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Fraser
2004-Oct-19, 04:57 PM
SUMMARY: Brand new planetary systems take much longer to form than previously thought, according to new data gathered by the Spitzer Space Telescope - and it's a nasty, chaotic period. Researchers pointed Spitzer at 71 dusty disks which are new planets in the making, and found that many seem choked with dust, hundreds of millions of years after the host star formed. The only way this could be possible is if mountain range-sized planetesimals were continuously crashing into each other on the long hard road to full sized planethood.

What do you think about this story? Post your comments below.

antoniseb
2004-Oct-19, 05:43 PM
I like these stories about the time-line for the formation of the solar system.
It won't be too many years before we have a pretty solid handle on how it happened, and how long it took.

lswinford
2004-Oct-19, 06:32 PM
What? :o Not simple swept circles of concentric consolidation? :rolleyes: You mean asteroids weren&#39;t always in "camps" and the strangely eccentric orbits of those rare "dirty snowballs" (comets) and petty rocks streaking across the sky every now and then(meteors) wasn&#39;t the picture of the early solar system? <_< The scars of the moon weren&#39;t from its own vulcanism and the passing of the Oort cloud? :unsure: How strange&#33; :blink:

Seriously, though, thanks for the article.

om@umr.edu
2004-Oct-19, 06:42 PM
Stable and radioactive isotopes and their decay products provide important time constraints on the early solar system.

1. The decay products of Pu-244, U-235 and U-238 (half-lives = 0.082-4.468 billion years) indicate that a supernova explosion occurred about 5 billion years ago.

2. Atoms made by different nuclear reactions in different parts of the star did not mix before condensation. For example, meteorite grains trapped various levels of
Helium-burning products like O-16 (fusion of He-4),
r-products like Nd-150 (rapid neutron-capture),
s-products like Ba-134 (slow neutron capture), and
p-products like Xe-124 (proton capture or (gamma,n) reactions).

3. The decay products of Al-26, Fe-60, Mn-53, Pd-107, I-129, Pu-244, etc. (half-lives = 0.74-82 million years) show that dust formed very quickly while these short-lived isotopes were still alive.

4. The decay products of I-129 and Pu-244 (16-82 million years) in the Earth&#39;s upper mantle show that Earth&#39;s crust, oceans and atmosphere were produced by rapid differentiation of the upper part of the Earth, which solidified and trapped live I-129 and Pu-244 in the depleted upper mantle.

5. Primordial He-3 leaking from the lower mantle shows that this region did not differentiate and release its volatile elements when the crust, atmosphere, and oceans formed.

Many of these findings are in pdf files at:
http://web.umr.edu/~om/abbre-resume.html

With kind regards,

Oliver
http://www.umr.edu/~om

TuTone
2004-Oct-19, 08:11 PM
It&#39;s amazing how these planets form. How do they form into a perfect circle? You would think some planets would be irregular shaped. How do gas planets form, same process?

jamerz3294
2004-Oct-20, 12:56 AM
This kind of story is what I live for&#33; ;) It&#39;s amazing how we have what we feel is a pretty solid view of things, only to be shown that (yet again) we always end up with more questions than answers.

dave_f
2004-Oct-20, 02:51 AM
Originally posted by jamerz3294@Oct 19 2004, 07:56 PM
This kind of story is what I live for&#33; ;) It&#39;s amazing how we have what we feel is a pretty solid view of things, only to be shown that (yet again) we always end up with more questions than answers.
I would say that these types of pictures are what I live for. Those computer animations are awesome&#33;

downunder
2004-Oct-20, 03:02 AM
Originally posted by TuTone@Oct 19 2004, 08:11 PM
How do they form into a perfect circle? You would think some planets would be irregular shaped.
If you had a bubble of water floating around in a space ship it&#39;d be a near perfect sphere. If you had a bubble of molten rock 8000 miles in diameter it&#39;d be a near perfect sphere. The surface gravity plus the plasticity of the outer layer determines just how far any point can be from a perfect sphere. If Mt Everest was much higher then the weight of it would make it sag until it reached a balance. Olympus Mons couldn&#39;t exist on Earth because it&#39;s far too high but on Mars there&#39;s no problem because the surface gravity is so much weaker.

