Skies to Stars: Moons
By Ed Downs
Notice, the title of this month’s Skies to Stars is “Moons,” the plural of “Moon.” No, Earth did not pick up another moon, but the one we have is fascinating. This writer’s 12” reflector is well adapted to study our moon in surprising detail. With a clear sky and 300 power magnification, the normal visual distance of about 250,000 miles can be cut down to a surprisingly close 800 miles. Not only can one see the vast number of craters that were created during the late heavy bombardment period (upwards to four billion years ago), but also the mountain ranges and “seas” that were formed by volcanic activity. Best observed when less than half full to improve shadow contrast, our moon is a wonder of discoveries. But our moon is not the only show in town. Mercury and Venus do not have moons, we have one and Mars has two small moons, leaving the inner rocky planets significantly “moon challenged.” You see, there are at least 180 moons (and still counting) in our solar system; many of which can be seen by amateur astronomers.
It is no surprise that Jupiter is champ, given a gravitational pull that is second only to the Sun. Some 65 moons circle this giant. The four largest (known as the Galilean Moons), Io, Europa, Ganymede and Calisto, are easily seen in some detail with amateur equipment. These moons are popular targets. It is truly amazing to view not only the huge planet, Jupiter, with an atmosphere that can change its appearance within a single viewing session but to also see moons in motion. In fact, the moons of Jupiter are so popular that cell phone apps exist to keep track of them. Saturn’s giant moon, Titan, (nearly the size of the planet Mercury) can be observed, but many of Saturn’s other 62 moons are just too small for amateur telescopes. The outer gas giants also have moons, 27 for Uranus and 13 for Neptune. Even Pluto, no longer considered an official planet and now called a Kuiper Belt Object (KBO), has five moons. One of those moons, Charon, is nearly half the size of Pluto itself. Even KBOs beyond Pluto, Iris, Haumea, Quaoar and Orcus have moons. Okay, one might think moons are fun to watch, but they are just dead worlds, right?
Wrong, our moon is still alive, with scientists having recently observed volcanic activity for the first time. Saturn’s giant moon, Titan, has a thick atmosphere and rivers and seas of liquid hydrocarbons. There is strong evidence that Titan also supports several sub-surface oceans of liquid salt water beneath its icy exterior. Europa, Ganymede and Enceladus also show evidence of sub surface oceans of salt water. Observations from the Galileo, Cassini and early Voyager 1 spacecraft are being combined with ground observations from the Keck observatory (Mona Kea, Hawaii) to paint an amazing story. These moons are alive, with warm interiors. The tremendous gravity of Jupiter and Saturn create “tidal forces” that work these moons like putty, crating heat. When combined with external radiation and the decay of radioactive material within the moons, what were once thought to be dead, round, ice cubes now sport fascinating possibilities for life. It is a wonderful experience to look through ones eyepiece and know that the reflected light from those small globes circling the gas giants might indeed prove worthy of the movie fantasy that featured blue creatures, living on the giant moon, circling a huge planet. To be sure, advanced life, as we would recognize it, is not expected, but the potential for microbial critters is quite real.
Yes, the secondary citizens of our solar system offer fascinating viewing and give the amateur astronomer the opportunity to see our solar system in motion, in real time. Sure, you can see all this in a number of beautiful coffee table books, but that is like flying with a computer game. The real thing is a lot more fun.
