Mars rover reaches convergence of sandstone formations

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The Mars rover Curiosity has been on its journey to Mount Sharp for several months, but for the past few weeks it has had the “pedal to the metal” to reach its next stop — a waypoint called Kimberley.

The plan is for Curiosity to stop there for several weeks to do science work on the four different sandstone rock formations that converge at Kimberley.

However, the trip has not been easy. As I discussed last month, wheel wear has been a potential problem. The rate at which holes developed in the thin aluminum tires was much higher than expected.

A combination of a safer route selection and careful driving has reduced the formation of new holes to less than one-tenth the rate of a few months ago.

The engineering team feels that the wheel problem is under control for now, although they know that there is challenging terrain to cross in the future.

The next problem was with communications. Curiosity does not communicate directly with Earth; data and commands are relayed through the Mars Reconnaissance Orbiter, a satellite orbiting Mars.

On March 9 the MRO went into safe mode when an unscheduled swap from one main computer to another occurred.

Data and commands could no longer be relayed through MRO, so the relay was switched to the Mars Odyssey orbiter. The data rate for Mars Odyssey is slower than MRO, which limited communications until March 13, when MRO returned to normal operations.

Another problem is caused by the fact that the Mars day, called a sol, is about 42 minutes longer than an Earth day.

This 24-hour, 42-minute Mars day means that Curiosity’s downlink time slips later and later each day, creating what mission planners call “restricted sols.”

Restricted sols occur when each day’s downlink comes so late in the Earth’s planning day that there is a one-day delay between when images are taken and when they can be used for planning. Planners then can drive and make targeted observations only on alternate sols.

This leaves very little time to insert science observations into each day’s plan.

Even with these problems, on April 2 Curiosity drove the final stretch of 98 feet and arrived at the Kimberley waypoint.

Kimberley is of interest because it is the intersection of four different types of terrain with different rock textures. The sandstone rocks in this area are made of larger grains than the mudstone that Curiosity studied at Yellowknife Bay.

The contrasting textures and durabilities of the sandstone are caused by the variations in the stuff that cements the grains together. While superficially similar, the rocks likely formed and evolved in quite different environments.

Sandstone with clay-mineral cement is quite soft. If you tap on these rocks with a hammer, they will crumble. On the other hand, sandstone with quartz cement is much harder. Hit it with a hammer, and it will ring.

The type of cement in the sandstone depends on the environmental history of the rock, so studying these rocks can tell us about the past environment.

The harder sandstone is also more resistant to erosion. We see something similar on Earth in the southwestern United States, where hard layers of sandstone form the capping layer of mesas and buttes, while the softer materials are often eroded away.

Understanding the types of cements in the Martian sandstone may help us to understand the shapes and causes of the landscape in Gale Crater. It may even provide information about why the crater has a large layered mountain, Mount Sharp, at its center.

Curiosity is expected to spend at least four weeks doing science work at Kimberley. This work could include a sample-drilling operation with onboard laboratory analysis. Curiosity is now conducting cleaning and calibration activities on instruments in preparation for this work.

Curiosity is also creating a mosaic of the outcrop using images from its Mars Hand Lens Imager camera. Many single images of potentially interesting locations for future contact science are also being obtained. In addition, stereo images of the outcrop are being created using the pair of mast cameras. These images will be used by mission planners to determine the science tasks that will be done during the stay at Kimberley.

It was a long slow journey to Kimberley. With the problems now behind us, we are ready for the science to begin.

Marty Scott is the astronomy instructor at Walla Walla University, and also builds telescopes and works with computer simulations. He can be reached at marty.scott@wallawalla.edu.

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