If you're trying to figure out how fast a gas giant rotates, you have your work cut out for you. Jupiter seems to present the easiest case because of the famed Red Spot, first observed by the Italian astronomer Giovanni Cassini. But gas giants are thought to have a relatively small solid core, one that is completely obscured by their atmospheres. Rotation involves atmospheric effects as the gases slosh and swirl. No wonder astronomers were glad to find Jupiter's pulsating radio beams, discovered in the 1950s. Rotation of the planet's inner core results in a magnetic field that produces these signals, offering our best estimate on the planet's actual rate of rotation. We now know that the largest of the planets is also the fastest rotating, completing one rotation every 9.9 hours. But even this turns out to be an average because the gaseous nature of the planet causes it to experience differential rotation. Head for the poles and you find a slightly slower rotation period than you do...

It's always good to dream big, but sometimes dreams take you in unexpected directions. Growing up with science fiction, I reveled in tales of manned exploration of the Solar System and nearby stars, many of which I assumed would eventually become reality. But I never dreamed about personal computers. You can go through the corpus of science fiction in the first two-thirds of the 20th Century and find many a computer, but there are few tales involving personal computers on the desktop. An exception is Murray Leinster's short story 'A Logic Named Joe,' which ran in the March 1946 issue of Astounding Science Fiction. Leinster invokes something like today's massively networked computers in a story that anticipates the Internet. How did science fiction fail to see something as huge as the PC revolution coming down the tracks? Maybe it's because the future still surprises even those whose business it is to imagine it. I'm musing about all this because of my own desktop PC and the views...

The return of the Genesis mission in 2004 was a spectacular event, its parachute failing to deploy upon re-entry, leading to a crash in the Utah desert that seemed to have destroyed the mission's solar wind collectors. But Genesis was a tough bird and we're getting good science from its remains. The latest news comes from study of an instrument designed to enhance the flow of solar wind onto a small target, with the aim of measuring oxygen and nitrogen. The Solar Wind Concentrator worked well and new papers out of Los Alamos National Laboratory have now appeared, with isotopic measurements of the Sun that illuminate our system's formation. It's astonishing that we have these results -- Genesis flight payload lead Roger Wiens (LANL) calls Genesis "...the biggest comeback mission since Apollo 13" -- but ponder what we've got here. The spacecraft spent two years at the Sun-Earth L1 Lagrange point, some 1.5 million kilometers from Earth, collecting atoms of the solar wind, the stream of...

The latest work involving Cassini's Cosmic Dust Analyzer (CDA) gives us fresh information about Saturn's intriguing moon Enceladus and the likelihood of an internal ocean there. You'll recall that plumes of water vapor and grains of ice have been found spewing from the 'tiger stripe' fractures at the moon's southern pole, feeding material to Saturn's E ring. Three times during the spacecraft's passes through the plumes of Enceladus in 2008 and 2009, the CDA measured the composition of plume grains. Some of these icy particles struck the detector moving at speeds of up to 17 kilometers per second, vaporizing them on impact. The particle constituents could then be separated for close study. What we find is that the ice grains most distant from Enceladus are poor in ice and match the composition of Saturn's E ring. But move closer to the moon and large, salt-rich grains begin to appear. If the plumes came only from surface ice, we would expect little salt rather than the 'ocean-like'...

New Horizons' encounter with Pluto/Charon in 2015 is eagerly anticipated, but let's not forget that the spacecraft will be operational afterwards as it moves deeper into the Kuiper Belt. Fuel will be tight, but there should be enough available for one and possibly a second encounter with a Kuiper Belt Object (KBO), assuming we can identify a likely candidate. I'm often asked how such targets would be chosen, and here's one answer: A new site called IceHunters has been set up at Southern Illinois University that will draw the public into the hunt for icy objects. At the heart of the IceHunters project are images made by some of the world's largest telescopes (most come from the 6.5-meter Magellan telescope in Chile and the 8-meter Subaru telescope on Mauna Kea), of the region where potential targets will be found. Like SETI@Home, IceHunters leverages widely distributed PCs in the hands of end-users worldwide. Check the site and you'll see that instead of conventional astronomical...

We've certainly gotten our money's worth out of the spacecraft once called 'Deep Impact.' A mission designed for close study of a comet (Tempel 1) winds up making extrasolar planet investigations in an extended mission called EPOCh (Extrasolar Planet Observations and Characterization), sends back imagery of the Earth and its moon that deepens our knowledge of terrestrial world observations, and flies by another comet, Hartley 2, in its DIXI phase (Deep Impact Extended Investigation ). Add it all up and you get the combined acronym EPOXI. Have a look at the range of comets that have been studied by spacecraft thus far: Image: Images at the same scale for all cometary nuclei observed by spacecraft. Differences in overall shape are dramatic, as are the differences in contrast between the nuclei and their associated jets, which are brighter than the nucleus at Halley and Hartley 2 and much fainter than the nucleus at other comets. Credit: Science/AAAS. Now we have further analysis of the...

With the Dawn spacecraft on its approach to Vesta, I've been scouting around for science fiction that involves this interesting asteroid. The one story that stands out is famous for its author more than its quality. It's "Marooned Off Vesta," which turns out to be Isaac Asimov's first published story. John Campbell rejected it at Astounding Science Fiction, so it was left to Amazing Stories' Ray Palmer to publish the Good Doctor's first, written at the age of 18. "Marooned Off Vesta" appeared in Amazing's issue of March 1939 and would have faded into obscurity if its author hadn't gone on to his spectacular career in fiction and non-fiction. The era when Asimov didn't make the cover of a magazine he was writing for didn't last for long. I don't particularly recommend you hunt this story down, although it appears (for sentimental reasons, I suppose) in 1973's The Best of Isaac Asimov. Here a trio of space travelers in trouble look out at the surface of Vesta from their crippled craft....

Our Voyager spacecraft are in a fascinating place indeed, where the stream of charged particles flowing out from the Sun -- the solar wind -- bumps up against what we might call the 'interstellar wind,' the tenuous material expelled from other stars in our neighborhood. We've looked at the solar wind's possibilities for propulsion many times, pondering whether it could push a 'magsail' at high velocity to the outer system, and whether such a push would be controllable (it looks to be a turbulent ride indeed). But new work reminds us that the Sun's magnetic field lines are likewise pushed outward by the solar wind. Merav Opher (Boston University) comments: "The sun's magnetic field extends all the way to the edge of the solar system. Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are, the folds of the skirt bunch up." We're learning from those same Voyagers as they move through the...

I'm sometimes asked why I write so seldom about Mars, a very interesting place indeed. The answer is that so many excellent sites are out there tracking events on the planet that I'm happy to keep my focus on the outer system and the starry gulf beyond. But now and then Mars news interrelates with broader stories about planet formation and what we might find in other solar systems. Such is the case with new work from Kevin Walsh (Southwest Research Institute) that looks at the migration of Jupiter during the formation of the Solar System. At issue is the question of why Mars is so small, because if you run simulations of the planet formation process for the four inner planets of our system, you get a Mars that's much heavier than the one we see. Tweaking the simulation parameters isn't enough -- it still doesn't produce the smaller Mars. But a major migration scenario involving Jupiter can help to explain the situation. The trick is that it relies upon an initial distribution of...