[extropy-chat] Our Solar System Planets

[Amara Graps]

Spike,

>Amara will be able to answer this one.
:-( No, I can't.

>Our solar system is now considered dustier and rockier than the average
>solar system.  True or false?  Or is it less dusty and more rocky?
>Icier?

I don't think that one can answer this question yet because I don't
think that observations can resolve well-enough the debris disks to the
resolution that you need; i.e. the instruments must have the the
sensitivity to resolve tenuous debris disks like our Asteroid or Kuiper
Belts, but around other stars. To answer your question of ice versus
rock needs modeling which includes albedo and emissitivity of the
dust grains too. From [1], the Fomalhaut debris has been resolved enough
for this kind of work, but the models haven't been 'fine-tuned' enough
to address this level of dust composition.

You must also compare the relative ages because debris disks always
change in time. And you must compare the same (relative to the star)
radii in the debris disks. For example, our inner Solar System has
experienced stochastic events producing sudden increases in dust flux
during the last few Myr, which could be caused by a number of factors
that are probably common in other debris disks too. Do we know
what are the likely time in a debris disk evolution for these events?
Not sure.

According to [1], our own solar system experienced a large dynamic
"re-arrangment' where the Asteroid Belt and the Kuiper Belt were
depleted by factors 10-100 times during their histories (because
collisional evolution would not produce the low-mass belts we see
today). A Late-Heavy-Bombardment (LHB) depletion event is one good
explanation, and there is some evidence for that in the lunar cratering
record, but the extra dust produced would be a one-time transient event
only. After a LHB event, the system would be cleared of debris and dust
and would evolve slowly. Models comparing with data for extrasolar
debris disks point in that direction and for our own Solar System too,
the models and data indicate that our own Asteroid Belt, the
earth-crossing asteroid population, and the zodiacal cloud have had
nearly constant density for the past ~3 Gyr. LHB events probably
happened in other debris disks too, but it is not clear if the timing of
our own event is typical.

Comparing to Spitzer targets, the authors of the paper [1] say that
"The general lack of observed mid-IR excesses in Spitzer targets older
than 30 Myr could mean: a) most systems do not have belts at
temperatures like our asteroid belt, or b) most have LHB-like events
earlier in their histories.

and

Comparing to Spitzer targets, the authors of [2, pg. 1169] say that for
stars with a single measurement of 70 micron excess, the dust properties
are generally consistent with Kuiper Belt configurations - distances of
several tens of AU -- but at temperatures of ~50K, which exceed our Kuiper
Belt's L_dust/L_star by factors of ~100.

I have not answered your question to a satisfactory level, but that is
all I can do now (would need to read some papers, not enough time).
To give you the references that I would use myself to answer better
this question, I suggest for you to take a look at the debris disk
papers; it is a full and comprehensive collection!

You can begin here:

Mark Wyatt's publication list
http://www.ast.cam.ac.uk/~wyatt/

But then go to this _very extensive_ site by Paul Kalas on debris disks:
http://www.disksite.com/
and click on "Virtual Library"


[1] Evolution of circumstellar disks around normal stars: placing our
solar system in context Meyer M. R., Backman D. E., Weinberger A., Wyatt
M. C. 2006. In Protostars and Planets V, eds. B. Reipurth, D. Jewitt and
K. Keil (Tucson: Univ. of Arizona Press).
http://www.ast.cam.ac.uk/%7Ewyatt/mbww06.pdf  (look at sections 5, 6)

[2] Planets and infrared excesses: Preliminary results from a SPITZER
MIPS survey of solar-type stars  -- pdf Authors: Beichman, C.A., Bryden,
G., Rieke, G. H., et al. Journal-ref: 2005, The Astrophysical Journal,
Vol. 622, pp. 1160 - 1170.
http://astro.berkeley.edu/~kalas/disksite/library/beichman05a.pdf


Amara