Small Steps, Giant Leaps: Episode 162: 6,000 Exoplanets and Counting

Andres Almeida (Host): On September 17, 2025, NASA introduced that the variety of exoplanets, planets exterior our photo voltaic system, tracked by NASA has reached 6,000. In the three a long time for the reason that groundbreaking detection of exoplanet 51 Pegasi b, the primary confirmed planet orbiting a Sun-like star, astronomers have concluded that unique worlds are all over the place. 

 These worlds are available all styles and sizes, from sizzling Jupiters to rocky Earth-like planets. And they’re increasing our understanding of what’s potential within the universe. 

 So, how do exoplanets get found and what does it imply for astronomy? And how do researchers decide if a planet could be within the liveable zone of a star, an space referred to as the Goldilocks zone. Here, the situations might be good for liquid water to exist on an exoplanet’s floor. Life on Earth began with water. 

Let’s speak about it on this episode of Small Steps, Giant Leaps.

[Intro music]

Welcome to Small Steps, Giant Leaps, the podcast from NASA’s Academy of Program, Project and Engineering Leadership, or APPEL. I’m your host, Andres Almeida. 

Today we’re joined by Dr. Eric Mamajek, deputy chief scientist of the Exoplanet Exploration Program at NASA’s Jet Propulsion Laboratory in California.  

Andres Almeida (Host): Hey, Eric, thanks for being right here.  

Dr. Eric Mamajek: Thanks for having me. 

Host: So, we’re now at 6000 confirmed detections of exoplanets and counting. How has our perspective of the universe modified since 51 Pegasi b in 1995? 

Dr. Mamajek: So, it’s been a exceptional 30 years. I’d say, you realize, there’s a number of issues we all know now that we didn’t know 30 years in the past, again after we have been simply discovering the primary planets. I feel the primary massive general discovery is planets are principally ubiquitous. Star Trek was proper: There’s planets all over the place. 

[Laughter] 

And it’s laborious to imagine, a technology in the past, we didn’t know that. I feel that was one of many key findings from the NASA Kepler mission. Statistically, most stars have, have planets, and there’s in all probability, you realize, maybe, trillions of planets in our galaxy. 

The different factor is that Earth-like planets, and I’ve to watch out with the time period “Earth-like.” I’ll say “Earth-size” planets receiving related quantities of sunshine from their star appear to be widespread, and one thing between maybe 10 to 50% of stars appear to have planets which can be related in dimension and mass because the Earth and orbiting the place the floor temperatures can be temperate. And given a correct environment, they may have liquid water, and who is aware of? Perhaps the situations for all times.

But that, that’s one other discovering from Kepler, that statistically, the planets, not less than related in gross traits to Earth, appear to be widespread. 

And I’ll say, simply the range of worlds has been unimaginable. I don’t assume folks foresaw…I’d say sizzling Jupiters have been a shock besides to a couple early theorists who have been interested by migration of planets and disks (they have been proper). 

You know, we’re discovering planets on extraordinarily shut orbits. We’re discovering planets on extraordinarily distant orbits. We’re discovering planets, you realize, small rocky planets orbiting, you realize, in lower than a day, round their star, and their surfaces are in all probability utterly molten. Kepler additionally confirmed us that planets intermediate in dimension between the Earth and Neptune seem like extraordinarily widespread, and maybe the most typical sort of planet in our galaxy, and we don’t have any in our photo voltaic system. I’d say that’s a shock. 

You know, the sphere is taking off the place we’ve gone from, you realize, little or no data about planets round different stars to all these nice findings simply in a single technology. And the great factor is that this subject is continuous to shock. So, you realize it’s ripe for extra discovery. 

Host: It’s fascinating you stated in our personal galaxy, there are trillions of probably planets. And figuring out what number of galaxies there in all probability are, that’s, that quantity is exponential, huh? 

Dr. Mamajek: Yeah, the newest numbers I’ve seen, our galaxy in all probability has one thing like 100 to 200 billion stars. And so, we’re in all probability speaking of order a trillion or trillions of planets, simply, simply extrapolating from the statistics for exoplanets that we all know from surveys like Kepler and from transit work and microlensing. 

Host: So what strategies have been first used to find the primary exoplanets, and what’s superior since then? 

Dr. Mamajek: I’ll begin with the very first one, which produced the planets which have survived with irrefutable proof. And that was pulsar timing. 

Back within the early ‘90s, astronomers have been utilizing the Arecibo radio telescope doing timing of pulsars, and so they discovered that, you realize, a pulsar was shifting backwards and forwards in a sinusoidal vogue, however truly an advanced vogue. It was suggesting a number of planets. So, a pulsar is a neutron star, so one thing about 1.4 occasions the mass of the Sun, down compressed to the dimensions of a metropolis and comprised of neutrons. 

