Download L1 Solar system

Lecture 1 Part I
Observational constraints from the
Solar System
and from
Extrasolar Planets
Lecture Universität Heidelberg WS 11/12
Dr. Christoph Mordasini
Partially based on script by Prof. W. Benz
Mentor Prof. T. Henning
Lecture overview
1. Introduction
2. Planet formation paradigm
3. Structure of the Solar System
4. The surprise: 51 Peg b
5. Detection techniques: radial velocity, transits,
direct imaging, (microlensing, timing, astrometry)
6. Properties of extrasolar planets: mass, distance,
eccentricity distributions, metallicity effect, massradius diagram, ...
1. Introduction
Galaxies, stars and planets
10 billion galaxies
How many harbor life?
100 billion stars
how many planets?
How frequent? Life?
First generation of human beings with
technology to answer this.
Important questions
- Planet formation:
From dust to planets
10 μm
10-100 million
years
How?
- Planet evolution:
Habitability
Earth
Mars
Terrestrial planets in the
solar system: similar initial
conditions very different
outcome.
The characterization also
of exoplanets has just
started.
Moon
Venus
Ways to understanding
Herschel’s 1789
For many
centuries
Sun
Stars
La Silla Obs. ESO
For a
decade
Formation in disks
Collisions
Gas accretion
Migration
Exoplanets
Solar System
Darwin ESA
In a
decade ?
Life
Cloud collapse
Hertzsprung Russel
Nuclear Fusion
Stellar Mass Funct.
Astrobiology
Habitable Zone
Biomarkers
Complex Life
Extraterrestrial Life ?
2. Planet Formation Paradigm
Planet formation: The paradigm
Gravitational
- remote observations
- in-situ measurements
- sample returns
- laboratory analysis
- theoretical modeling
Core
Minority
line
Party line
Accretion
Instability
A satisfactory theory should explain the formation of
planets in the solar system as well as around other stars.
Planet formation: Sequential picture
in presence of gas
Star & protoplanetary disk
dust
in absence of gas
107 years
107 years
giant
planets
giant
impacts
planetesimals
protoplanets
migration
type I
type II
108 years
terrestrial dynamical replanets
arrangement
Planet formation
Initial conditions, task and orders of magnitude
Initial condition
•disk of dust and gas orbiting a new born star
•total mass of the disk: ~1-10 % of stellar mass
•total mass of dust: ~2% of mass of gas
Task
•follow the evolution of the gas and dust for a period of about
100 Million years.
Orders of magnitude to remember
•Msun ~2 1033 g
•MJ ~ 2 1030 g ~ 1/1000 Msun ~ 318 ME
•ME ~ 6 1027 g
•RJ ~ 7.19 109 cm ~ 1/10 Rsun
•RE ~ 6.4 108 cm ~ 1/10 RJ
•AU ~1.5 1013 cm
•Lsun ~ 3.8 1033 erg/s
Challenges
in planet formation
gas giants
(∼10000 km)
size
runaway gas
accretion
Earth-sized
(∼1000 km)
protoplanets
planetesimals
(∼km)
dust
(μm)
Self.
Gravity
late stages
giant impacts
Difficulty:
-huge dynamical rage in size/mass
oligarchic - dynamical range in time: 100 million
growth
orbital timescales
-lots of physics involved, changing over
time: gravity, drag, hydrodynamics,
runaway
radiation transfer, magnetic fields,..
growth
- non-linearities (runaway growth)
-feedback mechanism (grav. scattering)
dust sticking
104-105
105-107
107-108
time
years
3. Structure of the Solar System
Solar system
System architecture
Orbital data major planets
Rocky
planets
gas giants
Inner system
Asteroids
Outer system
ice giants
Note
•Sun has 99.96% of the mass, but only 0.6% of the angular momentum. Solar Prot ~25 d.
•LJ/Ltot: 0.61, Lsaturn/Ltot: 0.25
•Jupiter is dominating the dynamics. Important during formation (small mars, Asteroids)
•mostly circular orbits, all prograde (same rotation direction as the sun)
•nearly co-planar orbits: formation in a disk
•spacing: Titius-Bode law an=aMercury+0.3 2n-1 n=1,2,...: Orbital stability in Hill units
Minor bodies
Asteroids
Solar system
System architecture II
•rocky composition, some with significant water content
•a few 100’000 known.
