Planetary migration -- as when a 'hot Jupiter' moves inward toward its parent star during system formation -- may not be as disruptive as we once thought. In fact, according to a new study led by the University of Colorado at Boulder and Pennsylvania State, solar systems with hot Jupiters may well harbor Earth-like planets covered with deep oceans. The research team's paper, just published in Science, paints a positively benign scenario, one in which the gas giant's migration actually becomes the trigger for the formation of water worlds that could well turn out to be habitable. Let's look at this more closely, because it's quite a shift from earlier studies, which assumed that a hot Jupiter's migrations would eject protoplanetary materials from the system or else absorb them. Working with computer simulations, the Colorado/Penn State researchers now think the hot Jupiters force rocky debris outward in the system, helping the formation of rocky planets. At the same time, and this is...

Putting a brown dwarf into the same stellar system with one or more known planets seems like a dicey proposition, but we know it sometimes occurs. Radial-velocity studies have already detected systems like HD 38529 and HD 168443 that include a brown dwarf and known planet. In both these cases, the brown dwarf involved is known to revolve around the exoplanet host star in an orbit at least ten times wider than that of the planet found there. But there are more unusual possibilities: A brown dwarf around the star HD 202206 actually moves inside the orbit of the known exoplanet there. Look no further if you need a new science fiction setting. Until now, we've never had a direct image of a brown dwarf around an exoplanet host star, but a new paper changes all that. A German team led by Markus Mugrauer (University of Jena) provides just such a detection, as shown in the image below. The star is HD 3651, a K-class dwarf near the boundary between Pegasus and Pisces some 11 parsecs from...

Among the 200-plus exoplanets discovered thus far, the system around the red dwarf Gl 876 stands out. For one thing, it contains the closest thing to a terrestrial-sized planet yet found, with a mass of about six times that of Earth and a tight, two-day orbit around its primary. For another, it houses two gas giants, the only planets of this type known to orbit an M-dwarf, and they exhibit a 2:1 mean-motion resonance -- one of them orbits the star twice in the same amount of time the other makes a single orbit. Such resonances provide clues in the study of how systems like these formed and changed over time. These gas giants, one in a 30-day orbit, the other in a 60, are fascinating in their own right, but the detection of the small inner planet by Doppler techniques shows just how far planetary detection methods have come in the past decade. Now a paper slated for publication in The Astrophysical Journal looks at Gl 876 in terms of planetary transits, for to arrive at the true mass...

Asteroseismologists -- the people who study the oscillations of stars to examine their internal structure -- can tell us a good deal about Alpha Centauri, and specifically about Centauri B, a K-class star which has also been carefully measured with the techniques of long-baseline interferometry. But a problem arises when you compare their mass estimates of the star with radial velocity studies, for the mass estimates of each differ by 28 Jupiter masses, plus or minus 9. Is the discrepancy a data analysis error or an indication of something more interesting? Pondering whether it might show the existence of a companion for Centauri B, a French team has searched for the presence of such an object and, in the process, has built a catalog of background objects detectable with adaptive optics, using the European Southern Observatory's Paranal site in Chile. Image: They look like one huge star in this photograph, but Centauri A and B simply overwhelm the view with their glare. Remember,...