So all planets have a certain amount of irregular shape. If one was entirely covered with a liquid then it&#39;s only irregularity would be the height of any waves. For it&#39;s size, Mars is more irregular than the Earth because it&#39;s got a much higher mountain on it. The smaller it gets the more the irregularity it can have until it&#39;s so lumpy it&#39;s obviously not a sphere. Probably for this reason there&#39;s still no definition of what&#39;s a "planet".

Janice
2004-Oct-20, 04:21 AM
:P Is it just me, or do we always seem to de exploring and looking for answers to things and never actually finding them. Or if we do find an answer it just leads to another question.
:huh: Seriously, is it just me? :huh:

eburacum45
2004-Oct-20, 07:39 AM
Hopefully, science will never stop unearthing unanswered questions. That is what it is for.

The history of the Solar System is set out very clearly in this essay by my colleague John Dollan (from Orion&#39;s Arm and the Arcbuilders Universe)
here;
http://j.dollan.home.bresnan.net/sunlife.html

jamerz3294
2004-Oct-20, 02:12 PM
Originally posted by Janice@Oct 20 2004, 04:21 AM
:P Is it just me, or do we always seem to de exploring and looking for answers to things and never actually finding them. Or if we do find an answer it just leads to another question.
:huh: Seriously, is it just me? :huh:
Thats kinda why we all are here (in this forum) pondering about this stuff. B)

wstevenbrown
2004-Oct-20, 03:07 PM
How do they form into a perfect circle?

With two hidden assumptions, the cutoff seems to be a diameter of 200 miles: larger objects will be more spherical, smaller ones more irregular. In our solar system, Uranus&#39; moon Miranda is a borderline object, with truly strange topography.
The assumptions:
1) Both the density and the cohesiveness of the material are near &#39;average.&#39;
2) The rotation of the object is near &#39;average.&#39; Fast-rotating objects are distorted into oblate spheroids, like both Jupiter and Saturn in our system. Regards, S.

lswinford
2004-Oct-20, 07:34 PM
I can put a pretty "square" block of wood in a lathe and turn it. While it spins I discover two things: whether I have it set according to the block&#39;s geometric center or its center of mass. Placing a cutting tool on the edge of its spin, I can trim (or "turn") the block down into a smooth circular form. But if the center of mass is different and I haven&#39;t fully compensated, or my lathe doesn&#39;t fully hold it firm, there may be a slightly oval, or off-circle, shaping. As I recall our lunar orbiters have a little bit of problem because the moon does not have a distinct and discrete center of mass. Some of the asteroids and comets discussed and described in the news here are not uniformly spherical or homogenously layered. Consider the earth, at a distance, it appears practically spherical with crustal features little different from the non-uniformities apparent when looking at a chicken egg&#39;s shell under a low-powered microscope. For that matter, I think we might find our planet&#39;s "solid" surface comparatively thinner than the average chicken eggshell. We have non-uniformity in the distribution of our mass as evidenced by zones where even sea-level is not on the level with other parts of the sea. Part of this is because of our spin and orbit. The center of gravity between the earth and the moon is not at the geometrical center of the earth. As Kepler even discovered in describing the sun in one of the two focii of our earth&#39;s eliptical orbit, this wobbly, molten-metal blob with a cold external crust also orbits a slightly eccentric center of gravity about the sun. Furthermore, that sun is in motion, adding still further measure of physical and structural stress. So, it is a tad bit difficult to expect perfect spheres even under the relatively pristine conditions of today&#39;s solar system. In light of the early solar system, I&#39;m amazed that things seem so neat and clean today.

om@umr.edu
2004-Oct-20, 11:20 PM
In a gravitational field, it seems natural to me that material forms a spherical shape.

The larger the gravitational field, the greater this tendency.

Mountains erode. Material naturally rolls down into the valley.

With kind regards,

Oliver
http://www.umr.edu/~om