Download Lecture23 - Indiana University Astronomy

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
Note that some exoplanets have been
discovered/confirmed uasing multiple
http://exoplanet.eu/
Keep in mind that we are exploring only the
nearby neighborhood.
if you shrunk our solar system to the size of a quarter:
Our whole Solar
System
Our Milky Way Galaxy
would be this big
would be the size of
the United States.
And the neighborhood
where we’ve found new
planets would only be
the size of Manhattan.
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.
MEarth
(x-axis is logarithmic)
http://exoplanet.eu/
Extrasolar Planets
Most of these planets are close to their central star.
Note: x-axis is logarithmic
http://exoplanet.eu/
Extrasolar Planets
Most have short periods. These are most easily found.
Note: x-axis is logarithmic
http://exoplanet.eu/
Results consistent with at least 40% of Sunlike 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.
Most are gas giants like Jupiter or Saturn and in
the wrong location.
The right location in our solar system
(habitable zone).
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Many of the new planets get too
hot or too cold to support life.
Too hot!
Just right!
Too cold!
Most of them have highly elliptical
orbits, or are too close to their
parent stars.
Kepler and other planned missions
will change of of this.
Too hot!
Just right!
Too cold!
Habitable Zone Planets
464 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
Analyze the reflected
light from the planet
to see if the planet
has an atmosphere
Look for liquid
water
Look for signs of
biological activity
(methane)
and rule out other explanations.
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Now the hunt for Earth-like
planets really blasts off…
Keck Interferometer
Large Binocular Telescope Interferometer
Kepler
Spitzer Space Telescope
…on the
ground
and in
space.
SIM PlanetQuest
Terrestrial Planet Finders
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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!