If you want to see planet building happening before your eyes, turn your attention to TW Hydrae. Located 180 light years from the Sun in the constellation Hydra (the water snake), TW Hydrae is ten million years old, a celestial infant, with a mass four-fifths that of the Sun. Now researchers have discovered that the protoplanetary disk surrounding it contains more than enough material to form at least one and probably more Jupiter sized planets. Behind the new study are David Wilner (Harvard-Smithsonian Center for Astrophysics) and colleagues, whose work was just published in the June 20, 2005, issue of The Astrophysical Journal Letters. The team has shown that a vast swarm of pebbles extending out a billion miles from the star is in the early stages of planet formation. The small objects, according to current models, should grow in size as they continue to collide and eventually form planets. "We're seeing planet building happening right before our eyes," said Wilner. "The...

An unseen planet is the cause of the unusual geometry of a dusty ring around the star Fomalhaut (HD 216956). So say University of California at Berkeley scientists after examining a detailed, visible light image from the Hubble Space Telescope's Advanced Camera for Surveys. What's striking about the image isn't the ring itself, but the fact that it seems to be offset, evidently the result of the hidden planet reshaping the ring with its gravitational pull. The suspected planet is thought to be orbiting far away from Fomalhaut, along the ring's inner edge, making it anywhere from 4.7 billion to 6.5 billion miles away from the star. What the Hubble observations show is that the ring's inner edge is much sharper than its outer one, a sign that the ring is being gravitationally shaped by the unseen body. Another key pointer: the ring's unusually narrow width, some 2.3 billion miles. It would be much more diffuse without an object keeping it confined. Image: The top view, taken by NASA's...

With exquisite timing, the SETI Institute has announced the first of a series of workshops to study the habitability of planets around M-class red dwarfs. The issue became highly visible recently with the announcement of the rocky planet discovered around the red dwarf Gliese 876, some 15 light years from Earth. Although thought to be too hot for life as we know it, the new planet is a solid world orbiting a main sequence star, raising the question of genuinely terrestrial worlds around such stars. 'Main sequence' refers to stars that burn hydrogen in their cores, those that show up in a well-defined band on the famous Hertzsprung-Russell (HR) diagram, which plots the intrinsic brightness of stars against their surface temperatures (intrinsic brightness is the observed brightness of the star corrected for distance). Moving off the main sequence takes you into the domain of red giants, red and yellow supergiants, and white dwarfs. But way down on the lower right of the HR diagram, and...

Yesterday's post "On Red Dwarf Stars and the Hunt for Life" incorrectly stated the lifespan of an M-class red dwarf star as 100 times that of the Sun. The correct figure is ten times as long, making an age limit of perhaps 100 billion years for the average red dwarf. G-class stars like the Sun are expected to live about ten billion years. The red dwarf Gliese 876 is about 11 billion years old, more than twice the age of the Sun.

'Normal' is a tricky word when you're talking about extrasolar objects. As in 'normal star,' a phrase used during yesterday's news briefing about the new planet detected around Gliese 876, and in much of the press coverage since. The planet's low mass (about 5.9 times the mass of Earth) rules out the possibility that it is in any sense Jupiter-like, and the natural assumption is that this is a rocky world in a tight orbit around an M-class red dwarf.

Finding a planet that resembles the Earth is the ultimate goal of our exoplanetary explorations. It implies the possibility of life on a world not so different from our own, and encourages the speculation that Earth-like worlds are out there in huge numbers. We certainly haven't found such a place yet, but we're getting closer. Which is why Gliese 876, a red dwarf some 15 light years from our Solar System, made news today at a National Science Foundation briefing. No planet yet found -- and that includes roughly 155 extrasolar planets to date -- is as similar to Earth as the one found here. Gliese 876 is in the direction of the constellation Aquarius, and it is known to possess two larger gas-giant worlds as well as this much smaller neighbor. Not that conditions on the newfound world would be exactly habitable by our standards. The planet, some seven and a half times the mass of Earth, orbits its host star once every 1.94 days, and it's only two million miles from it (about...

We should have some interesting news about exoplanets tomorrow afternoon. That's when a media briefing will be given to reporters at the National Science Foundation in Arlington VA. The briefing is titled "Scientists Make New Discovery About Planets Outside Our Solar System," and although I have a hunch what this one is about, I'm not confident enough to run with it here. But it's intriguing that Jack Lissauer (NASA Ames), who is participating in the briefing, has done groundbreaking work on planetary formation in binary systems, as discussed in these pages back in December. Other participants in the briefing include exoplanetary pioneers Geoff Marcy (University of California, Berkeley) and Paul Butler (Carnegie Institution), as well as Eugenio Rivera from Lick Observatory. Rivera has previously worked with Lissauer on the 'resonant' orbits of two planets around the red dwarf Gliese 876, some 15 light years from Earth. Michael Turner, who heads NSF's Directorate of Mathematical and...