•total mass 1/30 of lunar mass (1 lunar mass ~1/81 ME): not a destroyed planet.
•26 with diameters larger than 200 km. Largest: Ceres 900 km.
•2.2 AU < a < 3.2 AU for 95%: between Mars and Jupiter
•existence of families (groups with similar orbits and reflectance properties)
•All prograde, most have e<0.3 and i<25 deg.
•leftovers from formation phase: important obs. constraint on e.g. migration.
Solar system
System architecture III
Minor bodies cont.
Trans-Neptunian Objects (TNO) and Kuiper Belt objects (KBO)
•icy composition, not much altered (slow evolution). Low albedo (<coal).
•estimated 70’000 with diameter >100 km. Larger than typical asteroids.
•located beyond Neptune: 30 AU< a < 70 AU.
•3 classes:
•classical KBO: 42-47 AU, mean eccentricity ~ 0.07 (small), i < 30 deg.
•scattered KBO: large e, total M 0.5-1.5 ME ,source of short period comets, perihel at ~35 AU
•Plutinos: 3:2 resonance with Neptune, as Pluto, 0.1<e<0.34, 0<i<2 deg.
Oort Cloud
•hypothetical spherical cloud surrounding the sun, extending out
100’000 AU.
•Source of long period comets.
•Not (yet) directly observed.
•Weak gravitationally bound: effect of passing stars.
•Objects scattered outwards during planet formation.
Solar system
Physical properties
Physical data major planets
Approximately to scale
•Stars: burn hydrogen: M>~75 MJ
•Brown dwarfs: burn deuterium ~13<M/MJ<75
•Planet definition (IAU 2006) :
A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its selfgravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round)
shape, and (c) has cleared the neighborhood around its orbit.
Solar system
Physical properties II
Composition terrestrial planets
Earth
•Inner structure determination: observations (seismic waves, gravitational moments, surface
temperature and abundances) combined with modeling.
•Terrestrial planets: Iron core, silicate mantle.
•Size of core vs mantle varies: impact history
•Earth: core 1/3, mantle 2/3 (in mass). Close to chondritic (primitive meteorites) composition
Solar system
Physical properties III
Composition giants
Possible J,S compositions
Guillot 1999
Amount of metals [ME]
MJ=~318 ME, MS=~95 ME
Significant uncertainties: equation
of state (EOS) of H/He under
extreme p and T badly known.
•X=Hydrogen, Y=Helium, Z=”Metals”
•Solar composition (primordial): X0 0.71, Y0 0.27, Z0 0.015
•The gas giant planets (Jupiter, Saturn) are clearly enriched compared to solar composition.
Expected Jupiter solar: 4.8 ME, Saturn solar: 1.4 ME. This is much less than the inferred values.
They didn’t form like the sun from the same collapsing cloud. Important constraint
•The ice giants consist of ~25% rock, ~60-79% ice, and ~5-15% H/He
Historical perspective
Herschel’s big telescope
Selected discoveries in the Solar System
•until 1600 only six planets were known: Mercury, Venus, Earth, Mars, Jupiter and Saturn.
Extensively studied since antiquity.
•Aristarchus from Samos (270 BC): heliocentric system.
•beginning of 17th century: discoveries of satellites of Jupiter and Saturn by Galilei
(1564-1642), Huygens (1629-1659) and Cassini (1625-1712).
•1781 discovery of Uranus by William Herschel
•1846 discovery of Neptune by Johann Galle. Neptune was first theoretically predicted by
John Adams and Urbain Le Verrier who studied the perturbations of the orbit of Uranus.
•1930 discovery of Pluto by Clyde Tombaugh
•1978 discovery of Charon, Pluto’s moon by James Christy
•1992 discovery of the first TNO object (QB1) by Jane Luu and Jewitt
Historical perspective II
Some early formation theories
•Rene Decartes (1594-1650)
•space is filled with a universal substance. Planets form in vortices which form at
locations of least motions
•secondary vortices form around the vortices which make the moons.
