Site selection narrows for next Mars lander
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: 20 November, 2008

Four potential landing sites on Mars have been selected as candidates for the touch-down of NASA’s next roving Mars mission, the Mars Science Laboratory.

Location map of the proposed landing sites of the MSL (white labels) compared with the locations of previous Mars missions (marked in yellow). The MSL site selection has now been narrowed to Eberswalde, Holden, Gale Crater and Mawrth Vallis. Image: NASA/JPL.

Three other sites were eliminated in this round and the winning site will be announced next summer, after further evaluation of observations made by Mars orbiters have been made to assess the scientific value and safety risks of the proposed sites. In the running are locations known as Eberswalde, located in an ancient river delta and thought to contain clay minerals that might contain evidence for the carbon chemistry crucial for life; Gale crater, which sports a five kilometre high mountain of layered materials that would provide a record from environments that produced clay deposits near the bottom to later environments that produced sulfate deposits partway up; Holden crater, which bears witness to gullies carved by running water which deposited sediments and clays in lake beds; and Mawrth Valley, a flood channel on the mysterious boundary that separates the northern lowlands from the southern highlands of Mars.

"All four of these sites would be great places to use our roving
laboratory to study the processes and history of early Martian environments and whether any of these environments were capable of supporting microbial life and its preservation as biosignatures," says John Grotzinger, Mars Science Laboratory project scientist.

Several of the sites had been proposed for past missions such as the Mars Exploration Rovers (MERs) Spirit and Opportunity, but were ruled out as too hazardous for the capabilities of those rovers. The Mars Science Laboratory (MSL), however, has improved features that have opened up more areas for exploration. For example, it is larger and more robust than the MERs and is powered by nuclear fuel, allowing it to operate year round without the need for continuous solar power.

The Mars Science Laboratory will be winched down to the Martian surface by a sky crane. Image: NASA/JPL.

The rover will be lowered to the Martian surface via a new ‘skycrane’ technology, similar to how helicopters maneuver large objects through terrestrial skies. This method can accommodate more slope than the airbag method used for Spirit and Opportunity, and can be adjusted last minute to avoid any potentially hazardous boulders, for example. The target landing area is also considerably reduced from a safe area of about 70 kilometres for the MERs to a landing ellipse of just 20 kilometres for MSL.

"Landing on Mars always is a risky balance between science and engineering. The safest sites are flat, but the spectacular geology is generally where there are ups and downs, such as hills and canyons. That's why we have engineered this spacecraft to make more sites qualify as safe," says MSL mission manager Michael Watkins. "This will be the first spacecraft that can adjust its course as it descends through the Martian atmosphere, responding to variability in the atmosphere. This ability to land in much smaller areas than previous missions, plus capabilities to land at higher elevations and drive father, allows us to consider more places the scientists want to explore."

The mission plan calls for the rover to spend a full Martian year (23 months) examining the environment with a diverse payload of tools. The primary goals of the mission will be to characterise the local geology of the landing site and to determine whether life ever arose on the red planet. It will also characterise the climate of Mars and help prepare for human exploration. In order to fulfill these goals, MSL will complete a series of science objectives, such as determining an inventory of organic material and the chemical building blocks for life, and identifying features that might represent the effects of biological processes. MSL will also interpret the processes that have formed or modified rocks and soils at the landing site and surrounding area. The atmospheric measurements will help to assess the present state, distribution and cycling of water and carbon in the planet, and to help prepare for human visitors MSL will determine the nature and amount of radiation received on the Martian surface.

The Mars Science Laboratory will be much larger than previous Mars rovers Spirit and Opportunity. Image: NASA/JPL.

MSL is currently scheduled for launch in September 2009, arriving at the red planet in the summer of 2010. More information about the mission can be found in the Astronomy Now 2009 Yearbook, on sale now.