The Detection and Properties of Planetary Systems

Prof. Dr. Artie Hatzes

Artie Hatzes Tel:036427-863-51

Email: artie@tls-tautenburg.dewww.tls-tautenburg.de→Lehre→Vorlesungen→Jena

The Detection and Properties of Planetary Systems: Wed. 14-16 h

Hörsaal 2, Physik, Helmholz 5Prof. Dr. Artie Hatzes

The Formation and Evolution of Planetary Systems: Thurs. 14-16 h

Hörsaal 2, Physik, Helmholz 5Prof. Dr. Alexander Krivov

Exercises Wed. 12-14 and Thurs. 16-18 h

Seminarraum AIU, Schillergässchen 2Dr. Torsten Löhne

Detection and Properties of Planetary Systems

15. April Introduction22. April The Doppler Method29. April Results from Doppler Surveys I.29. April Results from Doppler Surveys II06. May The Transit Method from the Ground13. May The Transit Method from Space: Kepler and CoRoT13. May The Characterization of Planets20. May CoRoT-7: The first transiting terrestrial planet27. May Astrometry27. May Microlensing03. June Terrestrial Planets in the Habitable Zone10. June Future Space Missions or Direct Imaging17. 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 System1. Geocentric2. Heliocentric

2. Tour of Our Solar System3. Extrasolar Planets

1. Our expectations2. 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

In the Capellan model Mercury and Venus orbit the Sun, but the Sun and outer planets orbit the stationary Earth

• Martianus Capella (5th century)

• Paul Wittich (1546-1586)

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)

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?

Note: phases of Venus still compatible with Capellan model

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 good source for this is: www.nineplanets.org

and

solarsystem.nasa.gov

A quick tour of our solar system

Mercury

Distance: 0.38 AUPeriod: 0.23 yearsRadius: 0.38 RE

Mass: 0.055 ME

Density 5.43 gm/cm3 (second densest)Satellites: NoneStructure: Iron Core (~1900 km), silicate mantle (~500 km)Temperature: 90K – 700 KMagnetic Field: 1% EarthAtmosphere: Thin, bombarded by Solar Wind and constantly replenished

Venus

Distance: 0.72 AUPeriod: 0.61 yearsRadius: 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 mantleTemperature: 400 – 700 K (Greenhouse effect)Magnetic Field: None (due to slow rotation)Atmosphere: Mostly Carbon Dioxide

Magellan Radar Imaging

Pancake volcanoes

Sif Mons

Earth

Distance: 1.0 AU (1.5 ×1013 cm)Period: 1 yearRadius: 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 mantleTemperature: -85 to 58 C (mild Greenhouse effect)Magnetic Field: ModestAtmosphere: 77% Nitrogen, 21 % Oxygen , CO2, water

Mars

Distance: 1.5 AU Period: 1.87 yearsRadius: 0.53 RE

Mass: 0.11 ME

Density: 4.0 gm/cm3

Satellites: Phobos and DeimosStructure: Dense Core (~1700 km), rocky mantle, thin crustTemperature: -87 to -5 CMagnetic 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 yearsDiameter: 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 hydrogenTemperature: -148 CMagnetic Field: HugeAtmosphere: 90% Hydrogen, 10% Helium

The Oscillating Brown Oval(Hatzes et al. 1981)

Saturn

Distance: 9.54 AU Period: 29.47 yearsRadius: 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 JupiterTemperature: -178 CMagnetic Field: LargeAtmosphere: 75% Hydrogen, 25% Helium

Uranus

Distance: 19.2 AUPeriod: 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 hydrogenTemperature: -216 CMagnetic Field: Large and decenteredAtmosphere: 85% Hydrogen, 13% Helium, 2% Methane

HST Image

Voyager

Neptune

Distance: 30.06 AU Period: 164 yearsRadius: 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 CMagnetic Field: LargeAtmosphere: Hydrogen and Helium

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.

2006 IAU Definition of a Planet

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

8

Completing the Census: Satellites

Europa

Titan

Io

Triton

Planetary Rings

Saturn

Uranus

Jupiter

Neptune

5

Trans-Neptunian Objects

7

Name Radius (km)

Distance (AU)

Orcus 1100 39Ixion 980 40Huya 480 40Varuna 780 43Quaoar 1290 44Sedna 1800 486Pluto 2274 39.5

Plutoids

Comets

Why Search for Extrasolar Planets?

• How do planetary systems form?

• Is this a common or an infrequent event?

• 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!

• How unique are the properties of our own solar system?

Extrasolar Planets

"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."

Democritus (460-370 B.C.):

The Concept of Extrasolar Planets

Believed that the Universe was infinite and that other worlds exists. He was burned at the stake for his beliefs.

Giordano Bruno (1548-1600)

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.

• 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

Expectations of Exoplanetary Systems from our Solar System

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

1. 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.

2. 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.

3. 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).

IAU Working Definition of Exoplanet

In other words „A non-fusor in orbit around a fusor“

How to search for Exoplanets

1. Radial Velocity

2. Astrometry

3. Transits

4. Microlensing

Indirect Techniques

4. Spectroscopy/Photometry: Reflected or Radiated light

5. Imaging

Direct Techniques

Radial velocity measurements using the Doppler Wobble

The closer the planet, the higher the velocity amplitude: sensitive for near in planets

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

Radial Velocity measurements

Center of mass

= 8 mas at Cen1 mas at 10 pcs

Current limits:mas (ground)0.1 mas (HST)

• Since ~ 1/D can only look at nearby stars

Astrometric Measurements of Spatial Wobble

mM

aD

=

Jupiter only

1 milliarc-seconds for a Star at 10 parsecs

Microlensing

1.000.000.000 times fainter planet

4 Arcseconds

Separation = width of your hair at arms length

Direct Imaging: This is hard!

For large orbital radii it is easier

Transit Searches: Techniques

C5,C6,C8Imaging

Interferometry

Differential Imaging

-2.0 -1.5 -1.0 1.0 1.5 2.00.0-0.5 0.5

-2

-1.0

0.0

1.0

2.0Brown Dwarf

Jupiter

Saturn

Uranus

Log Semi-major axis (AU)

Earth

Log MJupiter

Microlensing

Astrometry

M5

M9

M7

Filling the parameter space requires ALL search techniques

A0

RV

M0

M6

G0

F3

A5

Astrometry w/interferometryM9

M5

M7

G2

COROT/KeplerDarwin

A0A5

M8

K5Transits

Another reason to search for exoplanets

To find another „blue dot“

The Earth as viewed from Voyager