Transcript Alien Earths Floorplan (3,000 sq. ft) Major Exhibit Areas

The
Traveling Exhibit
Science Background
Part C: Planet Quest
prepared by Dr. Cherilynn Morrow for the Space Science Institute
Boulder, CO
C. Planet Quest
Are there planets orbiting distant stars where life could exist?
Could we see them so far away?
 For the first time in human history,
we have detected planets orbiting
distant stars.
 During the past decade, we have
discovered over 150 (and counting) of
these extra-solar planets.
 We do not generally “see” these
planets, but infer their presence using
clever techniques to observe how they
affect their parent stars.
 Almost all of these planets are like
the gas giant Jupiter rather than
Earth, but new missions are planned
to detect Earth-sized worlds.
Some planets were known to the ancients who
watched them move against the night sky.
Courtesy NASA’s Navigator Program
2
Mercury, Venus, Mars, Jupiter, and
Saturn were the “Wandering Stars.”
“Planet” comes from the Greek word for “wanderer.”
Courtesy NASA’s Navigator Program
Over the centuries, telescopes
got better and better…
Galileo and his Refractive Telescope, 1609
Herschel’s Reflecting Telescope, 1789
The Hooker Telescope Mount Wilson, ca 1920
Courtesy NASA’s Navigator Program
And other planets were “discovered.”
Uranus
The year 1781
The first planet “discovered.”
William and Caroline Herschel
Neptune The year 1846
First observed by Galle and d'Arrest
(based on calculations by Adams
and Le Verrier).
Pluto
The year 1930
Discovered by Clyde Tombaugh
Courtesy NASA’s Navigator Program
5
But what about more distant worlds? Thousands
of years ago, Greek philosophers speculated.
“There are infinite
worlds both like and
unlike this world of
ours...We must
believe that in all
worlds there are living
creatures and planets
and other things we
see in this world.”
Epicurius
c. 300 B.C
Courtesy NASA’s Navigator Program
And so did medieval
scholars.
The year 1584
"There are countless suns
and countless earths all
rotating around their suns in
exactly the same way as the
seven planets of our system
. . . The countless worlds in
the universe are no worse
and no less inhabited than
our Earth”
Giordano Bruno
in De L'infinito
Universo E Mondi
Courtesy NASA’s Navigator Program
4
In 1995, a breakthrough:
the first planet around another star.
Didier Queloz and Michel Mayor
A Swiss team discovers a planet – 51 Pegasi –
48 light years from Earth.
Courtesy NASA’s Navigator Program7
Artist's concept of an extrasolar planet (Greg Bacon, STScI)
Methods to Detect Planets
Spitzer, for the first time,
captured the light from two
known planets orbiting stars
other than our Sun. But so far,
most of the extra-solar
planets are being detected
using INDIRECT methods.
Artist Concept:
NASA’s Spitzer Infrared Telescope
Methods to Detect Planets
There are several complementary methods
for detecting planets orbiting distant stars.
Wobble
Doppler – detecting the star wobbling in the line of
sight due to the planet’s gravitational pull
Astrometry – detecting tiny wobble of stars
against other stars in the background.
Planet Transit – detecting a tiny drop in brightness
of the star as a planet passes in front
Coronograph – blotting out the light of the star so
planets can be “seen”
Transit
Coronograph
Astrometry
Inside the Planet Quest Area
Finding Planets Orbiting Distant Stars
An Atlas of
new worlds
discovered
Keeping count
of the new
planets being
discovered
Planet Transit
Coronograph
Star Wobble
16
Alien Earths:
Spin the wobbling
star-planet toys
When the child chooses two
wooden balls and spins them,
one ball does not orbit around
the center of the other ball.
Rather, each ball orbits around
a common center of mass or
balance point.
Which ball is more massive, blue or red?
If the balls have different
masses, the balance point
moves closer to the more
massive ball. The more
massive ball wobbles as the
less massive ball goes around
it.
Massive Planets Cause Stars to Wobble
• Stars and their planets also move
about the common center of mass.
• Since the mass of a star is so much
greater than the mass of a planet,
the “center of mass” (i.e. “balance
point”) is located close to (but not at
the center) of the parent star.
