider and felt more than 10 times hotter than it does on Earth.

The comet survived. Still intact, Comet Pan-STARRS is emerging from the
Sun's glare into the sunset skies of the northern hemisphere. Solar
heating has caused the comet to glow brighter than a first magnitude
star. Bright twilight sharply reduces visibility, but it is still an
easy target for binoculars and small telescopes 1 and 2 hours after
sunset. As of March 15th, people are beginning to report that they can
see the comet with the unaided eye.

Discovered in June 2011 by astronomers using the Pan-STARRS survey
telescope atop the Haleakala volcano in Hawaii, the comet is paying its
first visit to the inner solar system. It hails from the Oort cloud, a
deep space reservoir of comets far beyond the orbit of Pluto. Because
Comet PanSTARRs is a newcomer, astronomers didn't know what to expect.

Now they know.

"It is a gorgeous comet--one of the brightest in years," says astronomer
Matthew Knight of the Lowell Observatory.

Comet specialist Emmanuel Jehin of the European Southern Observatory has
been monitoring Pan-STARRS using a remote-controlled telescope in Chile.
Based on his data, Knight concludes that "Comet Pan-STARRS seems to be
producing quite a bit of dust compared to an average comet. This is very
good for its visibility, because the extra dust is reflecting sunlight
and making Pan-STARRS appear brighter than it would otherwise."

The amount of dust and gas spewing from the comet implies a nucleus on
the order of 1 km in diameter--in other words, neither unusually large
nor small. Size-wise, it is a fairly typical comet.

The comet's tail is anything but typical. STEREO-B images processed by
Karl Battams of the Naval Research Lab in Washington DC reveal many wild
and ragged striations in the cloud of dust trailing behind Pan-STARRS.
"Wow!" says Battams. "The fine-structure is breathtaking. We think this
is caused by some fairly complex interaction between the solar wind and
the comet's rotating nucleus. We're going to need computer models to
figure this one out."

The comet is now receding from Earth. It will slowly dim as it heads
back into deep space. Ironically, though, its visibility will improve
for a while as it heads into darker skies away from the sun. In the last
weeks of March it could become an easy naked-eye object.

Step outside after sunset, face west, and take a look.

Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Fri 15 Mar 2013 04:50:31 PM PDT