Studying a nearby exoplanet

Paul Robertson, associate professor of physics and astronomy at UC Irvine, is co-author of a new paper in The Astronomical Journal on an exoplanet that is tantalizingly close to Earth. The proximity of this exoplanet helps astronomers glean more details about it. They want to know how it compares in size to Earth, if it has an atmosphere and if it is in the habitable zone, a distance from the host star that would enable the planet to have liquid water on its surface, a key ingredient to support potential life.

In this episode of The UC Irvine Podcast, Robertson discusses the tools he and his team used to characterize this exoplanet and what he hopes to learn in future exoplanet hunting efforts.

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TRANSCRIPT

Bell:

From the University of California Irvine, this is The UC Irvine Podcast. I’m Brian Bell.

When you look out into the night sky, there’s a strong likelihood that the stars you are seeing have their own planets, much like our solar system. UC Irvine astronomers have made it their quest to find, study and characterize these so-called exoplanets. They want to know if the bodies are rocky, like Earth and Mars, or if they’re gas giants like Saturn and Jupiter. They want to measure the planet’s masses and determine if they have atmospheres, and they want to know if they are in the habitable zone, a distance from the host star that increases the chance of there being liquid water on their surfaces and essential condition to support life.

Paul Robertson, UC Irvine associate professor of physics and astronomy, is a prolific exoplanet hunter. He and his team, in addition to dozens of international researchers, have recently found a new exoplanet at an M dwarf star called GJ 2 51 in the Milky Way Galaxy. In a newly published paper in the Astronomical Journal, the team describes the features of this planet, one of the most important of which is its closeness to earth.

In this episode of the UC Irvine podcast, Professor Robertson discusses the tools he and his colleagues used to study the exoplanet and why its proximity to our own planet helps astronomers better understand what they were observing.

Our discussion is up next.

Professor Paul Robertson, welcome to the UCI Podcast.

Paul Robertson:

Thanks for having me back on.

Bell:

So what is the essential finding of this recent work by your group?

Robertson:

Yeah, so my group has discovered an exoplanet, which is a name we give for planets orbiting any star, not the sun. Uh, this one’s especially exciting because it’s near the size of the earth, uh, and it orbits a very nearby star in what we call the habitable zone. And that’s the range of distances from the star where we think the temperatures on a planet might be in the right range to have liquid water on the surface. That’s the one thing that we know every known form of life on earth needs. And so if we’re looking for life elsewhere in the universe, follow the water is kind of the mantra that we’ve adopted.

Bell:

I read in the paper that your team used a variety of instruments to help characterize this exoplanet. What are some of the more important tools that your group used in this study?

Robertson:

Yeah, you’re right. We used a fleet of telescopic instruments all around the world, but there were two in particular that I actually was fortunate to get to help build that were really crucial for this. The first one is called the habitable zone, planet Finder. Uh, it’s a spectrograph on a 10 meter telescope in Texas, and it studies nearby stars in infrared light. Uh, so some of the closest stars to us are actually a lot smaller and cooler than the sun, and so they put out most of their light in the infrared, and this instrument really helps us with that. The other one we use is called nuid, which is a word from the language of the Hon Odom tribe where the telescope sits in Arizona. Um, it works in optical wavelengths, but is, uh, considerably more precise in its measurements than HPF. And that was what really pushed this discovery over the top statistically where we knew we had found something.

Bell:

And these are both ground-based telescopes?

Robertson:

Yes, these are very large instruments on very large telescopes. So the, um, the instruments themselves are about the size of an SUV, a little too heavy to launch into space and obviously more easy to maintain when they’re down here on the ground.

Bell:

And so how much interaction do you have with these instruments on a day-to-day basis or throughout the year, I guess, as an astronomer?

Robertson:

Yeah, we use ’em all the time. Uh, the way we use ’em is a little bit different from the traditional way of using a telescope. So the, the old model is you would be assigned a single night on a telescope. You would go sit there all night and collect only your data. Um, but both of these instruments use a model called Q scheduling where I might still get that one night a year of time, but it can be broken up into say, 10 minute chunks across many nights. And so actually more often than not, we’re collecting data on any individual night. We just don’t do it all night and we don’t do it ourselves. We have dedicated observers at those sites who collect everybody’s targets and distribute the time equitably, and we get our data in an email in the morning.

Bell:

So you have a paper coming out in the astronomical journal about this exoplanet finding, and I read briefly, I kind of skimmed through the paper. Sure. It’s a very dense, a lot of information in this paper. It’s, but I did see something about your team using archival data that was collected maybe over 20 years right. About this particular planet. How does that work? Right.

Robertson:

So this is a great example of how science builds on previous results. So this is one of the closest stars to the solar system. It’s been studied by many previous teams using a variety of different instruments. Uh, and along the way those teams have published their data. There was actually an exoplanet discovered previously around the same star. It’s a little closer to the star. It’s not in the habitable zone where we get really excited about it. But we took that finding, we took the data that led to it, and we put it together with our own data. And as we add to that, we see additional signals emerging, and that turned out to be a, a second planet and, and in this case a really exciting one.

Bell:

In addition to the basic detection of exoplanets, what are some of the characteristics you can observe? Can you tell if there’s an atmosphere, for example, or a delineation between land and water on the surface of the planet?