And they rotate very quick, and so they have sturdy magnetic fields, and so they beam radio radiation at us, and so they principally can act like clocks. And you’ll find periodic alerts, if different periodic alerts on prime of the pulsing and the pulsar. 

So, that was, that was truly, I’d say, an enormous shock within the early ‘90s. You know, that was a discovery that not only there are planets, but there’s planets round very odd objects. We thought the planetary system would have been destroyed round a neutron star that had shaped from a supernova.  

Shortly thereafter, the primary radial velocity detections have been going down, and that was 51 Pegasi in October ’95. I bear in mind as a result of I used to be an undergraduate. It was, it was an enormous deal. And, and that one was a Jupiter-size planet orbiting a Sun-like star on a interval of 4 days. 

And that was exceptional, as a result of the, the widespread knowledge on the time was different photo voltaic methods are in all probability going to appear like our photo voltaic system, and Jupiter and Saturn, they shaped far out the place there was extra ices. And we have been anticipating the massive planets to be, you realize, far out, and maybe rocky planets shut in. And I feel 51 Pegasi, the primary discoveries, proper, the pulsar planets, and 51 Pegasi b, that was already telling us that we have been going to begin seeing some actually bizarre instances that we weren’t suspecting. It wasn’t clear that our photo voltaic system was a typical final result of the star and planet formation course of. 

So, radial velocity was, was very, took off within the late ‘90s. There was a lot of large planets found orbiting nearby Sun-like stars. And then the first case of a hot Jupiter that passed in front of a star was found around 2000 and that was HD 20945 8b. That was a big deal, because now we knew for sure these really were planets. There was some controversy. Could these things be, you know, pull-on stars that were tugging on other stars, or brown dwarfs or something? And with 20945 8b, it was clear that, no, it was something the size of our Jupiter that was passing in front of a star. And then you could do things like measure densities of planets, right? You’ve received the dimensions and also you’ve received the mass. So now we’re beginning to get constraints on the composition of planets. 

And in order that opened up the world for transit observations. And now transits have discovered 1000’s of planets. We discovered there was much more sizzling Jupiters discovered from the bottom utilizing the transit approach, discovering these 1% dips within the mild of, of sun-like stars. 

And then in the event you go to house, you are able to do even higher photometry, even higher measurements of the celebs’ brightness, and in order that allowed the detection of smaller planets round many extra stars. Hundreds of 1000’s of stars might be surveyed, and so they have yielded 1000’s of planets. 

So, the NASA Kepler Mission discovered 1000’s of planet candidates, lots of which have been validated or have been detected by different strategies. And the TESS mission that’s, that’s up there now, is continuous to search out a whole lot of latest planets. So, the transit approach stays, stays lively, and so they’re discovering, you realize, many instances of small planets. 

And the, the opposite one which was took off within the 2000s was microlensing. If you stare at a large subject containing, you realize, many a whole lot of 1000’s of stars, maybe like in the direction of the galactic middle, you’re going to get instances the place the celebs and their planetary methods will gravitationally lens one other star, and also you’ll see a magnification in mild. And so there’s been many micro lensing detections discovered from ground-based surveys. And the NASA Roman telescope goes to do that on a on a large scale within the, in the direction of the galactic middle, within the years forward. 

And in the event you have been dwelling within the Eighties and also you have been going to say, what approach do you assume will yield the primary planets round different stars? I feel most individuals would have put their chips on astrometry… 

Host: Huh!

Dr. Mamajek: …detecting, you realize, the perturbations and the place of stars. And that was to not be, astrometry. There was makes an attempt within the twentieth century to search out planets by astrometry. It merely wasn’t doable from the bottom. It’s simply, it’s, it’s, you don’t have the wanted accuracy. 

If you go to house now, in the event you get to the micro arcsecond stage, or 10s of micro arcseconds stage, a whole lot of micro arcseconds stage, you can begin to detect large planets round stars. And so the European Space Agency Gaia mission is, is beginning to assist with discovering perturbations of stars on account of large planets. So, house astrometry is simply beginning to take off with the Gaia mission and hopefully different different missions sooner or later. 

Host: Astrometry, that’s much like how Neptune was found. Is that appropriate? Where they discovered a tug? 

Dr. Mamajek: Yes, that’s, that’s one model of it. Yeah, from the perturbations on Uranus’ orbit in our system. Yeah, you’re on the lookout for gravitational perturbation.

Host: In this case, it will be stars.

