Over the past year, NASA’s Curiosity Mars rover has traversed a transition zone between a region rich in clay and one filled with a salty mineral called sulphate. While the science team has targeted the clay-rich region and the sulfate-laden region for the evidence each can offer about Mars’ aquatic past, the transition zone is also proving scientifically fascinating. In fact, this transition may provide the record of a major shift in Mars’ climate billions of years ago that scientists are only just beginning to understand.
The clay minerals formed when lakes and streams once rippled through Gale Crater, depositing sediment on what is now the base of Mount Sharp, the 3-mile (5-kilometer) mountain whose foothills have been rising since 2014. on the mountain in the transition zone, Curiosity observations show that the streams have dried up in trickles and sand dunes have formed on top of the lake sediments.
“We no longer see the lake deposits that we saw for years lower on Mount Sharp,” said Ashwin Vasavada, Curiosity project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “Instead, we see lots of evidence of drier climates, like dry dunes that were sometimes surrounded by streams. This is a big change from the lakes that persisted perhaps millions of years before.”
As the rover climbs higher into the transition zone, it detects less clay and more sulfate. Curiosity will soon drill the last sample of rock it will take from this area, providing a more detailed look at how the mineral composition of these rocks has changed.
Unique geological features also stand out in this area. The hills in the area probably began in a dry environment of large, windswept sand dunes, hardening to rock over time. Interspersed within the remnants of these dunes are other waterborne sediments, possibly deposited in ponds or small streams that once threaded between the dunes. These sediments now appear as stacks of erosion-resistant foliated layers, like the one nicknamed “The Prow”.
To make the story even more complicated, you should know that there were several periods in which groundwater flowed and ebbed over time, leaving a jumble of puzzle pieces that Curiosity scientists must put together in a precise timeline.
Ten years later go strong
Curiosity will celebrate its 10th anniversary on Mars on August 5. As the rover shows its age after a full decade of exploration, nothing has stopped it from continuing its ascent.
On June 7, Curiosity went into safe mode after detecting a temperature reading on an instrument control box in the rover’s body that was hotter than expected. Safe mode occurs when a spacecraft detects a problem and automatically shuts down all but the most essential functions so engineers can assess the situation.
Although Curiosity exited safe mode and returned to normal operations two days later, JPL engineers are still analyzing the exact cause of the problem. They suspect safe mode was triggered after a temperature sensor provided an inaccurate reading, and there is no indication that this will significantly affect rover operations, as backup temperature sensors can ensure that the electronics inside the rover’s body don’t get too hot.
The rover’s aluminum wheels also show signs of wear. On June 4, the engineering team ordered Curiosity to take new photos of its wheels, which it did every 3,281 feet (1,000 meters) to check their overall health.
The team discovered that the left center wheel had damaged one of its lugs, the zigzag treads along Curiosity’s wheels. This particular wheel already had four broken studs, so now five of its 19 studs are broken.
The previously damaged lugs have recently drawn attention online because some of the metal “skin” between them appears to have fallen off the wheel in recent months, leaving a void.
The team decided to increase its wheel imagery to every 1,640 feet (500 meters) – a return to the original cadence. A traction control algorithm had slowed wheel wear enough to justify increasing the distance between frames.
“We have proven through ground testing that we can safely drive on the rims if necessary,” said Curiosity project manager Megan Lin at JPL. “If we ever got to the point that a single wheel had broken the majority of its lugs, we could take a controlled break to clear the remaining pieces. Due to recent trends, it seems unlikely that we’ll need to take a such measure. The wheels hold up well, providing the traction we need to continue our ascent.”
Curiosity Mars Rover ‘alligator-back’ away from rocks
Provided by Jet Propulsion Laboratory
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