SciTechTalk: Grab your erasers, there are more moons than we thought

By JIM ALGAR, United Press International  |  July 21, 2013 at 6:30 AM
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Quick: What's the total number of moons orbiting planets in our solar system? Don't worry if the answer's not on the tip of your tongue but it's still the Trivial Pursuit sort of question that's fun for a water cooler session at the office.

Oh, and if the last time you checked was more than a week ago, your answer will be incorrect.

Not to keep you in suspense, the answer is 178 moons. Granted, that number includes the 5 moons of Pluto, which has been demoted to dwarf planet status, so we now speak of our solar system's eight planets, not nine.

Still, it has moons, and even as a dwarf planet it is still considered part of our solar system, so let's be charitable, shall we?

The point to note here is that the answer to the "how many" question would have been different just a short while ago; just last week astronomers announced an analysis of existing Hubble telescope images and data revealed a new moon orbiting Neptune, bringing that blue-green planet's total to 14.

Moons in our solar system have fascinated us since Galileo used his primitive telescope to discover the first one -- well, four in fact, the large moons Io, Europa, Ganymede and Callisto orbiting Jupiter.

Of course, we have to qualify that "first discovered" tag a bit; early humans "discovered" their first moon the first time they looked into the sky and saw our moon silently gliding overhead.

Since Galileo, moon discovery has been an ongoing effort by astronomers, as last week's news aptly demonstrated.

An interesting side note is that there are "haves" and "have-nots" in our solar system when it comes to planets and moons.

Mercury and Venus, our close neighbors between us and the sun, have no moons.

Astronomers suggest it's their very proximity to the sun that's the reason; any moon orbiting beyond a certain distance eventually would be "kidnapped" by the greater gravitational pull of the sun, while any closer would crash down into the planets. The zone of distance where a moon could exist in a stable orbit is thought to be so narrow that neither Mercury nor Venus managed to ever capture one.

Earth has only managed one, of course, but it's a solar system standout because of its size. There are larger moons out there, but in relation to the size of its planet our moon is impressive, being slightly more than a quarter the size of Earth, a ratio seen nowhere else in the solar system.

Mars has two, Phobos and Deimos, aptly named for characters in Greek mythology representing panic and terror who accompanied their father, the god of war, into battle. Both are believed to be asteroids captured and pulled into orbit by Mars.

Jupiter, when it comes to a moon count, leads the solar system pack with 67, including the largest moon in the solar system, Ganymede, larger than Mercury and three times larger than Earth's moon.

Saturn's not far behind with 62, many of them tiny moonlets of less than 30 miles in diameter. Still, it can also boast Titan, second only to Ganymede in the moon diameter sweepstakes.

Uranus clocks in with 27 known moons, and the literary among you will be pleased to learn they all bear names taken from characters in the works of Shakespeare and Alexander Pope.

And we end with Neptune (sorry, Pluto, but back to the dwarf planet doghouse) and its new moon.

Its discovery suggests the count will not stop, and the total will no doubt increase with better telescopes and more space probes voyaging around the solar system, so by all means offer the 178 figure the next time astronomical trivia is the subject around the water cooler -- just be ready to amend that at a moment's notice.

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