5 Aug 2015
Mars date: Sol 1066 at Gale Crater
Catching our breath on Mars…
While we are studying everything we can about the rocks on the surface of Mars, SAM is busy making sure we also learn as much as we can about the atmosphere of Mars!
The inert gases are special because they don’t react with other chemical elements the way some other familiar elements like carbon, oxygen, sulfur, sodium, hydrogen, and silicon, do. That’s why the inert gases are also called noble. These noble gases are helium, neon, argon, krypton, xenon, and radon.
The noble gases are released from the interiors of planets. Over time, some of the gases inside planets escape into the atmosphere, and some of the atmospheric gases escape into space.
The noble gases have stable isotopes (varieties of the same element but with a different number of neutrons in their nuclei), which are useful in tracking evidence of processes that have affected planets over time. Scientists measure the amount of each stable isotope present in a planet’s atmosphere for a number of noble gases, and compare the ratios of these isotopes to each other and to values typical of the solar wind, primitive meteorites, meteorite samples from planets like Mars, and the atmospheres of Earth and Mars. The ratios of noble gas stable isotopes are different in each of these different environments which tells us something about where they came from and some of the processes that have affected them over time.
The noble gases krypton and xenon have lots of isotopes—krypton has six and xenon has nine! They are really big atoms, so they don’t get included in the formation of minerals and they are not very mobile. And now SAM has measured all the stable isotopes of these trace species in the atmosphere of Mars! This is important because it is the most precise measurement ever made of these gases directly in the martian atmosphere. It required a technological feat that has not previously been done on another planet.
Usually, gases flow directly through SAM’s measurement chamber and we measure them as they move. But in a special experiment called static mass spectrometry, SAM was able to hold gases inside its measurement chamber, accumulating enough gas pressure that there were sufficient atoms of the noble gas stable isotopes to count them before the gases were released.
What do these krypton and xenon measurements tell us? They help us better understand the evolution of the Mars atmosphere. Even though Mars has roughly the same total amount of xenon in its atmosphere as Earth does, for example, the ratios of the xenon isotopes in Mars’s atmosphere are different than the xenon isotope ratios in Earth’s atmosphere. The xenon and krypton isotope ratio measurements help us to infer is that Mars lost most of its original atmosphere pretty early in its evolution – a very important discovery.
Three years on Mars, breathing in and breathing out, and SAM is still learning new things about the martian atmosphere.