Transcript No Slide Title

A Search for Habitable
Planets
NASA’s first mission to
detect
Earth-size planets
Launched March 6, 2009
orbiting in the
habitable zone
of sun-like stars.
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How many Earths?
A Search for Habitable
Planets
How many Earth-size planets
are in the habitable zone of
sun-like stars?
NASA’s Kepler
mission will
have an answer
to this
question!
By 2013 . . .
Credit NASA Goddard Space Flight Center
http://visibleearth.nasa.gov/
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What have we found?
The planets around other stars
discovered so far are closer in mass
to Jupiter.
A Search for Habitable
Planets
This is what
we’ve found
This is what we
are looking for
Jupiter’s diameter is eleven times greater than the Earth’s, and it
has over 300 times the mass.
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Scientists use the Radial Velocity or
“wobble” of a star to detect planets.
A Search for Habitable
Planets
If an unseen
planet tugs the
star back and
forth…
Astronomers can
detect these shifts
by very carefully
observing the
spectra (or colors)
of the stars.
This method has revealed many stars with
large planets, but is not quite sensitive
enough to detect Earth-size planets.
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Kepler detectsTransits!
Size of Jupiter:
1% area of the Sun (1/100)
A Search for Habitable
Planets
Size of Earth or Venus:
0.01% area of the Sun (1/10,000)
A transit occurs when a planet crosses the line of sight between an
observer and a star and blocks a small amount of light from the star,
causing the light from the star to dim slightly for a few hours.
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Stars are far away …
A Search for Habitable
Planets
Let’s move this star away . . .
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Stars are far away …
A Search for Habitable
Planets
.
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Stars are far away …
A Search for Habitable
Planets
. . .and farther . . .
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Stars are far away …
A Search for Habitable
Planets
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Stars are far away …
A Search for Habitable
Planets
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Stars are far away …
A Search for Habitable
Planets
. . .and farther
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Stars are far away …
A Search for Habitable
Planets
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Stars are far away …
A Search for Habitable
Planets
Stars are very far away.
We cannot see the planet cross in front of the star.
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Detecting Planets by Transits
A Search for Habitable
Planets
The Kepler Mission is designed to detect the
slight dimming of the star when an Earth-size
planet crosses between us and the star.
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Detecting Planets by Transits
Amount of light detected from the Star
A Search for Habitable
Planets
Earth-size planet?
Jupiter-size planet?
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System Orientation!
A Search for Habitable
Planets
For which of these star(s) will Kepler be able to detect transiting planets?
B
A
B.
The star’s planets must orbit the star
edge-on from our viewpoint!
Not all planetary orbits are aligned
this way . . . So we must watch
thousands of stars to find several that
are correctly oriented.
C
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Where are we looking?
A Search for Habitable
Planets
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What is Kepler doing?
A Search for Habitable
Planets
Launch: March 6, 2009
Continuously and simultaneously
monitoring about 100,000 stars
for at least four years in an area
10 by 10 degrees of sky.
To detect two or more orbits of
each planet orbiting in the
habitable zone of sun-like stars.
The probability that a planet in the
habitable zone is aligned properly to
transit the star is about 0.5%.
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A Search for Habitable
Planets
Its mission is to detect:
Earth-size planets
orbiting in the
habitable zone
of sun-like stars.
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Why “Earth-size” planets?
A Search for Habitable
Planets
If a planet is:
•
Too small (less than 1/2 the mass of Earth):
Earth
Mars
Not enough gravity to hold onto a lifesustaining atmosphere (like Mercury or Mars)
•
Too big (More than about 10 times the
mass of Earth):
Holds onto too much of the light gases
(hydrogen and helium) and turns into
a giant (like Jupiter or Neptune)
Jupiter
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What is the “Habitable Zone”?
A Search for Habitable
Planets
Where evidence of life might be detected across the vastness of space:
An orbit around a star where liquid water might exist on the
planet’s surface year-round.
Our Solar System
And its Habitable Zone
Another sun-like star and its planets.
Which planets are in its habitable zone?
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What is the “Habitable Zone” of a “sun-like” star?
A Search for Habitable
Planets
On a cold night, how close would you stand to be comfortable?
These different sized fires represent different sizes of stars.
More massive stars are hotter stars!
Mass determines temperature and lifetime of the star.
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What is the “Habitable Zone” of a “sun-like” star?
A Search for Habitable
Planets
Cool Red stars: Less than the mass of the Sun
Lifetime:
Many billions to trillions of years
Very small & close-in habitable zone
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What is the “Habitable Zone” of a “sun-like” star?
A Search for Habitable
Planets
SUN-LIKE:
Yellow/White Stars: 1 - 2 times mass of Sun
Lifetime:
Several billion years
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What is the “Habitable Zone” of a “sun-like” star?
A Search for Habitable
Planets
HOT BLUE Stars: 3 - 60+ times mass of Sun
Lifetime:
Several million years
Not enough time and too much
radiation for life to evolve!
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Comparative Life Zones of Stars
A Search for Habitable
Planets
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What else makes a planet “habitable”?
A Search for Habitable
Planets
Would it matter if you wore a light jacket?
How about a very heavy jacket?
It also matters if a planet has an atmosphere and
how thick that atmosphere is.
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What does an atmosphere do?
A Search for Habitable
Planets
TOO HOT!
“Sun”
Mercury is too
close to the Sun
TOO COLD!
Venus’s “coat”
is too heavy
Earth is
“just right”
Mars is too far
away and only
lightly dressed!
It also matters if a planet has an atmosphere
and how heavy that atmosphere is.
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How much of the Galaxy are we searching?
A Search for Habitable
Planets
Solar
System
here
Image credit: NASA, STScI
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How much of the Galaxy are we searching?
A Search for Habitable
Planets
Solar
System
here
Image credit: NASA, STScI
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How much of the Galaxy are we searching?
A Search for Habitable
Planets
THIS
MUCH !
Solar
System
here
Image credit: NASA, STScI
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How big an area is that?
Imagine, if you shrunk our solar system
to a little larger than a quarter:
Our whole Solar
System
Our Milky Way Galaxy
A Search for Habitable
Planets
Kepler Search Area
Kepler would be
searching an area
about the size of
Connecticut.
would be this big
would span North
America.
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What’s next?
A Search for Habitable
Planets
When Kepler detects a possible
Earth-size planet in the habitable
zone of a sun-like star . . .
Follow-up work is
done by other
methods to make
sure it’s really a
planet . . .
. . . and other
observations try
to detect
evidence of life!
Credit NASA Goddard Space Flight Center
http://visibleearth.nasa.gov/
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What else causes starlight to dim?
A Search for Habitable
Planets
Is it a planet that’s causing the star to dim?
It might be a variable star that, for various reasons,
normally gets brighter, then dimmer.
L
i
g
h
t
It might be an eclipsing binary: two stars orbiting each
other, one passing in front of the other one.
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What is evidence of life?
A Search for Habitable
Planets
Look for evidence
of oxygen
Look for liquid
water
Look for signs of
biological activity
(methane)
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More Information
NASA’s Kepler Mission:
Using transits
A Search for Habitable
Planets
to detect
Earth-size planets
orbiting in the
habitable zone
of sun-like stars.
Kepler web site: http://Kepler.NASA.gov/
© 1999 Lynette Cook, all rights reserved. 36