Strange hollows discovered on Mercury

Oct 25, 2011 By Dauna Coulter
Hollows inside the Raditladi impact basin. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

NASA's MESSENGER spacecraft has discovered strange hollows on the surface of Mercury. Images taken from orbit reveal thousands of peculiar depressions at a variety of longitudes and latitudes, ranging in size from 60 feet to over a mile across and 60 to 120 feet deep. No one knows how they got there.

"These hollows were a major surprise," says David Blewett, science team member from the Johns Hopkins University Applied Physics Laboratory. "We've been thinking of Mercury as a relic – a place that's really not changing much anymore, except by impact cratering. But the hollows appear to be younger than the craters in which they are found, and that means Mercury's surface is still evolving in a surprising way."

Mars Reconnaissance Orbiter spotted similar depressions in the carbon dioxide ice at Mars' south pole, giving that surface a "swiss cheese" appearance. But on Mercury they're found in rock and often have bright interiors and halos.

"We've never seen anything quite like this on a rocky surface."

If you could stand in one of these "sleepy" hollows on Mercury's surface, you'd find yourself, like Ichabod Crane, in a quiet, still, haunting place, with a black sky above your head.

"There's essentially no atmosphere on Mercury," explains Blewett. "And with no atmosphere, wind doesn't blow and rain doesn't fall. So the hollows weren't carved by wind or water. Other forces must be at work."

Another example of hollows in crater Tyagaraja. Credit: Science/AAAS

As the planet closest to the Sun, Mercury is exposed to fierce heat and extreme space weather. Blewett believes these factors play a role.

A key clue, he says, is that many of the hollows are associated with central mounds or mountains inside Mercury's impact craters. These so-called “peak rings” are thought to be made of material forced up from the depths by the impact that formed the crater. Excavated material could be unstable when it finds itself suddenly exposed at Mercury's surface.

"Certain minerals, for example those that contain sulfur and other volatiles, would be easily vaporized by the onslaught of heat, solar wind, and micrometeoroids that Mercury experiences on a daily basis," he says. "Perhaps sulfur is vaporizing, leaving just the other minerals, and therefore weakening the rock and making it spongier. Then the rock would crumble and erode more readily, forming these depressions."

MESSENGER has indeed proven Mercury unexpectedly rich in sulfur. That in itself is a surprise that's forcing scientists to rethink how Mercury was formed. The prevailing models suggest that either (1) very early in Solar System history, during the final sweep-up of the large planetesimals that formed the planets, a colossal impact tore off much of Mercury's rocky outer layering; or (2) a hot phase of the early Sun heated up the surface enough to scorch off the outer layers. In either case, the elements with a low boiling point – volatiles like sulfur and potassium – would have been driven off.

But they're still there.

A fresh impact crater. Hollows are present on a section of the crater wall that has slid partway down toward the floor. Credit: Science/AAAS

"The old models just don't fit with the new data, so we'll have to look at other hypotheses."

To figure out how the planets and Solar System came to be, scientists must understand Mercury.

"It's the anchor at one end of the . Learning how Mercury formed will have major implications for the rest of the planets. And MESSENGER is showing that, up to now, we've been completely wrong about this little world in so many ways!"

What other surprises does hold? The sleepy hollows of the innermost planet may be just the beginning.

Explore further: A stunning look at the cliffs of comet 67P/Churyumov-Gerasimenko

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User comments : 12

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dschlink
not rated yet Oct 25, 2011
The five spectrometers should be able to compare the composition of the sinkholes to the uncollapsed areas around them, once enough data has been collected.
Pirouette
1 / 5 (12) Oct 25, 2011
Sinkholes absolutely. The ground underneath is soft and depressions can occur when movement of material(s) far below are no longer supportive and pull downward on the ground above. That's what sinkholes do. The flat terrain (plains) surrounding the depression(s) may have better support underneath it.
Pirouette
1 / 5 (12) Oct 25, 2011
Here in Florida (the sinkhole capitol of the world), sinkholes are made by water searching for its lowest level (which is sea level), and entering into the porous coral rock far underground. When that happens, the ground above shifts to move further down towards the coral and, you have a sinkhole topside. It's probably the basic principle with Mercury, but without the water.
omatumr
Oct 25, 2011
This comment has been removed by a moderator.
that_guy
3.9 / 5 (7) Oct 25, 2011
The comment above by omantumr does not apply in any way to the article at hand and only serves to push an agenda that has no relation to and was not brought up in said article or the comments and conversation that ensued.

Therefore, I reported this comment for abuse.
Isaacsname
not rated yet Oct 25, 2011
Looks like a bad case of acne.

Why not erosion, like this:

http://www.flickr...0618196/
Callippo
1.8 / 5 (4) Oct 25, 2011
My guess is, these rocks are formed with soft material and as such they're eroded with solar wind. The solar wind is surprisingly effective in erosion of ice surface at comets and many moonlets across solar system.
Pirouette
1 / 5 (11) Oct 25, 2011
article said, "There's essentially no atmosphere on Mercury," explains Blewett. "And with no atmosphere, wind doesn't blow and rain doesn't fall. So the hollows weren't carved by wind or water. Other forces must be at work."

If the sinkholes (depressions) weren't formed by what I suggested above, then the only thing else possible might be a bubble formed from an air pocket far below before the depression happened.Then the bubble or air pocket rose up, and when it reached the surface, it popped and the place where the bubble had been underneath, quickly filled with the ground material and sank, forming a depression. I would say that the hills or mountains within the depression(s) were there already before it sank, and then after the bubble appeared and dispersed, the mountains sank down along with everything else.
omatumr
Oct 25, 2011
This comment has been removed by a moderator.
scidog
not rated yet Oct 26, 2011
ok,back in the 50's the kids books on planets told us that lead would melt on the surface.so maybe something melted,boiled off,and the hollows are whats left.
jsdarkdestruction
3.9 / 5 (15) Oct 27, 2011
Oliver Manuel's recent efforts to plaster Physorg.com and other public news sites with his theories and personal URLs are a bit puzzling, as scientists have a variety of publications available to communicate directly to each other in. My best guess is that he is desperately trying to prop up his legacy in light of his arrest in his university office on 7 charges of rape and sodomy based on allegations by 4 of his own children. The charges have been reduced to one count of felony attempted sodomy, not necessarily because of his innocence, but because of the statute of limitations. One can only guess how the recent charges and decades of family strife have affected his ability to reason rationally and to remain objective while defending his unpopular theories.

http://mominer.ms...hildren/

http://www.homefa...uel.html

that_guy
5 / 5 (1) Oct 28, 2011
Oliver Manuel's recent efforts to plaster Physorg.com and other public nws sites with his theories and personal URLs are a bit puzzling, as scientists have a variety of publications available to communicate directly to each other in.


Agreed. But I wish I had quoted the comment before it was removed. While I'm sick of Oliver's BS, and disturbed by the things he did, it's not often that I feel like I have a strong case to report one of his comments despite the idiocy that comes out of him.

In this case, he had segued from the Mercury being near the sun to an anti-global warming neutron repelling opinion...Totally missing the fact that this article is about sinkholes on mercury.

That said, his next comment, the one you still see, still doesn't really address the subject at hand...Although, it does at least quote the article.
Pirouette
not rated yet Oct 29, 2011
I think that if a person were able to actually land on Mercury and step forth onto the surface without getting roasted, both feet would sink down into the ground material AT LEAST several feet, if not more.
Nerdyguy
5 / 5 (1) Oct 29, 2011
@that guy: Never fear, PhysOrg has a few hundred other examples of the exact same thing from his postings all over their site.

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