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Sunset Comet - presented by Science@NASA
For a comet, visiting the sun is risky business.
Fierce solar radiation
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.
This just in: 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
like a star of 2nd magnitude,
as bright as the stars of the Big Dipper.
Bright twilight reduces visibility,
but it is still an easy target for binoculars
and small telescopes 1 and 2 hours after sunset.
Discovered in June 2011
by astronomers using the PanSTARRS 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 Comet Pan-STARRS
using a remote-controlled telescope in Chile.
Based on his data,
Knight concludes that
Comet 'PanSTARRS 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 PanSTARRS 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're not sure what causes this.'
Possibilities include irregular outgassing in the comet's core,
fragmentation events,
and interactions with the gusty solar wind.
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.
It might even become a naked-eye object
in the closing weeks of March.
Step outside after sunset, face west,
and take a look.
For more news about comets and their risky behavior,
visit science.nasa.gov.