Download Detection and Properties of Planetary Systems

The Detection and Properties of
Planetary Systems
Prof. Dr. Artie Hatzes
Artie Hatzes
Tel:036427-863-51
Email: [email protected]
www.tls-tautenburg.de→Lehre→Vorlesungen→Jena
The Detection and Properties of Planetary Systems:
Wed. 14-16 h
Hörsaal 2, Physik, Helmholz 5
Prof. Dr. Artie Hatzes
The Formation and Evolution of Planetary Systems:
Thurs. 14-16 h
Hörsaal 2, Physik, Helmholz 5
Prof. Dr. Alexander Krivov
Exercises
Wed. 12-14 and Thurs. 16-18 h
Seminarraum AIU, Schillergässchen 2
Dr. Torsten Löhne
Detection and Properties of Planetary Systems
15. AprilIntroduction
22. AprilThe Doppler Method
29. April
Results from Doppler Surveys I.
29. April
Results from Doppler Surveys II
06. May
The Transit Method from the Ground
13. May
The Transit Method from Space: Kepler and CoRoT
13. May
The Characterization of Planets
20. May
CoRoT-7: The first transiting terrestrial planet
27. May
Astrometry
27. May
Microlensing
03. June
Terrestrial Planets in the Habitable Zone
10. June
Future Space Missions or Direct Imaging
17. June
Guest (TBD)
24. June
Guest (TBD)
Preliminary Program, subject to change, particularly on
„double“ lectures
Literature
Planet Quest, Ken Croswell (popular)
Extrasolar Planets, Stuart Clark (popular)
Extasolar Planets, eds. P. Cassen. T. Guillot, A.
Quirrenbach (advanced)
Planetary Systems: Formation, Evolution, and
Detection, F. Burke, J. Rahe, and E. Roettger (eds)
(1992: Pre-51 Peg)
Introduction Outline
1. Early Models of the Solar System
1. Geocentric
2. Heliocentric
2. Tour of Our Solar System
3. Extrasolar Planets
1. Our expectations
2. How do we find them?
The Geocentric Solar System
The Geocentric Solar System: Eudoxus
Eudoxus of Cnidus (410 -355
B.C.) developed the two sphere
model, a spherical Earth and a
spherical heavenly realm.
Each planet had its own
concentric sphere that rotated at
a different rate.
Problem: Could not predict
planet motions
Apollonius of Perga (262-190 B.C.): Epicycles
To account for the true motion of planets and to explain
retrograde motion Apollonius introduced epicyles
This could also explain
the changing brightness
of planets
Claudius Ptolemy (90-168 AD): The Ptolemaic System
In the Almagest he
extended the concepts
of the ancient Greeks
and Babylonians
The Ptolemaic System
dominated astronomical
thought until well into
the Renaissance
Capellan Geocentic Model
• Martianus Capella (5th century)
• Paul Wittich (1546-1586)
In the Capellan model
Mercury and Venus orbit the
Sun, but the Sun and outer
planets orbit the stationary
Earth
Tycho Brahe (1546-1601): The Tychonic Model
Proposed a more radical form of the Capellan system where all the other planets
orbit the sun, but the sun orbits the stationary earth. Reason: if the earth moved one
should observer stellar parallax, which he did not. In a sense, this combined the
Copernican and Ptolemaic systems
The Heliocentric Solar System
Aristarchus (310 – 230 B.C.)
• Believed that stars were infinitely far away and thus would
show no parallax
• Determined the diameter of the moon was about 4400 km
(actual 3500 km)
• Estimated the distance and size of the Sun (incorrectly, but due
to poor data)
• Proposed Heliocentric Model of the solar system
Copernicus (1473-1543)
First proposed a modern version of the heliocentric model. He
published this just before his death. Given the hostility of the
church, this was probably a good idea!
• Because Copernicus only used circular orbits he
could not reproduce the motion of the planets
• The Tychonic (Ptolemaic) System could because it
had more degrees of freedom.
• Purely on the basis of reproducing the observations
one would have to choose the Tychonic System over
the Copernican system
Support for the Copernican Model: Galileo (1564-1642)
Note: phases of Venus still compatible
with Capellan model
Galileo observed the phases of Venus which showed the
full set of phases. According to the Ptolemaic system,
only crescent phases could be observed. Strong support
of the geocentric model, but what about planet motion?
Kepler (1571-1630): Orbits Explained
Kepler was an assistant to Tycho and
used his observations to devise his
three laws that could explain all the
orbital motions of the planets.
