Kiwi astronomers help find first “cool” planet

Kiwi astronomers help find first “cool” planet

New Zealand researchers from Auckland, Canterbury, Massey and Victoria universities are part of a 12 country study that has discovered a new extrasolar planet about five times the mass of the Earth.

The planet is smaller than Neptune and is the first “cool” planet to be found.

The multi-national team includes Dr Denis Sullivan and PhD student Aarno Korpela from Victoria University and the discovery will be published this week in leading international science journal, Nature.

To find the planet the researchers used a technique called 'gravitational microlensing' which uses the gravitational fields of stars as huge naturally occurring lenses. This method was originally proposed by Albert Einstein but he thought that gravitational lenses would be too rare to be of practical value. The new generation electronic cameras (CCDs) and telescopes operated in survey mode have changed this.

Dr Sullivan says that the latest find brings the goal of locating a habitable planet outside our solar system a step closer.

"In the past decade, over 150 extrasolar planets have been discovered, including a few by the microlensing method, but all of them are gas giants like Jupiter or even Neptune and are in close orbits around their host star. Therefore they are much too hot to sustain life.

"Our new planet orbits a cool 'red dwarf' star at a distance about three times the distance between the Sun and Earth and has a temperature of about -220 C, which is too cold to sustain life. The planet will consist of rock and/or ice."

Dr Sullivan, who is a Reader in Victoria’s School of Chemical & Physical Sciences, says the future prospects for planet hunting by microlensing are very promising.

"Planets as small as Earth can be found now via gravitational microlensing and it surely is only a matter of time before one is found. Finding another Earth using the other techniques will have to wait for future planned space missions."

New Zealanders contributed in several ways to finding the planet, whose presence was revealed by a small one-day deviation away from the normal light amplification that occurs in a standard microlensing event. This event was detected by a Polish/US group called OGLE that operates a survey telescope in Chile, and their routine observations were later found to have data on the planet.

Drs Michael Albrow and Karen Pollard of the University of Canterbury are members of a large international microlensing group called PLANET/Robonet which operates a network of telescopes in Australia, South Africa, Chile and Hawai’i. The observer in Chile first detected the planetary signal and this was confirmed subsequently by the observer in Perth.

The NZ/Japan MOA group based in NZ also obtained data on the planet as part of their routine observations with the new Japanese-supplied telescope at Mt John in Canterbury. The MOA group includes Dr Ian Bond of Massey University, Professor John Hearnshaw of the University of Canterbury, Dr Sullivan and Associate Professor Philip Yock of the University of Auckland. Victoria PhD student Aarno Korpela contributed to the necessary computing-intensive modelling of the event using programs he has written to run on a computing grid engine at the university.

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