Scitech | Telescope scans the galaxy for Earth-like planets

Exoplanets detected using data from gravitational disturbances and luminosity

NASA recently launched the Kepler Mission, an initiative that will search for Earth-like planets in a northern constellation known as Cygnus over the next three and a half years. The mission began with the launch of its flagship telescope from Cape Canaveral Air Force Station, on March 6.

Astronomers did not find evidence of exoplanets – planets outside of our solar system – until the eighties. In 1988, a team of Canadian scientists working at the Canada-France-Hawaii Telescope published a paper in the Astrophysical Journal detailing their observations of a group of bright stars. The team claimed to have found a planet with a mass similar to that of Jupiter orbiting Gamma Cephei, a star approximately 45 light-years away.

At the time, the announcement was met with a great deal of surprise and scepticism. Previously, claims of exoplanet findings had turned out to be experimental mistakes, explains one of the paper’s authors, Gordon Walker, Professor Emeritus from the University of British Columbia.

“It was recognized that the observation was difficult to make,” said Walker.

Detecting an exoplanet is not an easy task and often must be done indirectly. Planets cause a very small gravitational disturbance on their parent star, where the star orbits a centre of mass between the two bodies. In our solar system, for example, Jupiter causes the Sun to orbit a point near the solar surface at a speed of 13 metres per second. By measuring these movements, astronomers can determine the characteristics of the planet causing them.

Due to limited precision, exoplanet discoveries have mostly been of large planets that have easily observable effects on their stars, explained Robert Lamontagne, a professor at the Université de Montréal.

“If you were an astronomer in another world [with our current technology], you would not be able to detect Earth,” he said.

The Kepler Telescope will change that, using another technique called differential photometry to detect exoplanets indirectly. Differential photometry allows astronomers to measure the changes in a star’s luminosity. Every time a planet orbits in front of its star, it creates a small, partial eclipse. Kepler detects these changes in luminosity and uses the information to calculate the mass and size of the planet.

The process will take some time, Walker explained, as the planet must complete several transits in front of its star before astronomers can confirm its existence.

“If you were looking to detect Earth, you would need to watch for three years,” Walker said.

Until very recently, the search for exoplanets generated little interest in academic circles. Walker explained that, after several bogus claims in the sixties, there was little appetite in the professional field for exoplanetary research.

“Some people felt that such an undertaking was not even a legitimate part of astronomy,” Walker said.

The Kepler Mission is merely one of several upcoming projects that are looking for exoplanets. For example, the European Space Agency plans to launch the Darwin Spacecraft in 2015 in order to detect and study exoplanets using infrared telescopes. This will allow analysis of the composition of the planet’s atmosphere, which could be an indicator of the presence of carbon-based life.

Three-hundred-and-forty-four exoplanets have been found to date, according to records kept by officials at the Paris Observatory. That number is only expected to increase as new telescopes are deployed in space, and as the technologies used for Earth-based observations progressively improve.

The discovery of an exoplanet capable of harbouring life would mark an enormous achievement in astronomy. Such an observation, Lamontagne remarked, would help determine how likely it is that life has arisen elsewhere in the universe.

“The answer will come within our lifetime,” he said.

The Kepler Mission will cost an estimated $600 million and will monitor approximately 100,000 stars in the Cygnus constellation.


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