Skip to comments.MESSENGER Finds New Evidence for Water Ice at Mercury's Poles
Posted on 11/29/2012 12:16:16 PM PST by Da Bilge Troll
New observations by the MESSENGER spacecraft provide compelling support for the long-held hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed polar craters.
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 today in Science Express.
Given its proximity to the Sun, Mercury would seem to be an unlikely place to find ice. But the tilt of Mercury's rotational axis is almost zero less than one degree so there are pockets at the planet's poles that never see sunlight. Scientists suggested decades ago that there might be water ice and other frozen volatiles trapped at Mercury's poles.
The idea received a boost in 1991, when the Arecibo radio telescope in Puerto Rico detected unusually radar-bright patches at Mercury's poles, spots that reflected radio waves in the way one would expect if there were water ice. Many of these patches corresponded to the location of large impact craters mapped by the Mariner 10 spacecraft in the 1970s. But because Mariner saw less than 50 percent of the planet, planetary scientists lacked a complete diagram of the poles to compare with the images.
MESSENGER's arrival at Mercury last year changed that. Images from the spacecraft's Mercury Dual Imaging System taken in 2011 and earlier this year confirmed that radar-bright features at Mercury's north and south poles are within shadowed regions on Mercury's surface, findings that are consistent with the water-ice hypothesis.
Now the newest data from MESSENGER strongly indicate that water ice is the major constituent of Mercury's north polar deposits, that ice is exposed at the surface in the coldest of those deposits, but that the ice is buried beneath an unusually dark material across most of the deposits, areas where temperatures are a bit too warm for ice to be stable at the surface itself.
MESSENGER uses neutron spectroscopy to measure average hydrogen concentrations within Mercury's radar-bright regions. Water-ice concentrations are derived from the hydrogen measurements. "The neutron data indicate that Mercury's radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 20 centimeters thick that is less rich in hydrogen," writes David Lawrence, a MESSENGER Participating Scientist based at The Johns Hopkins University Applied Physics Laboratory and the lead author of one of the papers. "The buried layer has a hydrogen content consistent with nearly pure water ice."
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.
"These reflectance anomalies are concentrated on poleward-facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near-surface water ice," Neumann writes. "Correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice." The MLA also recorded dark patches with diminished reflectance, consistent with the theory that the ice in those areas is covered by a thermally insulating layer. Neumann suggests that impacts of comets or volatile-rich asteroids could have provided both the dark and bright deposits, a finding corroborated in a third paper led by David Paige of the University of California, Los Angeles.
Paige and his colleagues provided 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. The measurements "show that the spatial distribution of regions of high radar backscatter is well matched by the predicted distribution of thermally stable water ice," he writes.
According to Paige, the dark material is likely a mix of complex organic compounds delivered to Mercury by the impacts of comets and volatile-rich asteroids, the same objects that likely delivered water to the innermost planet.The organic material may have been darkened further by exposure to the harsh radiation at Mercury's surface, even in permanently shadowed areas.
This dark insulating material is a new wrinkle to the story, says Sean Solomon of the Columbia University's Lamont-Doherty Earth Observatory, principal investigator of the MESSENGER mission. "For more than 20 years the jury has been deliberating on whether the planet closest to the Sun hosts abundant water ice in its permanently shadowed polar regions. MESSENGER has now supplied a unanimous affirmative verdict."
"But the new observations have also raised new questions," adds Solomon. "Do the dark materials in the polar deposits consist mostly of organic compounds? What kind of chemical reactions has that material experienced? Are there any regions on or within Mercury that might have both liquid water and organic compounds? Only with the continued exploration of Mercury can we hope to make progress on these new questions."
on... Mercury?? Wow
Let me know if they find Cilia-of-Gold.............
Baxter is my favorite current SF writer.
Its damn cold in the shade.
“Too bad there’s no space programany more!”
Yep, we’re watching the wind down of stuff that was in the pipeline. Too many folks here need Obamaphones!
I sure hope the Chinese accelerate their space program to fill the void that NASA is leaving.
So, we subsidize a bunch of techno elites whose membership includes NASA’s Hansen, the rabid Global Warming Criminal, while Obama sucks the real working people of this country dry?
The question should be these days “If we ever in a snowball’s-chance-in-hell get out from under this tyrant and we can retire the debt he’s amassed, is it worth it to subsidize ideologues in ventures that won’t produce anything?”
I can think of humans going (being sent) to Mars, maybe even Mercury, but it won’t be friggin’ astronauts from NASA.
Have you read “Cilia-of-Gold”?........
better than frying in a half second I guess
” - - - Only with the continued exploration of Mercury can we hope to make progress on these new questions.”
Duh, is “Progress” in the language of Obamanation Communism now the opposite of “Forward?”
As far as the shuttle’s concerned, there was once a secret military mission launched where it seemed to me that it rolled more than usual that might have put it into a polar orbital trajectory. Then, when it retuned, the landing was such where they seemed to hold the nosewheel up for what I thought was a longer period that I had ever seen it. That led me to wonder if they hadn’t taken a dead Soviet military satellite that the Russians had lost track of out of orbit.
As for practical knowledge the shuttle returned a lot of data and information that could one day be put to use regarding long termed manned space flight such as a mission to Mars, the asteroids, or eve the moons of Jupiter or even Saturn.
Information gleaned thus far and continuing from Mars from Mars would aid in that type of mission. Plus the idea that there is, or may once have been life on Mars is still an open possibility. I’d sure like to know the answer difinitively.
I’d rather some of our tax money went to these types of projects even though it may seem that the reduction or elimination doesn’t even make a dent in our other spending.
At least we’re exploring the beyond, and to paraphrase the poem “High Flight”, “I put out my hand, and touched the face of God.”
Yes, it's one one of Baxter's better early stories from the Xeelee sequence. I've read just about everything he's written.
Then you ‘get’ my reference to it in my first post!.............
As cripplecreek noted, it’s *really* cold at the poles because there is (virtually) no atmosphere. Without direct sunlight, any heat that reaches the dark craters is radiated away to the cold of empty space.
The water is thought to be formed by icy cometary impacts and/or solar wind protons reacting with oxygen on the surface. In either case, you end up with a rarified hot gas that will “bounce” around the planet until it “bounces” up and escapes gravity, or reaches the cold crater and freezes out.
A similar process occurs on the Moon for the same reason, and LRO has confirmed the presence of water in the poles in multiple ways.
MikeD, who built and aligned the UV spectrograph on LRO
Well, I’m not sure but I think it might be the biological imperative at work. Just as our ancestors pushed their technology to its limits in exploring the New World, could they help themselves and say, no, it costs too much money? Granted there was some rate of return involved though I suspect the overall balance sheet, if there ever could be one, reflected more debit than credit.
Or, perhaps it is the Romantic in me that wishes it were so, and wishing I could go sets me to dream that, for me, some small part of Heaven would be my soul’s ability to finally know...all of existence.
So I have to disagree. This is one endeavor I support, thinking as well that it takes a strongly structured and coherent society to be able to pull it of. But I guess we both see how that’s going.
Thanks always for your service. We could have been successful there too had it not been for the democrat party that pulled the plug on us.
Welcome home ...
Oh, sure. Now if we can just invent a GUT drive...
You too for sure.
God Bless You and Yours.