Results are in for the first search for Earth-sized planets using MOST, Canada’s suitcase-sized space telescope. UBC astronomer Jaymie Matthews will explain what has been “un-earthed” at the Jan. 11 American Astronomical Society (AAS) Meeting in Washington DC.

Taking advantage of the MOST (Microvariability & Oscillations of STars) satellite’s unique ability to measure minute changes in the brightness of stars, Matthews and other scientists from the team put a star 160 light years away under an astronomical “stakeout” to determine the existence of Earth-sized extrasolar planets — or exoplanets — that would escape detection by any other existing observatory.

MOST’s target was a Sun-like star called HD 209458, already known to have a giant planet 15 times the diameter of Earth and 220 times its mass. Named HD 209458b, the planet orbits its parent star extremely closely — at only 1/20th of the distance the Earth orbits the Sun.

By timing the regular faint dips in brightness as this planet passes in front of the star, the MOST team can detect the effects of the subtle gravitational tugs of other smaller planets that might be hiding in the system.

“We were able to rule out Earth-sized planets in some of the orbits where theorists believed they might be found,” says Matthews, lead mission scientist of MOST, a Canadian Space Agency mission.

The team’s analysis of reflected light signals of the planet is also ruling out many possible models of its atmosphere and cloud cover.

Likening the observations to making weather forecasts for a planet 160 light years away, Matthews says the job poses major challenges.

“Imagine trying to see a mosquito disappearing behind a 400-Watt streetlamp, not at the next street corner or a few blocks away, but 1,000 kilometers away,” says Matthews. “That’s equivalent to what we’re trying to do to detect the planet’s eclipse in the HD 209458 system.”

While the MOST team cannot yet rule out or detect Earth-like planets in larger orbits around HD 209458, as the data accumulate in the coming years, Matthews says MOST may be able to determine whether or not there are potentially habitable worlds around that star.

“Hugging so surprisingly close to its parent star, HD 209458b could never support life as we know it,” says Matthews. “But does it have any Earth-like neighbours at a more comfortable distance? That’s a question that no other observatory — on Earth or in space — can tackle at the moment, except MOST.”

MOST (Microvariability & Oscillations of STars) is a Canadian Space Agency mission. Dynacon Inc. of Mississauga, Ontario, is the prime contractor for the satellite and its operation, with the University of Toronto Institute for Aerospace Studies (UTIAS) as a major subcontractor. The University of British Columbia (UBC) is the main contractor for the instrument and scientific operations of the MOST mission. MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

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