A PUBLICATION OF NASA’S “AMAZING SPACE ......Another step forward in the search for extrasolar...
Transcript of A PUBLICATION OF NASA’S “AMAZING SPACE ......Another step forward in the search for extrasolar...
20 Years of Exoplanets: The Search for Worlds Beyond Our Own
Special Feature
By NASA’s Amazing Space reporters October 2015
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Credit: ESO/M. Kornmesser/Nick Risinger (skysurvey.org)
A P U B L I C A T I O N O F N A S A ’ S “A M A Z I N G S P A C E ” E D U C A T I O N P R O G R A M
WITNESSSTARTHE
National Aeronautics and Space Administration
As fAr bAck As Ancient Greece, humans have
wondered whether other
solar systems might exist in the
universe. in about 300 bce, Greek
philosopher epicurus, for example,
proposed that the universe’s
boundaries were limitless and that
space was full of other worlds.
Another Greek astronomer of that
era, Aristarchus of samos, had
proposed that the sun was the center
of the solar system, and that the stars
might be other suns.
However, those ideas faded away,
and the earth-centered solar system
became the common belief in
astronomy for thousands of years.
the sun and the stars, it was thought,
orbited our planet. in 1543, Polish
astronomer nicolaus copernicus
developed the mathematics of the
Extrasolar planet at 51 Pegasi: This artist’s view shows a giant extrasolar planet orbiting the star 51 Pegasi, located 51 light-years from Earth. Astronomers using ground-based telescopes found the planet in 1995, marking the first extrasolar planet discovered around a star similar to our sun. The planet is roughly half the size of Jupiter and is orbiting dangerously close to its star.
sun-centered solar system and caused
a great shift in scientists’ view of
the universe. His work led to the
recognition that earth does indeed
orbit the sun and to the follow-on
speculation that other stars had
planets circling them.
the invention of the telescope in the
early 1600s put our solar system into
even clearer focus, revolutionizing
astronomy. Galileo was one of the
first to use the telescope to search
the heavens. Among his findings
was spotting the four largest moons
orbiting around Jupiter. Over the next
two centuries, bigger and sharper
telescopes allowed astronomers to
make more solar-system discoveries,
including finding the planets Uranus
and neptune orbiting the sun.
the early 1900s saw another large
leap in our understanding of earth’s
place in the universe. Using the
Hooker telescope — the largest
telescope of its day — at Mt. Wilson
Observatory in california, astronomer
edwin Hubble found that some
nebulae, such as the Andromeda
nebula, were separate galaxies like
our own Milky Way galaxy. because
each galaxy contains hundreds of
billions of stars, the potential for
other worlds orbiting other stars
vastly increased.
The hunt pays off
Until the 1990s, however,
astronomers had not found
any planets circling other suns.
Uncovering planets outside our
solar system, or extrasolar planets, is
extremely difficult because they are
too small, dim, and far away to be
directly imaged by telescopes. to find
them, astronomers had to develop
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other methods, such as detecting
their effects on their host star.
in 1995, astronomers using ground-
based telescopes finally nabbed an
extrasolar planet that was orbiting
a star similar to our sun. the planet
was roughly half the size of Jupiter
and was orbiting dangerously close
to its star, called 51 Pegasi. the
system is located about 51 light-years
from earth. (nAsA’s Jet Propulsion
Laboratory is commemorating the
20-year anniversary of the first
extrasolar planet discovery around
a sun-like star with several special
events.)
the planet detection around 51
Pegasi began a gush of extrasolar
planet discoveries. Astronomers
attributed the boost in discoveries
partly to improvements in
technology. significant improvements,
for example, were made in
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spectrometers, instruments that
separate starlight into its component
colors for analysis. spectrometers can
help astronomers detect extrasolar
planets and sample the chemical
elements in the planet’s atmosphere.
faster computers and more
sophisticated computer software also
helped astronomers readily identify
slight changes in light from stars to
find planets circling them.
Space missions boost the extrasolar planet count
At the start of the twenty-first
century, several dozen planets
outside our solar system had been
found using ground-based telescopes.
in 2006, scientists launched the
french corot mission, the first space
mission dedicated to the extrasolar
planet hunt. the mission helped
astronomers discover dozens more
extrasolar planets.
Earth Earth
Moon Moon
Mercury Mercury
VenusVenus SunSun
MarsMars
Jupiter Jupiter
EARTH-CENTERED SOLAR SYSTEM SUN-CENTERED SOLAR SYSTEM
Saturn Saturn
Earth Earth
Moon Moon
Mercury Mercury
VenusVenus
SunSun
MarsMars
Jupiter Jupiter
Saturn Saturn
Historical models of the solar system
Space Telescope Science Institute, Graphics Dept.
