Curious Universe: Let’s Go Planet-Hunting!

01One of the really fun things about hunting for exoplanets is all the surprises.

02Before we found any worlds around other stars, we only knew our solar system.

03So when we came up with ideas of what other solar systems would look like, they very closely resembled ours.

04All of our theoretical models for how planets form were designed to recreate the solar system.

05If your model created something completely different, then you threw it away because it didn't create the solar system when we knew the solar system existed.

06But when we went out there, we have found anything but.

07We have found all of these other configurations of planets, big planets right next to their star, chains of small planets all packed really closely together, systems where they're all misaligned with each other.

08So it's been really, really exciting to just kind of see how much more imaginative nature is than we are.

09We think almost every star in the galaxy has at least one planet around it, which is incredible because there are a hundred billion stars in our galaxy.

10Just imagine how many worlds that is out there and how much potential that is.

11This is NASA's Curious Universe.

12Our universe is a wild and wonderful place.

13I'm Patti Boyd, and in this podcast, NASA is your tour guide.

14Today, we're taking you outside our solar system and into the planets that lie beyond.

15Exoplanets.

16There are eight planets in our solar system.

17Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

18But in the last few decades, scientists have discovered thousands of planets outside our solar system.

19We call them exoplanets, and evidence suggests that there might be hundreds of millions of planets in the Milky Way.

20So far, planet hunters have discovered and named over 4,000 worlds within our galaxy.

21When I'm not hosting this podcast, this is what I study the most.

22Exoplanets and stellar astrophysics.

23It's amazing to get to explore these faraway planets.

24Just a generation ago, we didn't even know if there were planets around other stars, and now we know that exoplanets are everywhere.

25And the types of exoplanets that we find are dizzying.

26And we can learn a little bit more about the Earth and our solar system by studying the variety of other planets out there and comparing them to our own.

27And the planets we're finding are really far away.

28Space is really big.

29And I think when I get to tell people that we found new planets, they're always disappointed by the answer of how far away they are.

30This is Jessie Christensen, an astrophysicist with the California Institute of Technology.

31On average, the exoplanets we found are hundreds or thousands of light years away.

32The problem is a light year is really, really big, much farther than we could ever imagine traveling.

33It's hard to imagine how far away that is.

34Even with the most powerful telescopes, only a handful of exoplanets, around 20, have been imaged directly.

35And even those we only see as dim points of light.

36So how do we know all those others are out there?

37One of the ways we find planets is called the transit method.

38Now that relies on the fact that some planets are lined up just right, so that from our point of view, as they're orbiting their star, they pass in front of the star, they eclipse their star and block some of the light.

39Now from our distance, we can't actually see that eclipse.

40But what we can do is measure the brightness of the star over and over again and wait for it to dim just a little bit and then go back up.

41So it's these tiny little dimmings in the brightness of stars that we're looking for in these data.

42Exoplanet research is still relatively young.

43The first one was officially discovered in 1992.

44But for millennia, humans have looked to the skies and wondered what else is out there.

45Ancient philosophers pondered the existence of other worlds.

46But we are the first generation that can start to answer some of these questions with data.

47When I work at NASA, I specifically work on several different space missions, making sure that they're providing and taking the best data that they can for everybody to investigate and explore.

48This is Nicole Colon, a research astrophysicist.

49Her team also uses the transit method to track down exoplanets transiting their stars.

50But sometimes stars have more than one planet orbiting around them, which can make things a little bit tricky.

51A lot of stars have more than one planet.

52That's what we would think, as we know from our own solar system.

53That means that we get a lot of overlapping signals when we're looking to study the individual planets.

54Scientists take those overlapping signals and carefully untangle them to reveal multiple worlds.

55One of Nicole's specialties is using that data to determine the compositions of those far-flung planets.

56We've also been able to study atmospheres of exoplanets.

57We have been finding water vapor in a lot of their atmospheres, which is expected and exciting because water is everywhere.

58But we're starting to find other things like helium vapor and different molecules that was a little bit of a surprise and not originally predicted until we started looking more at the chemistry of the atmosphere and what's really going on.

59In fact, we've already begun exploring what some exoplanets are made of.

60Luckily, when we can observe, for example, a planet that transits or passes in front of its star, if that planet has an atmosphere, we can actually see what starlight gets blocked or like filtered out by that atmosphere.

61By seeing what's missing, we can say, oh, you know, that planet has water in its atmosphere and that water is blocking starlight from reaching our telescope.

62In the future, we'll be able to look for additional molecules like methane and carbon dioxide as well.

