From: baalke@zagami.jpl.nasa.gov   
      
   Research Communications   
   Ohio State University   
      
   Contact:   
   Andrew Gould, (614) 292-1892; Gould.34@osu.edu   
      
   Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu   
      
   August 1, 2003   
      
   STUDY: SEARCH FOR LIFE COULD INCLUDE PLANETS, STARS UNLIKE OURS   
      
   COLUMBUS, Ohio -- The search for life on other planets could soon extend to   
   solar systems that are very different from our own, according to a new study by   
   an Ohio State University astronomer and his colleagues.   
      
   In fact, finding a terrestrial planet in such a solar system would offer unique   
   scientific opportunities to test evolution, said Andrew Gould, professor of   
   astronomy here.   
      
   In a recent issue of Astrophysical Journal Letters, he and his coauthors   
   calculated that NASA's upcoming Space Interferometry Mission (SIM) would be   
   able   
   to detect habitable planets near stars significantly more massive than the sun.   
      
   Scientists have typically thought that the search for life should focus on   
   finding planets like Earth that orbit stars like the sun, but this new finding   
   shows that "the field is wide open," Gould said.   
      
   "Here's a type of solar system that we never thought to look at," he added,   
   "but   
   now we'll have the tools to do it."   
      
   Gould is on the science team that is helping to plan the SIM mission, and he is   
   working to define the capabilities of the satellite.   
      
   The satellite was set to launch in 2009, but its fate is now uncertain. NASA is   
   considering whether to divert funds to maintain the Hubble Space Telescope   
   beyond its scheduled retirement in 2010, Gould explained, and he has been asked   
   to address the issue for an assembly of astronomers in Washington D.C. on   
   Thursday, July 31.   
      
   SIM would help astronomers find habitable planets, Gould said. The key is   
   detecting planets that circle a star at just the right distance to maintain a   
   supply of liquid water. The range of most promising orbits depends on the type   
   of the star, and is called the "habitable zone."   
      
   The earth resides directly in the habitable zone for our solar system, some 93   
   million miles from the sun. The nearest planets, Venus and Mars, barely lie   
   within the edges of the habitable zone.   
      
   Hotter, more massive stars have always been considered less likely to harbor   
   life, though not because they would be too hot. Planets could still enjoy   
   temperate climates, just at orbits farther away from the star.   
      
   The problem is one of time, not temperature, Gould said.   
      
   Hotter stars tend to "burn out" faster -- perhaps too fast for life to develop   
   there.   
      
   Our sun is approximately 4.5 billion years old; in contrast, one of the stars   
   examined in the study is 1.5 times more massive than the sun, and would   
   probably   
   only generate life-sustaining energy for about two billion years.   
      
   Given the billions of years required for evolution of life on earth, scientists   
   could question whether life would stand a chance in a shorter-lived solar   
   system.   
      
   "We have no idea how evolution would proceed on any planet other than our own,"   
   Gould said. "If we find a planet around a shorter-lived star, we may be able to   
   test what would happen to evolution under those circumstances."   
      
   SIM will use Interferometry -- a technique that involves the interference of   
   light waves -- to very accurately measure the position of stars in the sky. The   
   satellite would notice, for instance, if a point of light on the surface of the   
   moon moved the width of a dime.   
      
   In the case of distant stars, SIM will pick up on the tiny wobble in the   
   position of a star caused by the gravity of its orbiting planets.   
      
   That's what will make SIM ideal for studying hotter, massive stars, Gould said.   
   Planets that orbit far from a star -- as the habitable planets around a hot   
   star   
   would have to do -- create a larger wobble.   
      
   He and study coauthors Eric B. Ford of Princeton University and Debra A.   
   Fischer   
   of the University of California, Berkeley, determined that SIM is sensitive   
   enough for the task.   
      
   Previously, Gould and Ohio State professor Darren DePoy and graduate student   
   Joshua Pepper determined that another future NASA mission could be used to find   
   habitable planets around very small stars, which are much more plentiful in the   
   galaxy than stars like our sun.   
      
   That mission, the Kepler Mission, will detect planetary transits -- events   
   where   
   planets pass in front of a star and block the star's light from reaching earth.   
   Transits of planets orbiting close to a star are easier to detect, and because   
   these small stars are very dim, the habitable zone would also be very close to   
   the star.   
      
   "The point is that the various methods for planet detection complement each   
   other, and can be used to find habitable planets around a wide variety of   
   stars," Gould said.   
      
   NASA funded this research.   
      
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