Slashdot Mirror
Rover Exiting Crater To Continue Martian Marathon
Riding with Robots writes "The robotic geologist Opportunity has nearly reached the rim of Victoria Crater, which it is leaving after a year of exploration inside. Rover handlers decided to abandon attempts to approach the crater's cliff walls when they saw a power spike similar to the one that preceded a broken wheel on its twin, Spirit. Opportunity is already making do with a stuck robotic arm. The mission's manager said, 'Both rovers show signs of aging, but they are both still capable of exciting exploration and scientific discovery.' Opportunity is set to continue trekking across the Meridiani Plains of Mars, even though its wheels have already seen 10 times the use they were designed for. Meanwhile, Spirit has survived yet another harsh Martian winter to produce another striking panorama."
Adam Korbitz notes other Mars-related news that funding has been approved for the Search for Extra-Terrestrial Genomes (SETG) Project. The project was one of 15 selected to receive funds through a NASA research opportunity program. The stated goal of the proposal is to "develop a PCR detector for in situ analysis on other planets, most immediately, Mars. This instrument is so sensitive it should allow the detection very low levels of microbial life on Mars, and will determine its phylogenetic position by analysis of the DNA sequence of the genes detected in situ."
They would use random primers. A DNA hexamer (six-base sequence) is sufficiently long to serve as a PCR primer, but short enough that it would take only 4096 different types of molecule to comprise all possible sequences. Of course, we don't want the sample DNA to be plastered in our primers, so we'll pare those 4096 down to a handful, at least one of which, in any sample sequence of significant length, will nonetheless find somewhere to anneal. Once we've gone through enough cycles, it's likely that we'll have amplified at least some segment of the sample DNA. Then, getting the reaction contents purified and sequenced is simply a matter of applied microfluidics.
Use random primers, just like you do for reverse transcription when you want to pick up all the RNA sequences in your sample. The reaction's efficiency would take a hit, but if all they want to do is detect DNA (or maybe even sequence a few very short sections) it could probably be made to work.
A bigger problem is the enzyme used in the PCR. IANABiochemist, but I'd expect the PCR to only work if the Martian bugs hava genomes based on double-stranded DNA chemically very similar to ours.
There are plenty of stable nucleotides that could work as components of DNA but, for some reason, aren't used in Earth's life. Ditto chirality: Using the same constituent atoms, one can build almost identical but left- or right-"handed" versions of molecules. For some reason -- probably just chance -- Earth's life is based on "lefthanded" molecules, meaning that we can't produce or consume right-handed molecules. For example, if we synthesise right-handed sugars (easy for a chemist to do, but expensive), they have the same chemical composition, melting point etc, but the structure is such that our enzymes can't use it as a source of energy. Heck, even the sequence of any DNA scooped into the chamber will be important, as if influences the reaction conditions you need for the PCR to work.
If there is life on Mars, this test would only be able to detect it if Martian life is spookily similar to our own. Which would, I'll admit, be even more exciting than just "life on Mars" because it would hint toward evidence of Panspermia or possibly some sort of fundamental rules about what life is able to look like.
Kind of like the microscope on Phoenix? http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080814.html
100nm resolution. DNA however is only 3nm wide.
Here's a page that attempts to rebut this: http://www.donaldedavis.com/2008%20new/CLRMARS.html.
Saddle up: Riding with Robots