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 After a 10-year journey, Rosetta reached Comet
67P/Churyumov-Gerasimenko in August and put itself into orbit for an
unprecedented long-term study. In November it released a
piggyback-riding spacecraft, which descended to the comet’s surface
for a series of independent studies.
Comets are believed to be frozen leftovers from the formation of the
planets some 4.6 billion years ago. The Rosetta mission is intended
to shed light on the solar system’s early days by studying one of
its pristine comet remnants.
Results from the Philae spacecraft experiments are pending, but
scientists on Thursday released seven papers in the journal Science
that detailed Rosetta’s findings during its first two months around
67P.
The teams found the comet’s body, which is about 100 million times
more massive than the International Space Station, is covered in
dunes and ripples, with little detectable water ice on its surface
and generous quantities of hydrocarbons.
 Scientists say they expected to find more complex carbon-containing
molecules, but have found mostly simple hydrocarbons, which raises
questions about how organic compounds formed and spread through the
solar system.
Scientists must first figure out how the comet has changed over
time, details of which will emerge as 67P travels toward the sun and
heats up, developing a coma, or a visible atmosphere, and a tail.
Already, researchers have discovered wide variations in the gases
being released from the nucleus, the comet’s body. The changes in
the quantities of the gases appear to be tied to whether a section
of the rotating nucleus, which is made of dust, rock and frozen gas,
is in daylight or darkness.
Over time, seasonal effects also may be discovered, said Rosetta
scientist Myrtha Hassig, with the Southwest Research Institute in
San Antonio, Texas.
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Ultimately, the studies will have an impact on scientists’
understanding of comet formation and evolution.
“We're taught that comets are made mostly of water ice. For this
comet, the coma sometimes contains much more carbon dioxide than
water vapor,” said Rosetta scientist Stephen Fuselier, also with
Southwest Research Institute.
Overall, the comet’s nucleus seems to be fluffier and more porous
than computer models originally predicted. Scientists also are
working to figure out if 67P, which is shaped like a rubber duck,
actually was two smaller comets that melded together.
Rosetta will continue to fly around the comet as it moves toward and
then away from the sun. The closest approach, about 116 million
miles (186 million km) away from the sun, will be on Aug. 13.
(Editing by Jeffrey Benkoe)
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