Scientists have discovered 7 new planets just like Earth, and there's a high possibility that life exists on them.
It could be the best chance yet of finding life on other worlds - seven Earth-sized planets, some likely with oceans, have been found orbiting a dwarf star.
The find will have astronomers and stargazers excited, with the details of the spectacular discovery made public in a NASA announcement on Thursday morning (NZ time).
In May last year, Michael Gillon of Université de Liège, Belgium, and a number of colleagues found three of the exoplanets in the Aquarius constellation orbiting an ultracool dwarf star called TRAPPIST-1 around 39 light years from our own solar system.
That spurred their interest, leading them to discover four other planets nearby.
They've imaginatively been called TRAPPIST-1b, c, d, e, f, g and h in order of how far they are from their parent star.
Six of the inner planets are thought to be rocky planets of a similar mass to Earth, with possible temperatures between 0 to 100 degC.
But their comparatively small star means their 'years' are also much shorter than ours - between 1.5 and 13 days.
Research co-author Amaury Triaud says the small amount of energy coming from the star is a lot weaker than our Sun, meaning the planets need to be far closer than in our Solar System for surface water to exist.
"Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1," he says.
The team used ground and space-based telescopes to watch the transits of the planets around TRAPPIST-1 to help estimate their masses.
Dips in the star's light caused by each of the planets passing in front of it give scientists an idea of their sizes, compositions and orbits.
- TRAPPIST-1 is just 8 percent the size of our Sun and is marginally bigger than Jupiter.
- TRAPPIST-1b, c and d are probably too hot to support water, except possibly in small parts, climate models suggests.
- TRAPPIST-1e, f and g are in the 'Goldilocks zone' meaning they're not too hot or cold to have oceans.
- TRAPPIST-1h's orbital distance is unconfirmed, but is likely to be too cold and too far to hold liquid water.
The findings will prove important for astronomers, with new generations of telescopes such as the European Southern Observatory's Extremely Large Telescope and the James Webb Space Telescope able to search for signs of water.
Leiden University professor of observational astrophysics Ignas Snellen, who was not involved in the discovery, says while the authors may have been lucky to come across such a find in the vast expanse of space, it indicates such planets and systems are "even more common than previously thought".
He said it was possible that for every transiting planet found, there could be 20 to 100 times more which never pass in front of their host star.
As for life on those planets, Prof Snellen says a definitive answer may not come in our lifetime.
"Could any of the planets harbour life? We simply do not know. But one thing is certain: in a few billion years, when the Sun has run out of fuel and the Solar System has ceased to exist, TRAPPIST-1 will still be only an infant star.
"It burns hydrogen so slowly that it will live for another 10 trillion years - more than 700 times longer than the universe has existed so far, which is arguably enough time for life to evolve," he wrote in a comment piece in Nature - the journal in which the research was published on Thursday.
What is a light year?
Despite the name, a light year is actually measure of distance. It is the total distance a beam of light, moving in a straight line, can travel in one Earth year.
One light year is 6 trillion miles.
To put that in perspective, the distance between Earth and Mars is relatively short - between four and 20 light minutes, depending on how far the planets are from each other.
It would take 39 Earth years travelling at the speed of light to reach TRAPPIST-1.