NASA Blueshift - 2013
http://universe.nasa.gov/blueshift

Ring around the Exoplanet

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Maggie: Welcome to Blueshift, brought to you from NASA's Goddard Space 
Flight Center. I'm Maggie Masetti. Last year, we brought you a story 
from the 2012 American Astronomical Society meeting about bizarre and 
perhaps uncommon exoplanet systems. One of the presenters was a college 
friend of mine, Eric Mamajek, and he discovered an exoplanet system that 
they suspect has rings similar to Saturn's.

Our last two podcasts featured our interview with space artist, Ron 
Miller, who did an illustration for this exoplanet system. Now we'll 
talk to the scientist who discovered it to learn more.

Maggie: We covered the exoplanet session you presented at AAS last year 
so we thought it'd be fun to kind of catch up with you a year later. 
Backing up a little bit, can you tell us about this, perhaps unusual, 
exoplanet system you discovered and how you came to find it?

Eric: Well, we found it as an unusually eclipsing system among a survey 
of hundreds of new very young stars we've discovered. So my graduate 
student. Mark Pecaut, is doing a survey, looking for, essentially, baby 
suns and stars like the sun but only about 10 to 20 million years old in 
the nearest region of massive star formation, which is the Scorpius 
Centaurus Complex. So, if you're in the southern hemisphere, you can see 
a lot of the brightest members of the group in the night sky and 
Scorpius and Centaurus, and Crux and Lupus... some of those 
constellations. We had found that a lot of the objects that we had 
discovered as young, sun-like stars had been looked at by the survey 
called SuperWASP, which is a very tiny telescope that is imaging large 
regions of the sky looking for transiting exosolar planets.

They're looking for little dips in the signal among the bright stars in 
the sky, looking for planets passing in front of those stars. We were 
looking at data from that survey for our stars, and one of the stars had 
this huge, very unusual eclipse in it. That's where this got started. 
But, as soon as we saw the eclipse, we thought, "Well, this doesn't look 
like any sort of eclipse we've ever seen." The eclipse was going on over 
a period of about 52 days, at its deepest, about 95% of its star's light 
had been blocked out. This was a very odd eclipsing object.

Maggie: What do you think caused the eclipsing of the light?

Eric: The best model we have so far... I have a graduate student Erin 
Scott, who's following up on the modeling of this system. The eclipsing 
object seems to be a series of rings. It seems to be a fairly dense 
inner disc surrounded by several discrete rings and we're currently 
figuring out how to statistically distinguish, you know, how many rings 
are there, and how dense are they?

But it looks like there's a series of rings. And by rings, I mean 
they're probably composed of dust and they're probably fairly thin, like 
Saturn's rings, though the system appears to be much, much larger than 
Saturn's system. You know, a lot of people have found things around 
stars that they've called ring systems, but they're not really ring 
systems. They're usually these so-called "debris discs." The discs are 
on Fomalhaut and Vega, Beta Pictoris... Those are a few famous examples.

Those appear to be ground up dust from collisions of asteroids and 
comets over a very large scale, and they appear to be fairly puffed up. 
They're not very thin; whereas this system, the thinning of the light 
curve requires that these rings are very, very thin, almost like 
Saturn's rings. Although we don't have a very strong constraint on how 
thin they are. But we see very clean gaps between them. Something must 
be creating these gaps in the rings. 

Maggie: I was gonna ask, is that the first time something like has been 
seen? You mentioned these other systems might have puffy debris discs, 
but is this the first time we found an exoplanet that might have 
Saturn-like rings?

Eric: Well, I want to be careful because we don't quite know the nature 
of the object yet. Probably either a giant planet or a brown dwarf. Some 
sort of a failed star, a substellar object. It could be something that's 
tens of times the mass of Jupiter, but we've ruled it out being stellar. 
It doesn't appear to be a low mass star with a little disc around it. So 
I think right now it's probably consistent with being a giant planet or 
brown dwarf. But either way, it's still a very remarkable system.

I think it's going to be some time before we know the mass of that 
companion. We're going to continue to take data over the next few years 
and see where that goes. But there's some suspicious inconsistencies. If 
the object's too massive, it doesn't appear to have an inner gap. We 
don't detect a hole in the disc, so if it was a low mass star there 
should be a point at which the temperature's too high for dust to exist 
and the little [?] would just evaporate because it would be too hot.

So we think it's cooler. We think it's probably a brown dwarf or a giant 
planet. But either way, we're talking, you know, with this ring system 
and the gaps in these rings and if there's something in there creating 
the gaps, we're talking about if it's a brown dwarf, we're talking about 
a very tiny, miniature planetary system around a brown dwarf. I guess 
you'd call it a planetary system. Or, if it's a giant planet, we're 
talking about moons, carving things out.

But I think we have to be a little bit careful. I think we're not going 
to know exactly what the nature is of this companion is that has this 
very complex ring system. I think it's going to be a little while before 
we know exactly what that is. But the whole system appears to be smaller 
than perhaps a few tenths of an astronomical unit. So, I mean, you could 
fit it within the orbit of Mercury in our own solar system. It could be 
even smaller than that. 

Maggie: The exoplanet session at AAS last year, the theme was sort of 
"anything can happen with exoplanets." What are your thoughts on that? 
The fact that so many interesting and weird systems are being 
discovered?

