Centauri Dreams sometimes muses that we know all too little about nearby space. Ponder that it is only within the last decade that we have begun to characterize the whole category of objects known as 'brown dwarfs,' while our understanding of M-class dwarfs is evolving so rapidly that we're now seeing them as potential havens for terrestrial worlds. That makes both kinds of dwarfs interesting as mission targets once we've created the technologies to make such journeys. And it also means that we have to develop a better census of red and brown dwarf stars in our own neighborhood. It is within the realm of possibility, for example, that there may be a brown dwarf closer to us than the Centauri stars, and the discovery of a target, say, one light year away would give powerful impetus to interstellar propulsion studies. Even M-class stars are readily overlooked in a crowded sky, and the boundary between them and brown dwarfs can be tricky to establish. As witness a most interesting...

For Centauri Dreams, the most exciting part of the exoplanet hunt is the refinement of our models. We know, for example, of numerous planetary systems dominated by gas giants. Now we're trying to figure out which of these may contain smaller, rocky worlds, and that means learning more about solar system dynamics. A step in the right direction emerges from a June paper that analyzes what happens to moon-sized protoplanets as they evolve in systems with gas giants. Based on computer simulations, the work assumes a giant planet the size of Jupiter and manipulates the position and mass of the protoplanets in these settings over time, testing four systems with known planets: 55 Cancri, HD 38529, HD 37124 and HD 74156. The most interesting result is the ready formation of terrestrial worlds around 55 Cancri, often with orbits in the habitable zone. HD 38529 also produced a rocky world, one about the size of Mars, and showed conditions favorable to an asteroid belt as well. No further...

One of the beauties of the Spitzer Space Telescope is that it can pinpoint the swirling dust disks around distant stars. Such dust, heated by the star, puts out an infrared signature that Spitzer can analyze to a degree hitherto unattainable. Now a team of astronomers has observed some 500 young T Tauri stars in the star-forming regions of the Orion nebula. They've been looking at how young stars spin, and the effects that dusty disks have on slowing their rotation. T Tauri stars are ideal for this kind of work. They're young objects (less than 10 million years old) that are still in the process of gravitational contraction. Such stars often show large accretion disks, but a variant called weak-lined T Tauri stars have little or no disk. Figuring out the various phases of T Tauri formation and how they relate to planets is thus a substantial challenge. The answers Spitzer has provided are intriguing even if they leave many questions unanswered. Slow-spinning stars are five times more...

Hard to believe that it's been over ten years now since the discovery of 51 Peg B, the first exoplanet found around a main sequence star. So much has happened since, including over 160 exoplanet candidates identified within 200 parsecs, with most of these discovered through Doppler search methods examining radial velocities (although the nearby planet TrES-1 was found via transit methods). The last published list of exoplanets appeared in 2002, which is why the just published "Catalog of Nearby Exoplanets" is so welcome. Appearing in The Astrophysical Journal, the catalog confines itself to the 200 parsec limit for good reasons. Yes, we have located exoplanets far beyond it, including some in the direction of galactic center found by the OGLE survey and several found through microlensing projects elsewhere. But within 200 pc, high resolution imaging and stellar spectroscopy allows satisfactory follow-up work, and we're also working with stars whose parallax has been studied through...

We've recently discussed Greg Laughlin and Jeremy Wertheimer's work on the possible role of Proxima Centauri in destabilizing the Centauri A and B debris disk and bringing volatiles to the inner system. Our deepening knowledge of the Centauri system is one of the most energizing aspects of the exoplanet hunt, for its proximity inexorably makes Alpha Centauri of high astrobiological interest. And no one has done more significant work on planet formation around binary stars than Elisa Quintana and Jack Lissauer (NASA Ames). The two have examined the possibilities of terrestrial worlds around Centauri A and B and are continuing with the study of other binary scenarios. Now they have extended their analysis to binary systems whose stars are much closer to each other than Centauri A and B. Their new paper is significant for planet hunters because more than half of all main sequence stars are in binary or multiple systems, whereas our basic models for planet formation have been based on...