"The Use of Transit Timing to Detect Terrestrial-Mass Extrasolar Planets," by Matthew Holman (Harvard-Smithsonian Center for Astrophysics) and Norman Murray at the University of Toronto, appears in the February 25th issue of Science. The paper covers a new planet-finding technique that studies transit time; i.e., the amount of time it takes a planet to orbit its star. Transit timing studies the variation in apparent stellar brightness caused by the passage of a planet in front of its star as seen from Earth. Because the timing of the transit will vary depending on the presence of other planets in the system, astronomers should be able to make estimates about the mass of a second planet. And here's the best part: While the current radial velocity observations that have been used to detect most of the 150 known extrasolar planets cannot be used for terrestrial worlds, this method may just be sensitive enough to detect them. The method has implications for future transit studies,...

February's issue of the journal Icarus will refine an increasingly intriguing theory of planetary formation. Richard Durisen, a professor of astronomy at Indiana University - Bloomington used computer models to demonstrate the motion of gas as it condenses around a parent star. "These are the disks of gas and dust that astronomers see around most young stars, from which planets form," Durisen said. "They're like a giant whirlpool swirling around the star in orbit. Our own solar system formed out of such a disk." What Durisen's theory of gravitational imbalances adds to the picture is a model of how areas of stability within the planetary disks create places for denser gases to accumulate, allowing the formation of planets. That's valuable information, because until now we haven't understood how a gravitationally unstable disk could avoid violent interactions with other disks materials, thus destroying young planets before they could fully form. Image: The rings near the center of...

If the name Alex Wolszczan (pronounced VOL-shtan) isn't immediately familiar, it may be because we've become so inured to new extrasolar planet discoveries that we've forgotten about the first. But it was Pennsylvania State University's Wolszczan who, in 1991, was the first to detect planets outside our Solar System, around the pulsar PSR B1257+12, an incredibly dense neutron star that is the remnant of a once massive star in the constellation Virgo some 1500 light years away. These were the first new planets discovered since Clyde Tombaugh's detection of Pluto in 1930, and Wolszczan was able to learn a surprising amount about them. Using the Arecibo radio telescope in Puerto Rico, he found that two of them were roughly similar in mass to the Earth, while the other corresponded roughly to the mass of the Moon. Their spacing around the primary corresponded to that between Mercury, Venus and the Earth around our Sun. Image: An artist's conception of one of the planets around the pulsar...

The 2005 Winter Conference on Astrophysics is now in session in Aspen, with papers running through tomorrow. The topics here make up a wish list for those interested in learning more about the next steps in extrasolar planet detection and analysis. Tomorrow's last session, for example, is on new technologies for detection, includng the Terrestrial Planet Finder mission. Earlier sessions have included everything from theories of giant planet formation to planetesimals and how they form in protoplanetary disks. But the first story out of the conference to hit the media was the detection of possible planets around a small brown dwarf called OTS 44, which is only 15 times the mass of Jupiter -- before now, the smallest brown dwarf implicated in debris disk formation was almost 30 times the mass of Jupiter. You can see how this hypothetical planetary system scales next to our own in the image below. OTS 44 is approximately 500 light years away in the Chameleon constellation. Image: This...

How do solar systems form? The traditional model has been a slowly condensing cloud of matter within which planetary objects eventually emerge. But that view has been challenged sharply by Yunbin Guan and Laurie Leshin, from Arizona State University. Last year Leshin argued that our own system formed from the violent processes of star-birth within a dense nebula, one filled with supernova activity. Now a new meteorite find has provided solid backing for the idea. Working with a team from the Chinese Academy of Sciences, Leshin and Guan have found evidence of chlorine-36 in a meteorite that was formed shortly after the solar system appeared. Although chlorine-36 has a short half-life, it decays into sulphur-36, providing strong evidence for the past presence of the earlier form of chlorine, which would have been formed in the explosion of a supernova. The team found sulphur-36 in association with sodalite, a mineral rich in chlorine. "There is no ancient live chlorine-36 in the solar...

New photos from the Very Large Telescope at Paranal in the Chilean Andes have made it possible to measure the mass of a young object orbiting the star AB Doradus A. The low-mass companion to the star has been under study since the early 1990s, when the characteristic wobble of the parent star suggested a faint companion, either a planet or a brown dwarf. Using a high-contrast camera equipped with adaptive optics, the University of Arizona's Laird Close has now brought home photographs and measurements of the companion known as AB Dor C (click on the image to enlarge). Image: ESO PR Photo 03/05 is an enhanced, false-colour near-infrared image of AB Dor A and C. The faint companion "AB Dor C" - seen as the pink dot at 8 o'clock - is 120 times fainter than its primary star. The tiny separation between A and C, only 0.156 arcsec, is smaller than a one Euro coin seen at 20 km distance. Nevertheless, the new NACO SDI camera was able to distinguish it as a "redder" dot surrounded by the...

