A rare Earth-like planet has been detected in a "one-in-a-million" discovery by New Zealand researchers.

The astronomers at the University of Canterbury said the "Super-Earth" planet was one of only a handful that had been found with a size and orbit comparable to Earth.

The planet's mass was somewhere between that of Earth and Neptune. It orbited a host star which was about 10 per cent the mass of our sun.

Its smaller host star meant the planet would have a year of 617 days.


One of the lead researchers, Dr Antonio Herrera Martin, said it was an incredibly rare discovery.

"To have an idea of the rarity of the detection, the time it took to observe the magnification due to the host star was approximately five days, while the planet was detected only during a small five-hour distortion.

"After confirming this was indeed caused by another 'body' different from the star, and not an instrumental error, we proceeded to obtain the characteristics of the star-planet system," he said.

It was found using a technique called gravitational microlensing, when barely perceptible objects brighten stars which they pass in front of.

"The combined gravity of the planet and its host star caused the light from a more distant background star to be magnified in a particular way," said Herrera Martin.

"We used telescopes distributed around the world to measure the light-bending effect."

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Around one in a million stars in the galaxy are affected by microlensing at any one time, making the chance of such a discovery very rare.


"Furthermore, this type of observation does not repeat, and the probabilities of catching a planet at the same time are extremely low."

The event was first observed in 2018 through a Chilean telescope and was given the name OGLE-2018-BLG-0677.

The planet orbited a host star which was about a tenth the size of the sun. Photo / 123rf
The planet orbited a host star which was about a tenth the size of the sun. Photo / 123rf

It was then detected by three identical telescopes in Chile, Australia and South Africa, which were capable of measuring the light output from 100 million stars every 15 minutes.

"These experiments detect around 3000 microlensing events each year, the majority of which are due to lensing by single stars," said astronomer and lead researcher Michael Albrow.

"Dr Herrera Martin first noticed that there was an unusual shape to the light output from this event, and undertook months of computational analysis that resulted in the conclusion that this event was due to a star with a low-mass planet."

The researchers collaborated with an international team to make the finding, and the research was published in the Astronomical Journal.