Mars rover Curiosity is making steady progress toward Murray Buttes, at the base of Mount Sharp. The science lab on wheels will cross the basaltic sand dune field at Murray Buttes and begin the final approach to the layered, clay-rich rocks of Mount Sharp.
One of the primary goals of the mission is to study these layers in order to better understand the history of Mars.
After exploring the area around Yellowknife Bay near the landing site, Curiosity had started traveling to Murray Buttes on what was called the “Rapid Transit Route.” But the route took the rover over high ground made of bedrock, with pointy rocks that would neither crush nor roll out of the way of the wheels. About halfway to Murray Buttes, greater-than-expected wheel wear required a new route that would be safer to the wheels.
The new plan leaves the high ground and moves into the valleys, where Curiosity can drive over collected sand. This plan was tested on the final part of the drive to the Kimberly science stop. Wheel wear was significantly reduced, so planners developed a new “Safe Transit Route” to Murray Buttes.
On May 21, while traveling on this new route, Curiosity spotted two large rocks in the distance. The next day the rover imaged the first one, which was given the name Littleton. Several ChemCam photos were taken the same day, and the initial results indicate the rocks are most likely meteorites. On May 25, Curiosity passed by the other meteorite, Lebanon, and took several more ChemCam images, along with several multispectral images.
At about this same time, researchers discovered the largest fresh meteor-impact crater ever firmly documented with before-and-after images. The discovery was made using images previously taken by another spacecraft, NASA’s Mars Reconnaissance Orbiter. The spacecraft carries the Mars Color Imager (MARCI), a camera used to monitor the planet’s weather.
In March, while examining the daily MARCI images for evidence of dust storms and other observable weather events, Bruce Cantor, deputy principle investigator for MARCI, noticed an inconspicuous dark dot near the equator in one of the images. The spot looked unusual, with rays emanating from a central spot. He looked back at earlier images, skipping back a month or more at a time. He found that the dark spot was missing on the March 27, 2012, image but was present on the March 28, 2012, image.
Once it was determined to be a fresh crater, images were taken in April of this year with the orbiter’s sharpest camera, the High Resolution Imaging Science Experiment (HiRISE). The images revealed a dozen smaller craters near two larger ones. The chunks of an exploding meteor or secondary impacts of material ejected from the main crater could have caused the smaller craters.
The largest crater is slightly elongated, measuring 159 by 143 feet, and is quite shallow compared to other fresh craters. What created it is estimated to have been about 10 to 18 feet long. Because Mars has a much thinner atmosphere than Earth, meteors of the same size are more likely to reach the surface of Mars, whereas the Earth’s greater atmosphere would have heated them to the point of disintegration.
Another event worth noting is the first-ever set of images of a planet transiting the sun, as seen from a planet other than Earth. On June 4, 2014, Curiosity imaged the planet Mercury, visible as a very faint dark spot passing in front of the sun. This was also the first image of Mercury taken from Mars. Although Mercury is very small as seen from Mars, the position of the dark spot moved across the sun in the expected path of Mercury, based on orbital calculations.
You may remember the transit of Venus that was observed from Earth in June 2012. The next Mercury transit visible from Earth will be on May 9, 2016.
From Mars, transits of Mercury and Venus occur more frequently. The next Mercury transit visible from Mars will be in April 2016, and the next Venus transit will be in August 2030.
Another advantage of viewing from Mars is that there are also Earth transits. In November of 2084, the Earth will transit the sun as seen from Mars. Maybe there will be visitors from Earth to witness this one!
Marty Scott is the astronomy instructor at Walla Walla University, and also builds telescopes and works with computer simulations. He can be reached at firstname.lastname@example.org.