What can the Kuiper belt tell us
about the early solar system?
Part I (Part II next lecture)
Ge/Ay133
Kuiper’s Hypothesis (1950) – Pluto should not be alone!
1999 KR 16
First (non-Pluto)
trans-Neptunian
object found in
1992 (Jewitt &
Luu), now many
many hundreds.
They are found
through their
motion on the
sky, gives R,i
fairly quickly.
What size range is inferred (constant albedo, etc.)?
Where is the mass
Concentrated?
How might we
probe the small
size end of the
distribution?
One approach: The Taiwan-America Occultation Survey (TAOS)
Zhang et al. 2008, ApJ, 685, L157
Sizes/Albedos? Only known for the largest objects:
ERIS as seen by the HST
2002 AW197 as seen by the SST
Would like measurements BEYOND the blackbody peak!
Need ALMA/CCAT to
go as deep as optical
surveys. Can such
telescopes search for
large bodies very far
from the Sun (flux goes
as R-2, not R-4).
What are large KBOs made of?
Those with moons and measured sizes yield bulk
densities consistent with ice/rock mixtures.
The SURFACE
composition is
variable, but for large
KBOs typically is
dominated by volatiles
(water, methane,
carbon dioxide and the
like). Does this reflect
surface/atmosphere
interactions? Volatile
retention over solar
system history?
Population expected from primordial disk:
Why? Disk observations & theory on the one hand, and …
Wide Kuiper Belt binaries on the other:
Formation time
of wide binaries
at current Kuiper
Belt density is
extremely long;
& harkens to an
earlier epoch
with much higher
mass surface
densities and low
collisional
velocities. Likely
primordial.
1998 WW31
Small moons that
orbit big objects
likely collisional
(more later).
2003 EL61
Population expected from primordial disk:
What is observed?
Uranus crossing
Neptune crossing
Plutinos
3:2
?
2:1
scattered KBOs
classical KBOs
Plutinos
3:2
2:1
scattered KBOs
classical KBOs
scattered
inclination
plutinos
Dyamical definitions of various KBOs:
classical
semi-major axis (AU)
Mike argues for two inclination distributions. Any differences?
Only
color, so
far.
Does this
imply that
their origin or
composition
must be
different also?
Trujillo and Brown, 2002
Is there a sharp
edge to the Kuiper
belt, and if so the
solar system or
original disk?
S
J
U
N
P
Pluto
Mars
Saturn
Neptune
?
Venus
Kuiper belt
Pluto
Mars
Saturn
Neptune
?
Venus
Pluto
Quaoar
Neptune
J
Uranus
# discovered KBOs
Observed KBO radial distribution
S
Inferred KBO radial distribution
Pluto
Quaoar
Neptune
S
Uranus
J
number
0
50
100
heliocentric distance
number
r-3/2
0
50
100
heliocentric distance
number
r-11
0
50
100
heliocentric distance
number
Resume ~r-3/2
surface density
distribution @100 AU
0
50
100
heliocentric distance
Kuiper belt
Pluto
Mars
Saturn
Neptune
?
Venus
Kuiper belt
Pluto
Venus
The edge of the solar system
Neptune
Saturn
Mars
>
What processes shaped the
current Kuiper belt?
Neptune
migration?
S
J
Should move
out in a
planetesimal
swarm (why?)…
U
N
P
Need Jupiter!
External Sculpting:
Photoevaporation a la Proplyds?
Orion Proplyd
External Sculpting #2:
Stellar encounter?
(also a way to
truncate the gas disk)
Ida et al. 2000
35 deg
Need to see more distant objects!
Ida et al. 2000
e
i
Internal Sculpting:
Effect of a large scattered planetesimal? (Miso~r3/4, nearly 7 Mearth at 40 AU)
a
Petit et al. 1999
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. Hard to
explain i distribution of
`classical’ belt this way.