GUEST SCIENCE BLOG Moon hunters

SFX ‘s sister magazine Science Uncovered looks at "exomoons" as a possible place we should be looking for extraterrestrial life

“We were looking for exoplanets using a technique called microlensing,” says Professor Daniel Bennett, an astronomer at the University of Notre Dame in the US. But using the technique, Bennett may have had the first ever glimpse of a moon outside our Solar System.

Microlensing is a method that exploits the fact that gravity bends light. If an object passes in front of a distant star, its gravity focuses the starlight like a lens and the star’s brightness temporarily shoots up. In recently published research, Bennett revealed that, using the MOA-II telescope in New Zealand, he’d seen a sharp rise in a star’s brightness, followed an hour later by a second, smaller increase. A large object must have passed in front of the star with a smaller object in tow, hence the second spike. Bennett was able to measure the mass ratio of the two objects and it came out close to 2000:1.

“The best fit to the data is a planet accompanied by a moon,” he says. There’s a catch, however. The spike only tells you the relative mass of the two objects. It’s impossible to tell whether the two objects are close to us or far away, and both scenarios would give the same result. If the objects are close, they are likely to be small – a planet and a moon. But if they are further away, they could be a small star and a big planet.

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