„Exoplanets and Extraterrestrial Life‘‘...dwarf planets as planets. Under the new definition...

AST s309L

„Exoplanets and Extraterrestrial Life‘‘Second Summer Session11 July – Aug 12, 2011M,T,W,Th,Fr 1:30-3:00 pm

RLM 15.216B

Michael EndlOffice: RLM 16.328

Tel: (512) 471 8312

Email: mike@astro.as.utexas.edu

http://austral.as.utexas.edu/michael/teaching/

Week 1:

July 11, Mon: "Introduction Part I: Exoplanets"July 12, Tue: "The Doppler Method: Technique"July 13, Wed: "The Doppler Method: Results"July 14, Thu: "Astrometry: Technique and Results"July 15, Fri: "Microlensing & Timing Method: Technique and Results"

Week 2:

July 18, Mon: "The Transit Method: Technique"July 19, Tue: "The Transit Method: Results"July 20, Wed: "Direct Imaging"July 21, Thu: "Exoplanet Atmospheres"July 22, Fri: "Exoplanet Host Stars"

Week 4:

Aug 1, Mon: "Introduction Part II: Extraterrestrial Life" Aug 2, Tue: "The Evolution of Life on Earth“Aug 3, Wed: "The Search and Prospects for Life on Mars“Aug 4, Thu: "The Outer Solar System and Beyond“Aug 5, Fri: "Terrestrial Planet Finder"

Week 3:

July 25, Mon: "Planets in Exotic Locations"July 26, Tue: "The CoRoT Mission"July 27, Wed: "The Kepler Mission"July 28, Thu: "Toward Other Earths"July 29, Fri: "Exam 1: Exoplanets"

Week 5:

Aug 8, Mon: "The Search For Extraterrestrial Intelligence (SETI)"Aug 9, Tue: TBAAug 10, Wed: TBAAug 11, Thu: TBAAug 12, Fri: "Exam 2: Extraterrestrial Life"

Literature:

Exoplanets:„Planet Quest“, Ken Croswell

„Toward Other Earths“, Alan Boss

„The Crowded Universe“, Alan Boss (2009)

Extraterrestrial Life:

„Lonely Planets“, David Grinspoon (2004)

„The Living Cosmos“, Chris Impey (2007)

„The Eerie Silence“ , Paul Davis (2010)

ResourcesThe Extrasolar Planet Encyclopaedia (Jean Schneider): www.exoplanet.eu (note www.exoplanets.eu sends you to the Geneva Planet Search Program)

• In 7 languages

• Tutorials

• Interactive catalog (radial velocity, transits, etc)

• On line histrograms and correlation plots

• Download data

Resources: The Nebraska Astronomy Applet Project (NAAP)

http://astro.unl.edu/naap/

This is the coolest astronomical website for learning basicastronomy that you will find. In it you can find:

1. Solar System Models 2. Basic Coordinates and Seasons3. The Rotating Sky4. Motions of the Sun 5. Planetary Orbit Simulator 6. Lunar Phase Simulator 7. Blackbody Curves & UBV Filters 8. Hydrogen Energy Levels 9. Hertzsprung-Russel Diagram 10. Eclipsing Binary Stars11. Atmospheric Retention 12. Extrasolar Planets13. Variable Star Photometry

ResourcesThe Nebraska Astronomy Applet: An Online

Laboratory for Astronomyhttp://astro.unl.edu/naap/http://astro.unl.edu/animationsLinks.html

Pertinent to Exoplanets:1. Influence of Planets on the Sun2. Radial Velocity Graph3. Transit Simulator4. Extrasolar Planet Radial Velocity Simulator5. Doppler Shift Simulator6. Pulsar Period simulator7. Hammer thrower comparison

For iPhone users there is a free exoplanet app

There are ~200 billion stars in our galaxy…

…one of them is our Sun.

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Are there other planets in the universe?

Is there another Earth out there?

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Some planets were known to the ancients who watched them move against the night sky.

Mercury, Venus, Mars, Jupiter, and Saturn were the “Wandering Stars.”

“Planet” comes from the Greek word for “wanderer.”

A quick tour of our solar system

A good source for this is:

http://www.nineplanets.org

and

http://solarsystem.nasa.gov

The Structure Of Our Planetary 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 constantlyreplenished

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 (massive Greenhouse effect)

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

Earth Moon System from Surveyorand Mars Express: The Double Planet

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

Phobos13 x 11 x 9 km

Deimos7.5 x 6 x 5 km

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

Aurorae on Jupiter

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 yearsRadius: 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 of giant planets)Satellites: 7 Structure: Rocky Core, no metallic Hydrogen (like Uranus)Temperature: -214 CMagnetic Field: LargeAtmosphere: 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.

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Pluto before 2006 Pluto at the IAU 2006 Pluto today

Completing the Census: Satellites

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Europa

Titan

Io

Triton

Planetary Rings

Jupiter

Saturn

Uranus

Neptune

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Trans-Neptunian Objects

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Plutoids

Name Radius (km)

Distance (AU)

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

Comets

Debris Disks

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 othersthey are larger than in our world, and in others morenumerous. They are destroyed by colliding with eachother. There are some worlds without any livingcreatures, plants, or moisture."

Giordano Bruno (1548-1600)

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

What kinds of explanetary systems do we expect to find?

The standard model of theformation of the sun is thatit collapses under gravityfrom a proto-cloud

Because of rotation itcollapses into a disk.

Jets and other mechanismsprovide a means to removeangular momentum

The net result is you have a protoplanetary disk out of which planets form.

The net result is you have a protoplanetary disk out of which planets form (mostly) by a process called

accretion.

Expectations of Exoplanetary Systems from ourSolar System

• Solar proto-planetary disk was viscous. Anyeccentric 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 coreshould 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?There is no official IAU definition of an exoplanet.

We can simply use mass:

Star: Has sufficient mass to fuse hydrogen to helium.M > 80 MJupiter

Brown Dwarf: Insufficient mass to ignite hydrogen, butcan undergo a period of Deuterium burning.

13 MJupiter < M < 80 MJupiter

Planet: Formation mechanism unknown, but insufficientmass to ignite hydrogen or deuterium.

M < 13 MJupiter

IAU Working Definition of Exoplanet

1. Objects with true masses below the limiting mass forthermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars orstellar remnants are "planets" (no matter how they formed). Theminimum mass/size required for an extrasolar object to beconsidered a planet should be the same as that used in our Solar System.

2. Substellar objects with true masses above the limiting mass forthermonuclear 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 thelimiting mass for thermonuclear fusion of deuterium are not"planets", but are "sub-brown dwarfs" (or whatever name is mostappropriate).

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

How to search for Exoplanets

1. Radial Velocity (or Doppler Method)

2. Astrometry

3. Transits

4. Microlensing

Indirect Techniques

4. Spectroscopy/Photometry: Reflected or Radiated light

5. Imaging

Direct Techniques