Was there ever a fifth rocky, terrestrial planet in our Solar System? If so, it was located beyond the orbit of Mars in what is now the asteroid belt. John Chambers (Carnegie Institute of Washington) likes to call the hypothetical world 'Artemis,' and at the 2006 Astrobiology Science Conference in Washington DC this March, he described how the planet might have formed. The trick, of course, is to account for the orbits of the giant planets, which some believe underwent a shift from almost circular to more highly eccentric (elliptical) orbits. If you set up a simulation with Jupiter in a circular orbit, terrestrial worlds form out to about 2.2 AU. From an abstract of Chambers' presentation: Artemis could have formed in a region that was stable before the giant planets' shift, but unstable thereafter, probably between 1.8-2.2 AU. We simulate the giant planets' orbital shift to explore Artemis' demise, varying Artemis' mass and starting location. In each simulation, the giant planets'...

Centauri Dreams has great pleasure in recommending new movie views of the landing of the Huygens probe on Titan, released yesterday by NASA, the European Space Agency and the University of Arizona. The first sequence, titled "View from Huygens on Jan. 14, 2005" offers a spectacular four-minute ride that compresses what would have been seen by the probe during its 2.5 hour descent, using data gathered by the Descent Imager/Spectral Radiometer instrument aboard Huygens. Image: DISR view south at 5 miles above the landing site on Titan, Jan. 14, 2005. (Credits: ESA/NASA/JPL/University of Arizona). "At first, the Huygens camera just saw fog over the distant surface," said Erich Karkoschka, team member at the University of Arizona, Tucson, and creator of the movies. "The fog started to clear only at about 60 kilometers [37 miles] altitude, making it possible to resolve surface features as large as 100 meters [328 feet]," he said. "But only after landing could the probe's camera resolve...