Nobel-prize winning science from Boulder to serve as springboard for planet hunting

October 21, 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.

University of Colorado at Boulder

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