63With thousands of known exoplanets out there and more coming all the time, it's important to keep track of them all.

64Jesse works at the NASA Exoplanet Archive, which organizes and maintains information about the properties of known exoplanets.

65So the ancient Greeks, when they were naming our planets, they went for the gods and, you know, the big movers and shakers of the Greek philosophical world.

66Nowadays, we do it much more boringly, unfortunately.

67We have found over 4,000 exoplanets so far, and they're almost all named in a very particular way.

68We take the name of the star that the planet is orbiting, and the name of the star is usually pretty boring itself, like HD 189733.

69Then, the first planet in the system, we attach a little b to the name, so HD 189733 b.

70The second planet in that system is HD 189733 c.

71The third planet in the system, I'm sure you see the pattern, HD 189733 d.

72So they're all terrible, terrible names.

73I'm so sorry on behalf of astronomers everywhere that we give planets such boring names.

74One of the benefits of gathering all of this information in one place is that scientists can find new and engaging ways to explore it.

75What you're hearing now isn't just a pretty song.

76It's data that captures the discovery of exoplanets.

77This is a data sonification, where planetary information has been translated into sound.

78Here, each note represents a newly discovered exoplanet.

79The tone of each note reflects the planet's orbital period, with longer orbits reflected by lower tones.

80The music's increasing complexity reflects the rapidly changing pace of exoplanet discovery between 1992 and 2019.

81As you can hear, the discoveries came very slowly at first.

82Then there's a great rush of music reflecting the avalanche of discoveries made by NASA's Kepler mission.

83This was a huge leap in our catalog.

84Even today, Kepler's discoveries constitute more than half of all the exoplanets we know of.

85I have actually contributed to the discovery of several exoplanets.

86I don't know the number offhand.

87I wish I did.

88I should look into that.

89Again, this is astrophysicist Nicole Colon.

90I have helped discover new exoplanets, and of all kinds, ranging from small, rocky exoplanets that are about the size of Earth to these super giant planets that are like Jupiter.

91So it's pretty incredible being able to discover new planets.

92I used to remember a time when I could tell you something about every single exoplanet that we know.

93Now with 4,000, I'm like, oh wait, which one is that again?

94So things have been changing, but for the better.

95I do have a lot of favorites.

96There is one that stands out in terms of what my favorite exoplanet is.

97And it is actually one I helped discover, so that's certainly why it's one of my favorites.

98But it's a planet called KELT 11b.

99KELT was the survey that discovered it.

100First of all, it orbits around its star in less than five days.

101So it's very close to its star.

102Compared to the Earth orbiting around the Sun every 365 days.

103But it's also larger than Jupiter is, so it's a very giant planet.

104But then its mass is so low that when you look at it all together, this planet has a density that is basically the same as styrofoam.

105And so if you imagine how, you know, fluffy and light styrofoam is, right?

106You could just throw it around like it's nothing.

107We'd probably just float right off or crush the whole thing.

108I don't know.

109I mean, one of the two.

110So that intrigued me so much that I actually have worked on projects to study the atmosphere of the planet to find out more.

111I've used NASA's Hubble telescope to search for water vapor in the planet's atmosphere.

112Because that can tell us a little bit about where or how the planet formed by knowing how much water it contains.

113What we found was that the amount of water in its atmosphere is so small that it actually cannot be explained by current theories of planet formation.

114I'm hoping one day to use future telescopes as well to just really shed some light on, okay, how does such a puffy planet exist?

115A lot of the exoplanets we're discovering seem sort of wacky by Earthling standards, like Nicole's styrofoam planet.

116Can you imagine trying to walk around on a planet you might crush?

117But every once in a while, the data lines up in such a way that we think a planet might fall into the habitable zone.

118This is a range of distances from a star where a planet's surface might be able to contain liquid water on its surface, a requirement for life as we know it on Earth.

119Astrophysicist Jesse Christensen has paid special attention to one particular planet that might just be in a habitable zone.

120The exoplanet I would most want to visit is Kepler-452b.

121So this is the one planet that Kepler found which might be a rocky planet in the habitable zone, meaning it's the right temperature for liquid water, of a star like the sun.

122The problem is the data are just a little bit noisy and we can't tell from the data we have whether it's real or not.

123What I really want to do is just go there and look and be like, does this planet exist?

124Answering that question would be the top of my mind.

125We do know its size.

126It's a little bit bigger than the Earth.

127It's 1.5 to 1.6 times the radius of the Earth.