1. The orbit of every planet is an ellipse and the
sun is at one focus
2. A line joining the planet and the sun sweeps out equal
areas during equal intervals of time (conservation of
angular momentum)
3. P2 = a3
Retrograde Motion Explained
Our Solar System Today
A quick tour of our solar system
A good source for this is: www.nineplanets.org
and
solarsystem.nasa.gov
Mercury
Distance: 0.38 AU
Period: 0.23 years
Radius: 0.38 RE
Mass: 0.055 ME
Density 5.43 gm/cm3 (second densest)
Satellites: None
Structure: Iron Core (~1900 km), silicate mantle (~500 km)
Temperature: 90K – 700 K
Magnetic Field: 1% Earth
Atmosphere: Thin, bombarded by Solar Wind and constantly
replenished
Venus
Distance: 0.72 AU
Period: 0.61 years
Radius: 0.94 RE
Mass: 0.82 ME
Density 5.4 gm/cm3
Satellites: None (1672 Cassini reported a companion)
Structure: Similar to Earth Iron Core (~3000 km), rocky mantle
Temperature: 400 – 700 K (Greenhouse effect)
Magnetic Field: None (due to slow rotation)
Atmosphere: Mostly Carbon Dioxide
Pancake volcanoes
Magellan Radar Imaging
Sif Mons
Earth
Distance: 1.0 AU (1.5 ×1013 cm)
Period: 1 year
Radius: 1 RE (6378 km)
Mass: 1 ME (5.97 ×1027 gm)
Density 5.50 gm/cm3 (densest)
Satellites: Moon (Sodium atmosphere)
Structure: Iron/Nickel Core (~5000 km), rocky mantle
Temperature: -85 to 58 C (mild Greenhouse effect)
Magnetic Field: Modest
Atmosphere: 77% Nitrogen, 21 % Oxygen , CO2, water
Mars
Distance: 1.5 AU
Period: 1.87 years
Radius: 0.53 RE
Mass: 0.11 ME
Density: 4.0 gm/cm3
Satellites: Phobos and Deimos
Structure: Dense Core (~1700 km), rocky mantle, thin crust
Temperature: -87 to -5 C
Magnetic Field: Weak and variable (some parts strong)
Atmosphere: 95% CO2, 3% Nitrogen, argon, traces of oxygen
Phobos
Deimos
Are believed
To be captured asteroids
Jupiter
Distance: 5.2 AU
Period: 11.9 years
Diameter: 11.2 RE (equatorial)
Mass: 318 ME
Density 1.24 gm/cm3
Satellites: > 20
Structure: Rocky Core of 10-13 ME, surrounded by liquid
metallic hydrogen
Temperature: -148 C
Magnetic Field: Huge
Atmosphere: 90% Hydrogen, 10% Helium
The Oscillating
Brown Oval
(Hatzes et al. 1981)
Saturn
Distance: 9.54 AU
Period: 29.47 years
Radius: 9.45 RE (equatorial) = 0.84 RJ
Mass: 95 ME (0.3 MJ)
Density 0.62 gm/cm3 (least dense)
Satellites: > 20
Structure: Similar to Jupiter
Temperature: -178 C
Magnetic Field: Large
Atmosphere: 75% Hydrogen, 25% Helium
Uranus
Distance: 19.2 AU
Period: 84 years
Radius: 4.0 RE (equatorial) = 0.36 RJ
Mass: 14.5 ME (0.05 MJ)
Density: 1.25 gm/cm3
Satellites: > 20
Structure: Rocky Core, Similar to Jupiter but without metallic
hydrogen
Temperature: -216 C
Magnetic Field: Large and decentered
Atmosphere: 85% Hydrogen, 13% Helium, 2% Methane
HST Image
Voyager
Neptune
Distance: 30.06 AU
Period: 164 years
Radius: 3.88 RE (equatorial) = 0.35 RJ
Mass: 17 ME (0.05 MJ)
Density: 1.6 gm/cm3 (second densest)
Satellites: 7
Structure: Rocky Core, no metallic Hydrogen (like Uranus)
Temperature: -214 C
Magnetic Field: Large
Atmosphere: Hydrogen and Helium
2006 IAU Definition of a Planet
1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic
equlibrium (a nearly round shape), and
3. has „cleared the neighborhood" around its orbit.
If a non-satellite body fulfills the first two criteria it is termed a
„dwarf planet“. Originally, the IAU wanted to consider all
dwarf planets as planets.
Under the new definition Pluto is no longer a planet, but rather a
dwarf planet.
9
Pluto before 2006
Pluto at the IAU 2006
Pluto today
Completing the Census: Satellites
8
Europa
Titan
Io
Triton
Planetary Rings
Jupiter
Saturn
Uranus
Neptune
Trans-Neptunian Objects
5
7
Plutoids
Name
Orcus
Ixion
Huya
Varuna
Quaoar
Sedna
Pluto
Radius
(km)
1100
980
480
780
1290
1800
2274
Distance
(AU)
39
40
40
43
44
486
39.5
Comets
Extrasolar Planets
Why Search for Extrasolar Planets?
