1. H205 Cosmic Origins
APOD
Today: Exoplanets
Begin EP7

2. Today’s Topics Planets around other stars
how do we find them
what are they like?
what kinds of stars have planets?
How likely it is that life exists elsewhere than Earth? (Drake Equation)
How would we detect life on other planets?

3. Our Solar System
Gas Giants
Terrestrial Planets
Ice Giants

4. Searching for Planets How are planets discovered?
More than 300 “extra-solar” planets have been discovered
How are planets discovered?
Radial velocity
Transits
Gravitational lensing
Wobbles in stars’ positions

5. Discovering Planets from Spectra
Remember the Doppler Shift!
Absorption lines shift left or right if stars move toward or away from us
Planetary orbits cause stars’ radial velocities to change

6. Periodic velocity changes due to orbiting planet
Velocity vs. Time
VERY high precision is needed to measure these very small velocity changes

7. A Planet around e Eridani
A planet orbits the sun-like star e Eridani at a radius of 3.2 A.U.
e Eridani is only 10.5 light years away
The planet is similar to Jupiter, 7 year period
e Eridani has at least one more planet

8. u And has at least 3 planets
terrestrial
planets

9. Planetary Transits The planet passes across the face of the star
If the Earth lies in the same plane as the orbit of a planet we see a transit
The planet passes across the face of the star
Some of the starlight is blocked by planet and the star appears dimmer

10. The Kepler Mission – Finding Terrestrial Planets
Launched March 6

11. Searching for Planet Transits
100,000 stars
3.5 years
Why Cygnus?
Cygnus is rich in stars
The Sun does not get in the way (Cygnus is far enough north of the plane of Earth' orbit (the ecliptic) that the Sun will not encroach on Kepler's view)

12. How does Kepler Work?

13. Kepler Science Goals What kinds of stars have planets?
What fraction of stars have planets have terrestrial and larger planets in or near the habitable zone?
What are their orbits?
How many planets do stars typically have?
Properties of planets (orbit sizes, planet reflectivities, sizes, masses densities)

14. Seeing planets near stars is hard
Looking for an Earthlike planet around a nearby star is like standing on the East Coast of the United States and looking for a pinhead on the West Coast — with a VERY bright grapefruit nearby
Very large telescopes will help
We like to use our scale model from ch. 1 to explain why it is so hard to look for Earthlike planets around other stars…

15. This photo shows an image of the faint star GQ Lupi taken in the infrared. The faint object to the right of the star is a possible planetary companion. It is 250 times fainter than the star itself and it located 0.73 arcsecond west. At the distance of GQ Lupi, this corresponds to a distance of roughly 100 astronomical units. The planet probably has a mass of about 2 x Jupiter.
Imaging Planets?

16. Another possible planet
Location
of brown
dwarf
Possible planet
Another possible planet
Orbiting the brown dwarf ~225 light years away
Young, about 1000K
Further from its “sun” than Pluto is from ours
(brown dwarf is blocked out)

17. Gemini CH4S Two of three confirmed planets
The central star has been blocked and appears blank in this image to increase visibility of the planets. 
Two of three confirmed planets
b: ~7 Jupiter-mass planet orbiting at ~70 AU
c: ~10 Jupiter-mass planet orbiting at ~40 AU

18. Fomalhaut’s Planet Distance 25 LY Constellation Piscis Australis
200 million years old
Fomalhaut will last about a billion years
Fomalhaut is hotter than our sun and 16 times brighter

19. Fomalhaut’s Planet IRAS found dust excess in the early 1980s
Hubble imaged a ring of protoplanetary debris 21.5 billion miles across with a sharp inner edge, similar to the Kuiper Belt
The ring is modified gravitationally by a planet lying inside the ring
Hubble imaged the planet - Fomalhaut b is 1 billion times fainter than the star
Observations taken 21 months apart show that the planet orbits 10.7 billion miles from the star, or about 10 times the distance of the planet Saturn from the sun, with an orbital period of 872 years
Fomalhaut b ~ 3 Jupiter masses

