Tag Archives: geology

The Original Rolling Stones

rocks-at-racetrack_arno_gourdol

Who or what has been moving these Death Valley boulders? Theories have persisted for quite some time: unknown inhabitants of the desert straddling California and Nevada; mischievous troglodytes from Middle Earth; aliens sending us cryptic, geologic messages; invisible demons; telepathic teenagers.

But now we know, and the mysterious forces at work are, unfortunately, rather mundane — the rocks are moved through a combination of rain, ice and wind. Oh well — time to focus on crop circles again!

From ars technica:

Mario is just a video game, and rocks don’t have legs. Both of these things are true. Yet, like the Mario ghosts that advance only when your back is turned, there are rocks that we know have been moving—even though no one has ever seen them do it.

The rocks in question occupy a spot called Racetrack Playa in Death Valley. Playas are desert mudflats that sometimes host shallow lakes when enough water is around. Racetrack Playa gets its name from long furrows extending from large rocks sitting on the playa bed—tracks that make it look as if the rocks had been dragged through the mud. The tracks of the various rocks run parallel to each other, sometimes suggesting that the rocks had made sharp turns in unison, like dehydrated synchronize swimmers.

Many potential explanations have been offered up (some going back to the 1940s) for this bizarre situation, as the rocks seem to only move occasionally and had never been caught in the act. One thing everyone could agree on was that it must occur when the playa is wet and the muddy bottom is slick. At first, suggestions revolved around especially strong winds. One geologist went as far as to bring out a propeller airplane to see how much wind it would take.

The other idea was that ice, which does occasionally form there, could be responsible. If the rocks were frozen into a sheet of ice, a little buoyancy might reduce the friction beneath them. And again, strong winds over the surface of the ice could drag the whole mess around, accounting for the synchronized nature of the tracks.

Over the years, a number of clever studies have attempted to test these possibilities. But to truly put the question to rest, the rocks were going to have to be observed while moving. A team led by Richard Norris and his engineer cousin James Norris set out to do just that. They set out 15 rocks with GPS loggers, a weather station, and some time-lapse cameras in 2011. Magnetic triggers were buried beneath the rocks so that the loggers would start recording when they began to move. And the Norrises waited.

They got what they were after last winter. A little rain and snow provided enough water to fill the lake to a depth of a few centimeters. At night, temperatures were low enough for ice to form. On a few sunny days, the rocks stirred.

By noon, the thin sheet of ice—just a few millimeters thick—would start breaking up. Light wind pushed the ice, and the water in the lake, to the northeast. The rocks, which weren’t frozen into the thin ice, went along for the ride. On one occasion, two rocks were recorded traveling 65 meters over 16 minutes, with a peak rate of 5 to 6 meters per minute.

These movements were detectable in the time-lapse images, but you might not actually notice it if you were standing there. The researchers note that the tracks carved in the mud aren’t immediately apparent due to the muddy water.

The total distances traveled by the instrumented rocks between November and February ranged from 15 to 225 meters. While all moving rocks travel in the direction of the prevailing wind, they didn’t all move together—motion depended on the way the ice broke up and the depth of the water around each rock.

While the proposed explanations weren’t far off, the thinness of the ice and the minimal wind speed that were needed were both surprises. There was no ice buoyancy lifting the rocks. They were just being pushed by loose sheets of thin ice that were themselves being pushed by wind and water.

In the end, there’s nothing extraordinary about the motion of these rocks, but the necessary conditions are rare enough that the results still shock us. Similar tracks have been found in a few playas elsewhere around the world, though, and ice-pushed rocks also leave marks in the shallows of Canada’s Great Slave Lake. There’s no need to worry about the rocks at Racetrack Playa coming to life and opening secretly ferocious jaws when you look away.

Read the entire story here.

Image: Rocks at Racetrack Playa, Death Valley. Courtesy of Arno Gourdol. Some Rights Reserved.

Mars Emigres Beware

MRO-Mars-impact-craterThe planners behind the proposed, private Mars One mission to Mars are still targeting 2024 for an initial settlement on the Red Planet. That’s now a mere 10 years away. As of this writing, the field of potential settlers has been whittled down to around 2,000 from an initial pool of about 250,000 would-be explorers. While the selection process and planning continues, other objects continue to target Mars as well. Large space rocks seem to be hitting the planet more frequently and more recently than was first thought. So, while such impacts are both beautiful and scientifically valuable — they may come as rather unwanted to the forthcoming human Martians.

From ars technica:

Yesterday [February 5, 2014], the team that runs the HiRISE camera on the Mars Reconnaissance Orbiter released the photo shown above. It’s a new impact crater on Mars, formed sometime early this decade. The crater at the center is about 30 meters in diameter, and the material ejected during its formation extends out as far as 15 kilometers.

The impact was originally spotted by the MRO’s Context Camera, a wide-field imaging system that (wait for it) provides the context—an image of the surrounding terrain—for the high-resolution images taken by HiRISE. The time window on the impact, between July 2010 and May 2012, simply represents the time between two different Context Camera photos of the same location. Once the crater was spotted, it took until November of 2013 for another pass of the region, at which point HiRISE was able to image it.

Read the entire article here.

Image: Impact crater from Mars Reconnaissance Orbiter. Courtesy of NASA / JPL.

 

 

Curiosity’s 10K Hike

Scientists and engineers at JPL have Mount Sharp in their sites. It’s no ordinary mountain — it’s situated on Mars. The 5,000 meter high mountain is home to exposed layers of some promising sedimentary rocks, which hold clues to Mars’ geologic, and perhaps biological, history. Unfortunately, Mount Sharp is 10K away from the current home of the Curiosity rover. So, at a top speed of around 100 meters per day it will take Curiosity until the fall of 2013 to reach its destination.

[div class=attrib]From the New Scientist:[end-div]

NASA’S Curiosity rover is about to have its cake and eat it too. Around September, the rover should get its first taste of layered sediments at Aeolis Mons, a mountain over 5 kilometres tall that may hold preserved signs of life on Mars.

Previous rovers uncovered ample evidence of ancient water, a key ingredient for life as we know it. With its sophisticated on-board chemistry lab, Curiosity is hunting for more robust signs of habitability, including organic compounds – the carbon-based building blocks of life as we know it.

Observations from orbit show that the layers in Aeolis Mons – also called Mount Sharp – contain minerals thought to have formed in the presence of water. That fits with theories that the rover’s landing site, Gale crater, was once a large lake. Even better, the layers were probably laid down quickly enough that the rocks could have held on to traces of microorganisms, if they existed there.

If the search for organics turns up empty, Aeolis Mons may hold other clues to habitability, says project scientist John Grotzinger of the California Institute of Technology in Pasadena. The layers will reveal which minerals and chemical processes were present in Mars’s past. “We’re going to find all kinds of good stuff down there, I’m sure,” he says.

Curiosity will explore a region called Glenelg until early February, and then hit the gas. The base of the mountain is 10 kilometres away, and the rover can drive at about 100 metres a day at full speed. The journey should take between six and nine months, but will include stops to check out any interesting landmarks. After all, some of the most exciting discoveries from Mars rovers were a result of serendipity.

[div class=attrib]Read the entire article following the jump.[end-div]

[div class=attrib]Image: Base of Mount Sharp, Mars. Courtesy of Credit: NASA/JPL-Caltech/MSSS.[end-div]