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Asteroid Belt Around a Sun-like Star?

Finding solar systems similar to our own is a continuing quest for planet hunters. Now a star called HD69830, some 41 light years from Earth, has been found to contain a thick band of warm dust that may be an asteroid belt. Although planets have yet to be detected around the star, the find is exciting because HD69830 is similar to the Sun in age and size. And just as Jupiter seems to provide an outer limit to our own asteroid belt, there are suspicions that the asteroid belt around this star may be contained by the gravitational influence of a gas giant planet. If such planets exist around HD69830, they’ll likely be spotted by future planet-hunting missions like SIM, the Space Interferometry Mission, which is scheduled for a 2011 launch.

Asteroid belt viewsBut exoplanetary systems continue to confound our expectations. The newly discovered belt is not only 25 times as dense as our own, it’s also much closer to its star. Imagine a thick belt of primordial debris located inside the orbit of Venus, providing an unforgetable celestial panorama in the night sky of any planet nearby. Its light would be 1,000 times greater than the ‘zodiacal light’ thrown off by our own asteroid belt’s dust.

Image: This artist’s concept illustrates what the night sky might look like from a hypothetical alien planet in a star system with an asteroid belt 25 times as massive as the one in our own solar system (alien system above, ours below). In our solar system, anybody observing the skies on a moonless night far from city lights can see the sunlight that is scattered by dust in our asteroid belt. Called zodiacal light and sometimes the “false dawn,” this light appears as a dim band stretching up from the horizon when the Sun is about to rise or set. The light is faint enough that the disk of our Milky Way galaxy remains the most prominent feature in the sky. (The Milky Way disk is shown perpendicular to the zodiacal light in both pictures.) Credit: NASA/JPL-Caltech/R. Hurt (SSC).

The alien asteroid belt was found with the help of the Spitzer Space Telescope, a space-based infrared observatory. Dr. Charles Beichman of the California Institute of Technology led the team that made the discovery; its findings will be discussed in an upcoming paper in the Astrophysical Journal. Beichman’s group surveyed 85 Sun-like stars but found only a single asteroid belt, a thick band of dust likely augmented by frequent asteroid collisions.

“Because this belt has more asteroids than ours, collisions are larger and more frequent, which is why Spitzer could detect the belt,” said Dr. George Rieke, University of Arizona, Tucson, co-author of the paper. “Our present-day solar system is a quieter place, with impacts of the scale that killed the dinosaurs occurring only every 100 million years or so.”

But is this an asteroid belt or, perhaps, an enormous comet that became trapped in the inner planetary system and is slowly coming apart? Only future studies with Spitzer and other telescopes will provide a definitive answer, but the cometary hypothesis seems to be a long shot. You can read more in this Spitzer press release.

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  • ljk July 20, 2007, 9:57

    Debris Disks in NGC 2547

    Authors: N. Gorlova (Univ. Florida), Z. Balog, G. H. Rieke, J. Muzerolle, K. Y. L. Su (Univ. Arizona), V. D. Ivanov (ESO), E. T. Young (Univ. Arizona)

    (Submitted on 19 Jul 2007)

    Abstract: We have surveyed the 30 Myr-old cluster NGC 2547 for planetary debris disks using Spitzer. At 4.5-8 um we are sensitive to the photospheric level down to mid-M stars (0.2 Msol) and at 24 um to early-G stars (1.2 Msol). We find only two to four stars with excesses at 8 um out of ~400-500 cluster members, resulting in an excess fraction less than ~1 percent at this wavelength. By contrast, the excess fraction at 24 um is ~40 percent (for B-F types). Out of four late-type stars with excesses at 8 um two marginal ones are consistent with asteroid-like debris disks. Among stars with strong 8 um excesses one is possibly from a transitional disk, while another one can be a result of a catastrophic collision. Our survey demonstrates that the inner 0.1-1 AU parts of disks around solar-type stars clear out very thoroughly by 30 Myrs of age. Comparing with the much slower decay of excesses at 24 and 70 um, disks clear from the inside out, of order 10 Myr for the inner zones probed at 8 um compared with a hundred or more Myr for those probed with the two longer wavelengths.

    Comments: Accepted to ApJ, 29 pages, 13 figs. Full Tables 1 and 2 in the electronic form together with the article with full resolution figures are available at this http URL

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0707.2827v1 [astro-ph]

    Submission history

    From: Nadya Gorlova [view email]

    [v1] Thu, 19 Jul 2007 01:28:00 GMT (495kb)


  • ljk December 18, 2007, 10:47

    Sources of zodiacal dust

    Authors: S.I. Ipatov

    (Submitted on 17 Dec 2007)

    Abstract: Fractions of asteroidal particles, particles originating beyond Jupiter’s orbit (including trans-Neptunian particles), and cometary particles originating inside Jupiter’s orbit among zodiacal dust are estimated to be about 1/3 each, with a possible deviation from 1/3 up to 0.1-0.2. These estimates were based on the comparison of our models of the zodiacal cloud that use results of numerical integration of the orbital evolution of dust particles produced by asteroids, comets, and trans-Neptunian objects with different observations (e.g., WHAM [Wisconsin H-Alpha Mapper spectrometer] observations of spectra of zodiacal light, the number density at different distances from the Sun). The fraction of particles produced by Encke-type comets (with e~0.8-0.9) does not exceed 0.15 of the overall population. The estimated fraction of particles produced by long-period and Halley-type comets among zodiacal dust also does not exceed 0.1-0.15.

    Though trans-Neptunian particles fit different observations of dust inside Jupiter’s orbit, they cannot be dominant in the zodiacal cloud because studies of the distribution of number density with a distance from the Sun shows that trans-Neptunian particles cannot be dominant between orbits of Jupiter and Saturn. Mean eccentricities of zodiacal particles that better fit the WHAM observations were about 0.2-0.5, with a more probable value of about 0.3.

    Comments: Paper (4 pages) to proceedings of the conference ‘Near-Earth astronomy-2007’ (Terskol, Russia, 3-7 September 2007), in press

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0712.2624v1 [astro-ph]

    Submission history

    From: Sergei Ipatov [view email]

    [v1] Mon, 17 Dec 2007 04:31:55 GMT (126kb)