Re: Astronomy:Origin of Planets.

From: Amara Graps (
Date: Tue Feb 08 2000 - 14:18:29 MST

From: Doug Jones <> Sun, 06 Feb 2000

> wrote:
>> Wandering the web I found the following.
>> It relates to an earlier discussion on this list regarding Velikovsky. I
>> find it interesting that BBC would be so brazen as to publish such a thing!!
>> Get out the pitchforks and torches!!
>Actually, this seems to be in line with what I've followed in the more
>technical (but still popular) astronomy press... planetary orbits in the
>intense interactions in a the early solar system were very unstable. IIRC,
>the biggest planet tends to move inward as it tends to eject objects that
>lie inward from it, but I'm not sure I recall the disequilibrium condition
>that causes this. The presence of "hot jovians" in other solar systems,
>circling their stars in only days in orbits far smaller than Mercury's,
>shows that planatary evolution can be quite, er, dynamic.

Some of the theories for the "hot Jupiters"

(I personally like the name "Roasters" better...) are

The forming planetesimal is caught between adjacent parcels of
gas moving at different speeds within the accretion disk, and the
planetesimal gets dragged along with it, inward. (Lin et al's theory)


A planetesimal which forms in the outer portion of an accretion disk
by angular momentum exchange loses energy and sprials inward, but then the
magnetic field associated with the star sweeps up the gas in
the accretion disk, expels it, carves out a hole, and the planetsimal
is caught in the hole
(Marcy et al's theory, I think).


Long after the gas in the accretion disk has dispersed and planetisimals
are orbiting in the debris in the outer region of thet system, gravity of
the outer planets disturbs the orbits of the planetesimals in their
vicinity sending some of the debris inwards towards. That debris is now in
vicinity of planets orbiting nearer the (proto)star. Those close planet(s)
hurl some of the material by gravity, and some of it outward. Whenever
those inner planet(s) toss the material outwards, the planet loses a little
bit of energy, and moves inward slightly (Malhotra and Norman's theory).


Interaction betwen giant planets in the outer part of a planetary system
draws one of them to move closer to the central star. When that
happens a "slingshot effect" between the star and the planets throws
one of the planets out of the system and the other planet loses energy
and moves inward.



Too many for me to keep track of!

I have not been following closely enough these various theories to
know which are in "favor" and which have been ruled out. However
it's true that the extrasolar planets discoveries have totally
revitalized the planet-formation theory business. Every planetary
science meeting I'm at, I see new sessions devoted to the topic.

The work that EvMick pointed to is _yet another theory_ for planet

I didn't read the journal article, but I note that it is the same
work as Levison, Duncan et al, presented at the Division of
Planetary Sciences meeting last October in Italy:


[33.09] Uranus and Neptune: Refugees from the Jupiter-Saturn zone?

E. W. Thommes, M. J. Duncan (Queen's University, Kingston, ON), H.
F. Levison (SwRI, Boulder, CO)

Plantesimal accretion models of planet formation have been quite
successful at reproducing the terrestrial region of the Solar
System. However, in the outer Solar System these models run into
problems, and it becomes very difficult to grow bodies to the
current mass of the ``ice giants," Uranus and Neptune. Here we
present an alternative scenario to in-situ formation of the ice
giants. In addition to the Jupiter and Saturn solid cores, several
more bodies of mass ~10 MEarth or more are likely to have formed in
the region between 4 and 10 AU. As Jupiter's core, and perhaps
Saturn's, accreted nebular gas, the other nearby bodies must have
been scattered outward. Dynamical friction with the trans-Saturnian
part of the planetesimal disk would have acted to decouple these
``failed cores" from their scatterer, and to circularize their
orbits. Numerical simulations presented here show that systems very
similar to our outer Solar System (including Uranus, Neptune, the
Kuiper belt, and the scattered disk) are a natural product of this


Martin Duncan and Hal Levison also coauthored a related talk at the


[6.05] The Formation of the Oort Cloud

H. Levison, L. Dones (SwRI), M. Duncan (Queen's U.), P. Weissman

We are in the process of completing a detailed model of the
formation of the Oort cloud. We integrated the orbits of ~1800 test
particles, initially in low-inclination, nearly-circular orbits
between the giant planets for times up to four billion years. This
simulation included the gravitational effects of the Sun, four giant
planets (in their current configuration), galactic tides, and
passing stars. The trajectory of a particle was followed until it
was ejected from the solar system, or impacted the Sun or a planet.
We find that all regions of the proto-planetary disk contribute to
the Oort cloud. The Oort cloud was built in two distinct stages in
our models. In the first 5 \times 107 years, the Oort cloud was
built by Jupiter and Saturn. These planets delivered particles
initially from all regions of the proto-planetary disk directly to
semi-major axes between 10,000 and 100,000 AU. After this time, the
Oort cloud was built mainly by Neptune. Objects that entered the
Oort cloud during this time also came from all regions of the
proto-planetary disk, but spent some time in the scattered disk.


To help counter the idea that EvMick's BBC article is like a Velikovsky
strange theory, I will say that I've known previous work from these
people for at least 15 years, they are very reputable and some of the
smartest folks in the planet formation theory field. (They are not
quacks, in other words)

Some of you might enjoy browsing through the abstracts of the last
DPS meeting, in order to get a flavor for what people of working
on for planet formation.

Go to Abstracts
Or to Session List

In particular, these sessions have talks related to this planet formation

Session 5.Extra-solar Planets: Dynamics and Detection

Session 6.Celestial Mechanics of Planets and Comets

Session 10.Planet Formation Posters

Session 14.Celestial Mechanics of Planets and Comets Posters

Session 15.Edgeworth-Kuiper Belt Posters

Session 23.Edgeworth-Kuiper Belt I

Session 33.Planet Formation: Collisions and Perturbations

Session 36.Planet Formation: Solar Nebula

Have fun,


Amara Graps | Max-Planck-Institut fuer Kernphysik
Interplanetary Dust Group | Saupfercheckweg 1
+49-6221-516-543 | 69117 Heidelberg, GERMANY *
        "Never fight an inanimate object." - P. J. O'Rourke

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