Free Astronomy Magazine January-February 2020

45 JANUARY-FEBRUARY 2020 ASTRONAUTICS O n ancient Mars, water carved channels and transported sediments to form fans and deltas within lake basins. Examination of spectral data ac- quired from orbit show that some of these sediments have minerals that indicate chemical alteration by water. Here in the Jezero Crater delta, sediments contain clays and carbonates. [NASA/JPL/ JHUAPL/MSSS/Bro wn University] Below, a false- color image of Jezero Crater shows the edge of an ancient river delta where re- searchers have spied hydrated sil- ica, a mineral that’s especially good at preserving microfossils and other signs of past life. [NASA] biosignatures and microfossils. As a result, a rover capable of analyzing the soil and subsoil of sites in which hydrated silica and carbonates abound is more likely to recog- nize clues of past life. In the final stages of landing site selection, the mission team and the planetary science community considered over 60 candidates, concluding that the most promising desti- nation for the Mars 2020 rover is Jezero Crater. This 28-mile-wide crater is located on the western edge of Isidis Planitia, a huge impact basin visible just north of the Martian equator. In that part of Isidis Plani- tia are some of the oldest and scientifically interesting geological structures on the planet. Observations made by the orbiters suggest that the Jezero Crater depression was, in very remote times, occupied by a lake into which a delta flowed. Thus, the lake may have collected and preserved or- ganic molecules and potential traces of mi- crobial life present in both the water and signatures of hydrated silica deposits (a typ- ical clay compound) and carbonate deposits (minerals formed by the interaction be- tween water and carbon dioxide). These minerals are very effective at preserving