An artist’s impression of the planet HATS-6b, orbiting the star, HATS-6. (Supplied: ANU)
It was discovered by an international group of scientists called the HAT South team, from the Australian National University, Princeton and the Max Planck Institute – along with an amateur astronomer in Perth known as TG Tan.
George Zhou from the ANU Research School of Astronomy and Astrophysics said HATS-6b was about the size of Jupiter and was orbiting very close to a small, sun-like star called HATS-6.
“That means this is a really big planet… orbiting a relatively small star,” he said.
“It’s quite hard to form these big planets around small stars.”
Mr Zhou said he believed the planet must have formed further out and migrated in.
“But our theories can’t explain how this happened,” he said.
Mr Zhou said HATS-6b is a “puffy” planet – meaning it is large, but not particularly dense.
“This planet is not as heavy as Jupiter, but it is as big as Jupiter. So it is quite puffed up,” he said.
“We’ve been able to measure the mass and the radius of this planet, which gives us the density. We know that the density is less than Saturn.”
To explain just how light Saturn is, Mr Zhou used a simple analogy.
“If there was a large enough pool [of water] and you dropped Saturn into it, it would float,” he said.
“That’s also the case with this planet, and that means that it’s made of gas, probably hydrogen and helium, just like Jupiter and Saturn.”
Amateur Perth astronomer made ‘significant’ contribution
Mr Zhou said HATS-6b was discovered using telescopes around the world, including one in the Siding Spring Observatory in northern NSW.
“We used these telescopes to monitor the brightness of hundreds of thousands of stars in the night sky,” he said.
“When a planet passes in front of a star, from our perspective, what we see is that one of the stars will dip in the brightness that we observe, indicating that there’s a planet transiting in front of it.
By looking for planets around small stars we’re find a different way of identifying planets that might host life.ANU researcher George Zhou
“This is the transit technique that we’re using to discover these planets, and that’s how HATS-6b was discovered.”
It was that this point that Perth amateur astronomer TG Tan got involved.
“We’ve identified something like 1,000 planet candidates – what we think might be transiting planets,” Mr Zhou said.
“It’s a stretch for our resources to try to follow up these 1,000 potential planet candidates, so we enlist the help of amateur astronomers.
“TG monitored the transit of HATS-6b for us, and actually confirmed that it’s really a planet around another a star.
“His contributions were significant for this discovery.”
Mr Zhou said this kind of research was helping scientists understand the context of our solar system in the universe.
“Of course one of the biggest questions is whether there’s life out there,” he said.
“By finding planets around other stars, we’re going toward that direction. We’re trying to find places where potentially there might be other forms of life, which are not coming from Earth.
“Hopefully, this kind of research will lead us towards that.”
He said around small stars, like the one around which HATS-6b was orbiting, it was actually comparatively easier to find planets.
“Around a small star, the transit that we see is proportional to the size of the star,” he said.
“Around a small star, the same size planet would have a more easily detected dip [in light].
“So it’s much easier to find an Earth-like object, for example.
“By looking for planets around small stars we’re find a different way of identifying planets that might host life.”