Dr. Mamajek: Yeah, in the event you have a look at the place of a star within the sky, if a star is all by itself, it’s on its, its personal completely happy orbit across the galaxy, you’ll see a wobble backwards and forwards because of the parallax, on account of, because of the Earth’s movement across the Sun, you’ll see a reflex movement. And you then’ll see a web movement throughout the sphere, a correct movement, simply because of the variations within the galactic orbit of that star and our Sun. 

But on prime of that, you may see little bumps and wiggles if there are gravitational perturbations on account of, to, on account of orbiting our bodies. People have completed this detecting stellar companions for a very long time, however now, now the approach is getting precisely sufficient, correct sufficient you may measure planets. 

Host: So, what are a few of the challenges in separating false positives within the knowledge, all that noise? 

Dr. Mamajek: So, I simply talked about a few of the strategies. For instance, with radial velocity, you realize, each with radial velocity and astrometry, you’re on the lookout for perturbations on a star. And radial velocity, you’re on the lookout for the radial perturbations on the radial movement. For astrometry, you’re on the lookout for perturbations on the place of the star within the sky. 

And you realize, you may get false positives from stars tugging on different stars. You know, if their orbits are aligned good, they may produce a perturbation that appeared much like what you’d anticipate from a planet. 

And that was, that was one of many causes there was, there was some skepticism on the primary radio velocity planets within the early ‘90s. And in fact, one of the, one of the famous early discoveries, HD 11476 2b, that was thought to be an 11 Jupiter mass companion discovered in the late ‘80s, that ended up being a star orbiting another star in a nearly pull-on orbit. So there’s some well-known instances of these false positives. 

With transits, the large contamination is you’re on the lookout for dips within the mild of a star. One of the bizarre instances you may have is an eclipsing binary star, so one star passing in entrance of one other star, and if that system is way fainter than one other vivid star subsequent to it, it may produce a sign that, with out lights all smeared out, the entire thing may appear like one star that was having slightly, slightly dip in its mild on account of a planet. And as a substitute it was, it was truly a faint binary, binary star subsequent to a a lot brighter star. 

So there’s lively observing campaigns that have been vetting the Kepler targets and now vetting check targets, looking for these contaminant stars. So, all of the discoveries you’re listening to although, from the TESS mission, they’ve been imaged with high-contrast imaging like speckle imaging or adaptive optics on giant telescopes. And they’ll say, “Yes, the light appears to be from that star,” or there’s some faint stars round, however they don’t seem like vivid sufficient to be contaminating the sunshine. 

And there are some bizarre instances the place we don’t know which star is liable for the transit. The check pixels are very giant. They’re about 20-some arcseconds. So, there are some instances the place it’s slightly bit ambiguous which star truly has the transiting planet. 

Host: When you have been speaking about Earth-size planets, that makes me consider the Goldilocks zone. Are most of those Earth-size planets in that zone? 

Dr. Mamajek: So far, only a few of them are in that zone. And we’ll speak about a number of alternative ways. One is considering it when it comes to how a lot mild the planet receives from its star.

So, for stars just like the Sun, when you’ve got an environment considerably much like Earth, you realize, some combine, maybe, of nitrogen, carbon dioxide, oxygen. You know that principally the, the quantity of sunshine can be one thing like 95% to about 170% of the quantity of sunshine we get from the Sun, which, proper now could be a few kilowatt per, per sq. meter. 

So that’s been, that’s been referred to as the quote, unquote, liveable zone, or Goldilocks zone. 

And only a few of the planets truly are in that zone. And then numerous those which can be discovered are giant. You know, they’re Jupiters or Neptunes. They could have giant envelopes of fuel, envelopes, atmospheres of hydrogen, helium, and they also in all probability don’t have a correct, you realize, floor or oceans, as we consider them. They’re in all probability underneath very excessive pressures, extra analogous to, you realize, the Jupiter and Neptunes in our system. 

So, I truly, I’ve been monitoring the small liveable zone planets. And, you realize, as we’re hitting 6,000 identified exoplanets. The depend of small, rocky planets orbiting inside the liveable zone of stars stands at about, I feel it’s round 46 now (ballpark). 

So, it’s, it’s a, you realize, it’s a fairly small variety of those we discovered to date, and most of these are round pink dwarf stars. So, they’re not much like our Earth. In reality, only a few of them, perhaps one or two of them, are round stars extra much like our Sun. It’s simply simpler to detect the alerts of a small planet round a small star than it’s to detect a small planet round an enormous star. 

