As the number of confirmed planets and planet candidates has grown, we've gone through a variety of techniques for exoplanet hunting, as Michael Lemonick's new book Mirror Earth: The Search for Our Planet's Twin (Walker & Co., 2012) makes clear. I'm only a third of the way into the book but I bring it up because it's germane to today's discussion in two ways. The first is purely administrative. Readers of Centauri Dreams are used to seeing information about the book I'm reading on the front page, but as many emails have reminded me, lately it's been absent. What's happening is this: The software I use to display the book cover and progress bar is no longer being maintained by its creator, and the program has become flaky. I've discovered more and more that certain books will not display properly, so that although I can enter them in the configuration file, nothing shows up in the sidebar on the home page. As a result, I'm searching for alternatives that will display titles like...

In his new article on Alpha Centauri in Astronomy & Geophysics, Martin Beech (Campion College, University of Regina) noted that the Alpha Centauri stars seem to go through waves of scientific interest. Beech used Google's Ngram Viewer to look for references to the system in both the scientific literature as well as general magazines and newspapers, finding that there is a 30-year interval between peaks of interest. The figure is suspiciously generational, and Beech wonders whether it reflects an awakening of interest in this nearby system as each generation of scientists and publishers arises. I mentioned on Christmas Eve that the Beech paper was a real gift for the holidays, and for those of us who try to track developments about Alpha Centauri, it certainly is, drawing together recent work and commenting with care on the findings. The big issue for now is the existence of planets around these stars, a question Centauri B b will begin to answer if it can be confirmed. Everyone from...

We saw yesterday how a newly refined radial velocity technique allowed researchers to identify five planet candidates around the nearby star Tau Ceti. The latter has long held fascination for the exoplanet minded because it’s a G-class star not all that different from the Sun, and one of the planets around it -- if confirmed -- appears to be in its habitable zone. But smaller stars remain much in the news as well, as witness Gl 667C, a red dwarf (M-class) star in a triple system that also contains two closely spaced K-class stars with a semimajor axis of 1.82 AU. M-class stars offer a lot to planet hunters, as new work using the HARPS spectrograph at La Silla is making clear. For one thing, a planet of a given size induces more radial velocity variation around a low-mass star than around a larger one, making the planet easier to spot. For another, red dwarfs are dimmer than G and K-class stars, with a habitable zone much closer to the star. Here again we get a larger radial velocity...

I discovered while trying to get to my copy of Stephen Dole's Habitable Planets for Man that my office was so choked with stacks of books mixing with Christmas gifts about to be wrapped that I couldn't reach the necessary shelf. Thus space studies end inevitably in office cleaning, the only benefit of which is that there is now a clear path to the most distant of the bookshelves and Dole's book (this is the 1964 edition written with Isaac Asimov) now sits before me. I was feeling nostalgic and wanted the Dole volume to remind myself of my early enthusiasm for the nearby star Tau Ceti. The news that five planet candidates have been identified around this star -- one of them in the habitable zone -- brings back the fascination that was piqued when Frank Drake made Tau Ceti one of his two targets in 1960's Project Ozma, a search for extraterrestrial radio signals from Green Bank, WV. And in fact what I found in Dole's book on the subject of Tau Ceti was mostly about Drake's interest in...

Finding a way to extend the classical habitable zone, where liquid water can exist on the surface of a planet, is a project of obvious astrobiological significance. Now a team of astronomers and geologists from Ohio State University is making the case that their sample of eight stars shows evidence for just such an extension. The stars in question, drawn from a dataset created by the High Accuracy Radial Velocity Planet Searcher spectrometer at the European Southern Observatory in Chile, were selected because they match up well with the Sun in terms of size, age and composition. Seven of the eight, however, show signs of much more thorium than found in our star. It's an interesting result, as seen in this Ohio State news release. The slow radioactive decay of elements like thorium, potassium and uranium, all found in the Earth's mantle, helps to heat the planet. These are elements present at planetary formation and, according to Ohio State's Wendy Panero, they are involved in...

Do planets form easily around brown dwarf stars? Are they actually common? We're getting a glimpse of the possibilities in new work at the Atacama Large Millimeter/submillimeter Array (ALMA), where a brown dwarf known as ISO-Oph 102 (also called Rho-Oph 102) is under investigation. In most respects it seems like a fairly run-of-the-mill brown dwarf, about 60 times the mass of Jupiter and thus unable to ignite hydrogen fusion. It's also tiny, at 0.06 times the mass of the Sun, a dim object in the constellation of Ophiuchus. The work suggests that in the outer regions of a dusty disk surrounding Rho-Oph 102 there exist the same kind of millimeter-sized solid dust grains found around the disks of young stars. That's intriguing because astronomers have thought that earlier finer grains would not be able to grow into these larger particles in the cold, sparse disks assumed to be around brown dwarfs. Those that did form were thought to disappear quickly toward the inner disk, where they...