M-class red dwarf stars are unusually interesting. For one thing, they make up 70 percent of all stars in our galaxy, meaning the great bulk of stars are much less massive than our Sun and far less bright, not to mention being considerably longer-lived. For another thing, the closest known star, Proxima Centauri, is a red dwarf, so anything we could learn about planetary formation there or around other nearby red dwarfs would be all to the good. But that's just it -- we know very little about what's happening around red dwarfs. Attempts to find planets around Proxima Centauri have thus far come up short. Best known is a 1994 study that was suggestive (but not conclusive), of a near Jupiter-sized planet orbiting closer than the distance of Mercury to our Sun. Later Hubble data was also no more than suggestive, while observations at the European Southern Observatory found no evidence for planets as large as Jupiter, though remaining moot on the question of smaller worlds. Image:...

The dust disk around the star Beta Pictoris has been under study since 1983, when it was detected in IRAS (Infrared Astronomy Satellite) data. Last October, astronomers in Japan found three rings of planetismals circling the star, with a possible planet at 12 AU. Now the Gemini South 8-meter telescope in Chile has found telling new details in the disk. The upshot: a collision between large planetary bodies may have occurred there within the last few decades. This is intriguing news for those scientists who believe such collisions are a necessary part of planetary formation. From a Gemini Observatory news release: "It is as if we were looking back about 5 billion years and watching our own solar system as it was forming into what we see today," said Dr. Charles Telesco of the University of Florida who led the team. "Our research is a bit like a detective dusting for fingerprints to figure out a crime scene, only in this case we use the dust as a tracer to show what has happened within...

The American Astronomical Society's 205th national meeting, in San Diego, California, ends tomorrow. And this meeting is special: the last attendance projection Centauri Dreams saw was 2500, with 1640 papers submitted, 180 scientific sessions, and 70 new Ph.D dissertations presented. All in all, we'll have material for months ahead coming out of AAS, and as always, we'll pay special attention to extrasolar planetary studies, with the occasional foray into the mind-boggling world of cosmology. Let's start with Hubble data that support the idea there is a planet orbiting a brown dwarf 225 light years away in the constellation Hydra. Last spring, the European Southern Observatory's Very Large Telescope reported on a possible planetary companion to the star, which has the mind-boggling designation 2MASSWJ 1207334-393254 (we prefer its nickname: 2M1207). The object in question is one-hundredth the brightness of the parent star, burning (according to this news release at the European...

The 'concordance' model of the universe suggests that it is mostly composed of dark matter. In fact, a cluster of hundreds of galaxies would, in the concordance scenario, house fully 90 percent of its mass in dark matter. Never mind that we know almost nothing about dark matter -- theorists have still been able to simulate how it would clump together, forming an intricate substructure that should be capable of observation. Now a Yale astronomer and her colleagues have used gravitational lensing to study galactic clusters, finding a tight fit between the concordance model's predictions and their observations. A gravitational lens might be a galaxy that intervenes between us and a more distant object, focusing the light from that object so that we see things we would not otherwise be able to observe. Says assistant professor of astronomy and physics Priyamvada Natarajan: "We used an innovative technique to pick up the effect of precisely the clumps which might otherwise be obscured by...

Diana Valencia, a graduate student at Harvard, has been working with professor of geophysics Richard O'Connell in a study of the possible internal structure of large terrestrial planets around other stars. Their presentation "Internal Structure and Scaling Laws of Massive Terrestrial Planets" was given at the American Geophysical Union's fall meeting. From the abstract: "The focus of this study is to calculate the internal structure of massive terrestrial planets starting from the knowledge acquired on the Earth and other solar system planets. With the use of equations of state for the Earth and physical laws we obtain radial structure profiles of mass, pressure and density, including all major phase changes for massive Earth-like planets." Why is this work important? Because the first mission likely to detect a terrestrial-type planet is Kepler, scheduled for launch in 2006. The spacecraft will attempt to detect such planets by watching for their transit across a distant stellar...

