But, How?

It’s pretty common knowledge in planetary science circles that rocks blasted off of Mars by impacts and collisions have been landing on Earth as Martian meteorites. These rocks have been found in various places on our planet (deserts, the Antarctic), and chemical analyses prove that they came from Mars. (If you want to know more about how and why we know this, read here and here.)

The thing is, these rocks deliver timely information about conditions on Mars at the time they were blasted away. The mineral content tells us about what elements existed in the crust of Mars and the conditions that created and modified the surface rocks. So, you can think of Martian meteorites as snapshots of the Mars-that-was.

Not only could those rocks carry Mars-made minerals to Earth, but under certain conditions, they might be able to carry traces of life here as well. That very possibility has been a lively topic of research ever since the first rocks from Mars were identified as such.

Now, to be sure, life traces are delicate things, and they might not survive the trip through space and then the essentially hot, violent and shock-filled entry into our thick atmosphere. But, if such traces COULD survive, scientists would need to know what to look for. So, a group of researchers at the European Space Agency  created an experiment called STONE-6. They described their work at the European Planetary Science Congress 2008, held last week in Münster, Germany

Essentially these folks designed an artificial satellite that they mounted on a FOTON M3 capsule launched from Baikonur on September 14th, 2007. It contained two samples of terrestrial sedimentary rock and a control sample of basalt that were fixed to the heat-shield of the return capsule. It re-entered the atmosphere on September 26th after 12 days in orbit. The basalt was lost during re-entry, but interestingly enough, a sample of 3.5-billion-year-old volcanic sand containing carbonaceous microfossils and a 370-million-year-old sample of mudstone from the Orkney Islands each containing chemical biomarkers both survived.

When the scientists examined the surviving samples, they found that a 3.5-billion-year-old sample of sand from Pilbara in Australia had formed a thick, creamy-colored fusion crust (essentially a crust that melted and then solidified around the rest of the sample). The microfossils inside survived nicely. The sample from the Orkney Islands experienced the same fusion crust creation.  The rocks also transported an organism called Chroococcidiopsis. The heat of re-entry killed and carbonized this bacteria. But, there were “fossils” left behind.

So, it would appear that past Martian life forms (if they existed) could hitch a ride on a meteorite and survive the trip, we should be able to find them here on Earth when we search for Martian meteorites.  This doesn’t mean they did, so I should stress that NO life has been discovered, yet. The trick now is to look for rocks with Martian-type mineralogy AND which have the creamy-colored fusion crust that indicates their trip through the atmosphere. Examine those for signs of biomarkers that aren’t from Earth, and we’ll likely have a big story about life on Mars.

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