• This means that stars with planets
in orbit around them are not
stationary. Rather, they move slightly
about this balance point producing a
gravitational wobble!
• The gravitational wobble of the Sun
is dominated by the gravity of the
most massive planet Jupiter.
The animation illustrates a
planet's orbital affect on the
position of its parent star. The
effect is greatly exaggerated.
Star moving toward observer
(positive velocity)
far side
of orbit
near side
of orbit
Source of animation
Star moving away
http://astronautica.com/detect.htm
copyright 1997 Garber Astronautics
NASA’s SIM PlanetQuest Mission
Are there terrestrial planets orbiting nearby stars?
NASA’s SIM PlanetQuest
Mission will survey nearby
stars for Earth-size planets by
measuring the wobble of stars
against other stars in the
background.
Artist Conception: NASA’s SIM PlanetQuest
This method of detection is
called astrometry.
Scientists use the Doppler shift to measure the tug
of planets on stars. Here is how it works:
So far, nearly all extrasolar planets have
been discovered with
this technique
If an unseen
planet tugs the
star back and
forth…
Courtesy NASA’s Navigator Program
…the light from
the star shifts
slightly to the
red as the star
moves away
from you.
…and slightly to
the blue as it
moves toward
you.
Astronomers can
detect these shifts
by very carefully
observing the
spectra (or colors)
of the stars.
Detecting Planets: Transit Method
Kepler
Alien Earths:
Turn-the-Crank
Transit Device
Check out the dips in starlight
when a planet passes by!
NASA’s Kepler
mission will use
the transit method.
“Star”
Crank
“Planets”
Graphic data
When a planet passes by (or transits) a
star, we can detect a slight decrease in
the amount of light from the star.
NASA’s Kepler Mission
Are there planets orbiting distant stars where life could exist?
Could we see them so far away?
NASA’s Kepler Mission is
specifically designed to
survey our area of the Milky
Way Galaxy to detect and
characterize hundreds of
Earth-size and larger planets
in or near the habitable zone.
The “habitable zone”
encompasses the distances
from a star where liquid
water can exist on a planet's
surface.
Artist Conception: NASA’s Kepler Spacecraft
Coronograph: We will block out the bright light
from the star.
Telescopes that block the
light from the central star
can take images of planets
that might be in orbit around
them.
Keck Interferometer
The Keck Interferometer
Terrestrial Planet Finder will
combines the light of two 10search from space for planets
meter telescopes to take
as small as Earth and for
images of hot Jupiter-size
signs about whether they can
planets that shine bright in
support life.
infrared light.
The Terrestrial Planet Finder
Courtesy NASA’s Navigator Program
The Constellation of Orion
Using the Doppler method, two planets have been discovered
around a Sun-like star in Orion that can be seen with the naked eye!
Betelgeuse – red giant
Bellatrix – blue giant
HD 38529: Sun-like star
2 planets detected
Orion Nebula – star forming region
Rigel – massive blue giant
Artist’s Concept of the two planets in orbit around the star
called HD 38529 in the Orion Constellation (Lynette Cook)
NOTE: the giant worlds we are detecting in orbit around other stars
may well have moons (like Jupiter’s Europa) that might be habitable,
but we would not be able to detect their presence because they are so
small and distant.
Other Star Systems are Different
COMPARE
The orbits of planets
in our solar system
(dashed blue lines)
6 years
to orbit
the star
2 weeks
to orbit
TO
The orbits of the two
Jupiter-sized planets
detected in the star system
HD 38529
(solid blue & green lines)
WHAT DO YOU NOTICE?
The orbit of planet “b” is closer to its star than Mercury is to the Sun!
The orbit of planet “c” is more elliptical than Jupiter’s orbit.
C. Planet Quest
SUMMARY
For the first time in human history, we have detected
planets orbiting distant stars.
During the past decade, we have discovered over 150 (and
counting) of these extra-solar planets.
We do not generally “see” these planets, but infer their
presence using clever techniques to observe how they affect
their parent stars (e.g Doppler & Transit methods).
Almost all of these planets are like the gas giant Jupiter and
can have an important impact on whether there are
habitable planets in the system.
New missions are planned to detect Earth-sized worlds.