•Georges L. L. Buffon (1707-1804)
•catastrophe hypothesis: a huge comet hits the sun and ejects material which form the
planet. Conceptually similar to the giant hypothesis for Earth’s moon
•Immanuel Kant (1724-1804)
•nebula hypothesis (building on similar early work of Emanuel Swedenborg).
•nebula composed of gas and dust is flattened by rotation, particles are colliding, loose
energy and drift to the center to form the sun
•planets form out of local density enhancements which orbit the sun.
•Pierre Simon de Laplace (1749-1829)
•planets are formed during the contraction of the sun.
•the sun ejects rings of material which cool and form planets.
Swedenborg
Kant
Laplace
Planet formation theory
State of the art t<1995. Only one example to study..
Science, 267, 360 (January 1995)
s
p
Oo
Knowledge is evolving. What is believed correct today can
turn up wrong tomorrow!
4. The surprise: 51 Peg b
The discovery
Nature, 378, 355 (October 6, 1995)
confirmation by Marcy & Butler
(October 12, 1995)
A giant planet with a 4.15 days period!
The wake-up call
• First planet mass object in orbit around a G2 IV, d=15 pc, 5.49 mag
solar like star: 51 Pegasi b.
• Very different from theoretical
expectations:
• a = 0.052 AU
• P = 4.23 days
• M sin i = 0.468 MJ
• Such planets are now called “Hot
Jupiters” or Pegasi planets / Pegasids.
• About 0.5 -1 % of sun like planets have
such a hot Jupiter (as we know now).
Mayor & Queloz
Spektrometer ELODIE
Observatoire de
Haute-Provence
193 cm Teleskop
Migration: was not new after all
ApJ, 241, 425 (October 1, 1980)
discovered 15 years
earlier... by theorists!
5. Planet detection methods
Current status
692 planets
Candidates detected by radial velocity or astrometry
524 planetary systems
640 planets
76 multiple planet systems
Transiting planets
171 planetary systems
184 planets
14 multiple planet systems
Candidates detected by microlensing
12 planetary systems
13 planets
1 multiple planet systems
+ 1235 planet candidates from
the KEPLER satellite (transit)
Candidates detected by imaging
22 planetary systems
25 planets
1 multiple planet systems
Candidates detected by timing
9 planetary systems
14 planets
4 multiple planet systems
Extra-solar planet encyclopedia (http://exoplanet.eu/)
9.11.2011
Planet Detection Methods
Michael Perryman, Rep. Prog. Phys., 2000, 63, 1209 (updated April 2007)
[corrections or suggestions please to [email protected]]
Accretion
on star
Existing capability
Projected (10-20 yr)
Primary detections
Follow-up detections
n = systems; ? = uncertain
Planet Detection
Methods
Dynamical effects
Magnetic
superflares
??
Photometric signal
Timing
(ground)
Detectable
planet mass
Self-accreting
planetesimals
Miscellaneous
Radio
emission
Microlensing
Imaging
Astrometry
Reflected/
blackbody
Disks
Pulsars
Radial
velocity
White
dwarfs
Binary
eclipses
10MJ
Radio
Astrometric
4
Slow
10ME
ME
Millisec
206 planets
(178 systems,
of which 20 multiple)
4 planets
2 systems
Space
interferometry
(infrared/optical)
Optical
2?
MJ
Photometric
Ground
Space
Space
1?
4
Ground
Free
floating
Ground
(adaptive
optics)
Resolved
imaging
Detection
of Life?
Transits
1?
11
3
Ground
Timing Space
residuals
Large number of methods, but only few can detect
and allow the study of Earth-like planets!
5.1 Radial velocity (RV) method
Indirect detection - radial velocity
Star and planet move around common center of
mass. The stars move also (a little bit).
Use optical Doppler effect to measure motion
along the line of sight: → measure (periodic) shifts
of spectral lines i.e. the stellar radial velocities.
Shape and amplitude of the curve give the Msini
(minimal mass), period, eccentricity and T0.
But....
- motion of the Sun due to Jupiter: 12 m/s
→ shift of spectral line by ~50 angstroms or 10 Si atoms
on the CCD
→ average velocity of cyclist at the Tour de France...
