Stargazing 12-02

The Mars InSight lander is now on Mars! Millions of people tuned in to the live webcast to catch the celebration and first pictures. In two to three months, the instruments will be deployed onto the surface after checking out all of the lander’s systems. In a couple of years, the Mars 2020 rover will join InSight on Mars.

The Mars 2020 rover mission now has a definite destination: Jezero Crater, an impact crater on the western edge of Isidis Planitia just north of Mars’s equator. Isidis Planitia has some of the oldest and most scientifically interesting areas to explore, and Jezero Crater itself has the remnants of an ancient river delta in which ancient organic molecules and possibly the remains of microbial life are preserved. Well, if microbial life ever existed on Mars, Jezero Crater is probably the best place at the surface for us to look. The clays and carbonates in the river delta would be able to preserve signatures of past life from a time 3.6 billion or more years ago when Mars was a much more comfortable place. The river delta also contains a variety of minerals from inside and outside the crater that would have drained the large watershed into the river delta.

The river delta has all sorts of hazards such as large boulders, cliffs, depressions, small impact craters that could tip over the rover or trap it upon landing, but the Mars 2020 will have the next generation version of the sky crane landing technology used for the successful Curiosity rover still exploring the slope of Mount Sharp in Gale Crater. As the rover parachutes in, the Terrain Relative Navigation system will take pictures of the terrain below it, compare the pictures to pictures taken from orbit, and divert the sky crane if necessary to a safer spot. Once on Mars, the 2020 Rover (it’ll get a better name soon) will look for ancient habitable conditions and past microbial life. The rover will also have a drill to collect core samples of specially chosen rocks and soils and set them aside in a cache for later return to Earth via some future mission. Once brought back to Earth we can analyze the rocks and soil using laboratory equipment much too large to take to Mars. The ExoMars Mission built by the European Space Agency will also be heading to Mars in 2020 to look for signs of past life.

A column six months ago described how we’ll go about looking for “biosignatures” — ideal signs of ancient life. 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. Biosignatures 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.

Terrestrial life has a peculiar way of building hydrocarbons (chains of carbon and hydrogen atoms such as fats and oils, i.e. 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.

In the night sky

In other astronomy news, look for meteors during the Gemini meteor shower that peaks the night of Dec. 13-14. This shower has a broad peak, so you should be able to see many meteors in the few pre-dawn mornings before and after the peak. Also, the moon will be in a waxing crescent phase on the night of the peak, so it will set before the constellation Gemini is highest in the sky.

The Geminids are from the dust trail left behind by 3200 Phaethon, a now inactive comet. The dust particles hit our atmosphere at 22 miles per second and burn up to produce the brief streaks of light that surprise and delight us.

Last show of 2018

The final show for the William M. Thomas Planetarium’s fall season is the holiday tradition favorite “Season of Light” on Thursday. The spring season’s evening shows will start up in mid-February after the winter break.

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