March 3, 2008

Mars Rover Adjusts After Storm

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On Jan. 17, scientists from Cornell’s astronomy department moved the Mars Exploration Rover, Spirit, toward the sun after a dust storm last summer covered its solar panels, making it more difficult for the Rover to access energy. Both Spirit and the other rover, Opportunity, have had to function on low power since the storm.
Opportunity and Spirit have lasted much longer than the originally planned 90-day mission. However, after making many discoveries and functioning for more than 1,450 days, the rovers have been through their share of wear and tear.
Spirit is currently resting on a plateau of volcanic rock called Home Plate. The upcoming Martian winter poses a threat to the rover’s survival. With the sun lower in the sky, Spirit will have access to less concentrated sunlight. Also, there is little hope that wind will blow off any of the dust on the solar panels since the weather is much calmer during the winter season.
“Right now Spirit functions on 220 to 230-watt hours, which is enough to run a 100-watt light bulb for two hours. Spirit will use every single watt hour produced to heat the battery, operate its instruments and moves its arms,” said Prof. Steve Squyres ’82, astronomy, principal investigator for the Mars Exploration Rover mission.
In order for Spirit to conserve energy, the rover will remain stationary in the coming months. Scientists decided to drive Spirit down a 30-degree incline on Home Plate so that the rover and its solar panels are tilted North towards the sun. Spirit’s solar panels will receive the most concentrated sunlight it possibly can during the day so that the rover can stay warm enough to survive through the night temperatures, which can drop between -80 and -100 degrees Celsius.
“Spirit is looking good since we’ve been able to tilt the rover about 30 degrees on the edge of Home Plate. By tilting the rover into the sun the solar panels can collect more energy, just like a lizard lying on a rock,” Bell said.
Spirit will remain stationary for the remainder of 2008, using its cameras to observe its surroundings and the gradual change of seasons. The Mars Exploration Rover team hopes to be able to move Spirit in September.
“If Spirit survives through June, when the Martian winter solstice occurs, we will probably make it,” Squyres said.
If Spirit does make it through the winter, it will drive south of Home Plate and examine an area where a volcanic vent may have been. The rover will look for evidence of past hydrothermal activity in this region.
Hopes are high for Spirit’s future missions, considering the rover has already found evidence of hydrothermal activity. 200 days ago, Spirit stumbled upon its greatest discovery after its broken front wheel dug up dirt that appeared as white as snow. After further tests, the material was found to be silica.
“On Earth, silica forms in hot springs after water and steam rises through rocks and takes away all other elements,” said Ryan Anderson grad.
The other Mars Exploration Rover, Opportunity, is currently exploring the Victoria Crater, which is located near Mars’s equator. Opportunity has been driving slowly down the 25-degree slope of the crater, examining the layers of sedimentary rock. As the rover gets further down the slight incline into the crater, more layers of rock will be studied. These layers will hopefully provide clues about what the Martian environment used to be like.
“Opportunity is crawling down the slopes of Victoria Crater, a deep impact crater the size of the Cornell campus. It is studying layers of sedimentary rock that preserve evidence that there used to be water on Mars,” said Prof. Jim Bell, astronomy. Bell is the leader of the mission’s Pancam color camera team.
So far, Opportunity has discovered some convincing evidence of water that may have once been on the Martian surface. It has found tiny blobs of hematite that the rover’s team has called “blueberries.”
“Hematite is a ball of iron oxide that forms after water percolates through rock,” Anderson said.
Opportunity, too, has also run into some problems. Frayed cables in the Rover’s arm have made controlling the arm difficult. In addition, after the global dust storm last summer, its solar panels were dirtied and it has had to function on low power like the Spirit.
Once Opportunity finishes exploring Victoria Crater’s layers, the Rover will examine rocks known as “cobbles” located on the plains outside the crater. “Cobbles” are ejected matter that have been thrown from craters after meteorites collided with the Martian surface. These rocks will give astronomers access to materials from deep inside the Martian lithosphere, the outermost shell of the planet, that cannot be found any other way.
There is no way to tell how much longer the rovers will function but so far, they have gone above and beyond everyone’s expectations.
“There is no obvious way to predict when the rovers will stop functioning, but right now they are still working great,” Bell said.