Bakersfield Night Sky – June 16, 2018
By Nick Strobel
This past month has seen some important astrobiology announcements. The most recent was last week’s press release from the Mars Curiosity (rover) team about finding ancient organic compounds and seasonal variations of methane on Mars. Curiosity has found organic compounds before back in mid-December 2014 but those were chlorine-containing organic materials that probably are the result of perchlorate salts interacting with a different suite of organic compounds as they were heated up by the SAM instrument on Curiosity. The organic compounds of last week’s announcement were processed in a different way in SAM to determine the original form of the organic compounds in the rocks. The concentration of organic material is about 100 times greater than the 2014 announcement. Organic molecules identified in the latest announcement include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.
Last week’s announcement also clearly show that the variations in atmospheric methane we’ve seen in the past truly are seasonal because we now have three Mars years of data exhibiting an upswing in the warm, summer months and drop off in the winter every year. However, the organic materials and varying methane levels can be made by non-biological processes as well as the more exciting biological processes. The best we can say is that all the ingredients for life were present on Mars, Mars was habitable in the past, and biosignatures could be preserved in the rocks on Mars, just waiting for more advanced analysis to uncover them.
The year 2020 is going to see several orbiters, rovers and landers going to Mars to take the next steps in analyzing the biological possibilities on Mars. The techniques we will use to find past life on Mars are pretty much the same as what we use to find when and where life got started on Earth. Biosignatures—ideal signs of ancient life—have to possess three characteristics: 1) they are compounds that are essential and unique to cellular processes; 2) they need to be stable for a LONG time (billions of years); and 3) the molecules need to be reasonably abundant enough for us to detect them.
For signature #1, we know that life is exceedingly choosy about the chemical building blocks it uses. That’s good because that “pickiness” helps us distinguish a genuine biological remnant from a specimen produced by something else. Although both forms of carbon, Carbon-12 and Carbon-13, have the same chemical properties, Carbon-12 is a lighter form of carbon, so life enhances the amount of Carbon-12 in its reactions. Therefore, biological remnants will have a deficit of Carbon-13 compared to ordinary geological remains. Unfortunately, there hasn’t been enough carbon in the rock samples and methane to do a conclusive analysis of the Carbon-13 deficit.
Terrestrial life has a peculiar way of building hydrocarbons (chains of carbon and hydrogen atoms such as fats and oils = lipids) that would leave a distinctive preference of hydrocarbons chains with even numbers of carbon atoms. Life also prefers working with particular types of polycyclic carbon compounds such as “sterols” (these include cholesterol and steroids) and “hopanoids” that stabilize cell membranes. Hopanoids are rarely found outside of living cells, so they are good biosignature molecules. They are also very hardy and can survive for billions of years.
Even though martian life might use different biological reactions than terrestrial life, a martian biosignature will still have to be something that enhances certain isotopes and molecule types beyond what ordinary geological and chemical processes will do. Of course, we will also look for structures larger than molecules but we’ve been burned by past “discoveries” that sure looked like tiny bacteria fossils but later turned out to be something non-biological.
The other astrobiology news was last month’s announcement about the plumes or geysers on Jupiter’s moon, Europa (see my May 19 column). Finding life on Europa would be even more significant than finding life on Mars because there is practically zero chance that Europa life could be the result of contamination from Mars or Earth and it would mean that life could arise in a very different environment than what we have or had here and Mars. Because of Mars’ weak gravity, it’s possible that giant impacts could have blasted off rocks with martian microbes long ago and then were drawn inward toward Earth (contaminating Earth) because of the sun’s gravity. It’s much less likely for those rock chunks to move all the way out to Jupiter’s vicinity.
Back home: Next Saturday, June 23, is the free public star party hosted by KAS at Panorama Park (near where Linden meets Panorama Drive). Viewing starts with the waxing gibbous moon at 7 p.m. (visible even in daylight). Venus and Jupiter will be visible at the beginning of the star party and Jupiter and Saturn will be visible near the end of the star party (see the star chart below. Come look!
Summer officially starts with the June solstice at 3:07 a.m. Pacific time on June 21. It’s going to get hot, so check the Kern County cooling center website if you or a loved one are at risk from extreme heat.