courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The surface of Mercury. Scientists found evidence of ice and organic materials in craters near the planet’s North pole.

Since the 1990s, scientists have been intrigued by unusual radar observations of the closest planet to the sun, Mercury. Ground-based telescopes found that patches near the planet’s poles that looked unusually “bright,” suggesting that either the planet harbored ice in its craters or the surface was very rough.

On Thursday, a large team of scientists announced that a NASA mission, MESSENGER, launched in 2004, has found strong evidence of frozen water and the hints of organic materials, carbon-based molecules that are the building blocks of life on Earth—though the researchers emphasized the discovery does not mean there is, or ever was, life on inhospitable Mercury.

“It’s been so exciting,” said Maria T. Zuber, a scientist at the Massachusetts Institute of Technology who led the geophysics investigation and is a co-author of the research papers, published online in the journal Science Express. “We thought there could potentially be water ice at the poles of Mercury, and that would have been in our wildest dreams the most exciting result we could have conceived of. The fact that there could be organics there have made that even more interesting than we could have guessed. Nature can really fool you.”

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Mercury is a hot planet; the surface temperatures are hot enough to melt lead. But some of the craters near the north pole are in permanent shadow, meaning they could act as “cold traps” that hold water ice, or other volatile material deposited on the planet by asteroids or comets. David Paige, a MESSENGER participating scientist from the University of California, Los Angeles, said during a press conference that in permanently shadowed areas, the temperature could dip to around minus 369 degrees Fahrenheit.

The scientists used a combination of instruments mounted on the spacecraft and computer models to reach their conclusions. First, they found that when they tilted the spacecraft to map craters closer to the North pole, there were bright patches in the craters. Then, careful modeling that took into account the topography and the reflectivity of the surface suggested that the temperatures seemed to square with other measurements: the brightest areas were also the places where water ice would be stable at the surface.

A special instrument was used to measure the composition of the surface, providing evidence of pure water ice that was tens of centimeters thick below the surface.

All that does not suggest there is or has been life on Mercury—Zuber said that would be “a little crazy,” but she said it does suggest that the ingredients for life aren’t scarce and unusual on planets in the solar system.

“Water and organics, carbon, hydrogen-rich materials, are all building blocks of life as we know it on Earth,” Zuber said. “So if you start finding this stuff in even terribly inhospitable environments compared to what we know, it suggests the building blocks are out there. ... It raises the possibility that life could occur someplace itself, not necessarily Mercury.”