Thursday, July 23, 2015

Mysterious Spots on Ceres May Have Haze Over Them

The brightest spots on dwarf planet Ceres are seen in this image taken by NASA's Dawn spacecraft on June 6. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Tucked deep inside the asteroid belt between the orbits of Mars and Jupiter, is another dwarf planet called Ceres orbits the Sun and something wonderfully interesting has just been spotted by NASA’s Dawn spacecraft, which has been orbiting Ceres since March. The dwarf planet has a haze that appears occasionally in a crater above some of its mysterious white spots. The phenomenon, observed by Dawn, suggests that the bright spots “could be providing some atmosphere in this particular region of Ceres”, says Christopher Russell, a planetary scientist at the University of California, Los Angeles. Russell, the mission’s principal investigator, described its initial findings during an exploration meeting at NASA’s Ames Research Center in Moffett Field, California, on July 21.


“At noontime, if you look at a glancing angle, you can see what seems to be haze,” Russell said. “It comes back in a regular pattern.”

According to him, the haze covers about half of the crater and reaches as far as the rim.

So far, scientists have theorized that the bright spots could be concentrations of minerals or salts. Or they might be icy deposits; potentially evidence for cryovolcanism.

The spacecraft hasn’t yet been able to properly analyze the spots, but the discovery of haze above a crater filled with bright dots could indicate something is outgassing into space — possibly sublimating water ice.

Haze on Ceres would be the first ever observed directly in the asteroid belt. In 2014, researchers using the European Space Agency's Herschel Space Observatory reported seeing water vapour spraying off Ceres, which suggested that it was geologically active. At least one-quarter of Ceres’s mass is water, a much greater proportion than seen in most asteroids.

The Dawn spacecraft carries an infrared spectrometer that should be able to discriminate easily between ice or salt. But the instrument, which is mapping Ceres’s surface, has not had a chance to study the spots properly yet. It has been out of commission for small periods of time, leaving blank spots in the map, Russell says. The same spectrometer experienced problems back when Dawn was orbiting a different asteroid, Vesta, in 2011–12.

At nearly 1,000 kilometres across, Ceres is designated as a dwarf planet. Understanding it could improve scientists’ understanding of the relationships between all the objects in the Solar System. “Ceres is so big compared to all the other asteroids that it's really different,” says Andrew Rivkin, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “It’s sort of the penultimate step before a planet.”

Following a brief interruption in normal operations on 30 June, Dawn is now spiralling closer to Ceres. It is less than 4,000 kilometres above the asteroid’s surface, aiming for less than 1,500 kilometres in August.

Credit: nature.com, discovery.com

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