Today, Paul and I are up here at Mount Stromlo's observatory talking to Dr. Dan Bayliss about the HAT-South Telescope.
So, what is HAT-South?
HAT-South is a global network of telescopes. We've got telescopes in Australia, Namibia and Chile,
and they're small telescopes that are looking for transiting exoplanets around bright stars.
So, why is a global network a good idea rather than just having one telescope?
Yes, good question. So, the first transit surveys were just from a single sight,
but what happens there is, because of the day-night cycle, we miss a whole lot of the transit events.
They only last for a few hours, so by having global coverage, it means we can continually monitor the stars
and we can catch all of the transits that are happening.
So, if you had a transit that have happened, let's say, every four days or so,
you can imagine it happening, in a regular telescope would only have one,
it could happen at every daytime, at noon and you just never would find it, presumably.
Yes, exactly, and with a network for HAT-South, it's always dark on one of the sites so we would, therefore, catch a transit each time.
What is HAT-South Telescope in terms of the telescopes themselves?
The telescopes are actually quite small. The primary mirrors are only 18 centimetres, but we have four mounted on one unit.
What that allows us to do is cover a huge area of sky, about 128 square degrees.
We need that because we need to monitor tens of thousands of stars just to catch one of these transiting planets.
How is the network of small telescopes better than a big telescope for this?
A big telescope can obviously gather more light, but usually what you get with a big telescope is only a small field of view,
so even though you can monitor stars that are fainter, you don't cover a wide area of sky, so you can't monitor all of the bright stars.
Now, the reason we're really interested in bright stars is that if you see a transiting planet around a bright star,
there's lots more exciting follow up work you can do to work out things like
how hot it is, what the atmosphere is made of and it's orbital orientation.
So, this sounds like an interesting idea that, presumably, other people are doing.
How have you found it? Has it been an easy experiment to do or has it had its challenges?
It certainly had its challenges, for example, the HAT-South network runs in an automated and remote way,
so I don't stay up each night checking on the telescope. To get the telescope to run automatically is actually quite a challenge.
It actually has to be able to sense the weather and know when to open and when to close.
The other part of it that's been a challenge is working out which of our stars really have planets going around them.
We see a lot of signals that look like they could be transiting planets,
but there's a lot of work to then go and look at those candidates afterwards and see if they really are transiting exoplanets.
What fraction of your candidates actually turn out to be exoplanets, would you say?
Probably, in the end, only about 10 percent of our candidates turn out to be exoplanets.
There's many other things that look like exoplanets which aren't.
For example, eclipsing binary stars often look like a transiting planet signal,
but when you investigate more carefully, you work out that it's a star rather than a planet.
So, it sounds like you've made some discoveries. What are the types of discoveries you've made now with HAT-South?
Yes, so this year already we've published three transiting planets that we've found. They've all been interesting in their own right.
For example, HATS-2B is one of the planets that we found and that transits in front of a star which has got a lot of star spots on it,
just like the spots we see on our own sun, except much much larger.
When the planet passes in front of one of these spots, it actually appears to get brighter
because the planet isn't passing in front of a dark spot on the sun.
So, we've been able to start characterising, not just the planet, but the star itself using transiting planets.
So, we can use this method literally to see tiny little sun spots on a star on the other side of the galaxy.
Yes, that's right, as the planet passes in front of the star, it gives you a little map of that part of the star that it passes in front of,
so if there are spots, we can see them.
So, HAT-South is currently the cutting edge for ground-based transit searches, what's going to happen next? Where do you go from now?
Yes, so the real challenge is to try to find planets that are even smaller than what we can see at the moment.
To do that, we need to get to a higher precision on our light curves.
One of the ways to do that is from space, so the Kepler mission in space has been very successful in monitoring stars
and the next transit mission that NASA is planning is called TESS and that is similar to HAT-South,
it's quite small telescopes, but from space, it doesn't have the Earths atmosphere to interrupt the starlights,
so the precision of the light curves is much better.
It's hoped that, with a mission like that, we might be able to find much smaller planets right down to the size of just a few Earth masses.
What would be the most exciting thing that you could imagine discovering with one of these transit surveys?
Well, ultimately, we'd like to see planets that would have some possibility of having life.
Now, of course, we don't really know what that means.
On planet Earth, it means liquid water, so I guess finding a transiting planet that is a similar size to Earth
and in a zone around a star that could have liquid water would be really exciting,
and if that happened, I think we'd focus all of our attention on trying to work out what the atmosphere of that planet is
because there's some chemical signs that might give away life being on that planet.
Well, thank you very much for talking to us. (Yes, thank you.)
Thank you.