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Extrasolar Planets and the Search for Other Earths
A drought of planetary discovery (until recently)
Why should we expect to find other worlds?
How we found the thousands of worlds we now “know”
Why we haven't yet seen another of these worlds
(maybe one or two)
How we WILL see them soon?
How UVa is involved?
Can we find other Earth-like worlds?
Will we be able to detect life elsewhere?
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A Legacy of Extrasolar Planetary Expectations
35+ years ago in a Galaxy close to home....
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Why Should We Expect to Find Other Planets?
Planetary system formation is a natural by-product of star formation
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Why Should We Expect to Find Other Planets?
The planets grew via “accretion” - a process common to all forming stars.
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Why Should We Expect to Find Other Planets?
We see stars forming elsewhere.
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Why Should We Expect to Find Other Planets?
These forming stars are surrounded by flattened disks of dust and gas.... just what we expect!
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So Where Are All of These Planets?
We live in a Galaxy, the Milky Way, that contains ~100 billion stars.
Until 1995 there was no direct evidence for planets outside of the Solar System!
Since we've been using telescopes since the early 1600's you would think it should have been easier.
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Hide and Seek?
Stellar “glare” hides the planets (which are more than a billion times fainter than their star) from view.
– - This unwanted light is a consequence of the starlight being diffracted by and scattering within the telescope.
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Hide and Seek?
Stellar “glare” hides the planets (which are more than a billion times fainter than their star) from view.
– - This unwanted light is a consequence of the starlight being diffracted by and scattering within the telescope.
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Two Indirect Detection Techniques
1) Doppler Wobble
The planet swings the star around as it orbits.
We measure the velocity of the star using the Doppler shift.
Binary
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Doppler Wobble
» Jupiter's motion displaces the Sun roughly by the Sun's diameter (once every 12 years - a Jupiter year)
» If viewed from a nearby star this motion is equivalent to reading the date on a dime held at a distance of 10 miles.
» This motion shifts the Sun's velocity by about 20 meters per second (the equivalent of the shift in the pitch of sound produced by an object moving at one inch every hour)
» This technique works best if
– - the planet is quite massive (super-Jupiters)
– - the planet is quite close to its star
• - big velocity shift and very short orbital period
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Two Indirect Detection Techniques
1) Doppler Wobble
The planet swings the star around as it orbits.
We measure the velocity of the star using the Doppler shift.
Inventory
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Two Indirect Detection Techniques
2) Transits
The planet dims the star as it passes in front.
Requires precise alignment – solar system must be seen “on edge”
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Two Indirect Detection Techniques
2) Transits
The planet dims the star as it passes in front.
Requires precise alignment – solar system must be seen “on edge”
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The Kepler Mission
Launched in March 2009, Kepler is monitoring more than 100,000 stars for planetary transits with the sensitivity to see “earths”.
Mission website
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The Kepler Mission
The stability of space-based observation is far superior to that achieved on the ground.
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The Kepler Mission
The stability of space-based observation is far superior to that achieved on the ground.
AnimationAnimation magnified
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Two Indirect Detection Techniques
2) Transits
Spectroscopy can reveal atmospheric composition.
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Two Indirect Detection Techniques
2) Transits
Spectroscopy can reveal atmospheric composition.
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Do these newly discovered worlds and solar systems fit in nicely with our knowledge of how the Solar System formed?
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Do “Roasters” Fit into the Planetary Formation Picture??
» A simple view of planetary formation suggests that Jupiters form out where our Jupiter resides.
– - the abundant inventory of ice is needed to grow a core quickly enough to grab onto gas.
» Roasters don't fit in - Super-Jupiters closer than our Mercury is to the Sun.
» Planetary migration has come to the rescue.
– “Jupiters” do form out at large distance but their interaction with the circumstellar disk draws them in close to the star.
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Multiple Planet Systems
Multiple planet systems found regularly.
Systems that more closely resemble the Solar System are out there.
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The Steps to finding an “Earth”
1) Find Earth SIZED planets
- Happening now, primarily with the Kepler Mission.
- A few dozen candidates – many more to come
2) Find Earth-sized planets in the HABITABLE ZONE
- Planets can't roast or freeze if they are to be hospitable to our sort of life
- Maybe there are 1 or 2 candidates in this category now.
3) Find ones that are Earth-LIKE
- Note the fundamental difference between saying “earth-sized” and “earth-like”
- Similar atmosphere, liquid water abundant, etc.
- We're at the brink of having the necessary technology.
- Need to see the planets DIRECTLY and analyze the spectrum of the light they reflect from their stars
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Finding Earth Sized Worlds with Kepler
Current missions, like Kepler, are finding earth-SIZED planets around other stars.
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Finding Earth-sized Worlds with Kepler?
Based on the distance from their stars, some of these planets orbit in the “habitable zone” - where temperatures are right for liquid water.
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Finding Earth-sized Worlds - in the Habitable Zone with Kepler
Based on the distance from its star, Kepler-22b orbits in the “habitable zone” - where temperatures are right for liquid water.
Link
Fanciful Artist's concept.... this world is most likely a gassy “Neptune”
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Direct Detection: Back to Hide and SeekStellar “glare” hides the planets (which are more than a billion times fainter than their star) from view.
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Infrared to the Rescue
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“Warm” Objects are Self-Luminous in the Infrared
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“Warm” Objects are Self-Luminous in the Infrared
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Hot things like Stars are dimmer...Infrared Improves Contrast
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Seeing the (Infrared) Light from Planets
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Direct Imaging of Infrared Luminous Planets
Fomalhaut b (visible)
HR 8799 b, c, and d (infrared)
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Diffraction and the Challenge of Direct Imaging
Passing light through any hole (a telescope) blurs the image.
The smaller the telescope the greater the blur.
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Diffraction and the Challenge of Direct Imaging
A planet may be millions of times fainter than the star it orbits.
Theory
Practice
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Interferometry to the Rescue
Diffraction is a fundamental limit for a single telescope, however, combining light from multiple telescopes adds a new dimension
one slit
two slits
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Enhancing Contrast with Interferometry
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The Large Binocular Telescope
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LMIRcam
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LMIRcam
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“Warm Jupiters”
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LMIRcam
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LMIRcam
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LMIRcam
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Will This Technology Reveal Other Earths?
Eventually....
Solar System “Family Portraits”
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The Key to Detecting Life from a Distance
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The Key to Detecting Life from a Distance
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The Next Step – The James Webb Space Telescope
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Ultimately
With several telescopes flying hundreds of kilometers apart and held in place to 1/100th the width of a human hair....
Imaging another Earth becomes a possibility but is at least 20-50 years away.
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