Down the Lunar Rabbit-hole

Jul 13, 2010 by Dauna Coulter
This pit in the Moon's Marius Hills is big enough to fit the White House completely inside. Credit: NASA/ LROC/ ASU

A whole new world came to life for Alice when she followed the White Rabbit down the hole. There was a grinning cat, a Hookah-smoking caterpillar, a Mad Hatter, and much more. It makes you wonder... what's waiting down the rabbit-hole on the Moon?

NASA's Lunar Reconnaissance Orbiter (LRO) is beaming back images of caverns hundreds of feet deep -- beckoning scientists to follow.

"They could be entrances to a geologic wonderland," says Mark Robinson of Arizona State University, principal investigator for the LRO camera. "We believe the giant holes are skylights that formed when the ceilings of underground lava tubes collapsed."

Japan's Kaguya spacecraft first photographed the enormous caverns last year. Now the powerful Lunar Reconnaissance Orbiter Camera (LROC, the same camera that photographed Apollo landers and astronauts' tracks in the moondust) is giving us enticing high-resolution images of the caverns' entrances and their surroundings.

Back in the 1960s, before humans set foot on the Moon, researchers proposed the existence of a network of tunnels, relics of rivers, beneath the lunar surface. They based their theory on early orbital photographs that revealed hundreds of long, narrow channels called rilles winding across the vast lunar plains, or maria. Scientists believed these rilles to be surface evidence of below-ground tunnels through which lava flowed billions of years ago.

"It's exciting that we've now confirmed this idea," says Robinson. "The Kaguya and LROC photos prove that these caverns are skylights to lava tubes, so we know such tunnels can exist intact at least in small segments after several billion years."

These Kaguya images show the Marius Hills pit in the context of a meandering system of volcanic rilles. Because the pit is in the middle of a rille, it likely represents a collapse in the roof of a lava tube. Credit: JAXA/SELENE

Lava tubes are formed when the upper layer of lava flowing from a volcano starts to cool while the lava underneath continues to flow in tubular channels. The hardened lava above insulates the molten lava below, allowing it to retain its liquid warmth and continue flowing. Lava tubes are found on Earth and can vary from a simple tube to a complex labyrinth that extends for miles.

If the tunnels leading off the skylights have stood the test of time and are still open, they could someday provide human visitors protection from incoming meteoroids and other perils.

"The tunnels offer a perfect radiation shield and a very benign thermal environment," says Robinson. "Once you get down to 2 meters under the surface of the Moon, the temperature remains fairly constant, probably around -30 to -40 degrees C."

This cavern in Mare Ingenii is almost twice the size of the one in the Marius Hills. Credit: NASA/ Goddard/ ASU

That may sound cold, but it would be welcome news to explorers seeking to escape the temperature extremes of the . At the Moon's equator, mid-day temperatures soar to 100 deg C and plunge to a frigid -150 deg C at night.

Paul Spudis of the Lunar and Planetary Institute agrees that lunar lava tubes and chambers hold potential advantages to future explorers but says, "Hold off on booking your next vacation at the Lunar Carlsbad Hilton. Many tunnels may have filled up with their own solidified lava."

However, like Alice's Queen of Hearts, who "believed as many as six impossible things before breakfast," Spudis is keeping an open mind.

"We just can't tell, with our remote instruments, what the skylights lead to. To find out for sure, we'd need to go to the Moon and do some spelunking. I've had my share of surprises in caving. Several years ago I was helping map a flow in Hawaii. We had a nice set of vents, sort of like these skylights. It turned out that there was a whole new cave system that was not evident from aerial photos."

As for something similar under the lunar skylights?

"Who knows?" says Spudis. "The continually surprises me."

This could be a white rabbit worth following.

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User comments : 12

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deatopmg
1 / 5 (1) Jul 13, 2010
There are, what appear to be, "rabbit holes" on Mars too, but on Mars all the pixels are 255 for each color. In other words, absolute black.
Caliban
2 / 5 (2) Jul 13, 2010
I agree with Spudis- the Moon continues to surprise.

