Science: The truth About... Gravitational Microlensing
Friday 15 January 1999
Called "gravitational microlensing", this technique relies on the fact that light passing close to a massive object will be bent by a degree related to its mass. Exactly this method was used in 1919 to verify Einstein's theory of relativity. During a total solar eclipse, starlight that should have been hidden behind the Sun was actually visible, because it had been bent around the star's massive body by its gravity.
Microlensing, however, is a more subtle application of this effect. It requires two stars - a very distant one and a nearer one, around which the extrasolar planet revolves. When the distant star passes behind the nearer one, a ring of light is formed, as the distant star's light is equally bent around the nearer star's mass.
The diameter of this ring is measured in "arcseconds", subdivisions of a degree in a circle. But such events usually produce rings which are only micro-arcseconds in size; hence the name "microlensing", and typically last 40 days.
If the nearer star has a planet orbiting it, then there will be an extra peak in the microlensing ring's intensity, lasting perhaps a few hours for an Earth-sized planet. That was what the team observed.
Previously, extrasolar planets were detected - or their existence extrapolated - by examining the movements of stars for "wobble". This wobbling would be caused by massive objects moving elliptically around its parent star. But to induce enough wobble to be detectable from Earth, the planet had to be very big, and the star relatively close. Thus most of the 17 extrasolar planets so far identified lie less than 100 light years from Earth, and have masses at least as great as our own Jupiter - about 300 times greater than the Earth. They are unlikely candidates to foster life, as they are gas giants.
Microlensing, by contrast, can identify candidate stars thousands of light years away, and infer the existence of Earth-sized planets by the length of the peaks of intensity in the light emitted. The process can even be automated, and is the most effective method for detecting planets that range in mass up to 20 times that of Earth. Though the Search for Extraterrestrial Intelligence (Seti) has suggested putting systems into orbit which would watch stars for "transits" - the passage of a planet in front of a star - microlensing is accepted as the most effective tool available in the hunt for planets beyond our Solar System.
tv Review: Miranda Hart and co deliver the festive goods
tvReview: Older generation get hot under the collar this Christmas
comedy Erm...he seems to be back
tvReview: No ho-ho-hos with Nick Frost's badass Santa
tv Gymnast Louis Smith triumphed in the Christmas special
Film The critics but sneer but these unfashionable festive films are our favourites
TV We're so close to knowing what happened to Oliver Hughes, but a last-minute bluff crushes expectations
Arts & Ents blogs
- 1 The Boy in the Dress, TV review: David Walliams' Boxing Day treat is a celebration of being different
- 2 Exclusive: Abusers using spyware apps to monitor partners reaches 'epidemic proportions'
- 3 Andy Murray takes to Twitter to show off his Christmas jumper
- 4 Katie Hopkins speaks out on childhood obesity: 'Parents of fat children should be prosecuted for child cruelty'
- 5 Top 10 travel destinations for 2015: From Haiti and Alaska to Namibia and Iceland
Downton Abbey Christmas special 2014, review: Love is everywhere, actually
The Boy in the Dress, TV review: David Walliams' Boxing Day treat is a celebration of being different
The Interview finally gets US release after Sony hack and terror threats – but reviews of North Korea satire are mixed
Vagina canoe artist defends herself over ‘obscenity’ charges
Doctor Who Christmas special, review: No ho-ho-hos with Nick Frost's badass Santa
British actor Idris Elba cannot star as James Bond because he is black, says shock jock Rush Limbaugh
Rozanne Duncan: Ukip expels councillor for 'jaw-dropping' comments made in BBC TV interview
Germany anti-Islam protests: 17,000 march on Dresden against 'Islamification of the West'
Ukip member gets into Christmas spirit with Union Flag plea to Santa 'for our country back'
BBC director Danny Cohen: Rising UK antisemitism makes me feel more uncomfortable than ever
Katie Hopkins speaks out on childhood obesity: 'Parents of fat children should be prosecuted for child cruelty'