Download D. Jewitt

Solar System Science
David Jewitt, UCLA
Tuesday, October 25, 14:00 -14:40
Topics:
• Structure of solar system (Oort cloud, Kuiper belt, comets)
• Processes (impact, rotational disruption, capture, debris
production, binary formation, crystallization, endogenic activity)
Background movie by Alex Parker
Background
Three Domains of the Solar System:
• Terrestrial planets: Mercury - Mars (asteroids)
• Giant planets: Jupiter - Neptune
• Comets: Oort Cloud, Kuiper belt
Comets
Mass-Loss Lifetime << Age of Solar System
Long Period vs Short Period
Oort cloud vs Kuiper belt
100 AU
Oort Cloud
Oort Cloud
• No strong hyperbolics
• Width of peak < ∆EJ
• Comets in the peak are first
arrivals
• Too many first arrivals
relative to Nth arrivals.
Why?
Oort Cloud
• Dynamics alone cannot
explain the distribution of
orbital energies.
• Oort introduced a “fading
parameter” to reduce the
number of returning comets
relative to 1st arrivals.
Dones et al. (2004)
Oort Cloud
r ~ 50,000 AU
VK ~ 100 m s-1
12
• JWST canNassess
~ 1011the- 10
composition
of longperiod comet
from
M nuclei
~ 1 - 10
MEnIR
? spectroscopy
Isotropized ~ 1 Gyr
• Perhaps find evidence for “interstellar frosting”
Hot Topics
• Determine nucleus size distribution from
thermal
IR
photometry
of
pre-active
LPCs
• Two-step formation (emplacement efficiency =1-10%)
• Comet-sharing between stars in birth cluster?
• Existence/population of inner Oort Cloud?
• Nature of the fading parameter? (is it real?)
• Can OC be directly observed? How?
Kuiper Belt
Kuiper Belt in Perspective
Jewitt & Haghighipour (2008)
Centaurs
N
Scattered
Resonant
1:1
3:2
2:1
Detached
Classical
N
Edge
Jewitt & Luu (2002)
Kuiper Belt
• r ~ 30 to >2000 AU
• VK ≤ 5 km s-1
• N (a > 1km) ~ 109 - 1010
• M ~ 0.1 ME (now, 10 - 50 originally)
• Dynamical fossil
• Resonant objects indicate planetary migration.
• Migration offers novel possibilities for solar
system re-arrangement & a plaything for
dynamicists
Gomes et al. 2005
Attributes of the Nice Model
• Explains lunar Late-Heavy Bombardment @800 Myr post-formation
• Flexible model can fit many disparate solar system properties
• Might supply “niche” populations (Trojans, irregular satellites)
Problems with the Nice Model
• Model struggles to make any observationally testable predictions (too
flexible)
• Original Nice model expelled the Earth
• Requires 30 M Kuiper belt to survive ~800 Myr without agglomeration (to provide dynamical friction damping). How?
• The best data provide no evidence for the LHB: the model beautifully
Earth
explains something that did not happen
V = 27
25
23
V = 27
-> Radius ~ 10 or 15 km
Surface density ~ 100 deg-2
• KBO albedo & size determinations
• nIR spectroscopy for compositional studies
• Identify eclipsing/contact binary population
V = 27
25
23
r > 30 km - Primordial
r < 30 km - Collisionally modified
<--JFCs
Gould (2012)
Schlichting et al. (2013)
Large KBO Pluto
Hydrocarbon haze
Snakeskin terrain
Convective nitrogen sea
8:1 Binary
Planet Nine?
Trujillo & Sheppard (2014)
Nature, 507, 471
• Orbital and real-space alignment, if real,
could be produced by an external planet.
• If it exists, emplacement by planet-planet
scattering seems likely, but requires additional
perturbation (by another unseen planet?) to
raise the perihelion.
• Strong scattering seems strange in the context
of the dynamically cold system of known
planets (e ~ 0, i ~ 0).
• No direct evidence exists. Indirect evidence
seems to be weakening (as of Oct 2016).
Comets
67P from Rosetta
1 km
Planetesimal or collision fragment?
Sublimation:
Water ice sublimation drops precipitously
with increasing distance. It is incapable
of launching dust particles beyond about
5 AU.
But…the ice might be amorphous
Amorphous vs Crystalline Ice
8.5 AU
11.8 AU
7.9 AU
5.3 AU
5.5 AU
5.8 AU
17P/Holmes Outburst
3x105 kg/s, E/m ~ 105 J kg-1
Likely crystallization runaway
Li et al. (2011)
Hot Topics
• Is the ice amorphous?
• If so, why do KBOs appear crystalline?
• What is the nature of cometary organics & what is
their role in the origin of life?
JWST nIR spectroscopy will help decide
Transients
Impact
Ice Sublimation
Radiation torques - YORP
Crystallization energy
Endogenic activity
The Active Asteroids
Already have examples of…
• Hypervelocity impacts
• Sublimation
• Thermal and desiccation fracture
• YORP torque spin-up
• More?
2010 December
Asteroid Impact
Asteroid Ice
(596) Scheila
133P/Elst-Pizarro
30 m projectile
110 km target
∆v ~ 5 km/s
E ~ 1/4 Megatonne
Periodic emission of dust near perihelion
dm/dt ≤ 1 kg/s
Thermal trigger likely = sublimation
No gas yet detected
2010 December
Jewitt et al. (2011)
Hsieh & Jewitt (2006)
P/2013 R3 - YORP Disruption
a = 3.003, e = 0.273, i = 0.90, TJ = 3.18
Shedding & Satellite Formation by YORP spin-up
Kevin Walsh and Patrik Michel Observatoire de la Cote d'Azur (OCDA)
Hirabayashi et al (2014)
YORP Disruptions Observed
R3
Jewitt et al. (2014)
P5
Jewitt et al. (2013)
3
2
Predicted Number of Events Per Year
1
Rotational Disruption
0
-1
• Same may apply for
debris production around
other stars
-2
-3
• Radiation torques may
dominate collisional
destruction in the
asteroid belt (for sub-km
asteroids)
Impact Disruption
-4
-5
0.1
1.0
Diameter [km]
Marzari et al. (2011), Veras et al. (2014)
Endogenic activity
Active Objects
Enceladus D ~ 500 km
Enceladus production ~few x 100 kg/s
0.06"
Enceladus
• Planetary volcanology
• Activity vs. time - tidal trigger?
• Secular evolution
JWST can provide longterm, remote monitoring
of activity (Enceladus,
Europa, Io)
T ~ 100 K ->
BB peak @30 µm
Summary
Expect science impacts in
• Nature of primitive bodies (Kuiper belt, Oort Cloud, Centaurs,
Trojans, comets)
• Compositional studies of primitive bodies
• Active Objects (hypervelocity impact clouds, rotational
instabilities, weird volcanism)
BUT the most exciting science will come not from detailed
observing plans, but from observational surprises
END