128So if it's real and you could step out on its surface, it likely has a quite high surface gravity.

129When we walk here on Earth, we feel the Earth pull down on us and we feel that weight.

130Now, I'm sure you've seen images or videos from the Moon of the astronauts like kind of bounding on the Moon because the gravity on the Moon is much lower.

131So you actually just feel lighter and you can move much more easily.

132On Kepler-452b, the gravity would be higher because the planet is much bigger and therefore has much more rock underneath your feet pulling on you.

133So it might be very difficult to walk.

134You might feel like walking through quicksand or something.

135In 2017, NASA announced the discovery of seven rocky Earth-sized planets in the habitable zone of a single star called TRAPPIST-1.

136All seven planets in the TRAPPIST system have the potential for supporting water on their surface.

137But with a much smaller star and an entirely different planetary system, even these exoplanets aren't quite like our home here on Earth.

138While it's exciting to find planets that might be similar in some ways to our own, we're still very far away from being able to send probes to explore them directly.

139When I tell people that we have found Earth-like planets around other stars, I always see this light in their eyes, right?

140Like they see it, like maybe there's some kind of escape plan.

141Like maybe there's hope that humanity will like go out and colonize the galaxy.

142There's Earth-like planets everywhere.

143And I always try to squash that a little bit because in our solar system, we have four rocky planets.

144Only one of them is habitable.

145We have this window on this one planet around this one star that's habitable.

146So what I don't want is for people to hear this message, there are Earth-like planets everywhere in the galaxy, and be like, okay, cool, we can just trash ours because we've got all these other options.

147We don't have any other options, not even in our solar system.

148This is it.

149Earth is it.

150We have to take care of the one Earth that we have.

151One of the wonderful things about studying these faraway worlds is seeing how different they can be from our home on Earth or the familiar planets in our solar system.

152There are so many combinations of size, atmosphere, chemical composition, and distance from their stars that result in thousands of different places, each with its own unique characteristics.

153It's really interesting seeing exactly what all these exoplanets have shown us.

154Finding different molecules that we might not expect to see in Earth's atmosphere.

155It does bring you back home when you say, okay, are they weird or are we weird?

156Are we just the anomaly?

157What does that actually mean then when it comes down to kind of NASA's end goal and really, you know, my end goal?

158I think almost every astronomer who studies exoplanets, their end goal of knowing if some kind of life might exist out there in the galaxy, what does it mean that exoplanets are so different than Earth?

159There's a lot of NASA missions that will help answer that question.

160Scientists currently use information from ground telescopes and space telescopes to gather data on exoplanets.

161But there are a lot of exciting plans to expand the search.

162TESS, the Transiting Exoplanet Survey Satellite, launched in 2018 and has already confirmed over 100 new planets around bright, relatively nearby stars.

163And later this year, scientists across the globe will come together to witness the launch of the James Webb Space Telescope, which will allow us to gather even more information about these faraway worlds.

164You know, there are so many exoplanets that we know of so far, thousands.

165But there is still so much left to discover.

166And we're expecting to discover in the next few years, decades, tens of thousands of more exoplanets.

167Pretty soon we're going to be able to more definitively say how many there are because we have new NASA missions coming online that are just going to keep finding thousands of exoplanets to help us even better understand how common they are.

168Just really help us get to where we want to go, which is understanding our place in the universe.

169This is NASA's Curious Universe.

170This episode was written and produced by Christina Dana.

171Our executive producer is Katie Atkinson.

172The Curious Universe team includes Maddie Arnold, Kate Steiner, and Michaela Sosby, with support from Emma Edmond and Priya Mittal.

173Our theme song and the sonification you heard in this episode were composed by Matt Russo and Andrew Santaguida of System Sounds.

174Special thanks to Claire Andreoli, Ryland Hegey, Barb Madsen, Frank Reddy, Amber Strawn, and the astrophysics team.

175If you liked this episode, please let us know by leaving us a review, tweeting about the show at NASA, and sharing NASA's Curious Universe with a friend.

176Learn more about exoplanets by visiting exoplanets.nasa.gov.

177Still curious about NASA?

178You can send us questions about this episode or a previous one, and we'll try to track down the answers.

179You can email a voice recording or send a written note to nasa-curiousuniverse at mail.nasa.gov.

180Go to nasa.gov slash curiousuniverse for more information.

181Now I am recording on my end.

182Oh, my goodness.

183Just now, as soon as that happened, my cat is going to start crying at the door.

184Bye.

185Bye.

186Bye.