View Full Version : Dust discs

2006-Dec-11, 09:53 PM
I've been looking for information on the Solar System's dust discs for a while, but haven't found anything conclusive. First, how many are there? This article


suggests that a disc was only recently discovered but the Zodiacal dust disc has been known about since the 1930s. Are they two parts of the same disc? Or are they separate?

Secondly, what is their extent? Where are they and how far to they extend through the solar system?

Thanks for your help.

2006-Dec-12, 12:07 AM
Hubble reveals two dust disks around nearby star (http://www.spaceflightnow.com/news/n0606/28dustdisks/)

The finding ends a decade of speculation that an odd warp in the young star's debris disk may actually be another inclined disk. The recent Hubble Advanced Camera for Surveys view * the best visible-light image of Beta Pictoris * clearly shows a distinct secondary disk that is tilted by about 4 degrees from the main disk. The secondary disk is visible out to roughly 24 billion miles from the star, and probably extends even farther, said astronomers. ......:)

Tim Thompson
2006-Dec-12, 04:26 PM
I am not sure what you are asking. The ESA article refers to debris disks (or dust disks if you like, though they are rarely called that) around other stars, but are you asking specifically about dust disks in our own Solar System? Our own Solar System has its own zodiacal dust, which has been known for a long time, and has been subjected to much study (i.e., Reynolds, Madsen & Moseley, 2004 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004ApJ...612.1206R&db_key=AST&d ata_type=HTML&format=&high=4366fa465126854); Hahn, et al., 2002 (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Icar..158..360H&db_key=AST&d ata_type=HTML&format=&high=4366fa465126854)). But inside the solar system the dust environment is very complictead, and is the subject of thousands of reasearch papers; Jupiter & Saturn have very complicated dust environments that include charged dust in the large magnetic fields. Earth carries significant clouds of dust in its Lagrange points. The Spitzer Space Telescope will pass through Earth's Lagrange dust.

Or are you perhaps asking about debris disks around other stars? There are a lot of them, and the ESA article is by no means a first discovery. The Beta Pictoris (http://www.solstation.com/stars2/beta-pic.htm) disk has was the first observed around another star, in 1978, and has been imaged with the HST (http://hubblesite.org/newscenter/archive/releases/2006/25/). The Spitzer Space Telescope has imaged the dense debris disks around Fomalhaut (http://www.spitzer.caltech.edu/Media/releases/ssc2003-06/ssc2003-06i.shtml) and Vega (http://www.spitzer.caltech.edu/Media/releases/ssc2005-01/ssc2005-01a.shtml).

So what is it exactly that you are asking about?

2006-Dec-12, 05:23 PM
I'm confused. The dust disc mentioned in the ESA article as having been discovered by Markus Landgraf in 2002 was in our Solar System, not around another star. I thought the reference to other stars was merely an extrapolation of the discovery to other star systems.

Tim Thompson
2006-Dec-13, 05:45 AM
I'm confused.
That's because I barely glanced at the webpage. Indeed, it is on the dust in our own solar system, and I had not noticed that it was as old as 2002. It would appear that the associated research was published here: Origins of Solar System Dust beyond Jupiter (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.2857L&db_key=AST&d ata_type=HTML&format=&high=4366fa465129656), Landgraf, Liou, Zook & Grün, Astronomical Journal 123(5): 2857-2861, May 2002 (the press release is dated Feb 2002). Landgraf, et al., did not discover dust in the solar system, that was already long established. But in the absence of in-situ measurements, it is kind of hard to tell from here, just where all the dust is located. And its physical characteristics, such as particle size & shape distribution or mineralogy, can only be derived by modeling reflected sunlight & infrared emission (except for the few grains captured by high altitude aircraft).

What Landgraf, et al., did was to examine the in-situ data from the Pioneer spacecraft. This not only allows some determination of the physical characteristics, but also reveals the orbits that the dust particles are on. Absent collisions, dust particles are subject to the same laws of gravity as are planets & asteroids, and are equally restricted from wandering; they orbit the sun just like everything else, although more susceptible to radiation pressure & solar wind. Beyond the orbit of Saturn, only the Kuiper belt can serve as a source for dust, which must be replenished. So using the distant Pioneer data, Landgraf, et al., were able to identify the source of the dust, and to actually measure how much there is.

Most of the dust responsible for zodiacal light is in the sun, where scattered sunlight is still strong enough to be visible. By the time you get past Jupiter, the direct sunlight is already weak enough that sunlight scattered off the dust is too weak to see reliably. So they are sampling a dust population that is mostly inaccessible to Earth bound study.

I think I got it right this time.

2006-Dec-13, 06:35 AM
Simply put the age of this solar system has given the planets time to vacuum up most of that dust. Some of it is still to be found extending way out past the ort cloud... Its particles per million cubic kilometer's.. sparse.