Opportunity on the rim of Endeavor crater. Credit: NASA/JPL/MSS
Jul 21, 2015
One of the Mars Exploration Rovers is still going strong.
Recently, the Opportunity rover on Mars focused its camera on a grand vista from the summit of Cape Tribulation at the highest point of Endeavor crater’s rim—a view extending for more than 40 kilometers. Considering that its mission was to last only three months, the fact that Opportunity is still operational after almost 11 years is remarkable. The only trouble with the rover is its flash memory system that enables it to store data and then transmit it to Earth. Its functionality is degrading, so NASA engineers are writing new software that they hope will enable it to bypass the difficulty.
Opportunity was launched on July 7, 2003 and has been traveling across the face of the Red Planet since Sunday, January 5, 2004. As mentioned, Opportunity was meant for no more than a six month sojourn on Mars, but the data it gathered compelled NASA managers to fund its mission indefinitely.
Opportunity was preceded by its twin rover, Spirit. However, in June of 2009, Spirit became stuck in a sand trap and was unable to maneuver into a position where its solar cells could keep its batteries charged. After it lost power in the deep cold of the 2009 Martian winter, the rover ceased communications on March 24, 2010. On May 25, 2011 NASA announced that it would no longer send signals to Spirit, signifying the end of the “Spirit recovery project”.
During its many years of travel, Opportunity has provided a wealth of information about the topography of Mars, as well as an analysis of its chemical composition. The surface of Mars appears to be rich in silicon dioxide, otherwise known as quartz, and in various iron oxides, especially hematite and magnetite.
Among Opportunity’s most significant findings are the vast collections of so-called “blueberries” that have accumulated in their trillions on the surface. Note that the term “blueberry” is not because of their color but because the mission team was stunned by their presence within the matrices of several large rocks. They are so abundant that mission managers said they were like “blueberries in a muffin.”
The blueberries bear a striking resemblance to stone spherules on Earth called “Moqui marbles”, found in the Southwestern United States. Moqui marbles are unusual because of their interior construction: the majority of them are iron shells enclosing a sandstone core. They are also found embedded in the walls of some canyons and within large boulders. Some of the Moqui marbles are hollow.
On Mars, the blueberries come in various sizes, with the smallest gathered into drift-like dunes that literally stretch from horizon to horizon. Some of the largest lie within cracks inside shattered polygonal paving stones. The hematite blueberries are often associated with the expanses of shattered quartz, although the reason remains obscure to planetary scientists.
As mentioned, Mars is largely composed of iron and silicon, with massive quantities of oxygen bound into the soils and bedrock. On Earth, water vapor in the atmosphere forms a weak carbonic acid solution when it mixes with carbon dioxide, so that helps to wear away the rocks. On Mars, such erosion is impossible.
The presence of iron oxide in several different forms indicates that something not taking place on any large scale today did take place at some time in the past. Most Mars research groups speculate that there was once a dense, oxygen-rich atmosphere that allowed for the “rusting” of iron in its crust to take place. Whatever the source, Mars has hematite dunes a kilometer high, giant trenches that go on for hundreds of kilometers with their bottoms covered in hematite ripples, and seas of hematite dust tens of meters deep swallowing craters a hundred kilometers in diameter.
It is unusual that dark hematite is so intimately bound up with white silicon-dioxide rock. Could there be a connection between silica and hematite on Mars? Could electric arcs transmute elements: reforming the atomic structure of silicon (with 28 particles in its nucleus) into that of iron (with 56)? Perhaps that connection could also explain the Moqui marbles with their iron oxide and silicon dioxide composition.
Stephen Smith
