a search for habitable planets 1 nasa’s first mission to detect earth-size planets orbiting in the...
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A Search for Habitable Planets
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NASA’s first mission to detect
Earth-size planets
orbiting in the habitable zone of sun-like stars.
Launched March 6, 2009
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How many Earths?
How many Earth-size planets are in the habitable
zone of sun-like stars?
Credit NASA Goddard Space Flight Center
http://visibleearth.nasa.gov/
By 2013 . . . NASA’s Kepler mission will
have an answer to this
question!
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Jupiter’s diameter is eleven times greater than the Earth’s, and it has over 300 times the mass.
This is what we are looking for
This is what we’ve found
What have we found?The planets around other stars discovered so far are closer in mass to Jupiter.
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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.
Scientists use the Radial Velocity or “wobble” of a star to detect planets.
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Size of Jupiter: 1% area of the Sun (1/100)
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.
Kepler detectsTransits!
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Let’s move this star away . . .
Stars are far away …
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.
Stars are far away …
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. . .and farther . . .
Stars are far away …
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Stars are far away …
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Stars are far away …
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Stars are far away …
. . .and farther
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Stars are far away …
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Stars are very far away.We cannot see the planet cross in front of the star.
Stars are far away …
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Detecting Planets by Transits
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 TransitsA
mou
nt o
f lig
ht d
etec
ted
from
the
Sta
r
Jupiter-size planet?
Earth-size planet?
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For which of these star(s) will Kepler be able to detect transiting planets?
A
B
C
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.
System Orientation!
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Where are we looking?
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What is Kepler doing?
Launch: March 6, 2009
Continuously and simultaneouslymonitoring about 100,000 stars for at least four years in an area 10 by 10 degrees of sky.
To detect two or more orbits ofeach 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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Its mission is to detect:
orbiting in the habitable zone of sun-like stars.
Earth-size planets
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Why “Earth-size” planets?
If a planet is:
• Too small (less than 1/2 the mass of Earth):
Not enough gravity to hold onto a life-sustaining 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)
Earth Mars
Jupiter
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What is the “Habitable Zone”?
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 Another sun-like star and its planets.Which planets are in its habitable
zone?And its Habitable Zone
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What is the “Habitable Zone” of a “sun-like” star?
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?
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?
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?
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
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What else makes a planet “habitable”?
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?
It also matters if a planet has an atmosphere
and how heavy that atmosphere is.
“Sun”
TOO HOT! TOO COLD!
Mercury is too close to the
Sun
Venus’s “coat” is too
heavy
Earth is “just right”
Mars is too far away and only lightly dressed!
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How much of the Galaxy are we searching?
Solar System
here
Image credit: NASA, STScI
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How much of the Galaxy are we searching?
Solar System
here
Image credit: NASA, STScI
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How much of the Galaxy are we searching?
Image credit: NASA, STScI
Solar System
here
THIS MUCH !
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Kepler would be searching an area about the size of Connecticut.
Kepler Search AreaOur whole Solar System
would be this big
Imagine, if you shrunk our solar system to a little larger than a quarter:
How big an area is that?
would span North America.
Our Milky Way Galaxy
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What’s next?
When Kepler detects a possible Earth-size planet in the
habitable zone of a sun-like star . . .
Credit NASA Goddard Space Flight Center
http://visibleearth.nasa.gov/
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!
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What else causes starlight to dim?
Is it a planet that’s causing the star to dim?
It might be an eclipsing binary: two stars orbiting each other, one passing in front of the other one.
It might be a variable star that, for various reasons, normally gets brighter, then dimmer.
Light
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What is evidence of life?
Look for evidence of oxygen
Look for liquid water
Look for signs of biological activity (methane)
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More Information
Kepler web site: http://Kepler.NASA.gov/
NASA’s Kepler Mission: Using
transits
orbiting in the habitable zone
of sun-like stars.
to detect Earth-size planets
© 1999 Lynette Cook, all rights reserved.