7 November 2010
A long time ago, I started doing a series of posts about the instruments on Mars Science Laboratory, but I only got through the cameras before I got distracted by something shiny on the internet and forgot to finish the series. So, let’s remedy that, starting with APXS.
APXS stands for alpha particle x-ray spectrometer, meaning that this instrument bombards its target with helium nuclei (alpha particles) and x-rays, causing the atoms in the target to give off their own characteristic x-rays. Those x-rays are used to tell what elements are in the rock or soil that APXS is studying. Obviously, when you’re trying to learn about the geology of a planet, it’s nice to know what the rocks are made of, making APXS a very valuable instrument.
APXS instruments have been on every Mars rover: little Sojourner carried one, both Spirit and Opportunity have one, and now MSL will too. With each generation, the basic design of the instrument has stayed the same, but a lot of improvements have been made too. The new MSL instrument is much more sensitive than its predecessors and can detect a broader range of x-ray energies. It also has a cooler on the x-ray detector, which means that it can run during the day and still get a nice clean signal, whereas the MER APXS usually has to collect data overnight so that daytime temperatures didn’t result in noisy data.
Because of its greatly increased sensitivity, the new APXS on MSL can get a quick estimate of the composition of a rock or soil in about 10 minutes, and takes about 3 hours to do a full, detailed analysis. APXS is a “contact” instrument, meaning that the rover’s arm has to place the instrument within about 2 cm of the thing it is analyzing. This is a pain, especially compared to ChemCam, which will zap samples 7 meters away with a laser to tell what they are made of, but what APXS loses in speed and range it makes up for in accuracy, giving definitive compositions for martian samples.
To read in more detail about APXS and the other MSL instruments, check out the MSL science corner website.