by Paul Gilster | Dec 10, 2004 | Exoplanetary Science
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 Telescope indicates that stars with known planets (blue) are more likely to have “debris disks” than stars without known planets (red). Spitzer sampled 84 stars, 26 with and 58 without known planets. Of the 26 planet-bearing stars, six had disks; of the 58 stars without planets, six had disks. The presence of these debris disks was inferred from the amount of excess infrared light measured at a wavelength of 70 microns, relative to that emitted by the parent star. While most of the observed stars have a ratio near unity, indicating that the 70-micron light is coming from the star itself, several stars show a high degree of excess emission. It is these stars that are surrounded by Kuiper Belt-like debris disks. Credit: NASA/JPL-Caltech
Debris disks are significant because rocky planets are believed to form out of clouds of dust that surround young stars, their particles colliding and sticking together until rocky objects eventually form. Collisions between the larger objects create vast disks of debris whose centers are empty, cleared out by planets orbiting there. The Hubble images of HD 107146 showed such a gap in the disk, and so did the six disks studied by Beichman. Astronomers at Hawaii’s W.M. Keck Observatory had previously found a disk surrounding the red dwarf AU Microscopii, a young star located 32 light years away. JPL astronomer John Krist recently used Hubble to image the gap in that disk.
From a news release from the Space Telescope Science Institute (Baltimore, MD):
“Spitzer has established the first direct link between planets and discs,” Beichman said. “Now, we can study the relationship between the two.” These studies will help future planet-hunting missions, including NASA’s Terrestrial Planet Finder and the Space Interferometry Mission, predict which stars have planets. Finding and studying planets around other stars is a key goal of NASA’s exploration mission.
The Spitzer findings will be published in the Astrophysical Journal.
by Paul Gilster | Dec 9, 2004 | Outer Solar System
Discovered in June of 2002, Quaoar is a large Kuiper Belt object roughly a billion miles beyond the orbit of Pluto, and although its size is still controversial, the best estimates make it out to be about half Pluto’s diameter. Think of the Kuiper Belt as something similar to the Asteroid Belt, though containing up to 100 times more material. The region is critical to our understanding of the early Solar System because it seems to contain the System’s most primitive materials. The fact that temperatures in the Kuiper Belt are as low as -50 K tells us that ices existing there should have been preserved since the dawn of planetary formation.
Now a new study reporting near-infrared observations of Quaoar has revealed the presence of crystalline water ice and ammonia hydrate. Both, according to a letter by astronomers David Jewitt and Jane Luu that has just appeared in Nature, are peculiar. Crystallinity indicates that the ice has been heated to at least 110 K, and both water ice and ammonia hydrate should have been destroyed by radiation over the time scales we are talking about. The upshot: “We conclude that Quaoar has been recently resurfaced, either by impact exposure of previously buried (shielded) ices or by cryovolcanic outgassing, or by a combination of these processes.”
Source: “Crystalline water ice on the Kuiper belt object (50000) Quaoar,” Nature 432, 731 – 733 (09 December 2004). More on the Kuiper Belt can be found at the Kuiper Belt Homepage. Quaoar has a page of its own created by its discoverers, Chad Trujillo and Mike Brown at Caltech.
Image credit: NASA and A. Field (STSci).
by Paul Gilster | Dec 8, 2004 | Exoplanetary Science
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 illuminates the planet-formation process in the relatively low-radiation environments analogous to the solar system. Resolved images of these systems help to constrain their physical and geometrical properties. Scattered-light images sample the whole disk regardless of its temperature and this, coupled with the fact that optical and near-infrared detectors have higher angular resolution than far-infrared and submillimeter ones, allows for a rich understanding of the systems.
But Ardila and his colleagues argue that the dust disk around HD 107146 is not analagous to our own early Solar System, noting that it is larger and wider than the Kuiper Belt and contains significantly more dust. “We believe therefore,” write the team, “that HD 107146 is unlikely to evolve into a system like our own.”
Earlier in 2004, Ardila and other scientists working on planetary disks presented their findings on the debris around HD 141569A, a triple-star system 332 light years from the Sun. An abstract from their presentation at the AAS meeting in January, 2004 is available here.
by Paul Gilster | Dec 7, 2004 | Deep Sky Astronomy & Telescopes
Astronomers at Paranal Observatory (Atacama, Chile) caught this impressive image of the spiral galaxy NGC 6118, which is located near the celestial equator, in the constellation Serpens (The Snake). Note the bright star-like object indicated by the arrow. This is Supernova 2004dk, first reported on August 1, 2004; it’s a Type 1b or 1c supernova captured several days before maximum light.
According to the European Southern Observatory, this kind of supernova is apparently the end of a massive star that lost its hydrogen envelope because of transfer of mass in a binary star system before exploding. Excuse the low-res image, but it’s hyperlinked to a higher-quality one (click on the image). An ESO press release on several supernova photographs and associated findings is available.
Image: A composite colour-coded image of the “grand design” spiral galaxy NGC 6118, at a distance of 80 million light-years. It is based on images obtained with the multi-mode VIMOS instrument on the ESO Very Large Telescope (VLT) in three different wavebands. The image covers 6.7 x 5.8 arcmin on the sky. North is up and East is to the left. The position of supernova SN 2004dk is indicated by the arrow. Credit: European Southern Observatory.
by Paul Gilster | Dec 7, 2004 | Outer Solar System
We’ll be watching two sessions at the upcoming fall meeting of the American Geophysical Union with special interest. One will be a briefing held at NASA headquarters on December 14 and available via satellite for a live question and answer period. The topic: the Deep Impact spacecraft, which will launch a copper projectile into the surface of Comet Tempel 1 on 4 July 2005. The 370 kilogram (820 pound) “impactor” is to hit the surface at some 37,000 kilometers (23,000 miles) per hour, creating a crater that could be over 100 meters in size. Data will be collected by Deep Impact’s cameras and other instrumentation, to be supplemented by ground-based astronomy from Earth.
The second session with outer Solar System implications, to be held on the 16th of December, will highlight the latest findings from Cassini as it again makes a Titan flyby, this one the last chance scientists will have to study the Huygens landing site before that probe’s January descent. Two days later, on the 15th, Cassini will make its closest flyby of Dione, the curious Saturnian moon that seems to show signs of internal activity.
The AGU meets in San Francisco from December 13-17. More information available here. This database of fall meeting abstracts is a handy way to study the offerings.
