Transcript lec18_16nov2007

More on Jupiter, Neptune, the Kuiper belt,
and the early solar system.
Ge/Ay133
10Nov2006
The MMSN – Solid surface density near 1-3 g/cm2 at Jupiter
Simulations suggest
that surface densities
nearly a factor of ten
larger might be needed
to form Jupiter in ≤107
yr. The problem is
even worse for the `ice
giants’ Uranus and
Neptune if they
formed near their
current locations.
Alternatives?
e
i
What happens to the Kuiper belt if oligarchs migrate/are ejected?
(Miso~r3/4, nearly 7 Mearth at 40 AU)
a
Petit et al. 1999
Gas giants?
Depending on
dust opacity,
cores may
spend a long
time in the
“plateau” phase
before runaway
gas accretion.
Form cores
closely spaced
in higher
density region.
Radical idea: Investigate what happens dynamically if one of these
closely spaced cores reaches the runaway gas accretion stage first.
Step 1: Start with four cores+planetesimal swarm
Nebular surface density
(s0~10 g/cm2, a~2)
Hill radius
For s=r-2 and n~5-10rH, get ~equal mass cores (isolation mass),
choice of s0 leaves room for planetesimal swarm.
Step 1: Start with four cores+planetesimal swarm (pictorially)
Initial state,
no extensive
gas accretion
yet, so the
cores do not
strongly stir
the swarm or
interact.
The question is, can we get from this initial condition to now?
Plutinos
3:2
2:1
scattered KBOs
classical KBOs
Step 2: Let one core grow, and dominate gravitationally.
Nearby cores can be scattered, eccentricity evolves as
Steady state if
Protoplanet
Planetesimals
Thus the planetesimal swarm is key in damping eccentric orbits!
Early on, scattered protoplanet dominates, or
Time scale for eccentricity damping is:
For the default
case, the
damping time
is of order a
few to few tens
of Myr.
Statistically, how often do we go from here…
… to here?
From whence the Plutinos?
If Neptune’s
migration is
sufficiently
`slow’, KBOs
can be trapped
into orbital
resonances that
move outward
w/planet. Hard to
explain i
distribution of
`classical’ belt
with this much
movement!
From whence the Plutinos?
A bit better at
later times, but
the quantitative
results do not
match those
observed, esp.
for the scattered
population of
KBOs…
“Standard case”:
What if Jupiter forms in “slot #2”?
What happens if you change the number of cores?
What if you allow the planetesimal disk to be more massive?
Classical belt
much too
massive and
extends too far
to reproduce
observations…
How might you truncate
the classical KBO
population beyond 40-45
AU? Photoevaporation?
Stellar encounter?
(Shown here)
Ida et al. 2000
35 deg
Need to see more distant objects!
Ida et al. 2000
What happens if you let a second (“Saturn”) core accrete gas?
This also really helps
with the classical KBO
issue beyond 40 AU,
and keeps Saturn closer
to its position in our S.S.
From whence the Plutinos?
S
J
If Neptune’s migration is
sufficiently `slow’, KBOs
can be trapped into orbital
resonances that move
outward w/planet.
How smooth is Neptune’s migration? Depends on size distribution:
Numerically, provided most of the mass is in <200 km bodies, OK.
Objects further out? Look for slow movers…
S
J
U
N
P
Orbit refined by “historical” observations:
a=480 AU
e=0.85
i=12
q=76 AU
Q=900 AU
P=10,500 yr
Why is SEDNA’s orbit hard to understand from a solar
system (only) point of view?
Numerical integration studies of individual objects from Mike B.:
?
a=480 AU
e=0.85
i=12
q=76 AU
Q=900 AU
P=10,500 yr
Where did it come from?
-in situ formation
-scattered by modest-sized planet @ ~70AU
-close stellar encounter
Where did it come from?
-in situ
-scattered by modest-sized planet @ ~70AU
-close stellar encounter
Where did it come from?
-in situ
-scattered by modest-sized planet @ ~70AU
-close stellar encounter
-dense stellar birth environment
Include perturbers well beyond 30-40 AU:
Sampling bias:
To distinguish
between the
possible models for
Sedna’s origin, you
need to detect more
such objects. The
red arc indicates the
fraction of Sedna’s
orbit in which it can
be detected with
current technology.
Emerging picture: Dynamic environment, lots of movement!
Radial velocity surveys are
sensitive to ~Jupiter/Saturn
mass planets out to >5 AU,
Neptune masses further in.
http://exoplanets.org/exoplanets_pub.html
Next time: Can we study extrasolar Kuiper belts?