Pulling together decades of data from the Voyager, Galileo, Cassini, and New Horizon probes, as well as the Hubble Space Telescope, scientists at the US Geological Survey have put together a complete geological map of Io, the beautiful, mysterious Jovian moon. Io is the most volcanically active object in the solar system, and its surface reflects that: unlike everything else around, it has no craters, a sign that its surface is constantly being remade. That’s thanks to volcanoes that shoot out more than 100 times more lava per year than Earth’s.
The map is a lovely thing, and you can play around with it yourself here.
On January 7, 1610, Galileo Galilei pointed his “spyglass” to the heavens and stared up at Jupiter, one of the brightest lights in the evening sky, and noted what he at first assumed to be three bright stars near the planet. But over the following nights, he realized that those three bright bodies weren’t fixed in the heavens like stars, but rather seemed to dance around Jupiter along with a fourth, smaller body.
Galileo triumphantly announced his discovery of four “planets” that revolved around Jupiter in his March treatise, Starry Messenger [pdf]. Thinking of his pocketbook, he dutifully proposed naming them the Medicean Stars in honor of his patron, Cosimo de Medici. But the name didn’t stick, and today we honor the scientist rather than the patron by calling Jupiter’s four largest satellites the Galilean moons.
The discovery dealt a death blow to the Ptolemaic understanding of the universe, in which all planets and stars were believed to orbit the Earth. For, as Galileo wrote in his treatise, “our own eyes show us four stars which wander around Jupiter as does the moon around the earth.”
In the 400 years that have passed since Galileo first laid eyes on them, we’ve learned a great deal about the moons Io, Europa, Ganymede, and Callisto (all named after the mythological paramours of Jupiter). If all goes according to plan we’ll soon get to know them much more intimately–NASA and the European Space Agency are currently planning missions to closely observe three of the moons. Click though this gallery to view NASA’s most stunning photos of the four satellites, and to find out what we’ve discovered in the four centuries since Galileo began the work.
(For more on Galileo’s discovery and what it meant to science, check out this post from DISCOVER’s Phil Plait.)
Does Galileo Galilei deserve yet another notch in his belt? Besides discovering four of Jupiter‘s moons, studying sunspots, observing the phases of Venus, and examining the rough mountains and craters of the moon, Galileo may also have identified the planet Neptune more than two centuries before its official discovery, one researcher is arguing.
Its widely accepted that in 1612 and again in 1613 Galileo must have observed Neptune, although at the time he thought it was a star, spotted during his observation of Jupiter’s moons. But physicist David Jamieson from the University of Melbourne, Australia, says that history has judged Galileo incorrectly – and that his notebooks reveal that he knew he was looking at a planet after all [Nature blog].
Four hundred years ago, Galileo observed the phases of Venus as the planet orbited our sun and caught its light in different ways, helping to disprove the idea that all celestial bodies twirled around the Earth. Now, the professional descendants of Galileo have observed the phases of an exoplanet for the first time, observing the distant planet in the act of orbiting a foreign star.
The planet, CoRoT-1b, is about 1,600 light years away from Earth, and was discovered about 2 years ago. It’s a “hot Jupiter,” a class of exoplanets that are the size of Jupiter but orbit very closely to their stars (CoRoT-1b orbits its star in just 36 hours). Hot Jupiters are expected to be tidally locked, with one side always facing their stars, the other permanently dark (our own moon is tidally locked with the Earth, only showing its “near side” to us) [SPACE.com].