New Images Reveal "Pure" Water Ice at Low Latitudes on Mars
Written by Nancy Atkinson
MRO took these images of a fresh, 6-meter-wide (20-foot-wide) crater on Mars on Oct. 18, 2008, (left) and on Jan. 14, 2009. Credit: NASA/JPL-Caltech/University of Arizona
Images of recent impact craters taken by the HiRISE Camera on the Mars Reconnaissance Orbiter have revealed sub-surface water ice halfway between the north pole and the equator on Mars. While the Phoenix lander imaged subsurface ice where the top layer of soil had been disturbed at the landing site near the north pole, these new images – taken in quick succession, detecting how the ice sublimated away — are the first to show evidence of water ice at much lower latitudes. Surprisingly, the white ice may be made from 99 percent pure water.
"We knew there was ice below the surface at high latitudes of Mars, but we find that it extends far closer to the equator than you would think, based on Mars' climate today," said Shane Byrne of the University of Arizona, a member of the High Resolution Imaging Science Experiment, or HiRISE camera.
"The other surprising discovery is that ice exposed at the bottom of these meteorite impact craters is so pure," Byrne said. "The thinking before was that ice accumulates below the surface between soil grains, so there would be a 50-50 mix of dirt and ice. We were able to figure out, given how long it took that ice to fade from view, that the mixture is about one percent dirt and 99 percent ice."
Scientists used several instruments on MRO to take a series of images, detecting and confirming highly pure, bright ice exposed in new craters, ranging from 1.5 feet to 8 feet deep, at five different Martian sites.
Earlier and later HiRISE images of a fresh meteorite crater 12 meters, or 40 feet, across located within Arcadia Planitia on Mars show how water ice excavated at the crater faded with time. The images, each 35 meters, or 115 feet across, were taken in November 2008 and January 2009. Credit: NASA/JPL-Caltech/University of Arizona
The images here were taken of the Arcadia Planitia region, located northwest of the Tharsis region in the northern lowlands, at 40-60° North and 150-180° West. The before and after HiRISE images show a fresh meteorite crater 12 meters, or 40 feet, and reveal how water ice excavated at the crater faded with time. The images, each 35 meters, or 115 feet across, were taken in November 2008 and January 2009.
The discovery of these "white" impact craters began in August 2008, the orbiter's Context camera team examined their images for any dark spots or other changes that weren't visible in earlier images of the same area. Meteorites usually leave dark marks when they crash into dust-covered Mars terrain.
The HiRISE team followed up in September 2008 by taking high-resolution images of the dark spots.
"We saw something very unusual when we followed up on the first of these impact craters," Byrne said, "and that was this bright blue material poking up from the bottom of the crater. It looked a lot like water ice. And sure enough, when we started monitoring this material, it faded away like you'd expect water ice to fade, because water ice is unstable on Mars' surface and turns directly into water vapor in the atmosphere."
A few days later in September 2008, the orbiter's "CRISM" team used their Compact Reconnaissance Imaging Spectrometer for Mars and got the spectral signature of water ice exposed in one of the impact craters, further clinching the discovery.
The HiRISE camera on NASA's Mars Reconnaissance Orbiter took this image of a new, 8-meter (26-foot)-diameter meteorite impact crater in the topographically flat, dark plains within Vastitas Borealis, Mars, on November 1, 2008. The crater was made sometime after Jan. 26, 2008. Bright water ice was excavated by, and now surrounds, the crater. This entire image is 50 meters (164 feet) across. Credit: NASA/JPL-Caltech/University of Arizona
"All of this had to happen very quickly because 200 days after we first saw the ice, it was gone, it was the color of dirt," Byrne said. "If we had taken HiRISE images just a few months later, we wouldn't have noticed anything unusual. This discovery would have just passed us by."
How far water ice extends toward the equator depends largely on how much water has been available in the Martian atmosphere in the recent past, Byrne said: "The ice is a relic of a more humid climate not very long ago, perhaps just several thousand years ago."
This map shows five locations where fresh impact cratering has excavated water ice from just beneath the surface of Mars (sites 1 through 5) and the Viking Lander 2 landing site (VL2), in the context of color coding to indicate estimated depth to ice. Image Credit: NASA/JPL/University of Arizona
While Phoenix's discovery of sub-surface ice was not totally unexpected, finding highly pure ice far closer to the equator because of random meteor impacts was unexpected, he said.
There are several theories about how a layer of such pure ice could have formed beneath Mars surface. Byrne said he thinks that one of the most promising ideas is that this ice on Mars formed in the same way that pure ice lenses form beneath the surface of the Earth.
"That's where you have very thin films of liquid water around ice grains and soil grains and they migrate around to form clear ice lenses on top of the ice table, even at temperatures well below zero. This process is called 'frost heave' on Earth, and it's considered a nuisance in most places because it cracks up roads and tilts walls and destroys foundations of houses.
