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Some Comets Like it Hot.
Presented by Science at NASA.
Comets are icy and fragile.
They spend most of their time orbiting through the dark
outskirts of the solar system safe from the withering
depredations of intense sunlight.
Their natural habitat is the deepest cold.
Last November amateur astronomer Terry Lovejoy discovered a
different kind of comet.
The icy fuzzball he spotted in the sky over his backyard
observatory in Australia was heading almost directly for the sun.
On December 16th, less than three weeks after he found it, Comet
Lovejoy would swoop through the sun's atmosphere only
120,000 km above the stellar surface.
Astronomers would soon realize a startling fact: Comet
Lovejoy likes it hot.
"Terry found a sungrazer," says Karl Battams of the Naval
Research Lab in Washington DC.
"It appeared to be as wide as two football fields the
biggest such comet in nearly 40 years." Sungrazing comets
aren't a new thing.
In fact, the orbiting Solar and Heliospheric Observatory
(SOHO) watches one fall toward the sun and evaporate every few days.
These frequent "kamikaze comets" are thought to be
splinters of a giant comet that broke apart hundreds of
years ago.
Typically they measure about 10 meters across, small,
fragile, and easily vaporized by solar heat.
Based on its orbit, Comet Lovejoy was surely a member of
the same family, except it was 200 meters wide instead of
the usual 10.
Astronomers were eager to see such a whopper disintegrate.
There was little doubt that it would be destroyed.
When December 16th came, however, "Comet Lovejoy shocked us
all," says Battams.
"It survived, and even flourished."
Images from NASA's Solar Dynamics Observatory showed the
comet vaporizing furiously as it entered the sun's
atmosphere, apparently on the verge of obliteration yet
Comet Lovejoy was still intact when it emerged on the other side.
The comet had lost its tail during the fiery transit, a
temporary setback.
Within hours, the tail grew back, bigger and brighter than before.
"It's fair to say we were dumbfounded," says Matthew Knight
of the Lowell Observatory and the Johns Hopkins Applied
Physics Lab.
"Comet Lovejoy must have been much bigger and tougher than
we thought."
Only a few days after it left the sun, the comet showed up
in the morning skies of the southern hemisphere.
Observers in Australia, South America, and New Zealand
likened it to a search light beaming up from the east
before dawn.
The tail lined up parallel to the Milky Way and, for a few
days, made it seem that we lived in a double-decker galaxy.
Astronauts on the International Space Station also
witnessed the comet.
ISS Commander Dan Burbank, who has seen his share of
wonders, even once flying directly through the Northern
Lights onboard the space shuttle, declared Comet Lovejoy
"the most amazing thing I have ever seen in space."
An armada of spacecraft including SOHO, the Solar Dynamics
Observatory (SDO), NASA's twin Solar Terrestrial Relations
Observatory (STEREO) probes, Japan's Hinode spacecraft, and
Europe's Proba2 microsatellite recorded the historic event.
"We've collected a mountain of data," says Knight.
"But there are some things we're still having trouble explaining."
For instance, what made Lovejoy's tail wiggle so wildly
when it entered the solar corona?
Perhaps it was in the grip of the sun's powerful magnetic field.
What caused Lovejoy to lose its tail inside the sun's
atmosphere, and then regain it later?
"This is one of the biggest mysteries to me," says Battams.
And then there is the ultimate existential puzzle: How did
Comet Lovejoy survive at all?
The "Comet that liked it Hot" is returning to the outer
solar system, apparently still intact, leaving many
mysteries behind.
"It'll be back in about 600 years," says Knight.
"Maybe we will have figured them out by then."
To learn about more Solar System mysteries hot and cold
visit science.nasa.gov.