- motion of the sun due to Earth: 8 cm/s
→ difficult to detect because of surface fluctuations
The most precise RV instrument:
Instrument: High-precision spectrograph
Location: 3.6 m ESO at La Silla Observatory (Chile)
Consortium: Universities of Geneva and Bern (CH), Observatoire
de Haute Provence (F), Service d'Aéronomie (F), ESO.
Precision: down to 0.6 m/s.
Super-Earth planets in the habitable
zone of K dwarfs.
Vaccum chamber
Telescope
Control room
Progress in ground-based RV detections
Mordasini et al. 2009
Detection probability for a first
generation instrument (ELODIE)
Instrumental precision =10 m/s
Detection bias RV: The less
massive, and the further out, the
more difficult to find. Don’t forget
when interpreting discoveries!
51 Peg b
HARPS
Earth-like planet detection from the ground by 2012?
→ still indirect observations
→ only close-by planets
5.2 Transits (Photometry)
Transit detection
transit detection principle
Simple in theory, difficult in
practice.
=>Miniforschungsprojekt
at MPIA
Jupiter in front of the sun
Earth in front of the sun
(Rp/Rstar)2
1% change in luminosity
0.01% change in luminosity
But... Transits measure radius not mass. Follow-up is necessary to
measure mass (by RV).
Many false positives (look photometrically like planets, but are not.)
Characterization from transits + RV
After the indirect detection of Hot Jupiters by RV, some doubts
persisted about the origin of these observations (Stellar
pulsations?). Transits showed unambiguously the planetary origin.
HD209458b: first measured transit
Charbonneau et al. 2000
- radius of planets: From transit measurements
- mass of planet: From radial velocity measurements
↓
↓
Example HD209458b (first transiting planet, :
R = 1.27 ± 0.02 RJ
3
ρ
=
0.40
g/cm
gaseous planet
M = 0.63 MJ
(Jupiter: 1.34)
Mass-radius relation
for extrasolar
planets
Transit detection from space
•Detection of planets with a radius of only a few Earth radii is very difficult form the ground, due
to the noise in the photometric data introduced by the atmosphere.
•To detect such planets photometrically, one must go to space.
Kepler candidates (Feb. 2011)
Launch: 2008
Launch: 2006
•Kepler has revolutionized the transit method
by finding more than 1200 candidates.
•Warning: maybe ~10% are false positives
(no RV confirmation)
5.3 Direct imaging
Direct imaging:massive giant planets far out
Fomalhaut b
HR 8799 b,c,d,e:
M≈ <3 MJ
d= 119 AU
M≈ 5-13 MJ
d= 15-70 AU
Dynamical constraints
Kalas et al. 2008
Marois et al. 2008
Beta Pictoris b
M≈ 6-12 MJ
d= 8 AU
Reappeared!
8 AU from star 6 – 12 MJ
Lagrange et al. 2008
Very special systems can be imaged from the ground today...
far from terrestrial planets!
Direct detection: (dis)advantages
• Advantages
• Allows physical characterization: Temperature, log
g, chemical composition
• Direct detection, no other explanations possible
(must exclude background star chance alignment.)
• Disadvantages
• Very difficult, only young objects. Huge
brightness contrast, tiny projected separation.
• Measures intrinsic (or reflected) luminosity L.
Not mass M. L-M relation is model dependent
and very uncertain.
Direct detection: resolution
Difficulty: Resolution
typical numbers:
stars ~ 10-100 pc, planet 1 AU
→ θ = 0.01’’- 0.1” (seeing limits to ~ 0.5”)
Solution:
→ use adaptive optics
Direct detection: brightness ratio
Difficulty: Brightness ratio
Typical numbers:
visible: Fplanet / Fstar ≈ 10-9
infrared: Fplanet / Fstar ≈ 10-6
visible to near-IR
reflected light
mid-IR
intrinsic emission
Solution:
→ remove star light
- nulling
- coronograph
Favorable cases:
infrared observations
planets orbiting less luminous stars
→ M dwarfs
young planets
→ planet formation
Other techniques: Microlensing, timing, astrometry
Questions?