Amateurs help find distant planet

Two amateur astronomers in Auckland have played a central role in the discovery of one of the most distant planets ever found, using a pioneering technique that might one day find a world similar to our own.

Astronomer Grant Christie, based in Epsom, and a colleague from Stardome Observatory, Jennie McCormick, who built her own observatory at her Pakuranga home, used telescopes plenty of serious space scientists would scoff at.

Mr Christie's is just 25cm in diameter, when some of the world's biggest are around 2m.

"It's cringingly and embarrassingly small but the detectors you can get now have greatly increased its power and I think that's been overlooked by some professional astronomers," Mr Christie said.

The planet was discovered by looking for the effect of its gravitational field on light from a more distant star, called "microlensing".

During a microlensing event, when both the "lensing" star and the star providing the light source are in alignment, the source star's light is magnified around 100 times.

The planet discovery team was made up of 33 astronomers around the world, including a Polish team based in Chile named the Optical Gravitational Lensing Experiment, or Ogle, and Ohio State University's Professor Andrew Gould, and is being hailed as a breakthrough for the microlensing technique.

"This is the beginning of the age of microlensing," said astronomer Scott Gaudi from America's Harvard-Smithsonian Centre for Astrophysics. "We expect many more discoveries."

It was Professor Gould, working half a world away, who tipped off the New Zealanders that an event was unfolding that might be worth keeping an eye on.

The Aucklanders spent six hours over five nights in April, proving the existence of "OGLE-2005-BLG-071".

Sophisticated computer and camera software allowed backyard astronomers to play a critical role in microlensing because the magnification through gravity meant even small telescopes could detect the "spike" in light intensity during an event.

But the technique has had its detractors and a microlensing event has been dismissed as luck by some astronomers.

"We have proved it's not just luck. We are now very confident we can use this method to find a lot more planets," Mr Christie said.

"It's gravity, not light, that's the essential thing."

The new planet, about 1000 times the mass of Earth, will be investigated over the next few weeks by the giant orbiting Hubble telescope.

* Since 1995 about 150 planets outside our solar system have been discovered.


Einstein and the bending of light

"Gravitational micro-lensing" uses Einstein's general theory of relativity, which showed the path of a beam of light will be bent by the gravity of a massive object.

Einstein showed that, if two stars were to line up exactly and be observed from Earth, the light of the more distant star would be significantly brighter as seen through the gravitational "lens" of the intervening star.

While Einstein realised the chance of looking at the right star at the right moment was minuscule, a Princeton University-based astronomer realised measuring the brightness of millions of stars every night would give a reasonable chance of detecting a gravitational lensing event - a bit like trying to win Lotto by taking more tickets. Scientists now watch hundreds of millions of stars, able to distinguish between naturally occurring light variations and a microlensing event.