Homework 8

Due: Monday, Nov. 28, 9:00 pm,

Exam 2: Weds., Nov. 30

Remember:

attendance is mandatory next week.

Searching for Exoplanets…

What have we found?

As of November 27, 2011, 704 extrasolar planets have been detected and confirmed (increase of 200 in one year). The Kepler spacecraft has discovered over 1200 candidate objects; estimates are that ~ 50% of these are planets.

Discovery technique Planets

Radial velocity 650

Astrometry 4

Microlensing 13

Imaging 29

Transit 186

http://exoplanet.eu/Note that some exoplanets have been discovered/confirmed uasing multiple methods

Keep in mind that we are exploring only the nearby neighborhood.

would be the size of the United States.

Our Milky Way Galaxy

where we’ve found new planets would only be the size of Manhattan.

And the neighborhoodOur whole Solar System

would be this big

if you shrunk our solar system to the size of a quarter:

Extrasolar Planets The rate of discovery is increasing rapidly.

Extrasolar Planets Most orbit stars with masses similar to or less than the Sun.

http://exoplanet.eu/

Extrasolar Planets Most of these planets have masses similar to, or

somewhat less than, the Jovian planets.

http://exoplanet.eu/

MEarth

(x-axis is logarithmic)

Extrasolar Planets Most of these planets are close to their central star.

http://exoplanet.eu/Note: x-axis is logarithmic

Extrasolar Planets Most have short periods. These are most easily found.

http://exoplanet.eu/Note: x-axis is logarithmic

Results consistent with at least 40% of Sun-like stars having at least one low-mass planet.

The majority of planets with masses greater than Neptune appear to reside in systems with multiple planets.

If the results to date are typical, then there are

~ 15,000,000,000 low mass planets in Milky Way!

~ 3,000,000,000,000,000,000,000 in Universe!

If the goal is to find planets with evidence of life, most of those discovered so far are not good candidates.

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Most are gas giants like Jupiter or Saturn and in the wrong location.

The right location in our solar system (habitable zone).

Most of them have highly elliptical orbits, or are too close to their parent stars.

Many of the new planets get too hot or too cold to support life.

Too hot! Too cold!Just right!

Kepler and other planned missions will change of of this.

Too hot! Too cold!Just right!

Habitable Zone Planets464 known as of November 27, 2011

http://www.hzgallery.org

Habitable Zone Planets

http://www.hzgallery.org

Habitable Zone Planets Known exoplanets that spend at least a portion of their orbit in the Habitable

Zone (464 total). Size of points represents the fraction of time spent in the HZ – largest points are planets that reside full time in the HZ.

http://www.hzgallery.org

“Super-Earths” An extrasolar planet that is somewhat more massive than the Earth but less than ~ 10 Earth masses: ~20 known.

Kepler-10b

Gliese 581 g Mass ~ 3 - 4 Earth Masses Radius ~ 1.5 x Earth In habitable zone May have liquid water on surface Orbits a red dwarf Period = 37 days May have magnetosphere Needs confirming observations Probably tidally locked

LIFE?

How will we know if a planet can support life?

Look for evidence of oxygen

Look for liquid water

Analyze the reflected light from the planet to see if the planet has an atmosphere

Look for signs of biological activity (methane)

and rule out other explanations.17

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Now the hunt for Earth-like planets really blasts off…

…on the ground and in space.

Keck Interferometer

Spitzer Space Telescope

SIM PlanetQuest

KeplerLarge Binocular Telescope Interferometer

Terrestrial Planet Finders

We shall not cease from exploration And the end of all our exploring Will be to arrive where we started And know the place for the first time.

T.S. Eliot Four Quartets

Group Activity

Organize your groups in the usual manner.

Life on a synchronously rotating planet

Planets in the Habitable Zone of M stars are likely to rotate synchronously with their orbit. Computer simulations suggest that on a synchronously rotating planet with a thick atmosphere, winds will carry heat from the side constantly facing the star to the back, dark side. If this is correct, there would be a ring-like zone between the light and dark halves of the planet that might be habitable.

Life on a synchronously rotating planet

What kind of adaptations would you expect for life in this zone? Explain.

Speculate on what life might be like on such a planet. Let your imagination run free!