Was anyone else annoyed by the lack of appropriate images to back up the claim of these skylights being located along the rilles? The photodiagrams presented left much to be desired,IMO. However, I'm sure this had more to do with editorial deadline than any willing attempt to misinform.

ONTH- riddle me this, Batman- if these skylights are formed by the collapse of lava tunnels' roofs, then why does the top photo clearly show a hole with a raised rim, as if it burst outwards? And why does the shadow appear to be misaligned with the incident sunlight(from Left).

And if I am misinterpreting the image, and the sunlight is incident from the other direction, why is there such a noticeable change in the density of the shadow from right to left?

Either way, it's not consistent with a "collapsed roof".

Thoughts, anyone?
Caliban
2 / 5 (2) Jul 13, 2010
If they were saying that these holes are caused by the collapse of Bubble-like structures on the lunar surface, I would feel much less reluctance to agree with them. But that would raise another set of issues, in and of itself.
PieRSquare
3.7 / 5 (3) Jul 13, 2010
Sunlight is coming from the top right. Raised and lowered can look the same if viewed from above but it looks lowered to me. The pit is pure black in photo because surface is very bright. If you exposed the picture long enough to see any detail in the shadows then most of the surface would be a blown-out highlight (pure white)
Caliban
3 / 5 (2) Jul 13, 2010
Sunlight is coming from the top right. Raised and lowered can look the same if viewed from above but it looks lowered to me. The pit is pure black in photo because surface is very bright. If you exposed the picture long enough to see any detail in the shadows then most of the surface would be a blown-out highlight (pure white)


PieR,
Well, I've stared at both photos for extended periods, now, and watched it transform from a "swiss cheese" surface to a "chicken pox" surface. It would be helpful if there was a little info in the article in regards to interpreting the topography and lighting.
Apparently an error in perception on my part.
Graeme
not rated yet Jul 13, 2010
Are the cameras on the orbiters flexible enough to take a super long exposure to see more detail in the dark?
RobertKarlStonjek
not rated yet Jul 14, 2010
Either the sunlight is coming from the left or all the objects seen in the pictures are depressions with no raised mounds at all ~ note that all the shadows are to the right.
Caliban
3 / 5 (2) Jul 14, 2010
Either the sunlight is coming from the left or all the objects seen in the pictures are depressions with no raised mounds at all ~ note that all the shadows are to the right.


Yeah- that's what I perceived initially. However- if you stare at the image long enough, it will begin to resolve from mounds to depressions- ie, impact craters. Then everything makes sense.
kevinrtrs
3 / 5 (2) Jul 14, 2010
However- if you stare at the image long enough, it will begin to resolve from mounds to depressions- ie, impact craters.

As an aside, just to be sure, as I understand it, not all depressions are impact craters from objects external to the moon.
Most depressions are the result of fallout from a single external object impact. There's some large ratio of fallout depressions to single external object impact.
visual
5 / 5 (4) Jul 14, 2010
The article's summary, also displayed when you mouse over the article on the front page, goes like this:
A whole new world came to life for Alice when she followed the White Rabbit down the hole. There was a grinning cat, a Hookah-smoking caterpillar, a Mad Hatter, and much more. It makes you wonder... what's that got to do with a science website?

No comment.
Skeptic_Heretic
5 / 5 (3) Jul 14, 2010
ONTH- riddle me this, Batman- if these skylights are formed by the collapse of lava tunnels' roofs, then why does the top photo clearly show a hole with a raised rim, as if it burst outwards? And why does the shadow appear to be misaligned with the incident sunlight(from Left).
Looks to me like the light source is to the right of the hole. As for the pronounced differences in shadow gradient, remember, there is little to no atmosphere on the moon so the sunlight at sunset is just as powerfully illuminative at "noon" as it is at "dusk". On Earth the appearance would be greatly different due to our atmosphere.

To experiment, take a bowl, or several and go into a dark room. Shine a flashlight from the left and from the right at varying angles and you can match the light source from the right rather easily as you move the angle of source closer to parallel with the basin of the bowl.
note that all the shadows are to the right.
Nifty optical illusion.
CouchP
5 / 5 (3) Jul 14, 2010
The bottom image in this page shows distinctly the bottom of the pit with rubble clearly present!