A
comet-chasing spacecraft swinging by Earth this week has snapped magnificent new
images of our home planet.
The new
photos come from the European Space Agency's Rosetta spacecraft, which will
make its closest approach by Earth Friday at 2:45 a.m. EST (0745 GMT), during
its third and final flyby past the planet.
The Rosetta
spacecraft's OSIRIS narrow-angle camera captured three images of Earth with an
orange, green and blue filter, and from a distance of about 393,330 miles (633,000
km). The resulting illuminated crescent is a combination of the trio.
The combined
image shows the Earth as blue sliver, with the South Pole roughly in the
center. The outline of Antarctica is visible beneath the clouds that form the
south-polar vortex, a natural continent-wide tornado of sorts. Pack ice in
front of the coastline, due to its strong reflectivity, causes bright spots in
the image.
Besides
capturing stellar images, the flyby could help unravel a mystery that has
stumped scientists for two decades. Space scientists have noticed craft vary
the amount
of orbital energy they exchange with Earth during planetary flybys. This
variation shows up as a tiny difference in speed either gained or lost when
compared with that predicted by fundamental physics and that actually measured
after the event.
During
tomorrow's flyby, scientists will track the craft's orbital energy, as they
have no idea whether Rosetta will get a slight boost, brake, or experience no
speed-change at all.
Rosetta was
launched in 2004 with a 2014
goal of entering low orbit around the comet Churyumov-Gerasimenko, before
selecting a landing spot so its small lander Philae can travel with the icy
object as it moves toward the center of the solar system. Then, Rosetta should
have a front row seat as the comet gets heated by the sun and sheds its outer
layer, finally producing comets' claim to fame — its tail.
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