PDA

View Full Version : Oldest Meteorites Hint at Early Solar System



Fraser
2005-Sep-20, 03:57 PM
SUMMARY: Of all the meteorites found around the world, on 45 formed before our Solar System. They provide a unique insight into the composition of the stellar nebula that went on to form our Sun and planets. These early rocks have very few volatile materials in them, like zinc, lead and sodium. So this "volatile depletion" must have been one of the first things to happen in the stellar nebula, and not during planetary formation as previously believed.

View full article (http://www.universetoday.com/am/publish/old_meteorites_early_solar.html)
What do you think about this story? post your comments below.

Greg
2005-Sep-21, 04:14 AM
Great find, Fraser. To me this is a very interesting finding. It makes perfect sense and I believe that volatile depletion has been detected in protoplanetary discs as evidenced by silicate and calcium rich signatures within the inner discs of young stars.

www.geocities.com/CapeCanaveral/ 9278/protected_append5.htm - 27k

The above is a link to a site describing in fairly plain English how this might happen. Basically the inner disc is hotter than the outer disc which separates out minerals and elements with higher melting/evaporation points which are more stable and accumulate in this part of the disc for this reason (2-5AU around a star like the sun.)

Like any dense object in the center of an accretion disc, the proto-sun was not an efficient eater of matter rapidly infalling onto it. The heating process during infall formed these dense minerals(now separated from volatile elements), some of which escaped incorporation into the protosun and fell into a stable orbit from 2-5 AU. This material enriched in Calcium/Silicon/Aluminum based minerals became the planetoid building blocks, some of which are left today as primordial chondrules.

I prefer this method over theories which posit that the interstellar medium and the original solar nebulae was volatile depleted since to me it makes the outer solar system harder to explain.

If You can't access the above link, I also have a link to an abstract outlining the leading models to explain volatile depletion in the inner solar system.

http://ouzo.wustl.edu/~fjs/publications/p108abs.html

cran
2005-Sep-21, 09:39 PM
Right on, Greg!
And it's good to see the evidence of volatile depletion limited to before terrestrial planet formation, rather than a 'hadean' event ...
that just leaves the intriguing little mystery of Mercury's sodium atmosphere...

Greg
2005-Sep-22, 02:44 AM
Thanks. This is a puzzling question indeed. My own guess is that the volatiles detected emanating from Mercury are vaporized from the surface alright, but deposited there by previous impacts. There isn't alot of data to back up or refute this supposition. Fortunately this will change in a few years (2009 I believe) when the Mesenger spacecraft arrives in orbit. The mission has gone well so far, and barring any unexpected malfunctions such as from untimely solar flares, it should arrive intact and answer this question definitively.

For details on how it will do this, just click the link below to the NASA website. It is crammed with alot of good info and links on Mercury as well as the mission.

http://messenger.jhuapl.edu/why_mercury/