The largest object in the asteroid belt, Ceres, is shooting out wisps
of water at a prodigious rate. This unexpected finding allows Ceres to
join other small bodies in the solar system, including Saturn’s moon
Enceladus and Jupiter’s moon Europa, as an icy world with gushing jets.
Because of its mass, Ceres is classified as a dwarf planet, so it’s
more like frozen Pluto and less like the lumpy potato-shaped objects
that we typically think of as hanging out in the asteroid belt.
Scientists have long suspected that the object contains an abundance of
frozen water, roughly the same amount as all the fresh water on Earth.
Recent observations with the European Space Agency’s Herschel space observatory showed for the first time unmistakable signatures of water vapor shooting out from Ceres.
Water jets have been spotted on asteroids and comets before, perhaps most famously on comet Hartley 2,
which was photographed by NASA’s Deep Impact spacecraft as it flew by
in 2010. Icy objects are known to heat up as they approach the sun,
producing the watery outflow. Plumes on moons such as Encleadus and
Europa are thought to form as tidal forces from the mass of Saturn and
Jupiter squeeze and release the tiny worlds. But Ceres is not barreling
toward our central star nor does it orbit close to a massive planet,
which presents scientists with something of a conundrum: What is
powering these jets?
It’s possible that sun is responsible for some of the activity. Like
any object in orbit around the sun, Ceres swings closer and farther at
different times. Herschel saw no plumes when Ceres was farthest from the
sun. Scientists also suspect that decaying radioisotopes could be
heating the asteroid’s subsurface, creating cryovolcanos, which act like
normal volcanoes except that they spew ice and water vapor instead of
molten rock.
The discovery of Ceres’ plumes comes at a fortuitous time. NASA currently has a probe, the Dawn spacecraft,
speeding toward the object. Dawn will arrive and enter orbit around
Ceres in 2015, giving researchers a front-row view of the activity. Dawn
previously visited Vesta, the second largest object in the asteroid
belt. These two worlds could not be more contrary to one another, with
Vesta being a rocky world that has clear indications of heating and
volcanic eruptions. Because both objects orbit out approximately 2.5
times the distance between the Earth and the sun, figuring out why one
world is icy and the other rocky will be a major topic of Dawn’s
research.
The current best guess for the two asteroids’ opposite appearance is
that Ceres formed much farther out from the sun, where the colder
environment allowed it to hold on to its ice. According to the Nice model
of the solar system’s origin (named for the town in France, not the
enjoyable formation scenario) the gas giants such as Jupiter and Saturn
formed far from their current positions. As these enormous objects
migrated around in the early solar system, they scattered everything
else like billiard balls and caused objects such as Ceres and Vesta —
which formed far from one another — to come much closer together.
Adam is a Wired Science staff writer. He lives in Oakland, Ca near a lake and enjoys space, physics, and other sciency things. Read more by Adam Mann
The largest object in the asteroid belt, Ceres, is shooting out wisps
of water at a prodigious rate. This unexpected finding allows Ceres to
join other small bodies in the solar system, including Saturn’s moon
Enceladus and Jupiter’s moon Europa, as an icy world with gushing jets.
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