Talk about a land of fire and ice. The surface of Mercury is hot enough in some places to melt lead, but it is a winter wonderland at its poles — with perhaps a trillion tons of water ice trapped inside craters — enough to fill 20 billion Olympic skating rinks.

The ice — whose long-suspected presence has now been confirmed by NASA's orbiting MESSENGER probe — seems to be much purer than ice inside similar craters on Earth's Moon, suggesting that the closest planet to the Sun could be a better trap for icy materials delivered by comets and asteroids. Three papers detailing the findings are published today in Science.

Despite Mercury’s blistering 400°C temperatures, the floors of many of its polar craters are in permanent shadow, because the planet's rotational axis is perpendicular to its orbital plane, so its poles never tip towards the star. Indeed, radar pinged to the planet from Earth in the past 20 years has revealed bright regions near the poles consistent with meters-thick slabs of pure water ice.

But “radar does not uniquely identify water ice,” says David Lawrence, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Sulfur, for example, could have produced a similar radar signature.

Now, three different lines of evidence back the water-ice interpretation. Infrared laser pulses fired at the planet by MESSENGER's Mercury Laser Altimeter have revealed bright regions inside nine darkened craters near the planet's north pole. These bright regions, thought to be water ice, line up perfectly with ultra-cold spots that, according to a thermal model of the planet that takes into account Mercury's topography, should never be warmer than –170°C.

A third team, using MESSENGER's Neutron Spectrometer, has spotted the telltale signature of hydrogen — which they think is locked up in water ice — in those same regions. "Not only is water the best explanation, we do not see any other explanation that can tie all the data together," says Lawrence, lead author of the spectrometer study.

So where did the water come from? The bright icy spots identified by MESSENGER's laser are surrounded by darker terrain which receives a bit more sunlight and heat. The neutron measurements suggest that this darker area is a layer of material about 10 centimeters thick that lies on top of more ice, insulating it.

Dark materials
This darker material around the bright spots may be made up of complex hydrocarbons expelled from comet or asteroid impacts, says David Paige, a planetary scientist at the University of California, Los Angeles, and first author of the thermal-model paper.

Paige and his colleagues suggest that when these icy bodies slam into Mercury, their components migrate over time — by repeatedly vaporizing and precipitating — to the cooler poles, where they get stuck in the frigid polar craters.

But even there, sunlight will sometimes hit parts of the craters' interiors, vaporizing the water ice and leaving behind ‘lag deposits’ of hydrocarbons that gradually become thicker and darker as they are chemically altered by sunlight.

7 Comments

1. 1. metamorphmuses 11:02 PM 11/30/12

   As a fact alone, this is very cool. Immediately it makes me think, however, about what this could mean for the future of space travel. I have long been intrigued by the possibility of finding a suitable asteroid or comet with low gravity/escape velocity and lots of water that could be used as a staging ground for spacefaring vehicles that could convert water to hydrogen for fuel. For that reason, I have been more enthusiastic than others about Obama's plans for American astronauts to visit an asteroid. For the same reason, although the gravity/escape velocity is higher on the Moon than on any asteroid, I have been keenly following the detection of water on our natural satellite.
   
   So this news makes Mercury look like a good candidate as well. I looked up the gravity and escape velocity: .38g and 4.25km/s respectively. This is significantly more than the Moon's (0.165g and 2.38km/s), but better than Mars in escape velocity (.378g and 5.027km/s). Of course, the Moon is much closer to Earth than Mercury or Mars, so it is still the best candidate so far, but Mercury starts to look attractive nonetheless. Certainly generating solar power on Mercury wouldn't be a problem, either!

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2. 2. metamorphmuses in reply to metamorphmuses 11:12 PM 11/30/12

   Small correction: The Moon is still the best candidate of the three: Moon, Mars, Mercury. However, an asteroid or comet with enough water and close enough to Earth is still, to my mind, the best option as a base/construction platform/staging area for serious interplanetary exploration and colonization.

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3. 3. Laird Wilcox 11:14 PM 12/1/12

   This is good news. If America ever sends a man to the Sun he could find water on the way. One more problem solved.

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4. 4. dadster 11:43 PM 12/2/12

   Folks, in future it won't be men doing space travel. It would be robots guided by other robots ( I.e . Not bio- intelligence but non- bio- intelligence and non- bio- structures ) who would do interplanetary traveling. The requirement of water for drinking and oxygen for breathing or bio- degradation of our bio- structure ( heart, lungs, kidneys etc) are no more limitations . Much water has flowed under the bridge since star trek days. Human foibles and frailties no more affect space - exploration. It would be purely for business purposes by businessmen to mine for minerals and precious stones and other exotic stuff for the consumption of the very few bio- mass( bio- humans ) left on earth. Even down on planet earth events and markets would be controlled by non- bio- intelligence .Bio- reproductions will be a rarity enjoyed by the ultra rich only , who would have eliminated other bio-humans .
   By the second half of 21 st century humans, as we know it, would have been replaced by non- bio-beings. I am giving that to happen a little more time than Ray Kurzweil who has marked year 2045 as the upper limit for such take over ,in his 1999 book " The Singularity is Near ", updated in 2005 . But , he won't be too far off the mark. Humans, enjoy now as best as you can now;wonder as much as you can , now ; you have very little time left on planet earth where at least bio- intelligence, if not the entire bio- life itself , is getting replaced by Non- bio- intelligence.

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5. 5. eanassir 11:54 AM 12/4/12

   Such explanation that Mercury has water ice, I think is not correct.
   The explanation of sulfur given by David Lawrence seems better.
   
   My explanation which may be more realistic:
   
   At the start, Mercury stopped its axial spinning since long time ago. And now it circles around the sun with only one face facing it, while the other side is unseen by the sun (just like the moon in relation to the earth.)
   
   Therefore, the side facing the sun has extreme heat, while the opposite side has extreme coldness.
   
   Then at the start, the atmosphere became turbid and its gases mixed with each other to become like Venus now.
   
   Then it lost its atmosphere to the outer space, so that its surface appears clearly not like Venus, the surface of which cannot be seen because of its thick smoke due to its mixed gases.
   
   Then its water vaporized and disappeared into the outer space and it was lost.
   
   So now Mercury has no air, no water and its surface appears clearly, and it has extremes of heat and coldness.
   
   Sulfur is more likely, more than water ice: because specially when the gases of the atmosphere mixed with each other: one of the gases is SO2 which reacted with the initially present water vapor to precipitate H2SO4 and the sulfides.
   
   http://www.quran-ayat.com/universe/new_page_4.htm#How_the_Terrestrial_Planets_Will_Standstill_
   

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6. 6. metamorphmuses 01:22 AM 12/8/12

   I regret having posted anything here. I was hoping for rational discourse, but the SciAm forums are now apparently just for wingnuts. I didn't get the memo!

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7. 7. eanassir in reply to metamorphmuses 02:15 PM 12/8/12

   The idea that water came to our Earth from a comet is extremely imaginative and not realistic.
   Their mistake comes from an erroneous presumption that the comet is a dirty ice.
   
   The origin of water of Earth and the planets:
   
   Water of Earth (and the planets) came from the earth (and the planet) itself, as is the atmosphere.
   
   The explanation:
   Earth was a fire object at the start, because it was part of an exploded sun. From every fire object, gases and smoke emerge; the smoke was a mixture of seven gases; among these gases was the O2 and H2, then by electric current the H2O resulted.
   
   http://www.quran-ayat.com/universe/index.htm#The_Gaseous_Heavens
   
   http://www.quran-ayat.com/universe/index.htm#Question_10
   
   
   

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