20. Properties of KNOWN Extra-Solar Planets
All are gas giants like Jupiter and Saturn
Most are larger than Jupiter
Many orbit close to their parent stars
Some are in systems with multiple planets

21. Known Planets Are Close to Stars

22. Hot Jupiters
These hot Jupiters form further out, and migrate inward as they eject smaller bodies from their planetary systems

23. Selection Effects Radial Velocity: Imaging – Far-out planets
Close-in, massive planets are easier to detect
Far-out planets and light-weight planets are MUCH HARDER to detect
So far, we’ve only been able to detect massive, close-in planets
Imaging – Far-out planets
Transits can detect terrestrial planets!

24. How Do Planets Form? Two models Core accretion Disk instabilities
Terrestrial planets
Gas giants
Disk instabilities
Far-out planets

25. Habitable Planets?
Too hot!
Too cold!
Just right!
The planet needs to be the right distance from the star - WHY?
The star needs to have the right mass - WHY?

26. A planet needs the right star!
Constraints on star systems:
Old enough to allow time for evolution (rules out high-mass stars - 1%)
Need to have stable orbits (might rule out binary/multiple star systems - 50%)
Size of “habitable zone”: region in which a planet of the right size could have liquid water on its surface.
First question in the search for habitable worlds is how many stars could be homes to life…
Even so… billions of stars in the Milky Way seem at least to offer the possibility of habitable worlds.

27. There are 400 Billion Stars in our Galaxy. How many harbor life?
You are
here
There are 400 Billion Stars in our Galaxy. How many harbor life?

28. How common is life of any kind in the Milky Way?
Very Rare Rare Common Very Common
How common is intelligent, technological life?
Very Rare Rare Common Very Common

29. Simulation of the spectra of 55 Cancri’s planets
Can we find life?
Simulation of the spectra of 55 Cancri’s planets
With a 30-meter
telescope we can
obtain the spectra
of planets around
other stars to search
for the signatures
of life
Simulation by Sudarsky
et al. 2003c

30. The Drake Equation Start with 1011 stars in the Milky Way…
What fraction of the stars are similar to the Sun?
What fraction of solar type stars have planets?
What fraction of solar type stars with planets have planets in the habitable zone?
On what fraction of these planets will life emerge?
On what fraction of these will intelligence emerge?
What fraction of these will develop technology?
What fraction of a star’s life will a technological civilization survive (assume a solar-type star remains on the main sequence for 1010 years)?

31. All stars in the Milky Way
The Drake Equation
What are the odds that there are intelligent, advanced, communicative civilizations out there? How many can we expect to exist in all of the Milky Way Galaxy?
All stars in the Milky Way
fraction with planets?
fraction in the habitable zone?
fraction with simple life?
with intelligence?
with technical society?
with long-lasting technology?
Make your own calculation of the number of intelligent, communicative, technologically advanced civilizations in the Milky Way.

32. We do not know the values for the Drake Equation
= NHP  flife  fciv  fnow
We do not know the values for the Drake Equation
NHP : probably billions.
flife : ??? Hard to say (near 0 or near 1)
fciv : ??? It took 4 billion years on Earth
fnow : ??? Can civilizations survive long-term?

33. Search for Extra-Terrestrial Intelligence
Emphasize that current SETI efforts could not detect signals as weak as our own radio/TV broadcasts. For now, at least, we are looking for deliberately broadcast signals..
SETI experiments look for deliberate signals from E.T.

34. Can We Find Extra-Terrestrial Intelligence?
Looking for SIGNALS is the easiest way
We can also transmit a signal (but it’s a long wait for the answer...)
Different kinds of signals to listen for:
local communication signals: on Earth, this includes TV, radio, etc.
communication between the planet and another site, such as satellites and spacecraft
A BEACON signal used to try to communicate with other civilizations.

