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...

Microlensing Planet Finder is a proposed mission that would use the gravitational lensing effect to achieve extraordinary detection capabilities. As presented in The Microlensing Planet Finder: Completing the Census of Extrasolar Planets in the Milky Way (PDF warning), MPF could find planets down to 0.1 Earth mass, in locations as close as 0.7 AU to their parent stars. And unlike any other planet-finding technology, MPF would be able to find free-floating planetary bodies unassociated with any star. Gravitational microlensing is perhaps the most exotic planet-finding technique. A star or planet can act as a kind of lens, magnifying a more distant bright star behind it. It is the gravitational field of the foreground star that, as Einstein predicted, focuses the light of the distant star, just as a glass lens focuses light in a telescope. By analyzing the light produced by such an event, astronomers can find telltale anomalies that indicate the presence of planets around the...