Back in 2003, while researching Centauri Dreams, I interviewed physicist Geoffrey Landis at Glenn Research Center in Cleveland. At that time, Landis’ office was packed with Mars images, apropos for a man who had done so much work on rover technology. I asked him whether, after all this study, Mars had taken on the aspect of a real place to him, like Cleveland. Not surprisingly, he said that it had, and he credited 3-D images from Mars Pathfinder for that. Wearing glasses, Landis said, “It was as if you were standing on Mars. You could see ups and downs, ridges and valleys. That changed the view of Mars from another planet to a place you could go out and walk around.”
We’re a long way from 3-D close-ups, but I suspect some astronomers are starting to feel that way about Beta Pictoris, a young star some 63 light years away in the southern constellation Pictor that first drew attention to itself because of excess infrared radiation. A warm circumstellar disk was surely the cause, and indeed, such a disk was imaged by ground-based telescopes in 1984, revealing itself to be nearly edge-on to Earth. Since those observations, the Hubble space telescope found what seemed to be a warp in the disk, one studied extensively by Sara Heap at GSFC.
Is the warp evidence of more than one disk? The image below makes a strong case, showing in visible light a distinct secondary disk tilted about four degrees from the main one. It took the use of a coronagraph with Hubble’s Advanced Camera for Surveys to get this image, blocking out light from the star itself to reveal the disk structure (Beta Pictoris puts out a lot of light; in fact, it’s nine times more luminous than the Sun). The secondary disk is visible out to 24 billion miles from the star.
Image: This Hubble Space Telescope view of Beta Pictoris clearly shows a primary dust disk and a much fainter secondary dust disk. The secondary disk extends at least 24 billion miles from the star and is tilted roughly 4 to 5 degrees from the primary disk. The secondary disk is circumstantial evidence for the existence of a planet in a similarly inclined orbit. Credit: NASA, ESA, D. Golimowski (Johns Hopkins University), D. Ardila (IPAC), J. Krist (JPL), M. Clampin (GSFC), H. Ford (JHU), and G. Illingworth (UCO/Lick) and the ACS Science Team.
What’s causing this unusual disk situation? An unseen planet is the most likely culprit, a gas giant perhaps 20 times the mass of Jupiter. In orbit within the secondary disk, the planet would be tapping the primary disk for its building materials. And that leads to an interesting thought: what if Beta Pictoris is not so unusual? Perhaps planetary systems often form this way, from two or even more disks whose interactions are fertile ground for planetesimals. Listen to what David Golimowski (Johns Hopkins) has to say about this; he led the team that made this find:
“The Hubble observation shows that it is not simply a warp but two concentrations of dust in two separate disks. The finding suggests that planetary systems could be forming in two different planes. We know this can happen because the planets in our solar system are typically inclined to Earth’s orbit by several degrees. Perhaps stars forming more than one dust disk may be the norm in the formative years of a star system.”
And that several degree spread around Beta Pictoris isn’t really so different from the several degree separation of planets in our own Solar System’s plane. There is even some evidence from work at the Keck II Observatory in Hawaii of a possible third disk, one the size of our own Solar System that Golimowski’s team couldn’t see because it was covered by the coronagraph in Hubble’s Advanced Camera for Surveys. Whatever the case, Beta Pictoris, that unique laboratory for the study of planet formation, is becoming more and more of a ‘place’ all the time, one that will be visited by astronomers for years to come as it slowly gives up its secrets.
The paper is Golimowski, Ardila, Krist et al., “Hubble Space Telescope ACS Multiband Coronagraphic Imaging of the Debris Disk Around β Pictoris,” Astronomical Journal 131:3109-3130 (June, 2006).