Mississauga Centre RASC

116th Meeting

                                                      Speaker’s Night  

           

 

Day:                Friday November 21, 2008

 

Speaker:          Dr. Rolf Gellert

                     

 

How to Explore with Robots the Planet Mars

 

Dr. Rolf Gellert, a nuclear physicist from the Max Planck Institute in Germany, and currently associate professor of the University of Guelph spoke about robotic exploration of Mars. He is the principal investigator of the Alpha Particle X-ray Spectrometer (APXS) for the Mars Exploration Rovers (MER), and the Mars Science Laboratory (MSL) to be launched in 2009.   NASA builds and sends rovers to Mars whereas the small space agencies build the instruments that do science.  For example, the Canadian Space Agency is funding the Spectrometer for the MSL, built at MDA in Brampton.

 

Mars’ gravity is 40% that of the Earth, the atmosphere is much less dense and there are huge temperature swings from -12 in the day to -80 at night.  The Martian year is 687 sols (or Martian days) long.  We want to know whether there were ever habitable conditions (water) and life on Mars.  High and low profile imaging shows a number of interesting places relevant to this question.  Gusev Crater, the landing site of the Spirit Rover, is a 150 km diameter depression with a channel leading into it.  The hole has an age of some billions of years and may have been filled with water in the past.  Spirit’s mission is to find lake deposits such as carbonates.  Phoenix landed near the north pole where frozen water and frozen carbon dioxide occur.  Orbiters have also shown a valley likely formed by water 3 billion years ago, as well as ice and mapped minerals which need to be confirmed by ground studies. 

 

Instruments on the MERs must use low power, have low weight and be very robust for launch.  Its goal is to search for water, clues for water in the past such as salt, layered sediments and minerals altered by water in the past.  MER itself is a robotic field geologist with wheels, arms, eyes. Tools include a microscopic imager, a rock abrasion tool, two spectrometers, and the APXS. 

 

The APXS is the size of a coke can weighing 250 grams.  It measures the elemental composition of rocks from sodium to bromine and documents how elemental chemistry changes in different parts.  The instrument has a long history and was on the Apollos, on the 1997 Pathfinder, on the 2003 Rosetta.  The instruments got better with time. Pathfinder needed 10 hours and could only work at night. MER needed 5 hours and night only, but MSL requires only one hour and can work anytime.  The APXS contains a radioactive source that bombards rocks with x-rays and alpha particles and detects x-rays. Each element emits distinct x-ray energy and so a unique fingerprint of elements can be found with about 20% of rock composition being iron. 

 

The MER spacecraft were launched in a specific time period to reach Mars.  The entry speed of 5km/sec is decreased by a heat shield, parachute, air bags and retrorockets.  Phoenix landed in the north polar region using retrorockets.  It cannot move but uses an arm to put soil into sensitive instruments.  White material was seen but, lacking an APXS, it could not decide quickly what it was (silica, salt, ice).  The MSL scheduled for launch in late 2009, weight 650kg.  It is a lander with no mobility thus saving weight. It has an arm extending meters but there is the possibility of contamination of the landing site by the thrusters.  The rovers, on the other hand have an operational radius of 10 km and area of 100 km2 and they can reach a point identified from orbit although daily decisions have to be made whether to stay or move on.  To operate a robot on Mars, it takes at least 10 minutes for a radio signal to travel one way. Thus there is no joy-stick real time operation possible.  A list of commands is sent out daily, pictures are sent back at night and commands for the next day sent out. 

 

The MER Spirit in Gusev Crater at first found no signs of lake sediments.  After the Columbia Hills, white material was found in the “Dead Sea” area. APXS showed that this was nearly pure hydrated ferrous sulphate salt with silica.  Ian Campbell found 16% bound water from the APXS scatter peaks.  The rover nearly got stuck in pure silica – a sign of old fumaroles when steam with acidic gas goes through cracks and forms ferrous sulfate.  MER Opportunity at Meridium Planum landed on a huge plane the size of Oklahoma and found that the origin of the hematite there were concretions and bedrock rich in sulfate salts formed in a wet environment.  For 4 years, Opportunity has been hopping from crater to crater.  Water rushed through a large area in Meridium Planum. APXS determined the composition in Victoria Crater and showed that magnesium, sulfate and chlorine rose in parallel and that the area was once filled with water with magnesium sulfate and chloride in solution.    

 

The MSL Rover is a combination of MER and Phoenix on wheels.  It will “digest” rock samples. Dr. Gellert showed images of the APXS in Guelph University. It was then given to NASA in Pasadena and  assembled into the spacecraft. 

 

In summary, Mars is very sulphate and salt rich.  In the past it was hotter and water was present.  Carbonates have not been detected on Mars possibly due to acidity from sulphates.  It is challenging for life to arise there.  It is an interesting planet to investigate with scientific robots and is an attractive goal inspiring young people to go into engineering and science, improving science instruments and exciting scientists and the public. 

 

 

 

 

 

Chris Malicki, Secretary