Spitzer and Hubble Capture Evolving Planetary Systems
Two of NASA's Great Observatories, the Spitzer Space Telescope and
the Hubble Space Telescope, have provided astronomers an
unprecedented look at dusty planetary debris around stars the size of
Spitzer has discovered for the first time dusty discs around mature,
Sun-like stars known to have planets. Hubble captured the most
detailed image ever of a brighter disc circling a much younger Sun-
like star. The findings offer "snapshots" of the process by which our
own solar system evolved, from its dusty and chaotic beginnings to
its more settled present-day state.
Image left: This artist's concept depicts a distant hypothetical solar system, similar in age to our own. Looking inward from the system's outer fringes, a ring of dusty debris can be seen, and within it, planets circling a star the size of our Sun. This debris is all that remains of the planet-forming disk from which the planets evolved. Image credit: NASA/JPL-Caltech. + Click for larger image.
"Young stars have huge reservoirs of planet-building materials, while
older ones have only leftover piles of rubble. Hubble saw the
reservoirs and Spitzer, the rubble," said Dr. Charles Beichman of
NASA's Jet Propulsion Laboratory, Pasadena, Calif. He is lead author
of the Spitzer study. "This demonstrates how the two telescopes
complement each other," he added.
The young star observed by Hubble is 50 million to 250 million years
old. This is old enough to theoretically have gas planets, but young
enough that rocky planets like Earth may still be forming. The six
older stars studied by Spitzer average 4 billion years old, nearly
the same age as the Sun. They are known to have gas planets, and
rocky planets may also be present. Prior to these findings, rings of
planetary debris, or "debris discs," around stars the size of the Sun
had rarely been observed, because they are fainter and more difficult
to see than those around more massive stars.
Image right: This image from the Hubble Space Telescope is a false-color view of a planetary debris disk encircling the star HD 107146, a yellow dwarf star very similar to our Sun, though it is much younger (between 30 and 250 million years old, compared to the almost 5 billion years age of the Sun). The star is 88 light-years away from Earth. This is the only disk to have been imaged around a star so much like our own.
Image credit: NASA/STScI/JHU. + Click for larger image.
"The new Hubble image gives us the best look so far at reflected
light from a disc around a star the mass of the Sun," said Hubble
study lead author, Dr. David Ardila of the Johns Hopkins University,
Baltimore. "Basically, it shows one of the possible pasts of our own
solar system," he said.
Debris discs around older stars the same size and age as our Sun,
including those hosting known planets, are even harder to detect.
These discs are 10 to 100 times thinner than the ones around young
stars. Spitzer's highly sensitive infrared detectors were able to
sense their warm glow for the first time.
"Spitzer has established the first direct link between planets and
discs," Beichman said. "Now, we can study the relationship between
the two." These studies will help future planet-hunting missions,
including NASA's Terrestrial Planet Finder and the Space
Interferometry Mission, predict which stars have planets. Finding and
studying planets around other stars is a key goal of NASA's
Rocky planets arise out of large clouds of dust that envelop young
stars. Dust particles collide and stick together until a planet
eventually forms. Sometimes the accumulating bodies crash together
and shatter. Debris from these collisions collects into giant
doughnut-shaped discs, the centers of which may be carved out by
orbiting planets. With time, the discs fade and a smaller, stable
debris disc, like the comet-filled Kuiper Belt in our own solar
system, is all that is left.
The debris disc imaged by Hubble surrounds the Sun-like star called
HD 107146, located 88 light-years away. John Krist, a JPL astronomer,
also used Hubble to capture another disc around a smaller star, a red
dwarf called AU Microscopii, located 32 light-years away and only 12
million years old. The Hubble view reveals a gap in the disc, where
planets may have swept up dust and cleared a path. The disc around HD
107146 also has an inner gap.
Beichman and his colleagues at JPL and the University of Arizona,
Tucson, used Spitzer to scan 26 older Sun-like stars with known
planets, and found six with Kuiper Belt-like debris discs. The stars
range from 50 to 160 light-years away. Their discs are about 100
times fainter than those recently imaged by Hubble, and about 100
times brighter than the debris disc around the Sun. These discs are
also punctuated by holes at their centers.
Both Hubble images were taken with the advanced camera for surveys.
They will be published in the Astronomical Journal and the
Astrophysical Journal Letters. The Spitzer observations are from the
multiband imaging photometer and will appear in the Astrophysical
Journal. Electronic images and additional information are available
Donald Savage (202) 358-1727
Whitney Clavin (626) 395-1877
NASA's Jet Propulsion Laboratory
Ray Villard (410) 338-4514
Space Telescope Science Institute, Baltimore