This article offers some new ideas for planet-hunting.
NASA Telescope Ferrets Out Planet-Hunting Targets
Astronomers have come up with a new way of identifying close, faint stars with NASA's Galaxy Evolution Explorer satellite. The technique should help in the hunt for planets that lie beyond our solar system, because nearby, hard-to-see stars could very well be home to the easiest-to-see alien planets.
The glare of bright, shining stars has frustrated most efforts at
visualizing distant worlds. So far, only a handful of distant planets,
exoplanets, have been directly imaged. Small, newborn stars are less
blinding, making the planets easier to see, but the fact that these
are dim means they are hard to find in the first place. Fortunately, the
young stars emit more ultraviolet light than their older counterparts,
makes them conspicuous to the ultraviolet-detecting Galaxy Evolution
"We've discovered a new technique of using ultraviolet light to search
young, low-mass stars near the Earth," said David Rodriguez, a graduate
student of astronomy at UCLA, and lead author of a recent study. "These
young stars make excellent targets for future direct imaging of
Tantrum-Throwing Baby Stars
Young stars, like human children, tend to be a bit unruly -- they spout
greater proportion of energetic X-rays and ultraviolet light than more
mature stars. In some cases, X-ray surveys can pick out these youngsters
to the "racket" they cause. However, many smaller, less "noisy" baby
perfect for exoplanet imaging studies have gone undetected except in the
most detailed X-ray surveys. To date, such surveys have covered only a
percentage of the sky.
Rodriguez and his team figured the Galaxy Evolution Explorer, which has
scanned about three-quarters of the sky in ultraviolet light, could fill
this gap. Astronomers compared readings from the telescope with optical
infrared data to look for the telltale signature of rambunctious junior
stars. Follow-up observations of 24 candidates identified in this manner
determined that 17 of the stars showed clear signs of youth, validating
"The Galaxy Evolution Explorer can readily select young, low-mass stars
are too faint to turn up in all-sky X-ray surveys, which makes the
an incredibly useful tool," Rodriguez said.
Cool, Red and in the Neighborhood
Astronomers call the low-mass stars in question "M-class" stars. Also
as red dwarfs, these stars glow a relatively cool crimson color compared
the hotter oranges and yellows of stars like our sun, and the whites and
blues of the most scorching stars. With data from the Galaxy Evolution
Explorer, astronomers could reap a bounty of these red dwarfs still in
cosmic youth, under 100 million years old.
In many ways, these stars represent a best-case scenario for the direct
imaging of exoplanets. They are close and in clear lines-of-sight, which
generally makes viewing easier. Their low mass means they are dimmer
heavier stars, so their light is less likely to mask the feeble light of
planet. And because they are young stars, their planets are freshly
and thus warmer and brighter than older planetary bodies.
The Better to See Planets With
So far, only a handful of the more than 500 exoplanets on record have
actually been "seen" by our ground- and space-based telescopes. The vast
majority of foreign worlds have instead turned up via indirect means.
common technique, for instance, relies on detecting the slight
"wobbles" exoplanets impart to their host stars. Another technique, the
"transit method," registers the tiny dip in a star's light as an
crosses in front of it relative to our vantage point. NASA's Kepler
in just its first four months of operations, has already come up with a
of more than 1,200 candidate exoplanets using the transit method.
At a very basic level, directly imaging an exoplanet is worthwhile
after all, "seeing is believing," Rodriguez said. But catching a glimpse
an exoplanet also opens up novel scientific avenues.
Direct imaging is well suited for seeing big planets circling host stars
considerable distances, comparable to Uranus and Neptune in our solar
system. Observing such arrangements is useful for testing concepts of
system evolution, Rodriguez said. Plus, gleaning details about the
atmospheres of imaged exoplanets is less difficult than indirectly
investigating worlds that transit their stars.
As for actually imaging clouds or surface features of exoplanets,
that will have to wait. Current images of exoplanets, while full of
information, resemble fuzzy dots. But as technology advances, ever more
information about our close-by planetary brethren will emerge.
Data from NASA's Wide-field Infrared Survey Explorer (WISE) mission
also reveal stars that would make good candidates for imaging planets.
all-sky maps will allow scientists to pick out nearby, young stars
surrounded by warm disks of planetary debris that glow with infrared
Such stars are similar to the ones where planets have already been
The new study was published in the February issue of The Astrophysical
Journal and includes co-authors Mike Bessell (Australian National
University), Ben Zuckerman (UCLA), and Joel Kastner (Rochester Institute
The California Institute of Technology in Pasadena leads the Galaxy
Evolution Explorer mission and is responsible for science operations and
data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena,
the mission and built the science instrument. Caltech manages JPL for
The mission was developed under NASA's Explorers Program managed by
Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by
University in South Korea and the Centre National d'Etudes Spatiales
in France collaborated on this mission.
More information on NASA's planet-hunting efforts is online at
Written by Adam Hadhazy
Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
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