Australian National University astronomer Tom Evans is searching for planets outside our solar system. Evans, an Honours student based at Mount Stromlo Observatory in Canberra, is scrutinising stars in the southern constellation Lupus for signs of planets orbiting them.

Remote planets are invisible because, unlike stars, they do not generate light. However, they can be detected indirectly through their effect on light from their stars. Evans is using a relatively new method, photometric transiting, involving the detection of the tell-tale dimming of light from a star when a planet passes in front of it. He is using ANU’s 40-inch diameter optical telescope at Siding Spring, near Coonabarabran in northern NSW.

The telescope focuses light from the target star onto a sophisticated instrument called a charged coupled device, which measures the brightness over long periods. “Our team watches thousands of stars night after night, monitoring their brightness,” he says. “If a dip in the brightness occurs periodically, we can infer a planet might be responsible. “If we know the depth of the dip and some properties of the star itself, we can infer some properties of the planet, such as its radius.” And the astronomers can calculate the mass of the planet from the frequency of wobbles in the starlight caused by the planet’s gravitational tug. The mass of the planet and its radius give its mean density.

More than 300 extra-solar planets have been found since the first was discovered in 1995 orbiting the star in the constellation Pegasus. Just over 50 have been found so far using photometric transiting, a method still in its infancy but promising to be powerful.

Evans, a Novocastrian, gravitated to ANU to undertake a Bachelor of Philosophy (Honours) degree, a course designed to expose undergraduate students to research. He says the university’s reputation for research in astrophysics was a big attraction.

Currently, the photometric transiting method can only detect planets about as big as Jupiter, the biggest in our solar system, and which are in tight orbits around their stars. However, the technology is expected to improve, and Evans hopes to undertake a PhD using the method to detect smaller, Earth-like planets in work that would have implications for questions about extra-terrestrial life. The number of Earth-like extra-solar planets goes to the heart of the question of the likelihood of life on other worlds.