For months, scientists have puzzled over weirdly bright spots of material shining on the asteroid Ceres, but now they say the spots are probably made of salty ice.
That determination, based on a detailed analysis of spectral data from NASA’s Dawn orbiter, comes in a paper published today by the journal Nature. Dawn’s images highlight one particular patch in a 60-mile-wide impact basin known as Occator Crater, but other spots are spread across the surface of the 590-mile-wide dwarf planet.
“The global nature of Ceres’ bright spots suggests that this world has a subsurface layer that contains briny water-ice,” the study’s principal author, Andreas Nathues of the Max Planck Institute for Solar System Research, said in a NASA statement. He and his co-authors suggest that cosmic impacts dig up enough surface material to expose the shiny ice.
The best match for the brightness of the spots is a type of hydrated magnesium sulfate known as hexahydrite, but there might be other salts in the mix.
Readings from Dawn and the European Space Agency’s Herschel space telescope also point to patches of haze that regularly rise up from Occator Crater. Scientists say that suggests the salty ice is sublimating – that is, changing directly into water vapor as it warms. Such sublimation would leave bright deposits of salt behind.
“The Dawn science team is still discussing these results and analyzing data to better understand what is happening at Occator,” UCLA astronomer Chris Russell, the Dawn mission’s principal investigator, said in NASA’s statement.
Another study published by Nature lays out evidence that Ceres’ surface contains ammonia-rich clays. Ammonia and some of the other nitrogen compounds detected by Dawn are more commonly found in the outer solar system. That’s leading scientists to suspect that Ceres has an interesting origin story: Either it formed farther out in the solar system and moved inward, or it somehow picked up materials that came in from farther out.
Dawn has been studying Ceres from orbit since March, but its science mission isn’t over yet: This week, the car-sized probe reached its final mapping orbit, about 240 miles above Ceres’ surface. Up-close scientific observations are to begin later this month.
In other far-out news this week:
A search for laser signals turned up nothing anomalous coming from KIC 8462852, a star that exhibited a weird pattern of dimming several years ago. The earlier data from NASA’s Kepler space telescope set off speculation that the dimming could be due to the construction of an alien megastructure around the star. But the latest study, conducted using the Boquete Optical SETI Observatory in Panama and submitted to the Astrophysical Journal Letters, is in line with other recent searches that have come up empty.
“The hypothesis of an alien megastructure around KIC 8462852 is rapidly crumbling apart,” Douglas Vakoch, president of SETI International, said in a news release. Scientists say a storm of crumbling alien comets provides the likeliest explanation for the Kepler data.
Japan’s Akatsuki spacecraft successfully entered orbit around Venus, five years after an initial try failed. The probe was launched in May 2010 and should have entered Venusian orbit in December of that year; however, its main engine failed during a preparatory maneuver. It took years to set up the trajectory for a second attempt on Sunday, using the spacecraft’s attitude control thrusters.
Now Akatsuki (which means “Dawn” in Japanese) will get ready to study Venus’ atmosphere from a highly elliptical orbit that ranges in altitude from 250 miles to 273,000 miles. “Akatsuki is in good health,” the Japan Aerospace Exploration Agency reported in a news release.