I wonder how many millions of people looked up at the full moon last night and saw Mars. What a sight! Once the clouds parted here in Duluth, we were all talking about the big, orange star next to the big, bright moon. Members of the Arrowhead Astronomical Society and I set up telescopes for passers by near Duluth’s iconic Aerial Lift Bridge. Depending on when people happened to walk by, they got to see Venus, Jupiter, Saturn, Mars and the moon fanned out from west to east across the sky.
If you’re ever feeling under-appreciated, grab a telescope and show someone the planets. People who looked through the telescope expressed such gratitude, we all felt heartened and happy. Some of us may not know it, but we all relish a connection with the cosmos.
So what did we see? Jupiter showed excellent cloud band detail and three moons until about 11 o’clock when Ganymede reappeared after occultation; Saturn along with its moons Titan, Rhea and Dione; the half-moon appearance of Venus and even hints of detail on Mars. My favorite comment was a woman’s reaction to seeing Saturn for the first time: “That’s the real deal!”
Around 11:30 p.m., when Mars had finally risen high enough for a clear view, I could make out hints of the south polar cap, faint gray markings beneath the veil of dust and the bright north polar hood, a region of clouds and frost forming near the Martian north pole as autumn deepens there. While dust from the big storm still obscures much of the planet’s surface, there’s hope now the material will settle and the atmosphere will clear at least temporarily. I say that because Mars normally experiences its worst dust seasonal dust storms starting about August and September our time. More could be in store.
The Red Planet continues to make news. A team of astronomers used the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on European Space Agency’s Mars Express, which has been in orbit about the planet since 2003 to probe the Martian polar regions. The instrument beams radar down to the planet that can penetrate the surface to a depth of several kilometers. MARSIS turned its piercing eye toward the south polar region between May 2012 and December 2015 and collected 29 radar profiles that show strong evidence of liquid water trapped below the ice of the South Polar Layered Deposits (alternating layers of dust deposits and ice). Water’s a strong reflector of radar and shows up as white highlights in radargrams.
Crisscrossing the area, they hit on a very radar-bright, 12.4-mile-wide (20 km) zone about a mile (1.5 km) below the surface at 81°S latitude. The pocket stood apart from everything else — it was neither rock nor ice — and was spotted many times over the 3 year study. Based on signal strength and location the most likely explanation is a Martian lake, similar to giant lakes found beneath glaciers on Earth.
But how do you keep a Martian lake from freezing? Remember, Mars is much colder than Earth. The temperature at that depth is predicted to be –90° F (–68° C), way too chill for liquid water. Not unless you add salt to it. A LOT of salt. Salt depresses freezing temperatures, making it possible for water to remain liquid even well below the freezing point. On Earth, lakes beneath Antarctic ice have been found with water temperatures of 8° F (–13° C).
Mars has lots of magnesium, calcium, and sodium perchlorate salts that if concentrated enough could keep water liquid at depth. Perchlorates are especially good at lowering freezing points — down about –90° F (–70° C) — making it possible for a lake to exist below Mars’ south polar ice cap. The briny, silty mix may not be good for swimming, but it may have once encouraged (or still preserve) the beginnings of life on the Red Planet, if that ever became a thing.