"But on Mars it would be of great interest if we could discover a process that involved liquid water in today's climate, and not just in some of the warmest areas of the planet but in some of the coldest areas of the planet in the high latitude regions," Byrne said.
Source: EurekAlert
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September 24th, 2009 at 12:29 pm
Water on Mars. What, nobody is claiming it's frozen CO2? Now find life – at least microbial life – and correct the huge vacuum in human knowledge that has been created over the last 50 years.
September 24th, 2009 at 2:05 pm
Say what? What vacuum was created, by whom?
Just because people predicted we would find life on Mars, doesn't mean that if we do eventually find it that we have somehow corrected previous mistakes.
Predicting anything in the total absence of scientific evidence is nothing more than a shot in the dark, and the thing about shots in the dark is that they can sometimes hit their target, but not through any supposed skill of the shooter. Just dumb luck.
September 24th, 2009 at 3:04 pm
OK, someone has to say it. This, and particularly the following quote:
Is HUGE news. A more humid climate means the presence of a full water cycle on Mars, which exists today (hence the clouds of water ice that are occasionally seen), but would have to be much more intense. It also means higher global temperatures, a thicker atmosphere and maybe even superficial liquid flows, even if very limited in size and extension. And all very recently.
I mean: wow!
September 24th, 2009 at 5:15 pm
tacit – Chill, man. I didn't necessarily imply that a gap in knowledge was created by anyone specific, or intentionally. (But now that you mention it, it is an interesting thought). But 50 years ago scientists cherished every photon of sunlight that bounced off Mars and came to Earth. They deduced surface temperature, identified spectroscopic evidence of organics, and observed detailed seasonal changes. Then came Viking, and Mars was forgotten as a dead, frozen CO2 covered wasteland. Now we are finally getting back to science…..and the discovery of life, that scientists like Slipher spent their entire lives studying Mars for, is finally within reach. Life off the Earth – the greatest discovery in the history of science…finally seems imminent. This is a great time.
September 25th, 2009 at 4:02 am
A couple of quickies:
- As someone noted, Phoenix found both dirty and pure ices. But it now seems dirt poor ices is the norm.
- If frost heaving was responsible it would (I think) explains pure or at least purified ices. It also means _flow transport by saturation_:
"Frost heave relies on soils in which there is a supply of liquid water to feed growing ice lenses, established in a thermal gradient, that are capable of displacing the soil perpendicular to that gradient. This requires:
* freezing temperatures
* a supply of water
* a soil that has:
o the ability to conduct water
o a high affinity for water
o saturation (i.e. the pore spaces are filled with water) [Wikipedia]"
Wow indeed!
@ TD:
I'm sorry, but I'm not buying that. It was science that painted Mars "a dead, frozen CO2 covered wasteland" in the first place.
Also, I'm curious: what would be the spectroscopic evidence for organics before the more recent observations of methane? I never heard of them, but it would be good confirmation.
September 25th, 2009 at 6:09 am
TD Wrote:
"But 50 years ago scientists cherished every photon of sunlight that bounced off Mars and came to Earth. They deduced surface temperature, identified spectroscopic evidence of organics, and observed detailed seasonal changes. Then came Viking, and Mars was forgotten as a dead, frozen CO2 covered wasteland. Now we are finally getting back to science….."
What a lot of nonsense.
Almost everything that people thought, Slipher included, about Mars 60 years ago was utterly wrong.
Viking showed us more of the true Mars than everything discvovered in the past 500 years put together.
Viking (and Mariner 9 before it) showed evidence for subsurface water ice. What HiRISE is doing is confirming conclusions amde of Viking data.
September 25th, 2009 at 2:47 pm
I believe the water found on the moon did not originate on the moon, nor did it come from earth. I believe it came from meteorites and comets that have impacted the moon millions of years ago. This is the only possible reason for the small amounts found around impact sites. The earth also gained it's quantities of ice from the same form of impacts. The reason the ice still remains is due to the deep cold of not having an atmosphere. In my personal opinion I believe many moons have the same icy deposits around impact sites.
September 25th, 2009 at 7:08 pm
@ Mr. Larsson – spectroscopic observations of organics I was thinking of were the the "Sinton bands", discussed in several articles in Science back in the day. None of the alternative explanations which exclude organics have been sustained. Also, back in the day (1969) , was a spectroscopic report of methane by Mariner 7, the discoverers were Pimentel and Herr. they withdrew their claim one month later.