• How do planetary systems form?
• Is this a common or an infrequent event?
• How unique are the properties of our own solar system?
• Are these qualities important for life to form?
Up until now we have had only one laboratory to test planet
formation theories. We need more!
The Concept of Extrasolar Planets
Democritus (460-370 B.C.):
"There are innumerable worlds which differ in size.
In some worlds there is no sun and moon, in others
they are larger than in our world, and in others more
numerous. They are destroyed by colliding with each
other. There are some worlds without any living
creatures, plants, or moisture."
Giordano Bruno (1548-1600)
Believed that the Universe was infinite and that other
worlds exists. He was burned at the stake for his
beliefs.
What kinds of explanetary systems do we expect to find?
The standard model of the
formation of the sun is that
it collapses under gravity
from a proto-cloud
Because of rotation it
collapses into a disk.
Jets and other mechanisms
provide a means to remove
angular momentum
The net result is you have a protoplanetary disk out
of which planets form.
Expectations of Exoplanetary Systems from our
Solar System
• Solar proto-planetary disk was viscous. Any
eccentric orbits would rapidly be damped out
– Exoplanets should be in circular orbits
• Giant planets need a lot of solid core to build up
sufficient mass to accrete an envelope. This core
should form beyond a so-called ice line at 3-5 AU
– Giant Planets should be found at distances > 3 AU
• Our solar system is dominated by Jupiter
– Exoplanetary systems should have one Jovian planet
• Only Terrestrial planets are found in inner regions
• Expect that satellites and rings to be common
So how do we define an extrasolar Planet?
We can simply use mass:
Star: Has sufficient mass to fuse hydrogen to helium.
M > 80 MJupiter
Brown Dwarf: Insufficient mass to ignite hydrogen, but
can undergo a period of Deuterium burning.
13 MJupiter < M < 80 MJupiter
Planet: Formation mechanism unknown, but insufficient
mass to ignite hydrogen or deuterium.
M < 13 MJupiter
IAU Working Definition of Exoplanet
1.
2.
3.
Objects with true masses below the limiting mass for
thermonuclear fusion of deuterium (currently calculated to be 13
Jupiter masses for objects of solar metallicity) that orbit stars or
stellar remnants are "planets" (no matter how they formed). The
minimum mass/size required for an extrasolar object to be
considered a planet should be the same as that used in our Solar
System.
Substellar objects with true masses above the limiting mass for
thermonuclear fusion of deuterium are "brown dwarfs", no matter
how they formed nor where they are located.
Free-floating objects in young star clusters with masses below the
limiting mass for thermonuclear fusion of deuterium are not
"planets", but are "sub-brown dwarfs" (or whatever name is most
appropriate).
In other words „A non-fusor in orbit around a fusor“
How to search for Exoplanets
Indirect Techniques
1.
Radial Velocity
2. Astrometry
3. Transits
4.
Microlensing
Direct Techniques
4. Spectroscopy/Photometry: Reflected or Radiated light
5. Imaging
Radial velocity measurements using the Doppler Wobble
The closer the planet, the higher the velocity
amplitude: sensitive for near in planets
Radial Velocity measurements
Requirements:
• Accuracy of better than 10 m/s
• Stability for at least 10 Years
Jupiter: 12 m/s, 11 years
Saturn: 3 m/s, 30 years
Astrometric Measurements of Spatial Wobble
Center of mass
q= m
M
a
D
2q
2q = 8 mas at a Cen
2q = 1 mas at 10 pcs
Current limits:
1-2 mas (ground)
0.1 mas (HST)
• Since D ~ 1/D can only look
at nearby stars
Jupiter only
1 milliarc-seconds for a Star
at 10 parsecs
Microlensing
Direct Imaging: This is hard!
1.000.000.000 times
fainter planet
4 Arcseconds
Separation = width of your hair at arms
length
For large orbital radii it is easier
Transit Searches: Techniques
Filling the parameter space requires ALL search techniques
2.0
Brown Dwarf
Interferometry
A0
1.0
C5,C6,C8
A5
A0
0.0
Log MJupiter
-1.0
Imaging
RV
F3
A5
Jupiter
Differential Imaging
M5
K5
Transits
Saturn
M7
Astrometry
G0 M9
M0
M8
Uranus
M6 G2
Darwin
M5
COROT/Kepler
-2
Microlensing
Earth
-2.0
M7
-1.5
-1.0
-0.5
0.0
M9
0.5
Astrometry
w/interferometry
1.0
Log Semi-major axis (AU)
1.5
2.0
Another reason to search for exoplanets
The Earth as viewed from
Voyager
To find another „blue dot“