Brown dwarfs are often called 'failed stars,' objects without enough mass to sustain the hydrogen-to-helium fusion reaction that powers the Sun. They're dim enough that it was only in 1995 that the first brown dwarf, Gliese 229B, was discovered and the spectral classes L and T created to accomodate the category. The nearest known brown dwarfs are found around the star Epsilon Indi, a main sequence K-5 dwarf star; intriguingly, the first brown dwarf discovered in the system was subsequently found to have another brown dwarf orbiting it. Image: An artist's impression of a brown dwarf, a 'failed star' too cool to sustain nuclear fusion. Credit: Douglas Pierce-Price, Joint Astronomy Centre (Hilo, HI). Now a team from Arizona State University led by Russell Ryan has used date from the Hubble Space Telescope to look for brown dwarfs above and below the galactic plane, with an eye toward determining their total population in the Milky Way. The team's near infrared data tracked down 28 stars...

The Project Daedalus starship, designed by members of the British Interplanetary Society in the 1970s, was the first full-scale attempt to work out the parameters of a realistic interstellar mission. The target of this unmanned probe was Barnard's Star, a red dwarf some 5.9 light years from Earth. The Daedalus team leader, Alan Bond, made a key assumption: technology had reached the point where an interstellar mission could be designed without assuming any further breakthroughs in physics. The inertial confinement fusion techniques Daedalus would use have been the subject of much refinement in the days since and continue to be fertile ground for study. But the question I most often hear about Daedalus is, why Barnard's Star, when the Alpha Centauri system is considerably closer? The answer is addressed in an article by astronomer Alan Boss (Carnegie Institution of Washington) that appears on the Astrobiology Magazine Web site. And it involves a planetary detection that only failed...

Response to the August 12 post about Fermi's Paradox was heavy, an indication that the physicist's famous question -- Where are they? -- will not go away. A number of readers asked for background on my statement (drawn from Milan ?irkovi?'s paper) that the average age of Earth-like planets in the Milky Way is now thought to be 6.4 billion years, an indication that there should be planets that have had a two billion year head start on Earth in terms of evolving intelligent life. The number 6.4 billion is a broad estimate, to be sure, but it has been the subject of intense investigation by Charles H. Lineweaver and colleagues. Lineweaver's key paper "An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect" ran in Icarus Vol. 151, No. 2 (2001), pp. 307-313 (available here in PDF form), and was followed by a paper in collaboration with Yeshe Fenner and Brad Gibson titled "The Galactic Habitable Zone and the Age...

We now have 156 confirmed extrasolar planets orbiting 133 stars, making for 17 multiple planet systems. Keeping up with these fast-breaking discoveries is a challenge, but Julia Espresate at the Instituto de Astronomía (Ciudad Universitaria, Mexico) has produced two useful catalogs now available on the arXiv site. The first lists stellar data including spectral type, luminosity, rotation period, stellar metalicity, age and other factors for the 133 stars. The second provides a breakdown of data for the 156 extrasolar planets so far detected. Good information on extrasolar planets has been available on the Internet for a while, as witness the Extrasolar Planets Encyclopaedia. What has been lacking is a source that ties together the planetary information with data on the characteristics of the parent stars -- the latter tend to be widely scattered in the scientific literature. Thus the utility of Espresate's work, which also reveals how great are our gaps in knowledge of these systems....