@ jonclark "Almost everything that people thought, Slipher included, about Mars 60 years ago was utterly wrong" OK, I admit I go over the top at times, but that's ridiculous and unfair to a great man. Did you ever read his 1964 book? What don't you like – the meticulous observations of martian clouds, including the W cloud that we now know forms near the summits of the high volcanoes on Mars? The observations and photos of seasonal color/shade change, which to this day have not been filmed in any meaningful way? The observations of fine linear features years before HiRise produced images we know call "fossae" (Latin for "ditch") The discovery of Mariner Valley years before Mariner got there? The "Blue clearing" events which have still been explaind only by conjecture? The observations of the ring of color surrounding the receding pole, which are undoubtedly the first observatons of what scientists claim now are erupting pockets of CO2. But you can chill, too, because nobody cares at all. Everyone is so brainwashed that an alien could walk down Broadway and the only people who noticed would be called whacky. Congratulations.
September 26th, 2009 at 3:36 pm
@ Mr D – thanks, you jogged my memory. I thought those bands, which I recently heard of, was shown to be (mostly) Earth HDO. Which is presumably why I forgot them.
Now when I google them, I happen on a 1999 conference, that discuss a remaining unexplained 3.4 region. It was mentioned since the NASA IRTF telescope found similar bands in 1995, originating from Syrtis Major. This is, of course, one of the locations for later finds of methane.
But it is a very small signal of 10 % relative absorption. I dunno about Sinton's observations, as the methane release isn't correlated with season, happens rarely and have a surprisingly fast removal rate. As people find more and more evidence for primordial methane clathrates and their release, for example explaining Titan methane by way of same ammonia action that may explain Enceladus water release, I have to use it as a null hypothesis. (And of course, as methanogens seems to be the very latest metabolism evolved on Earth, making it an unlikely development.)
Btw, I think jonbaker make a very persuasive argument for Viking testing a lot of older hypotheses as bunk, including the remnants of Sinton's hypothesis.
September 26th, 2009 at 3:39 pm
"the methane release isn't correlated with season," – the methane release isn't correlated with season, what I know of,
September 26th, 2009 at 5:42 pm
TD Says:
"…but that's ridiculous and unfair to a great man…"
Slipher was a great man, one of the greatest planetary astronomers of his day (one of the few planetary astronomers of his day) and did great work, but his science was limited by the tools available. There is nothing not to like in work that I know of, but that does not mean he did not get a lot wrong.
"..observations of martian clouds, including the W cloud that we now know forms near the summits of the high volcanoes on Mars?"
Also made my many others. Pity they all, Slipher included, missed the volcanoes. But recognising them as volcanoes is probably impossible with Earth based instruments – You can bareful see them as such in Hubble and Keck images, vastly superior to anything Slipher used.
"The observations and photos of seasonal color/shade change, which to this day have not been filmed in any meaningful way?"
There are certainly secular changes, but MGS observations over a decade showed conclusively they aren't seasonal. The main season changes are variations in cloud cover, the frequency of dust storms, and the extent of the polar caps. Slipher and everyone else got this wrong.
"The observations of fine linear features years before HiRise produced images we know call "fossae" (Latin for "ditch")."
No Earthbound telescope can resolve features this small.
"The discovery of Mariner Valley years before Mariner got there?"
Many observers saw a linear feature called Agathadaemon (one of the few "canals" that has any correspondence with a real surface feature.
"The "Blue clearing" events which have still been explaind only by conjecture?"
Again widely observed by others. We don't understand it, but it does seem trivial compared to study.
"The observations of the ring of color surrounding the receding pole, which are undoubtedly the first observatons of what scientists claim now are erupting pockets of CO2."
The polar collar was widely observed. It is best observed at the North Pole, not the south, which is where the jets appear to be.
"But you can chill, too, because nobody cares at all. Everyone is so brainwashed that an alien could walk down Broadway and the only people who noticed would be called whacky."
Brainwashed? By whom, to believe what, and why?
Let's look at the things that astronomers of Slipher's day thought they know about Mars that are wrong.
Absence of relief. Atmospheric pressure. Temperature gradient in the atmosphere. Absence of craters. The presence of seasonal colour changes. The high probability of vegetation. The thickness and composition of the polar caps. Canals (some of them). The importance of the light and dark markings. There actually is very little they actually got right, beyond the most general observations and measurements of the orbital and rotational parameters.
But so what, they did the best they could, and the nature of scientific knowledge is that it advances.
I suggest you read a few more modern books on Mars, starting with Hartmann. The difference between what we have learned about Mars since 1965 is like the difference before and after Galileo.
September 26th, 2009 at 7:47 pm
"jonbaker" – jonclarke. My mixup, my apologies.
September 26th, 2009 at 7:52 pm
A couple of ammendments. Basic physical parameteres – diameter, density, gravity etc. were also correctly measured prior to spacecraft, at least to instrumentation limits.
Also Slipher thought there were canals on Mars until 1962. Not surprisingly since he was a director of Lowell observatory.