Bakersfield Night Sky - August 4, 2018
by Nick Strobel
The night before Mars’ closest approach to Earth, I pointed out the bright orange object in the southeastern sky to my wife, Lisa. It was high enough above the smoky haze layer from the various California fires to see it clearly and compare it to Saturn in the south and Jupiter in the southwest. Usually, Jupiter dominates the night sky but not during this close approach of Mars. Mars was definitely much brighter than Jupiter and will continue to be brighter for about another month. The global dust storm, still going on as I write this, contributes to Mars’ reflected sunlight.
As we were about to head back inside, Lisa looked at the waning gibbous moon in the west and did some quick mental math that warmed this astronomer’s heart by noting that the sky should be nice and dark for the Perseid meteor shower. She’s right—the moon will be at new phase on August 11 (there will even be a partial solar eclipse visible for those in Greenland and northern Europe on that day) and the Perseids will peak the night of August 12-13. There will be plenty of meteors to see a few nights before and after the peak, so still try to look for the meteors even if you can’t make the night of August 12-13. Try to get away from the city lights and even better would be to get up out of the valley, so that you’re looking through less smog and dust.
The number of meteors you see every hour should increase after midnight as the Earth’s rotation positions you running into the stream of interplanetary dust particles left behind from Comet Swift-Tuttle. The comet dust hits our atmosphere at 37 miles per second and quickly burns up tens of miles above the surface. Larger pieces will penetrate deeper to produce brighter and longer streaks across the sky. The comet dust chunks from Comet Swift-Tuttle tend to be larger than the average of bits from comets that make our other meteor showers, so the Perseids are known for putting on a good show.
On the night of August 14, shortly after sunset, take a look at the thin waxing crescent moon just to the left of bright Venus low in the west (see the star chart below). Between the moon and Venus will be the star Porrima in Virgo. Further west in the solar system chain across the sky will be Jupiter, Saturn, and Mars.
Back to Mars: the possible presence of a subglacial lake of water underneath the south polar ice cap made quite the splash in the popular media (yes, pun intended). It’s understandably exciting news because liquid water is one of the necessary ingredient for life as we know it. However, notice that I said “possible presence” because the discovery is indirect and one possible conclusion of the radar data.
The MARSIS instrument on the Mars Express spacecraft that has orbited Mars since 2003 sends out low-frequency radio pulses into the planet from a pair of boom antennae that each extend out 20 meters from the spacecraft (so it’s 40 meters from end to end). The radio waves can penetrate as much as three miles below the surface. Boundaries between layers of different materials can be good radio reflectors. The MARSIS team crunched the numbers from an intense observation campaign that ran from late May 2012 to late December 2015 and after a few years of looking at other possible explanations for an unusually radio reflective feature about one mile below the polar ice surface, the team announced its possible discovery for scrutiny by the larger scientific community.
The twelve-mile across feature’s temperature is probably about -68 deg C. Water could still be liquid at that very low temperature if there is a lot of salt, especially perchlorate salts, mixed in it to make it a very briny lake. Mars has plenty of perchlorates, so a liquid water buried lake is possible. However, another possible explanation is that the feature could be a muddy sludge.
The SHARAD instrument on the Mars Reconnaissance Orbiter is also a ground-penetrating radar and it has not detected radio-bright features below the southern polar ice cap. Although SHARAD operates at a different radio frequency than the MARSIS instrument and can’t penetrate as far, it should be able to pick up the radar reflection from a briny lake. SHARAD would have a hard time detecting water-saturated sediments, so perhaps its non-detection means that the MARSIS instrument has found a pocket of muddy sludge instead. More observations with MARSIS and SHARAD and sending more advanced instruments to Mars are what’s in store for the future.
Could this possible subglacial lake be a source of water for future human explorers? Probably not, for the first sets of explorers at least. The lake would be buried too deep to drill down to and concerns about harming possible martian life in the lake from contamination by Earth microbes hitching a ride to Mars on the drilling equipment. The first human explorers are going to be close to the equator and they will melt the ice just below the surface that covers much of Mars for their water.