A mountain on Mars that’s nearly as tall as Denali in Alaska seems to be surprisingly gentle, scientists reported on Thursday.
For greater than 4 years, NASA’s Curiosity rover has been exploring Mount Sharp, positioned inside an historic meteor affect crater referred to as Gale and rising greater than three miles excessive. Now measurements of tiny modifications in gravity, recorded by the rover because it climbed in elevation, might assist resolve the query of how the mountain shaped.
The official identify of the mountain is Aeolis Mons, however mission scientists have nicknamed it after Robert P. Sharp, a Mars knowledgeable who died in 2004. It consists of layer upon layer of sedimentary rock, which supply an easy-to-read historical past e-book of Martian geology. That was one of the attractions that led NASA to choose the site for the Curiosity mission, which landed on Mars in 2012.
However sedimentary rocks sometimes kind on the bottoms of lakes and oceans, not on the tops of mountains.
Some scientists surmised that the 96-mile-wide Gale crater was as soon as a lake that slowly crammed to the brim with sediment, which was then blown away by winds, leaving Mount Sharp. Others urged that particles blew in from different elements of the planet and piled up on the heart of the crater within the form of a mountain.
Within the new analysis, published on Thursday in the journal Science, the gravity measurements indicated that the rocks beneath Curiosity weren’t stable however porous, reducing their density. This discovering urged that the crater was by no means utterly full of sediment, as a result of the porous rocks wouldn’t have been sturdy sufficient to help the entire weight with out being compressed.
That conclusion matches in with the notion that each hypotheses of Mount Sharp’s formation are true partly, mentioned Ashwin R. Vasavada, the mission’s undertaking scientist and an writer of the Science paper. Its backside might include carved-out lake sediments, whereas the highest half might have constructed up from windblown particles.
“That’s an concept that’s been gaining power,” Dr. Vasavada mentioned.
The findings had been the results of a intelligent technical improvisation, utilizing sensors that had been meant to supply engineers with info on the standing of the rover. Doing so successfully added a brand new scientific instrument to Curiosity, years after the rover landed on Mars.
The brainstorm got here from Kevin W. Lewis, a professor of earth and planetary sciences at Johns Hopkins College and a member of the mission staff. He realized that trendy gadgets similar to smartphones have chips that measure the forces of acceleration. That’s how an iPhone is aware of to rotate the display relying on whether or not you might be holding it vertically or horizontally.
This type of sensor, referred to as an accelerometer, can measure modifications within the pull of gravity. On Earth, geologists use variations in gravity to probe for underground options similar to earthquake faults and ore deposits. “Wouldn’t it’s wild if we had one thing like that on Mars?” mentioned Dr. Lewis, the lead writer of the Science paper.
Then he realized that there have been certainly accelerometers on Mars. The Curiosity rover was utilizing such gadgets to trace the lean of the automobile because it moved throughout the floor.
These measurements supplied a file of the pressure of gravity on Curiosity. “Fortunately, the engineers had already been taking an ideal knowledge set, mainly since day one,” he mentioned.
As a result of the sensors weren’t meant for Dr. Lewis’s objective, the information had been “fairly noisy,” he mentioned. “The info would leap round fairly severely from daily.”
After calibrating the measurements and averaging out the variations, the researchers discovered that gravity certainly waned barely as Curiosity climbed about 1,000 toes in elevation. But it surely was lower than what would have been measured if Curiosity had been hoisted 1,000 toes into the air. That’s due to the extra gravitational attraction from the mass of the mountain.
The change within the pressure was small. For an individual who weighs 150 kilos on Earth (and simply 57 kilos on Mars due to the weaker gravity), climbing 1,000 toes up Mount Sharp would shed about one-tenth of an oz.
The researchers calculated that the bedrock underneath Curiosity had a density of about 100 kilos per cubic foot. Nevertheless, the minerals that make up the rocks had been about 70 % extra dense than that. This led Dr. Lewis and his colleagues to conclude that the rocks have to be porous.
John P. Grotzinger, a geology professor on the California Institute of Expertise who served because the undertaking scientist throughout Curiosity’s first three years on Mars, mentioned Dr. Lewis’s thought to faucet into the engineering knowledge was “an awesome instance of actual scientific creativity.”
However he was much less sure of the conclusions.
Curiosity’s examination of the rocks on the floor counsel that sediment grains are tightly cemented collectively, not porous. Dr. Grotzinger additionally famous sizable swings within the gravity measurements, even when Curiosity was shifting on roughly degree floor. That implies that the fabric beneath Mount Sharp won’t be as uniform as assumed within the calculations by Dr. Lewis and his colleagues. The gravity knowledge may replicate low-density geological buildings deeper underground, not the properties of the Mount Sharp rocks.
“You simply need to in some way invent a geologically believable situation,” Dr. Grotzinger mentioned. “To me, it leaves some wiggle room.”