Kiwi boffins bid up Earth-like planet prediction

We'll see your lousy 17 billion Earth-like planets, Smithsonian, and raise you 83 billion: that's the message coming out of a New Zealand group that's proposing a new detection technique in the Monthly Notices of the Royal Astronomical Society.

The Japan-New Zealand collaboration proposes using gravitational micro-lensing in combination with Kepler space telescope data to try and detect planets that are orbiting their stars at around double Earth-Sun distances.

As Dr Phil Yock from the University of Auckland's Department of Physics explains, previous estimates based on Kepler data of 17 billion Earth-like planets comes from detecting objects close to their parent stars.

“These planets are generally hotter than Earth, although some could be of a similar temperature (and therefore habitable) if they're orbiting a cool star called a red dwarf,” he says in a Royal Astronomical Society release.

“Our proposal is to measure the number of Earth-mass planets orbiting stars at distances typically twice the Sun-Earth distance. Our planets will therefore be cooler than the Earth. By interpolating between the Kepler and MOA results, we should get a good estimate of the number of Earth-like, habitable planets in the Galaxy. We anticipate a number in the order of 100 billion.”

Gravitational lensing is a phenomenon first predicted in Einstein's general theory of relativity: the bending of light caused by the gravity of a massive object between the light source and the observer. It's considerably easier to observe for very massive objects: Wikipedia notes that the first observation of lensing caused by galactic clusters was made in 1979.

Observing the micro-lensing caused by a planet orbiting a star is more challenging. Dr Yock's collaboration used microlensing data from the MOA (Microlensing Observations in Astrophysics) project at the Mt John Observatory in New Zealand. From this, the group carried out simulations and concluded that a linked network of Earthside optical telescopes would provide the sensitivity needed to turn up the cooler planets missed by Kepler.

Such a network is already being drawn together: the Las Cumbres Observatory Global Telescope Network, in collaboration with SUPA/St Andrews belonging to the Scotish Physics Alliance, will link three telescopes in Chile, three in South Africa, three in Australia, one in Hawaii, one in Texas, and the Liverpool Telescope in the Canary Islands owned and operated by Liverpool John Moores University. Supplemental data is expected to be provided by the MOA telescope at Mt John, Poland's OGLE telescope in Chile, and the Harlingten telescope in Tasmania. ®