Posted on 12/28/2018 11:08:58 AM PST by ETL
The processes that led to glaciation at the cratered poles of Mercury, the planet closest to the sun, have been modeled by a University of Maine-led research team.
James Fastook, a UMaine professor of computer science and Climate Change Institute researcher, and James Head and Ariel Deutsch of Brown University, studied the accumulation and flow of ice on Mercury, and how the glacial deposits on the smallest planet in our solar system compare to those on Earth and Mars.
Their findings, published in the journal Icarus, add to our understanding of how Mercury's ice accumulations—estimated to be less than 50 million years old and up to 50 meters thick in places—may have changed over time. Changes in ice sheets serve as climatic indicators.
Analysis of Mercury's cold-based glaciers, located in the permanently shadowed craters near the poles and visible by Earth-based radar, was funded by a NASA Solar System Exploration Research Virtual Institute grant for Evolution and Environment of Exploration Destinations, and is part of a study of volatile deposits on the moon.
Like the moon, Mercury does not have an atmosphere that produces snow or ice that could account for glaciers at the poles. Simulations by Fastook's team suggest that the planet's ice was deposited—likely the result of a water-rich comet or other impact event—and has remained stable, with little or no flow velocity. That's despite the extreme temperature difference between the permanently shadowed locations of the glaciers on Mercury and the adjacent regions illuminated by the sun.
One of the team's primary scientific tools was the University of Maine Ice Sheet Model (UMISM), developed by Fastook with National Science Foundation funding. Fastook has used UMISM to reconstruct the shape and outline of past and present ice sheets on Earth and Mars, with findings published in 2002 and 2008, respectively.
"We expect the deposits (on Mercury) are supply limited, and that they are basically stagnant unmoving deposits, reflecting the extreme efficiency of the cold-trapping mechanism" of the polar terrain, according to the researchers.
Explore further: Dawn maps Ceres craters where ice can accumulate
More information: James L. Fastook et al. Glaciation on Mercury: Accumulation and flow of ice in permanently shadowed circum-polar crater interiors, Icarus (2018). DOI: 10.1016/j.icarus.2018.07.004
Provided by: University of Maine 
“The new data indicate the water ice in Mercury’s polar regions, if spread over an area the size of Washington, D.C., would be more than 2 miles thick,” said David Lawrence, a MESSENGER participating scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of three papers describing the findings in the online edition of Science Express.
Mercury's north pole. Red denotes areas that are in shadow in all images acquired by MESSENGER to date.
(The mapping of shadows is still incomplete near the pole.) Yellow shows the locations of bright polar deposits
imaged by Earth-based radar. Updated from N. L. Chabot et al., Journal of Geophysical Research, 117, doi: 10.1029/2012JE004172 (2012).
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 water ice might be trapped in those shadowed areas 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 researchers weren’t sure if the radar-bright patches detected by Arecibo corresponded to shadowy places in the craters.
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 show that radar-bright features at Mercury’s north and south poles are within shadowed regions on Mercury’s surface.
Now, the newest data from MESSENGER confirm that water ice is the major constituent of Mercury’s north polar deposits. In the coldest places, the ice is exposed on the surface. In slightly warmer spots, some kind of dark insulating material appears to cover the ice.
MESSENGER uses neutron spectroscopy to measure average hydrogen concentrations within Mercury’s radar-bright regions. Ice concentrations are derived, in turn, from the hydrogen measurements. This is possible because water, or H2O, is two parts hydrogen.
“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,” says Lawrence. “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 ice hypothesis, writes Gregory Neumann of the NASA Goddard Flight Center. In a second paper, Neumann and his colleagues report that the first laser measurements of the shadowed north polar regions reveal irregular dark and bright deposits near Mercury’s north pole.
“Nobody had seen these dark regions on Mercury before, so they were mysterious at first,” Neumann says.
Neumann suggests that both the dark and bright materials were brought to Mercury by comets or asteroids, a finding corroborated in a third paper led by David Paige of the University of California, Los Angeles.
“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,” Paige says.
This dark insulating material is a new wrinkle to the story, adds 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.”
https://science.nasa.gov/science-news/science-at-nasa/2012/29nov_iceonmercury
Cilia-of-Gold......................
Interesting.
Water in any form (except gas at 900°F, i.e. Venus) means human exploration or colonization is possible. I wonder what the temperature in Mercury’s polar craters are? Larry Niven wrote a short story “The Coldest Place” about Mercury when we thought it had a permanent dark side. That story might still apply, though.
And no atmosphere to transmit heat from the sunny regions even a few feet to the permanently dark and icy areas.
Amazing a planet where the daytime temp can be 800°F can have glaciers. Shows that the near-vacuum of Mercury’s atmosphere provides an excellent thermal break for anything in the Sun’s shadow.
hunh - I would have thought that conduction through the soil would have prevented it.
Wouldn’t the extremely low atmospheric pressure on Mercury result in boiling away the water.
Wait till the new session starts, though...
I would imagine any sunlight hitting the ice would result in the ice sublimating directly to a vapor state. The diagram in the article refers to a sublimation "lag" deposit on the ice. Not sure what that means.
Referenced (very) indirectly in Baxter’s latest pair of Xeelee books.
Ok, so the polar regions may never get direct sunlight. But aren’t we told that Mars doesn’t have water because the low vapor pressure of its atmosphere allows the ice to sublimate and escape? So how does Mercury, with virtually NO atmosphere, manage to avoid that condition?
One of my 1960-61 Jr.Hi buddies won a set of encyclopedias from the Ask Andy newspaper column by asking:
“Could Mercury sustain life?”
The answer at that time was: probably at that perpetual twilight region that separates the constantly baked side from the constantly frozen side.
Now we learn that Mercury can also sustain Slushees! Ain’t science grand???
Note: this topic is from . Thanks ETL.
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