UH scientists seek planets to study
Smaller Earth-like planets, some perhaps even having conditions for life, might be detected by astronomers with improved techniques, University of Hawaii-Manoa researchers say.
"Detecting another 'Earth' around the 'sun' is still beyond our grasp," Eric Gaidos, associate professor in the Department of Geology and Geophysics and the NASA Astrobiology Institute, said in an e-mail. "But detecting somewhat bigger planets on closer orbits around smaller stars ... is becoming feasible."
New methods used to find planets also can be combined sometimes to estimate a planet's density, Gaidos said, "which will tell us whether the planet is composed mostly of rock and metal, like Earth, or something else such as water ice."
He was lead author of a paper recently reporting the findings in the journal Science. Co-authors were Nader Haghighipour, planetary researcher at the UH Institute for Astronomy and Astrobiology Institute, and Sean Raymond, NASA postdoctoral fellow, University of Colorado at Boulder.
"The discovery of another life-bearing planet would be a scientific triumph for humanity," Gaidos said, "but the study of many lifeless, un-Earthly worlds would nevertheless tell us about how planets form and help us appreciate the Earth all that much more."
More than 200 planets have been found around sunlike stars since the first one was reported by astronomers in 1995. All were believed to be "gas giants" composed mostly of hydrogen and helium like Jupiter and Saturn.
The most successful method for discovering planets so far spreads light from a host star into its wavelengths or colors, Gaidos said. "A shift in wavelength, analogous to the change in pitch of the horn of a passing automobile, reveals any motion of the star along the line of sight."
Another method is to observe a slight decrease in light from the star as an orbiting planet passes in front of it, the scientists said.
Gaidos said a planet the size of Jupiter blocks about 1 percent of the light of a star the size of the sun as it passes in front of it, but that small dimming is still detectable from the ground.
An Earth-size planet blocks one-hundredth of 1 percent of the light, and it is not detectable because of effects of the atmosphere, gravity and warming and cooling, he said.
Planets smaller than Jupiter could be found from telescopes such as those on Mauna Kea using the Doppler velocity technique, where the star moves back and forth due to the planet's gravitational force, he said.
Earth-size planets could be found by spacecraft.
Scientists can determine if a planet is partly composed of water and ice if they know how much light from the star it blocks, the star's diameter and estimated mass, Gaidos said.
Haghighipour, who did computer simulations, explained by e-mail: "Our Earth has a density 5.5 times that of liquid water and 6 times that of water ice. A planet with a density much less than that of the Earth, as is the case for the major satellites of Jupiter and Saturn, could be presumed to be partly composed of water ice.
"The origin of water in such planets is a major scientific question," Haghighipour added, noting the UH Astrobiology Institute is doing research to try to explain the conditions under which such planets might acquire water.