David J. Stevenson, who is George Van Osdol Professor of Planetary Science at CalTech, has an entertaining way with titles. The average scientific paper has a title whose tone is dry, direct and frequently off-putting. Stevenson gives us these, as any scientist must, but give him the chance and he produces the Swiftian "A Modest Proposal: Mission to Earth's Core," which ran in Nature in 2003 (available here). He has also written, fascinatingly, on the possibilities of oceans on worlds other than Europa; thus his 1999 essay "An Ocean in Callisto?" (The Planetary Report Vol. 19 No 3, pp. 7-11), and "An Ocean in Uranus?" (The Planetary Report Vol. 6 No 16, 1986). At the recent American Geophysical Union meeting, Stevenson produced the ultimate in what we writers call the 'omniscient viewpoint' by presenting "How to Build a Planetary System." So how do you build a planetary system? It turns out that we know surprisingly few answers. Stevenson argues that while such systems are common (at...

More than half of all main sequence stars occur in multiple star systems, and we've already found 19 planets in such systems (Tau Bootis and 55 Rho Cancri are examples). But most of our models of planetary formation have been based upon single stars. Are planets common in double star systems? The answer has huge implications for the number of possible planets, and it's a fascinating issue because the the nearest stars, the Alpha Centauri triple star system, are now considered capable of sustaining planets. Paul Wiegert and Matt Holman showed in 1997 that stable orbits can exist within 3 AU of Alpha Centauri A or B, and they calculated a habitable zone around Centauri A of 1.2 to 1.3 AU, with a zone around Centauri B of 0.73 to 0.74 AU. Planets at Jupiter-like distances seem to be ruled out around Centauri because of the disruptive effects of the two primary stars; after all, Centauri A and B sometimes close to within 10 AU, roughly the distance of Saturn from the Sun. The red dwarf...

David Ardila's work with the debris disk around the star HD 107146, covered in these pages on the 8th, has been complemented by new findings from the Spitzer Space Telescope. While Ardila's team surveyed a young Sun-like star whose debris disk was relatively thick, the Spitzer study looked at six stars whose age approximates the Sun, about 4 billion years old. The disks around such stars are 10 to 100 times thinner than those around young stars. The Spitzer study scanned 26 Sun-like stars with known planets, ranging from 50 to 160 light years away; six of them showed debris much like our Sun's Kuiper Belt. Dr. Charles Beichman of the Jet Propulsion Laboratory is lead author of the study. "Young stars have huge reservoirs of planet-building materials," Beichman said, "while older ones have only leftover piles of rubble. Hubble saw the reservoirs and Spitzer, the rubble. This demonstrates how the two telescopes complement each other." Image: This graph of data from NASA's Spitzer Space...

Although we've been able to see disks of debris around other stars, astronomers have yet to resolve one around a Sun-like star. But that may have just changed: HD 107146, a G2 star some 93 light years away, is the subject of a paper now available at the ArXiv site. Working with the Hubble Space Telescope and its ACS coronagraph, a team of astronomers led by Johns Hopkins' David Ardila has directly viewed such a disk. "A Resolved Debris Disk around the G2V star HD 107146" is slated to appear in Astrophysical Journal Letters, but is now online here (PDF warning). From the paper: The presence of dusty disks around main-sequence stars serves as a marker for the existence of planetesimals. Without collisions among planetesimals, or their evaporation, the dust would not be replenished, and it would have disappeared from the system long ago. Thus, debris disks indicate that the planet-formation process is occurring, or has occurred. In particular, the study of disks around low-mass stars...

It was two years ago that astronomers at the Geneva Observatory in Sauverny, Switzerland, released their findings on the star HD 202206. The conclusion: An object 17 times as massive as Jupiter orbits the star at 0.82 AU. A second planet has now been found at 2.55 AU, this one over twice as massive as Jupiter. So is the heavier object a planet or a brown dwarf? The issue is called into question by the second discovery. Science News is running a story in its November 27 issue pointing out that by the standards of the International Astronomical Union, brown dwarfs must be heavy enough to burn deuterium at their core, while remaining light enough so as not to burn any other nuclear fuel. The heavy object around HD 202206 fits this category well, since brown dwarfs normally range from 13 times the mass of Jupiter to 75. But there's a twist. The two objects are gravitationally locked in a peculiar synchrony that has not previously been observed, with the inner body orbiting the star...

New infrared studies of the dust around three young stars lend credence to the idea that Earth-like planets may circle other stars. Using the European Southern Observatory's Very Large Telescope Interferometer (VLTI), a team of astronomers studied the proto-planetary disks around the stars, homing in on the inner region of the discs. The results: the inner discs, in the area analogous to that swept out by the Earth around the Sun, are loaded with crystalline silicate grains -- sand -- with an average diameter of about 0.001 mm. Much smaller grains (about 0.0001 mm in size) would have contributed to the creation of this material, being heated in the inner system near the young star and coagulating into larger grains in this dense region. From an ESO press release: An important conclusion from the VLTI observations is therefore that the building blocks for Earth-like planets are present in circumstellar discs from the very start. This is of great importance as it indicates that planets...