One of the oddest moons of the solar system looks like a walnut. Maybe it is. But it is a black and white walnut. Actually, we’re sure it isn’t a real nut, but pictures from the Cassini spacecraft orbiting Saturn sure make you ready to grab the nutcracker.
One of the oddest moons of the solar system looks like a walnut. Maybe it is. But it is a black and white walnut.
Actually, we’re sure it isn’t a real nut, but pictures from the Cassini spacecraft orbiting Saturn sure make you ready to grab the nutcracker.
This moon, Iapetus, has an equatorial ridge going around a good portion of its surface, appearing like this world has a top and bottom half ready to be split open.
Since its discovery in October 1671, we have known this is one strange moon. The Italian/French astronomer who found it, Giovanni Domenico Cassini, stared to notice the moon varies in brightness as it shifts around in its orbit. With his first telescope he was able to track it only the western side of Saturn, when it was brightest. Finally in 1705, with an improved instrument, he was able to see the moon on the eastern side, in its much fainter phase.
Astronomers have found that one entire side of the satellite is white, and the other, soot black.
Iapetus varies by two orders of magnitude in brightness, from about +10.2 to +11.9.
How Iapetus became two-faced is subject of theories. One view is that the dark material is a coating of particles from a more distant, dark moon, Phoebe.
Volcano-like eruptions may also be spreading the dark material.
The third largest moon of Saturn, Iapetus is about 914 miles wide, smaller than the Earth’s moon (about 1,200 miles). It takes about 79.3 days to go around Saturn, some 2,213,000 miles from the planet. Like our own satellite, Iapetus is tidally locked; Iapetus always presents the same face towards Saturn.
Its equatorial ridge is a chain of mountains as high as six miles. Some astronomers have theorized that the ridge developed when the moon once spun around much faster than it does today. Others speculate that the ridge formed from a collapsed ring of particles orbiting Iapetus.
If you have a telescope with at least a three inch mirror or lens, you can detect Iapetus at least on its brighter side, which appears like a dim star in the vicinity of the ringed planet. A finder chart or careful inspection is needed to pick out the satellite from actual background stars. Much easier to see if Saturn’s largest satellite, Titan, which is closer to the planet.
You can see Saturn the next clear evening this May. It is high up in the south at around 9:30 p.m., appearing like a bright yellow star. It is close by a dimmer but noticeable star, Porrima, in the constellation Virgo. A telescope that can magnify about 30 to 40x will begin to show the famed ring system around the planet.
How about our own moon? Ever hear the phrase “dark side of the moon”? There is always a dark side and a bright side - one side is always in the night, facing away from the sunlight, just like the Earth. It is better to say “the far side of the moon” when referring to the side of our satellite always facing away from us. Our own moon does have areas of darker surface material, of lower reflectivity (albedo). We know these as the features of the “man in the moon” and are vast plains of hardened lava, known as “maria.” Interestingly, the far side of the moon has very little areas of maria.
Last-quarter moon is on May 24.
Send your comments to firstname.lastname@example.org.
Keep looking up!