NASA's Spitzer Marks Beginning of New Age of Planetary Science
NASA's Spitzer Space Telescope has for the first time captured the
light from two known planets orbiting stars other than our Sun. The
findings mark the beginning of a new age of planetary science, in
which "extrasolar" planets can be directly measured and compared.
"Spitzer has provided us with a powerful new tool for learning about
the temperatures, atmospheres and orbits of planets hundreds of
light-years from Earth," said Dr. Drake Deming of NASA's Goddard
Space Flight Center, Greenbelt, Md., lead author of a new study on
one of the planets.
Image above: This artist's concept shows what a fiery hot star and its close-knit planetary companion might look like close up if viewed in visible (left) and infrared light. In visible light, a star shines brightly, overwhelming the little light that is reflected by its planets. In infrared, a star is less blinding, and its planet perks up with a fiery glow. Image credit: NASA/JPL-Caltech.
More images and animations are available at http://www.spitzer.caltech.edu/Media.
+ Video: Spitzer Sees Light of Distant Planet (closed caption)
"It's fantastic," said Dr. David Charbonneau of the Harvard-
Smithsonian Center for Astrophysics, Cambridge, Mass., lead author
of a separate study on a different planet. "We've been hunting for
this light for almost 10 years, ever since extrasolar planets were
first discovered." The Deming paper appears today in Nature's online
publication; the Charbonneau paper will be published in an upcoming
issue of the Astrophysical Journal.
So far, all confirmed extrasolar planets, including the two recently
observed by Spitzer, have been discovered indirectly, mainly by the
"wobble" technique and more recently, the "transit" technique. In
the first method, a planet is detected by the gravitational tug it
exerts on its parent star, which makes the star wobble. In the
second, a planet's presence is inferred when it passes in front of
its star, causing the star to dim, or blink. Both strategies use
visible-light telescopes and indirectly reveal the mass and size of
In the new studies, Spitzer has directly observed the warm infrared
glows of two previously detected "hot Jupiter" planets, designated
HD 209458b and TrES-1. Hot Jupiters are extrasolar gas giants that
zip closely around their parent stars. From their toasty orbits,
they soak up ample starlight and shine brightly in infrared
To distinguish this planet glow from that of the fiery hot stars,
the astronomers used a simple trick. First, they used Spitzer to
collect the total infrared light from both the stars and planets.
Then, when the planets dipped behind the stars as part of their
regular orbit, the astronomers measured the infrared light coming
from just the stars. This pinpointed exactly how much infrared light
belonged to the planets. "In visible light, the glare of the star
completely overwhelms the glimmer of light reflected by the planet,"
said Charbonneau. "In infrared, the star-planet contrast is more
favorable because the planet emits its own light."
The Spitzer data told the astronomers that both planets are at least
a steaming 1,000 Kelvin (727 degrees Celsius, 1340 Fahrenheit).
These measurements confirm that hot Jupiters are indeed hot.
Upcoming Spitzer observations using a range of infrared wavelengths
are expected to provide more information about the planets' winds
and atmospheric compositions.
The findings also reawaken a mystery that some astronomers had laid
to rest. Planet HD 209458b is unusually puffy, or large for its
mass, which some scientists thought was the result of an unseen
planet's gravitational pull. If this theory had been correct, HD
209458b would have a non-circular orbit. Spitzer discovered that the
planet does in fact follow a circular path. "We're back to square
one," said Dr. Sara Seager, Carnegie Institution of Washington,
Washington, co-author of the Deming paper. "For us theorists,
Spitzer is ideally suited for studying extrasolar planets known to
transit, or cross, stars the size of our Sun out to distances of 500
light-years. Of the seven known transiting planets, only the two
mentioned here meet those criteria. As more are discovered, Spitzer
will be able to collect their light - a bonus for the observatory,
considering it was not originally designed to see extrasolar
planets. NASA's future Terrestrial Planet Finder coronagraph, set to
launch in 2016, will be able to directly image extrasolar planets as
small as Earth.
Shortly after its discovery in 1999, HD 209458b became the first
planet detected via the transit method. That result came from two
teams, one led by Charbonneau. TrES-1 was found via the transit
method in 2004 as part of the NASA-funded Trans-Atlantic Exoplanet
Survey, a ground-based telescope program established in part by
Artist's concepts and additional information about the Spitzer Space
Telescope are available at http://www.spitzer.caltech.edu/Media
Whitney Clavin (818) 354-4673
NASA's Jet Propulsion Laboratory
Dolores Beasley (202) 358-1753