Friday, April 21, 2017
Thursday, April 6, 2017
Tomorrow night, Jupiter makes its closest approach to Earth in 2017 so it'll be big and bright. This only happens every 13 months, and you can spend all night watching it, weather permitting. Opposition means that Jupiter will be opposite the sun so, as the sun sets in the west, Jupiter rises in the east. It'll be straight overhead at midnight, and will be near Spica, the brightest star in the constellation Virgo. And, if it's cloudy you can still catch nearly the same view for nearly a month after opposition.
So, what are those stripes across Jupiter? They are ammonia (NH3) clouds in its upper atmosphere bounded by powerful winds like our own terrestrial jet stream. The dark bands are called "belts" and the light ones are called "zones." Gas rises in the light bands, and sinks down in the dark bands. The colors arise from slightly different temperatures and chemicals in the bands. Adjacent bands have winds in opposite directions. There is quite a bit of uncertainty about what actually gives the bands their colors (blue, orange, brown bands, and the "red" great spot (not visible in this photo). At the cool cloud temperatures, the chemicals in the atmosphere should be colorless, so some have suggested that hydrogen compounds tint the cloud tops. Or, maybe there's sulfur. The clouds do indicate the altitude of the clouds--blue is the lowest, red is the highest. The colors of the clouds are ever changing! There's a cool video of the belts and zones here.
Jupiter has 67 known moons! The four largest ones (Io, Europa, Ganymede, and Callisto) were first discovered by Galileo in 1610, and they are the first objects found in the Solar System to orbit another planet. They are called the Galilean satellites. Ganymede is the largest moon in the Solar System, bigger than the planet Mercury. Europa is the smallest, slightly smaller than our own Moon. It's got a smooth bright surface covered with ice, and perhaps liquid water 100 km deep. It's a favorite of the astrobiologists in their hunt for life elsewhere in the universe. Callisto is the second largest of the Galilean satellites and is believed to be composed of about equal amounts of rock and ices. It's a candidate for a base for a human base if we ever get that far out and explore the Jupiter system because it's the furthest from the intense radiation of Jupiter. Finally, Io, the moon that looks like a pizza, is the most active moon in the solar system, with geysers and volcanoes erupting constantly to spew sulfurous compounds into its atmosphere and across its surface.
With a reasonable telescope, you'll be able to see these moons during the opposition!
Posted by Susan W. Kieffer at 6:45 PM