Thursday, October 22, 2009
The University of Colorado at Boulder and the National
Institute of Standards and Technology have been awarded a $495,000 grant to
look for Earth-like planets around other stars using technology based on 2005
Nobel Prize-winning research conducted at JILA, a joint institute of the two
Boulder institutions.
The funding from the National Science Foundation is to
develop a precise "laser ruler" to measure tiny changes in infrared
light caused by the gravitational wobble of small, cool stars as they are
tugged back and forth by their rocky planets. The gravitational dance depends
on the size of the star and the size of the planet and produces changes in the
star's radial velocity -- the speed it is moving toward or away from Earth
during such faint wobbles, said CU-Boulder Research Associate Steve Osterman,
principal investigator on the project.
While astronomers have used the radial wobble of stars to
detect several hundred planets outside our solar system, almost all have been
giant, gaseous planets orbiting extremely close to their parent stars, said
Osterman. The new technology involves devices known as mode-locked lasers that
deliver ultrashort pulses of infrared laser light less than a billionth of a
second long, enabling a much more precise planet detection system, he said.
Linked to an atomic clock, the laser ruler consists of
thousands of closely spaced "tick-marks" representing successive
infrared light frequencies that resemble the teeth of a comb, said NIST
scientist Scott Diddams, a co-investigator on the effort who is collaborating
with Osterman. The comb makes it possible to measure minute changes in the
light waves created by the motions of small, relatively cool M stars as they
interact with planets by providing a precise calibration for spectrographs that
analyze light coming from stars and planets.
The technique will allow the team to observe the stars in
the near-infrared spectrum where they shine the brightest, according to the
researchers.
The key to finding Earth-like planets is measuring the
Doppler shift of the stars as they wobble during planet interactions, said
Osterman. When a star is moving toward Earth, its wavelengths "bunch
up" and shorten, and when the star is moving away from Earth, the
wavelengths stretch out. By detecting extraordinarily faint wobbles, the
researchers should be able to deduce the size of the planets and the distance
of their orbit from the parent star, said Osterman.
"We have come up with a good ruler for measuring
changes in the wobble of these small stars in the near-infrared wavelength of
the spectrum," said Osterman of CU-Boulder's Center for Astrophysics and
Space Astronomy. "Since these M stars are much more common than larger
stars, this gives us a lot more targets and should make it easier for us to
detect rocky and perhaps even habitable planets."
The new technology was spun off from research by JILA's John
Hall and Theodor Hänsch of the Max Planck Institute of Quantum Optics in Munich, Germany,
who shared in the 2005 Nobel Prize in physics for their contributions to the
development of laser-based precision spectroscopy, including the optical
frequency comb technique.
Osterman said M stars can be as small as one-tenth the mass
and significantly older than Earth's sun. "We think our new calibration
technology will make it as much as 10 to 20 times easier to detect habitable
planets around these M stars," he said.
Astronomers are particularly interested in the habitable
zones of planets around other solar systems -- zones marked by relatively
moderate temperatures and which have the potential to host liquid water. While
at least one rocky planet slightly larger than Earth was recently identified by
a French-led team, it orbits so close to the parent star that high temperatures
and high radiation preclude the chances for life as we know it, said Osterman.
The Boulder researchers plan to take the new laser
instrument to the Apache Point Observatory northeast of Las Cruces, N.M., in
spring 2010 and integrate it with a new planet-finding instrument being
developed at the University of Florida, said Osterman. "This will begin
our search for Earth-like planets around these tiny stars."
CU-Boulder is part of a consortium of seven universities
that are conducting research using a 3.5-meter telescope at Apache Point
Observatory. CU-Boulder shares in the cost of operations and maintenance and is
annually allotted one-eighth of the available telescope observing time.
In addition to looking for Earth-like planets around
low-mass stars, the comb technology will allow researchers to peer through the
dust clouds of young stellar systems more clearly, said co-investigator John
Bally of CASA. The technology may make it possible to learn more about the
movements of massive, Jupiter-like planets in young planetary systems as they
migrate toward their parent stars, he said.
Other projects that will be made possible by the technology
include studies of the atmospheres of young or cool stars as well as precise
near-infrared observations of planetary atmospheres in our own solar system,
according to the team.
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