These simplified diagrams show an Earth-centered and a sun-centered solar system. In the ancient world, people thought that the sun and other objects orbited Earth (shown in the diagram at left). However, Polish astronomer Nicolaus Copernicus’ models of a sun-centered solar system (shown in the diagram at right) ignited a change in that thinking in 1543.
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Andromeda
Another step forward in the search
for extrasolar planets began with the
launch in 2009 of the kepler space
observatory, nAsA’s first extrasolar
mission. kepler’s goal was to search
hundreds of thousands of stars for
signs of planets.
the spacecraft has found a diverse
array of planets, including exotic,
multi-planet solar systems. More
importantly, kepler has found that
smaller planets (earth-sized rather
than Jupiter-sized) are likely to be
the most common in the Milky Way
galaxy. kepler uncovered several
planets that are about the same size
as earth and orbit within the star’s
habitable zone, where liquid water,
which is necessary for life, can exist.
Overall, kepler has added more
than 1,000 confirmed planets to the
extrasolar planet count, which now
stands at nearly 2,000.
Astronomers also have used nAsA’s
spitzer space telescope, which
observes in infrared light, to study
extrasolar planets. in 2007, the
spitzer telescope detected water
vapor for the first time on another
world.
Hubble contributes to the search
nAsA’s Hubble space telescope
has made some unique
contributions to the planet
hunt. Hubble made one of the
first visible-light images of an
extrasolar planet circling the
nearby, bright star fomalhaut,
located 25 light-years from earth.
the planet is orbiting about 10
times farther away from its star
than saturn is from the sun.
Hubble also helped astronomers
analyze the atmospheres of
extrasolar planets. Hubble made
the first measurements of the
makeup of the atmospheres
of two Jupiter-sized extrasolar
planets. the giant planets are
orbiting too close to their stars
and are therefore too hot for life.
but the Hubble observations
demonstrate that the basic
chemistry for life can be measured
on planets orbiting other stars.
even if a planet is rocky, earth-
sized, and just the right distance
from its star, it also must have
an atmosphere that contains the
correct ingredients to foster and
sustain life. Venus, for example, is
earth’s twin by size, but its dense
atmosphere is made up mostly of
carbon dioxide, which helps keep
the planet sizzling hot. Venus,
therefore, is not hospitable for life.
the distant worlds observed by
Hubble and other telescopes
are just the tip of the iceberg,
according to a Hubble survey of
the center of our Milky Way.
the study revealed that our
galaxy should be brimming with
Our Milky Way galaxy’s nearest large neighbor is the Andromeda galaxy, shown in this image. In the early 1900s, scientists generally thought that Andromeda was a nebula within our Milky Way. Astronomer Edwin Hubble’s observations in the 1920s revealed that Andromeda and other similar nebulae are separate galaxies like our own Milky Way galaxy.
Credit: Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF
see MOre Hubble images and read more
star Witness news stories at Amazing space,
nAsA’s award-winning educational website
for k-12 students and teachers. amazing-space.stsci.edu
www.nasa.gov
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100 billion planets, at least one planet
for every star.
The future looks bright
Within our own solar system,
astronomers are still learning new
information. nAsA’s new Horizons
mission, for example, was the first
spacecraft to visit Pluto in the outer
solar system. the spacecraft’s images
of Pluto show a surprisingly complex
world with giant ice mountains that
had never been seen before.
the study of worlds outside our solar
system will be continued by future
spacecraft, such as nAsA’s transiting
exoplanet survey satellite (tess)
and James Webb space telescope.
tess will find planets in the same
manner as kepler, but search stars
that are closer to our sun. the Webb
telescope will use infrared light to
examine in detail the extrasolar
planetary systems found by tess
and other telescopes. it will even
study the chemical makeup of an
extrasolar planet’s atmosphere. Who
knows what new discoveries these
observatories will uncover?
Looking to the far future, it is clear
that planets in the universe are really
just getting started. A new analysis
of data from Hubble and kepler
considers the expected rate of new
planet formation over the entire
predicted lifetime of our galaxy. Our
planet earth formed relatively early
in that context. About 90 percent of
the planets that ever will form are yet
to be born. With roughly 100 billion
planets in our galaxy, 100 billion
galaxies in the universe, and trillions
of years ahead, planet studies in the
universe have vast possibilities across
both space and time.
Credit: NASA, ESA, and G. Bacon (STScI)
Extrasolar planet HD 189733b: This artist’s illustration depicts extrasolar planet HD 189733b, with its parent star peeking above its top edge. Astronomers used the Hubble Space Telescope to detect methane and water vapor in the Jupiter-sized planet’s atmosphere. They made the finding by studying how light from the star filters through the planet’s atmosphere.