Robertson:

Yeah, this is one of the things that we hope down the line we’ll get to learn more. Because when we first find these planets, we typically don’t know all that much about ’em. We, we can get a sense of how big they are and how far from the star they are. Those are the two things that we can usually pin down. But to get more sophisticated than that, we have to use next generation telescopes. So something like the James Webb Space Telescope, or in this case we’re especially excited about a group of new ground-based telescopes that we refer, refer to collectively as the 30 meter telescopes. Um, these are telescopes that will be big enough that we can, instead of doing what we do to discover the planets, which is look for indirect evidence from the star, we can measure light directly from the planet. And when we can do that, we can answer some of the questions you mentioned. We can say, does this planet have an atmosphere? We could potentially see if there are large bodies of water like oceans. If the planet is at just the right angle from the star and its orbit, the um, light will reflect very strongly at a specific angle off of liquid water. And so that would potentially be a way for us to tell if there, if there are oceans on that planet

Bell:

With these white dwarf stars. The, the type of solar radiation that you get from these stars, is it similar to what we get from our star? I mean, would it, would it support photosynthesis for example, uh, or other life, uh, you know, life molecules or that sort of thing? You say it’s habitable zone means the water could potentially be liquid on the surface of the planet, but would the radiation from the star help support life?

Robertson:

Right. So you raised some really fascinating questions and the, the true answer is we don’t entirely know. So, so, um, one correction. This is a red dwarf star, not a white dwarf. Okay.

Bell:

Sorry about that <laugh>.

Robertson:

There are both kinds. This is a red dwarf, which means most of the light it puts out is infrared. So could photosynthesis happen with that light? Maybe, but not in the same way the plant life and other photosynthetic organisms on earth use very specific wavelengths of optical light from the sun. And this star doesn’t put out much of that. And so people have speculated plant life might be entirely black, uh, at least to our eyes, on the surfaces of those planets, you might need other forms of energy to support life. And, and that’s why it’s so important for us to be able to see the atmosphere of a planet like this, to see what chemical compounds might be present, what does its surface look like, what’s there that might be able to support life.

Bell:

In the paper, you say the proximity of this plant, exoplanet to earth makes it a little bit easier to study than, than perhaps one that’s much further distant from us. Why is that?

Robertson:

That’s right. So this just has to do with how far apart the star and the planet are on the sky. This is the great challenge of studying exoplanets is that they’re very small and dim and they orbit very close to their host stars. Now the further the system is away from us, you can imagine as we look at that system, if you, if you just hold your hand closer to or further away from your face, you can see that as you move your hand away, your fingers appear closer or closer together. And so it’s the same with stars and planets on the sky. The closest ones move the planet further away so that we can get a telescope on the planet and, and separate it from light from the star.

Bell:

Very interesting. Tell me a little bit about the team that you had put together to make this discovery and do this characterization. Uh, you have some graduate students on your, in your group, you work with other universities. What is your team like for this research?

Robertson:

Yes, all of that. It’s a large team. This discovery was led by my research group here at UCI and specifically the study was led by my former PhD student, Corey Beard, who graduated about a year ago. But this was done through a larger team of scientists who built the habitable zone, planet finder and knew Nuid spectrometers. This is a brilliant team that consists of more than 50 astronomers at institutions all around the world. And we get together at least once a week and talk about science and collaborate to overcome the challenges that we naturally encounter as we make these really challenging measurements. And so it’s incredibly rewarding. I’ve been fortunate to have some incredibly talented people work for me here at UCI, but also to be part of this larger global team is just rewarding every day to, to work with those folks.

Bell:

You’re chair of the UC Observatories Advisory Committee. What does that job entail and what are some of the instruments that are under your purview in this job?

Robertson:

Sure. So the UC Observatories is a multi-campus research initiative that encompasses all of the campuses of the University of California, manages our partnerships in the Lick Observatory and Keck Observatory and the upcoming Thirty Meter Telescope. So we advise the observatory director on things like science priorities, which instruments we should be developing for Keck and Lick observatories, and also working towards the future of the Thirty Meter Telescope, which is what we hope will be the next great observatory in the UC system.

Bell:

You mentioned that as a tool that you could potentially use to study exoplanets.

Robertson:

Yes. So the, as the name suggests, TMT will have a 30-meter primary mirror. And that’s so important for exoplanets because the larger the mirror, the fundamentally the better imaging resolution you can get on the sky. And for planets like the one that we’ve discovered here, that mirror is what we really need in order to potentially take direct pictures of this planet and look for signs of life. So we’re really hoping that this telescope is going to get built. It’s the only one of the 30-meter class telescopes that is slated to be built in the northern hemisphere, which is where this particular planet is located. And so it’s our one opportunity to potentially get a shot of a habitable zone, potentially earth-like exoplanet.

Bell:

It’s going to take a while for it to get built even if it does sort of break ground soon.

Robertson:

I would imagine. Yes, there are all kinds of financial logistical challenges and yes, schedules only tend to slip in one direction, but, we’d rather have it later than not have it at all. And, and I think there, there’s a rich scientific ground for it to, to help us out with.

Bell:

So what do you have going on now or what’s coming up next for you?

Robertson:

Well, so this star that we’re talking about today, GLAC 2 51 is one of just many stars that both of these instruments are surveying. And we’re at a really exciting time in our program where we’ve been studying these stars long enough that we’re starting to see planets like this one emerge in our data. And so we’re currently working to confirm a few other really exciting systems and get those ready to share with the world. And at the same time, we’re always working to improve our techniques. Can we get better measurements out of our equipment? Can we understand the host stars themselves better in order to separate signals from stars and planets? And, and that’s just going to push the field forward as we work towards finding habitable exoplanets and potentially down the line looking for life on them.

Bell:

That’s very interesting. Well, I thank you very much for spending some time with me today.

Robertson:

You got it.

Bell:

Cheers. Thank you.

Robertson:

All right, thanks.

Bell:

You can learn more about Professor Paul Robertson’s latest exoplanet discovery at news.uci.edu and much more about his earlier work in this field at physics.uci.edu.

The UC Irvine Podcast is a production of Strategic Communications and Public Affairs at the University of California, Irvine.

I’m Brian Bell. Thank you for listening.