[ExI] Scientists Find Solar System Like Ours

Amara Graps amara at amara.com
Sat Feb 16 15:59:19 UTC 2008

>The gift you meant is not the exoplanets, it is the technique they used
>to find them, ja?

Not really, although that is very very cool in many ways, including how
the network of amateurs contributes.

Look at the Science Lead-In article I gave the link to:

"Alien Planetary System Looks a Lot Like Home"

and think about the extrasolar systems that have been discovered so far.

I'll paste what I wrote before:

1) It represents a SCALED version of our solar system with a
less-massive host star.

It found planets of mass:
	2/3 M_jupiter AND 1/2 M_saturn orbiting at distances of
	about 2.3 and 4.6 AU

	(in our own solar system we have M_jupiter and M_saturn
	orbiting at distances of 5 and 10 AU)

- Equilibrium temperatures of T ~82K and T ~59 K

	(30% less than Jupiter and Saturn)

- Orbiting around a reddish star of mass 1/2 M_sun

Here is text from the preprint arXiV preprint paper (I have the Science
paper too, if anyone wants it)



<begin quote>

Before the detection of extrasolar planets, planet formation theories
generally predicted that other systems should resemble our solar system.
In the core-accretion paradigm, the most mas- sive giant planet forms at
the 'snow line,' the point in the protoplanetary disk exterior to which
ices are stable. Immediately beyond the snow line, the surface density
of solids is highest and the dynamical time is the shortest, and
therefore the timescale for planet formation is the short- est. Beyond
the snow line, the formation timescale increases with distance from the
host star. Thus in this 'classical' picture of planet formation, one
would expect planet mass to decrease with increasing distance beyond the
snow line, as is observed in our solar system (30). The discovery of a
population of massive planets well interior to the snow line
demonstrated that this picture of planet formation is incomplete, and
considerable inward migration of planets must occur (31). Nevertheless,
this classical picture may still be applicable to our solar system and
some fraction of other systems as well. The OGLE-2006-BLG-109L planetary
system repre- sents just such a 'scaled version' of our own solar
system, with a less-massive host. This system preserves the
mass-distance correlation in our solar system, and the scaling with
primary mass is consistent with the core-accretion paradigm in which
giant planets that form around lower- mass stars are expected to be less
massive but form in regions of the protoplanetary disk with similar
equilibrium temperatures and are therefore closer to their parent star

The majority of the ~ 25 known multi-planet systems are quite dissimilar
to the OGLE- 2006-BLG-109L system and to our own solar system. Many of
these systems have the very close-in massive planets indicative of
large-scale planetary migration, or they have a 'normal hierarchy', in
which the masses of the giant planets increase with distance from the
parent star. There are two multi-planet systems with properties roughly
similar to those of OGLE-2006- BLG-109L. The 47 UMa and 14 Her systems
each contain a giant planet at a semimajor axis of ~ 3 AU and a second,
less massive giant planet at a separation of ~ 7 AU (33). However,
because of their higher-mass primaries, the equilibrium temperatures of
these planets are considerably higher than those of OGLE-2006-BLG-109L
or Jupiter and Saturn, so these systems cannot be considered close
analogs of our solar system.

OGLE-2006-BLG-109Lb and OGLE-2006-BLG-109Lc are the fifth and sixth
planets to be detected by microlensing. Although, given the detection of
planet c, the a priori probability of detecting planet b in this event
was high, it was not unity. Furthermore, only two other jovian-mass
planets have been detected by microlensing (8, 9), and neither event had
substantial sensitivity to multiple planets. These facts may indicate
that the stars being probed by microlensing that host jovian-mass
companions are also likely to host additional giant planets. If the
OGLE-2006-BLG-109L planetary system is typical, these systems may have
properties similar to our solar system. Regardless, the detection of the
OGLE-2006-BLG-109L planetary system demonstrates that microlensing
surveys will be able to constrain the frequency of solar system analogs
throughout the Galaxy.

<end quote>


Amara Graps, PhD      www.amara.com
Research Scientist, Southwest Research Institute (SwRI), Boulder, Colorado

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