35. Can Earth Be Heard from Space?
YES! Earth has been broadcasting TV and radio communications for the last 50 years. Is anyone listening?
We can “listen” but radio wavelengths may be best
Biggest collecting area - Arecibo telescope.
The background sky is the quietest at about 0.1 mm.
At shorter wavelengths, the galaxy is noisy
At longer wavelengths, interstellar clouds absorb signals

36. Message to M13 Nov 1974
Message was beamed from the Arecibo radio telescope
toward the M13 star cluster
24,000 light-years away
a 1679 (23 x 73) pulses and spaces
The message was transmitted only once and was intended to serve as a exercise in how we might go about trying to contact extra-terrestrials.

37. Message to M13 Formed a picture showing when arranged in a rectangle
numbers 1-10
elements, chemicals of life
a DNA molecule
a stick figure of a human
solar system
diagram of radio telescope

38. Searching for ET NASA funded SETI until 1993
Present efforts all privately funded
SETI Institute (Frank Drake)
-- help analyze SETI data
Planetary Society
META (million channel extraterrestrial assay) -- scans one million channels in the band
BETA (billion channel version of META)
84 ft. dish antenna at Harvard Univ.
connected to supercomputers that look for non-random patterns in the signals (most of the signals come from natural sources such as stars)
250 megabytes of data each second

39. Your computer can help! SETI @ Home: a screensaver with a purpose.
Optional:There’s a lot of data to sift though, and you can be a part of the effort… .
Your computer can help! Home: a screensaver with a purpose.

40. Visiting ET?
With foreseeable technology, we can achieve speeds of 10% of the speed of light
We can travel 10 light years in 100 years
We can reach the nearest star in 43 years
Allow each new colony 5000 years to duplicate the technology
Colonies could spread out about 50 light years every 25,000 years

41. How long to colonize? Assume 100,000 years per 20 parsec hop 30,000 pc
Total time to cover the
Galaxy:
1500 hops x 100,000 years
= 150,000,000 years

42. The Fermi Paradox Enrico Fermi Edward Teller Herbert York
Emil Konopinski
Emil Konopinski
LANL Tech Area
Enrico Fermi
LANL Fuller Lodge Cafeteria

43. The Fermi Paradox WHERE IS EVERYBODY?????
The Drake Equation – A few hundred technical civilizations
150,000,000 million years
to colonize the Galaxy
WHERE IS EVERYBODY?????

44. Where is Everyone?
Some factors in Drake equation may be much smaller than we believe – is life, or intelligent life, very rare?
Do civilizations hide to avoid a “galactic scourge?”
Do technological civilizations self-destruct?
Is no one more advanced than we are?
The Zoo hypothesis…

45. Possible solutions to the paradox
Civilizations are common but interstellar travel is not. Perhaps…
Interstellar travel more difficult than we think
Desire to explore is rare
Civilizations destroy themselves before achieving interstellar travel
These are all possibilities, but not very appealing…

46. Possible solutions to the paradox
We are alone: life/civilizations much rarer than we might have guessed.
Our own planet/civilization looks all the more precious…
OR - There IS a galactic civilization…
… and some day we’ll meet them…

47. Difficulties of Interstellar Travel
Far more efficient engines are needed
Energy requirements are enormous
If you discuss the difficulty of interstellar travel in any detail, you might wish to discuss the implications to UFOs; see box on p. 483.
Ordinary interstellar particles become like cosmic rays
Social complications of time dilation

48. Traveling to Another Star?
Distances between stars are much greater than we can imagine
Sci-fi books and movies have dramatized space travel to make it seem possible
Interstellar travel may never happen
Even the Voyager spacecraft (some of the fastest ever flown) traveled at only 20 km/s through space - not even 1% of the speed of light, they would take 60,000 years to reach even the nearest star

49. Maximum Speed Achieved
Space Shuttle
Plane
Automobile
Train
Horse

50. Can we travel to new worlds?
Within the lifetime of today’s children we will be able to send robotic spacecraft to visit our nearest neighbors
At 10% of the speed of light (30,000 km/sec) travel time will be about 100 years
Then wait another years for the data to return

51. For Wednesday The Origin of the Elements Finish EP7
Final Reflection due by 4:45 PM on Friday, May 8. Earlier submission is welcome!