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MOST Space Telescope Plays 'Hide & Seek' With An Exoplanet
Montreal QC (SPX) May 17, 2005 MOST, Canada's first space telescope, has turned up an important clue about the atmosphere and cloud cover of a mysterious planet around another star, by playing a cosmic game of `hide and seek' as that planet moves behind its parent star in its orbit. The exoplanet, with a name only an astrophysicist could love, HD209458b (orbiting the star HD209458a), cannot be seen directly in images, so the scientists on the MOST (Microvariability & Oscillations of Stars) Satellite Team have been using their space telescope to look for the dip in light when the planet disappears behind the star. "We can now say that this puzzling planet is less reflective than the gas giant Jupiter in our own Solar System," MOST Mission Scientist Dr. Jaymie Matthews announced today at the annual meeting of the Canadian Astronomical Society in Montreal. "This is telling us about the nature of this exoplanet's atmosphere, and even whether it has clouds." Many of the planets discovered around other stars, known as exoplanets or extrasolar planets, hug surprisingly close to their parent stars; HD209458b orbits at only 1/20th of the Earth-Sun distance (an Astronomical Unit or AU). It could never support life as we know it. But understanding HD209458b is a key piece in the puzzle of planet formation and evolution that is revising theories of our own Solar System, and estimates of how common are habitable worlds in our Galaxy. How a giant ball of gas that is larger than the planet Jupiter (which orbits 5 AU from our Sun) got so close to its star, and how its atmosphere responds to the powerful radiation and gravitation fields of that star, are still open questions to exoplanetary scientists. "The way this planet reflects light back to us from the star is sensitive to its atmospheric composition and temperature," describes Jason Rowe, a Ph.D. student at the University of British Columbia who processed the MOST data. "HD209458b is reflecting back to us less than 1/10,000th of the total visible light coming directly from the star. That means it reflects less than 30-40% of the light it receives from its star, which already eliminates many possible models for the exoplanetary atmosphere." By comparison, the planet Jupiter would reflect about 50% of the light in the wavelength range seen by MOST.
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