Galileo's Moons

Io and Europa in the same frame March 2, 2007, two days after New Horizon's flyby of Jupiter. As the spacecraft sped away it took this long-lens photo. The moons are in fact separated by 790,000 kilometres. Eruption of the volcano Tvashtar is still very visible. Io's night side is lit by Jupiter, a planet which gives off twice as much radiation as it receives from the Sun. Europa's night side is dark because it is on the other side of Jupiter.

The night of January 7, 1610 Galileo first noticed strange objects around Jupiter. By January 13 he had seen 4 moons. Discovery of new worlds was truly exciting and kept Galileo up every night. By March 22 he had finished his observations, and immediately started writing his observations in book form.

STARRY MESSENGER was published that same year and was immediately popular. The book was also controversial, because not everyone believed in the new moons. Someone named Horky, who had been a student of Johannes Kepler, wrote a book claiming that the moons were a fraud designed to gain fame and wealth. Kepler was very unhappy, but he counseled Galileo not to respond to such attacks.

Pictured to scale by New Horizons are Io, Europa, Ganymede and Callisto. The moons will be there long after the doubters are underground. Kepler's advice to Galileo was right on.

New Horizons at Jupiter

On its way to reach Pluto in 2015, the New Horizons spacecraft swung by Jupiter for some gravitational assist. As practice, it took the best picture yet of the Great Red Spot and the new Spot. Little Spot was formed from the merger of 3 smaller spots, and continues to grow. As in a tub of water, smaller vortices eventually merge into one big one.

The Great Red Spot was first observed by Domenico Cassini around 1665. It is shaped like an Earthly cyclone, but has lasted far longer. These storms form coloured spots because they extend deep into the atmosphere. They are signs of some unknown phenomena inside Jupiter. We recently saw that brown dwarfs, which occupy a size range between Jupiter and stars, are home to massive sources of energy. There is more inside Jupiter than meets the eye.

Below in 3-D is the eruption of volcano Tvashtar on Io. This moon itself emits a lot of heat. New Horizons also discovered a new volcano just reaching the surface of Io. Near Hawaii we have a submerged volcano named Lo' ihi that will someday form a new island. Objects from gas giants to little moons like Enceladus contain sources of energy. Something is going on literally beneath our feet.

Io is one of the four satellites discovered by Galileo. Objects circling a body other than Earth were a direct threat to the old Ptolemaic system. Scholars of the day refused to peer into Galileo's telescope for fear of upsetting their world view. Galileo spent the last 10 years of his life under house arrest for promoting heresy. (A bit like saying the speed of light isn't constant.) Despite his persecution, a Jupiter probe and a STAR TREK shuttle would be named for Galileo.