Ice on Mercury? NASA Probe May Solve That Mystery and Others

A view of the horizon of Mercury, taken by NASA's Messenger spacecraft on March 29, 2011. The picture shows a stretch of land about 750 miles long, from top to bottom.
A view of the horizon of Mercury, taken by NASA's Messenger spacecraft on March 29, 2011. The picture shows a stretch of land about 750 miles long, from top to bottom. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

A NASA spacecraft now circling Mercury is set to tackle some big mysteries of the scorched, tiny world – including whether or not water ice lurks in its shadowy craters.

NASA's Messenger probe became the first spacecraft ever to orbit Mercury when it arrived at the planet on March 17. While the spacecraft won't officially start its yearlong science mission until April 4, the observations it's already made hint at many discoveries to come, researchers said.

"We're really seeing Mercury now with new eyes," Messenger principal investigator Sean Solomon, of the Carnegie Institution of Washington, told reporters today (March 30). "As a result, an entire global perspective is unfolding, and will continue to unfold over the next few months." [New Photos of Mercury From Messenger]

The search for water ice on the blisteringly hot planet is one of the mission's driving motivations. Though Mercury's surface temperatures can top 842 degrees Fahrenheit (450 degrees Celsius), ice may survive on the floors of permanently shadowed polar craters.

And about 20 years ago, radar data first picked up intriguing evidence of reflective materials at Mercury's poles that might just be water ice, researchers said.

"Could ice be trapped there? The thermal models say yes, it's possible," Solomon said. "But is it water ice? There are alternative ideas."

Messenger will also investigate other questions about Mercury — why it's so much denser than the other rocky planets, for example. Also, the mission team wants to learn more about how the planet's core is structured, the nature of its global magnetic field and other aspects of Mercury's composition and history.

That work will start in earnest next week. In the meantime, scientists are sifting through the spacecraft's increasing pile of new Mercury photos. By the end of tomorrow, it will have snapped 1,500 photos of the planet from orbit, researchers said — more than it captured during its three previous flybys of the planet in 2008 and 2009.

The first photos

Messenger — whose name is short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging — is still officially in a commissioning phase, during which time mission scientists are checking out its cameras and other instruments.

But the probe has not been idly waiting for its main mission to start. Messenger snapped the first photos of Mercury from orbit yesterday (March 29), imaging previously unseen areas of the planet — terrain near the poles that Messenger missed on its three flybys.

Bright rays, consisting of impact ejecta and secondary craters, radiate from Mercury's Debussy crater, located at the top. The image, acquired by NASA's Messenger spacecraft on March 29, 2011, shows a small portion of Debussy's large system of rays in greater detail than ever before. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

The pictures show the battered, crater-strewn surface of Mercury in great detail.

"We are delighted to be able to see the surface at the very high latitudes," Solomon said.

So far, everything is going well with Messenger's mission and its instruments.

"All subsystems and instruments are on and operating nominally, within specifications," said Messenger mission systems engineer Eric Finnegan, of Johns Hopkins University's Applied Physics Laboratory. "This is a tremendous achievement for the entire Messenger team."

Much more to come

Over the next 12 months, Messenger will continue taking pictures and peering at Mercury with its seven instruments, mapping the planet's surface and helping scientists better understand its composition, tenuous atmosphere and geologic history. [Most Enduring Mysteries of Mercury]

This information could shed light on how our solar system formed and evolved — and perhaps, by extension, how alien planetary systems have come about as well, researchers said.

NASA's Mercury Messenger probe captured this historic image of Mercury, the first ever obtained from a spacecraft in orbit about the solar system's innermost planet. The photo was taken on Tuesday (March 29) at 5:20 am EDT. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

The observations Messenger has made from orbit thus far suggest the probe will beam home all sorts of eye-opening information, researchers said. It may, for instance, help researchers learn why Mercury — like Earth — has a global magnetic field, while its rocky planet cousins Mars and Venus do not.

In its first five days in orbit, Messenger tripled the number of spacecraft observations of Mercury's magnetic field available to astronomers, researchers said.

"We are rapidly ramping up a much larger dataset with which to characterize the geometry of Mercury's magnetic field," Solomon said. "That will tell us a lot about Mercury's internal structure and dynamics."

A busy year ahead

The $446 million Messenger probe launched in August 2004. The spacecraft is now in an extremely elliptical orbit that brings it within 124 miles (200 kilometers) of Mercury at the closest point and retreats to more than 9,300 miles (15,000 km) away at the farthest point.

While Messenger is the first mission ever to orbit Mercury, it is not the first spacecraft to visit the planet. NASA's Mariner 10 spacecraft flew by the planet three times in the mid-1970s.

On April 4, Messenger will start mapping and studying the entire surface of Mercury, a process that is expected to require about 75,000 images. But the early science returns have whetted the appetites of mission scientists, who can't wait for the data to really start pouring in.

"It's just a wonderful adventure for those of us on the science team that have front-row seats for these new data that are coming down," Solomon said. "It's a wonderful time in the history of exploration of planet Earth's neighborhood, and we are delighted to be a part of that."

You can follow senior writer Mike Wall on Twitter: @michaeldwall. Follow for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.