Why Should We Expect to Find Other Planets?
Planetary system formation is a natural by-product of star formation
Why Should We Expect to Find Other Planets?
Young stars are surrounded by accretion disks
Detecting Jupiter from Afar
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Consider our Solar System seen from a distance of 20 parsecs (a
distance large enough that from the Earth's perspective there would
be thousands of stars, and dozens of sun-like stars to examine).
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How separated (in an angular sense) would Jupiter be from our Sun.
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How bright would Jupiter be?
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How bright would the Sun be?
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Important numbers – There are 206265 AU in a parsec. The Earth is 1 AU from
the Sun, Jupiter is typically 5 AU from the Earth.
Detecting Jupiter from Afar
●
Consider our Solar System seen from a distance of 20 parsecs (a
distance large enough that from the Earth's perspective there would
be thousands of stars, and dozens of sun-like stars to examine).
●
How separated (in an angular sense) would Jupiter be from our Sun.
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How bright would Jupiter be?
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How bright would the Sun be?
Two Indirect Detection Techniques
1) Doppler Wobble
The planet swings the star around as it orbits.
We measure the velocity of the star spectroscopically via the Doppler shift.
Doppler Wobble
Jupiter's motion displaces the Sun roughly by the Sun's diameter (once
every 12 years - a Jupiter year)
How much will this affect the Sun’s velocity?
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
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.
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”
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”
The Kepler Mission
Launched in March 2009, Kepler is monitored 150,000 stars every 30
minutes for 4 years with the sensitivity to see “earths” transit their stars.
The Kepler Mission
The stability of space-based observation is far superior to that achieved
on the ground.
The Kepler Mission
The stability of space-based observation is far superior to that achieved
on the ground.
Transit Spectroscopy
2) Transits
Spectroscopy can reveal atmospheric composition.
Slide from a presentation by Heather Knutson (Caltech)
Slide from a presentation by Heather Knutson (Caltech)
Slide from a presentation by Heather Knutson (Caltech)
Slide from a presentation by Heather Knutson (Caltech)
Slide from a presentation by Heather Knutson (Caltech)
Seeing the (Infrared) Light from Planets
Slide from a presentation by Heather Knutson (Caltech)
Slide from a presentation by Heather Knutson (Caltech)
Do these newly discovered worlds and solar
systems fit in nicely with our knowledge of how the
Solar System formed?
Do Hot Jupiters Fit into the Planetary Formation
Picture??
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A simple view of planetary formation suggests that Jupiters form out
where our Jupiter resides.
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- the abundant inventory of ice is needed to grow a core quickly enough to
grab onto gas.
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Hot Jupiters don't fit in
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Planetary migration has come to the rescue.
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“Jupiters” do form out at large distance but their interaction with the
circumstellar disk draws them in close to the star.
Planetary Migration
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The distribution of discovered exoplanets, particularly the position of
Jupiter analogs is not consistent with our simple model of solar
system formation.
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Jupiters are supposed to form beyond the “ice line” at several astronomical
units.
Planetary migration is considered a viable mechanism for
substantially changing the orbital radii of planets.
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Angular momentum must always be conserved.
Planets couple to the disk mass, moving inward while disk material moves
outward.
Direct Detection: Back to Hide and Seek
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Stellar “glare” hides the planets (which are more than a billion times
fainter than their star) from view.
“Warm” Objects are Self-Luminous in the Infrared
“Warm” Objects are Self-Luminous in the Infrared
Infrared Improves Contrast
Direct Imaging of Infrared Luminous Planets
Fomalhaut b (visible)
HR 8799 b, c, and d (infrared)
Enhancing Contrast with Interferometry
The Large Binocular Telescope
Searching out “Warm Jupiters”
LMIRcam
Core Accretion or Gravitational Collapse
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There remains controversy as to whether giant planets form via
accretion (growth of an Earth-sized core which then accretes gas)
or via gravitational collapse.
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The first leads to a planet with a core, the second no.
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From its shape, we know Jupiter has a core.
Core Accretion or Gravitational Collapse
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There remains controversy as
to whether giant planets form
via accretion (growth of an
Earth-sized core which then
accretes gas) or via
gravitational collapse/instability.
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It is still possible giant planets in
other systems form via
gravitational collapse.
These “hot start” gravitationally
collapsed planets (dashed lines)
are luminous early on – providing,
ultimately, a way of differentiating.
Will This Technology Reveal Other Earths?
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Eventually....
Solar System
“Family Portraits”
Multiple Planet Systems
Multiple planet systems are found
regularly.
Systems that more closely resemble
the Solar System are out there.
The Steps to finding an “Earth”
1) Find Earth SIZED planets
- Happening now, primarily with the Kepler Mission.
- A few dozen candidates , some confirmed
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
- Now several confirmed.
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
Finding Earth-Sized Worlds with Kepler
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Current missions, like Kepler, are finding earth-SIZED planets around
other stars.
Kepler monitored 150,000 stars making precise measurements every
30 minutes for 4 years.
Finding Earth-sized Worlds with Kepler?
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Based on the distance from their stars, some of these planets orbit in
the “habitable zone” - where temperatures are right for liquid water.
http://www.pnas.org/content/early/2013/10/31/1319909110
Finding Earth-sized Worlds - in the Habitable Zone
with Kepler
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Based on the distance from its star, Kepler-22b orbits in the
“habitable zone” - where temperatures are right for liquid water.
Fanciful Artist's
concept.... this world is
most likely a gassy
“Neptune”
Kepler is no longer capable of precision photometric
measurement, but TESS will be launched in 2017.
The Next Step – The James Webb Space Telescope
The Key to Detecting Life from a Distance
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.