Eric: This is a great time to be studying this topic. It's amazing to 
think even 15 years ago, we knew of one or two planetary systems outside 
the solar system. Now we know of many hundreds. NASA's Kepler satellite 
has found over 2,000 candidates. Most of those are probably real 
planetary systems. It'll take a long time to confirm them through other 
means. You know, literally we're finding planetary systems everywhere, 
and we're seeing interesting patterns in the types of planets and their 
characteristics.

The thinking two decades ago that we would just find a whole bunch of 
clones like our solar system is out the window. We're finding very 
strange planetary systems; we're finding giant planets orbiting very 
close in; we're finding very, very compact, tiny planetary systems 
around some objects. In the Kepler field, they're finding things that 
are sort of intermediate between Earth and Neptune. They're either mini 
Neptunes or super Earths, so scientists are still trying to constrain 
what the properties of these things are.

There are classes of planets out there that don't exist in our own solar 
system. We're finding our solar system does not appear to be typical.

Maggie: What's funny is that when we were college, the first exoplanet 
discovery was pulsar planets, which isn't exactly what you would think 
of as a normal star system either. But it is funny how far we've come 
since then.

Eric: Yeah, that was around 1991, 1992. And I think there's only been a 
couple other planets discovered on pulsars, if any. That was a very 
strange system that was discovered.

Maggie: It's funny that that was the first one, though. Just such an 
odd, oddball system.

Eric: Yeah, and so far they haven't... again, they haven't really been 
found in great number around other pulsars so that appears not to be a 
terribly good birth site for planets. There was a trend that people were 
finding about five or ten years ago. They were finding that stars that 
had more metal content than the sun, so things like iron, nickel, 
magnesium, silicon - stars that have chemical composition that has more 
metals, what astronomers call metals, other fields may not call them 
metals.

First off, anything heavier than helium is basically metal. Planets need 
metals to form. There was this trend found that the more metal rich a 
star was, there was a stronger tendency for those stars to have planets. 
But they're also finding that there's trends in the types of planets 
that are found. They're tending to find those close-in Jupiters more 
around the metal rich stars, but they're also finding these stars that 
have lower metal composition, they tend to have smaller planets.

So, even these stars that you would think that the discs that they 
formed out of probably had less materials to form planets, the process 
must be going on. But I think the Kepler results are showing us that 
even these metal poor stars can form planetary systems so there's 
probably lots and lots and lots of very small planets out there. 

Maggie: When we were just starting out in astronomy at Penn State, again 
the pulsar planets were sort of the first thing out there, what was it 
that made you eventually study exoplanets? Was there something that 
triggered your interest back then or was it something you just fell 
into?

Eric: Well, I've been interested in astronomy since I was around eight 
years old, and I remember some of the interesting, tantalizing clues 
that there might be planets out there. That was certainly an interesting 
motivator for me. People had found some substellar objects in the late 
80s and early 90s. They found the pulsar planets in the early 90s. They 
found a companion around... the first hot Jupiter was discovered in 
1995. It was this Jupiter-like planet orbiting a sun-like star. In four 
days, a sort of barbecued gas giant. They found that in 1995.

So, it was clear that this was going to be a new, interesting field to 
get into. But most of my work has been on studying the discs around 
stars as sort of either a... studying of the initial conditions of 
planetary systems or the ground up dust that's created from the asteroid 
belts around those stars. And finding young stellar populations where we 
can study the birth of these discs and planets, and assessing the ages 
of stars, that's where most of my work has been. This eclipsing system 
has been a bit of a surprise, and a really fun project to work on.

Maggie: Do you think you might want to look for other exoplanet 
systems, or are you just going to focus on learning all you can about 
this one?

Eric: Well, that's a good question. Certainly this discovery spurred 
some work by myself, my students and a few collaborators, and we're 
looking for more of these and I think this may be a fruitful technique 
for trying to find the signpost of giant planets forming around the very 
youngest stars.

If this transiting system, we've been calling it J1407, if that really 
is a giant planet with a moon-forming disc around it, we've done some 
calculations on how often we think we'd expect to find systems like 
that. I think this will be an interesting technique for... once we start 
finding more of these things, I think that'll give us some of the first 
observational constraints on the environments where moons are forming 
around giant planets, the timescale for forming these giant planets. So 
there's a lot of scientific questions we can answer with those.

So, right now, we're searching. We're looking through some surveys, and 
so far we're following up one other interesting candidate, but we think 
it's probably a stellar companion with a disc and it's actually in 
another galaxy, of all things.

Maggie: Oh, wow!

Eric: We don't think that one's a giant planet, but we're looking.

Maggie: We interviewed the space artist, Ron Miller, and I understand he 
did art that was representative of your system. Can you tell us anything 
about that?

Eric: I found that randomly just a few months after our AAS press 
conference, and I'm a fan of Ron Miller's work, and a book out of the 
mid 80s, "Out of the Cradle". So, I was in my early teens, and I had a 
copy of that book.

Maggie: Yeah, I had one too.

Eric: It's a very inspiring book. He's very good at capturing scenery in 
space, both with humans and without humans in it. Yeah, I was just 
delighted when I saw that he did some artwork for it. It's now the 
background on my laptop. I'd like to thank Ron for doing that artwork. I 
was delighted when I found it.

Maggie: Visit our website at universe.nasa.gov/blueshift to see Ron 
Miller's art of this exoplanet system and listen to the podcasts where 
he talks about his work. You can follow us on Twitter or Facebook, where 
we're NASAblueshift, all one word. We'd love to hear from you, through 
our blog or any of our social media to get your thoughts on this podcast 
or what you'd like to find out more about in the future. I'm Maggie 
Masetti, bringing the Universe closer to you with Blueshift.

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