Harrow and Hillingdon Geological Society
Exploring Mars
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Exploring Mars: Curiosity, water and life.
Peter Grindrod
(UK Space Agency Research Fellow, University College, London)
Introduction
This presentation aimed to set the context for the current Curiosity mission and give some of the publicly available results.
The importance of water on Mars lies in the fact that studies of water and habitability drive and constrain the search for life in the coming decade and beyond. The best chance of finding life outside the earth is on Mars.
Viewed through a telescope from the surface of the earth, Mars is and orange-coloured planet, which is slightly darker in the middle. A lot of spacecraft have been sent to Mars since early exploration in the 1960s. Most of the missions were failures, particularly in the early days when we were still learning about space exploration. However, NASA’s Mariner missions were largely successes, as were the Viking missions in the 1980s. The picture that we get of Mars has gradually improved.
In 1975, the Viking camera had a resolution of 150m per pixel (150m/px). The Mars Global Surveyor and Mars Orbital Camera had 1.5m/px. In 2004, the Mars Express stereo camera had 10m/px and, in 2005, the MRO Hi-rise camera had 25cm/px, a similar resolution to Google Earth.
Landers have included Viking 1976, Pathfinder 1997, Spirit Rover 2004-2010 (a 90-day mission that lasted for 6 years), Opportunity 2004 to present day and Phoenix 2008, which found ice just beneath the surface.
Curiosity
The Curiosity Mars Science Laboratory Rover is 3.0m long, has a mass of 900kg and nuclear powered output of 150W and a speed of 30m/hour. Launched on 26 November 2011, after an 8-month journey, it landed on 06 August 2012 in the Gale Crater.
Looking at Mars as a whole, the northern hemisphere is low and flat, while the southern hemisphere is high and cratered, with large volcanoes (Olympus Mons) and large impact structures. Early landers landed in rocky areas but these are now avoided. Because of its size (the largest object to be landed on Mars), Curiosity could not land anywhere above 1km in altitude (the parachute needs long enough to slow it down). 60 possible landing sites were examined. The best communications are within 30o of the equator and after short-listing 4 sites, all of which had their merits, Gale Crater was chosen.
Gale Crater does not have a sharp rim and it has a mound in the middle (Mount Sharp), which has 5.5km of elevation between the bottom and the top of the mound. The plan was to land in the crater and, after testing of all the instrumentation, for the rover to climb Mount Sharp. 08 -14 August was occupied by landing and initial checkout, 14-22 August by mechanical testing, 22 August to 04 September was an intermission with mast camera checkouts and 04-13 September arm work-outs.
Curiosity landed on the edge of possible alluvial fan deposits and the landing revealed bedrock, having blown away the dust. Chemcam testing using laser ionisation of target rock showed it to be basaltic rock. Atmospheric tests carried out showed no methane present and Ar isotopic ratios shows that Mars has lost 90% of its atmosphere. One rock seen was a cemented conglomerate, thought to have been deposited in flowing water between ankle and waist-deep. One analysis showed basalt altered by water to mugearite. On Sol60 (ie Mars –day60, each Sol being 24 hours 37 minutes) the first scoop sample was taken of surface dust and x-ray diffraction showed it to comprise mg-rich olivine, albite and diopside – ie basaltic dust. On Sol90, investigators switched to earth time, to avoid the constant change from day to night-time working.
Gypsum veins have been found and on Sol229, the first 2 drill holes were made, reaching the target depth of 8cm much faster than expected because the rock was very soft, comprising about 30% smectite and 5-10% gypsum/anhydrite.
Mount Sharp is twice the height of the Grand Canyon and is expected to show olivine-rich dunes followed by phyllosilicates, polyhydrated sulphates and anhydrous phases with increasing height.
Mars has 3 geological epochs from its formation at 4.5 billion years – Noachian to 3.7 billion years, Hyperian, 3.7-3.1 billion years, and Amazonian from 3.1 billion years. The time scale may represent change from phyllosilicates to sulphates to anhydrous phases, representing ph neutral, acidic and dry/frozen condition of water and conditions changing from habitable to less habitable.