Earth-based telescopes have been collecting evidence for ice on Mercury for 20 years, but the finding of organics was a surprise, say researchers with NASA’s Messenger spacecraft, the first probe to orbit Mercury.
The frozen water is located in regions of Mercury’s north pole that always are in shadows, essentially impact craters. It’s believed the south pole harbors ice as well, though there are no hard data to support it. Messenger orbits much closer to the north pole than the south.
“It’s not something we expected to see, but then of course you realize it kind of makes sense because we see this in other places,” such as icy bodies in the outer solar system and in the nuclei of comets, planetary scientist David Paige, with the University of California, Los Angeles, told Reuters.
Three independent lines of evidence support this conclusion: the first measurements of excess hydrogen at Mercury’s north pole with Messenger’s Neutron Spectrometer, the first measurements of the reflectance of Mercury’s polar deposits at near-infrared wavelengths with the Mercury Laser Altimeter (MLA);
And the first detailed models of the surface and near-surface temperatures of Mercury’s north polar regions that utilize the actual topography of Mercury’s surface measured by the MLA. These findings are presented in three papers published online yesterday in Science Express.
NASA reports, that data from Messenger’s Mercury Laser Altimeter (MLA) – which has fired more than 10 million laser pulses at Mercury to make detailed maps of the planet’s topography – corroborate the radar results and Neutron Spectrometer measurements of Mercury’s polar region, writes Gregory Neumann of the NASA Goddard Space Flight Center.
In a second paper, Neumann and his colleagues report that the first MLA measurements of the shadowed north polar regions reveal irregular dark and bright deposits at near-infrared wavelength near Mercury’s north pole.
It means, that the ice vaporized, then re-solidified where it was colder, leaving dark deposits on the surface. Radar imagery shows the dark patches subside at the coldest parts of the crater, where ice can exist on the surface.
“There’s enough polar ice at Mercury, in fact, to bury an area the size of Washington, D.C., by two to 2 1/2 miles deep”, said David Lawrence of the Applied Physics Laboratory at Johns Hopkins University.
For two decades, radar measurements taken from Earth have suggested the presence of ice at Mercury’s poles. Now scientists know for sure, thanks to Messenger, the first spacecraft to orbit Mercury.
The discoveries of ice and organics, painstakingly pieced together for more than a year, are based on computer models, laboratory experiments and deduction, not direct analysis.
Scientists believe the organic material, which is about twice as dark as most of Mercury’s surface, was mixed in with comet- or asteroid-delivered ice eons ago.
Columbia University’s Sean Solomon, principal scientist for Messenger, stressed that no one is suggesting that Mercury might hold evidence of life, given the presence of water. But the latest findings may help explain how water and other building blocks of life arrived elsewhere in the solar system, he said.
Mercury is becoming the subject of new interest “where it wasn’t much of one before,” Solomon said.
Messenger was launched in 2004 and went into orbit 1½ years ago around Mercury, where temperatures reach 800 degrees. Messenger, which stands for Mercury Surface, Space Environment, Geochemistry and Ranging, is due to complete its two-year mission at Mercury in March. NASA hopes to continue observations well into next year.