So, there’s numerous instances, like, for instance, the closest star, Proxima Centauri, has a Earth-size planet in its liveable zone. But that’s planet has in all probability undergone a really, very totally different evolution than, than our, our Earth has. It goes round its star each 15 days. It’s acquired much more stellar winds and flares from this lively pink dwarf star. It’s tidally locked. It, I imply, for any for some primary assumptions concerning the composition of the planet, the age of the star, the system is sort of definitely tidally locked. You know, one face of the planet is dealing with the star on a regular basis. 

So, we know of dozens of, of Earth-size planets orbiting stars and the place their temperatures could be temperate, however they’re largely round pink dwarfs. 

Host: What traits do researchers search for for habitability? 

Dr. Mamajek: The place to begin, I’d say, is, you realize, how removed from the star does it, does it orbit? You know, we will measure the luminosity of the star, and we will calculate how far it orbits the star and the way a lot radiation it receives from its star. So that’s in all probability a place to begin. 

The methods are normally delicate to both normally mass or for the transit approach, radius, so we will, we will get an thought of the dimensions of the planet. Is it in a position to is it in a position to retain an environment? Or it’s not too massive, if it retains an excessive amount of environment? The planets greater than about one and a half occasions the radius of the Earth appear to be a distinct sort. They appear to be the so-called sub-Neptunes that in all probability have thick gaseous envelopes. They’re extra analogous, in all probability to Neptune than the Earth. So, that’s a place to begin. 

You know, sooner or later, for instance, one of many, one of many tasks NASA is simply getting underway now, is the Habitable Worlds Observatory. You know, we’re hoping to truly launch an area telescope, maybe by 2040 or so, that may be capable of picture Earth-size, temperate Earth-size planets round close by stars, and measure their spectrum. And after getting the spectrum, then you may say one thing concerning the chemistry of the gasses in its environment. 

And so, in the event you’re wanting on the Earth, you’ll see gasses like oxygen and water, carbon dioxide. If you go to the UV [ultraviolet] you begin to see ozone. 

And the Earth, as we all know it, has modified over time. The Earth has had very totally different atmospheres up to now as evidenced from the geological document, and so folks have been making an attempt to assemble, properly, what would an Earth, even a planet that had an evolution much like ours, what may it have appeared like when it was solely a billion years previous, a pair billion years previous, versus 4 billion years previous now? 

So I, I’m actually wanting ahead to the, you realize, after we’re beginning to get extra detailed spectra. And additionally, you realize, for instance, James Webb Space Telescope, that may be a NASA and ESA effort. We received to recollect, there are, there’s alternatives for, for worldwide cooperation on these very giant telescopes. 

So, you realize, there’s definitely, folks have been desirous to publish their outcomes, even, even when the outcomes are, you realize, you may contemplate boring, proper? Where a few of the latest outcomes with James Webb Space Telescope of close-in rocky planets, they’re on the lookout for atmospheres. And to date, a few of them have been constant. The spectra have been kind of according to a line as if it was only a rock, which they might be, or they may simply have very, very, you realize, dense atmospheres of heavy fuel. 

Host: I feel that’s fascinating, although, as a result of even 10 years later, you may have a look at the info once more, and… 

Dr. Mamajek: Yeah, I imply, that’s, there’s at all times alternative for doing, you realize, analysis on archival knowledge. There’s, there’s numerous nice stuff that may be present in these, these previous knowledge units. Once, you realize, as soon as the missions launched, it’s taking knowledge. People assume the outcomes simply come out instantly. And there’s numerous, there’s numerous knowledge that come from these missions, numerous alternatives for evaluation and discovery. 

For instance, you realize, the WISE mission. NASA WISE mission was imaging the sky within the the infrared. There’s, you realize, there’s efforts which can be nonetheless discovering, you realize, faint, heat sub stellar objects simply free-floating within the galaxy.

Host: So, there are methods for the general public to get entangled in citizen science. Can you clarify how?

Dr. Mamajek: There’s Backyard Worlds discovering principally there’s a lot knowledge, that it truly helps to get citizen scientists concerned and on the lookout for faint, shifting infrared blips on the sky. And a few of these have turned out to be very attention-grabbing objects, type of intermediate in scale between planets and stars. 

Exoplanet Watch is one other one. One of the attention-grabbing instances is that when you’ve got an enormous, costly telescope like James Webb Space Telescope, you need to just remember to’re pointing on the planet passing in entrance of its star, passing behind its star, and also you need to know the precise time so that you could plan the observations you need. You’ll need knowledge earlier than the, the transit and after the transit. 

The ephemerities for these orbits can go stale, proper? They’re found, any person you realize will quote an orbit, and that orbit has uncertainties, and the longer time goes on, those uncertainties can add up. 

And you realize, we’re definitely getting, you realize, extra epochs from TESS, however TESS doesn’t cowl the entire sky, and there’s alternatives for measuring a few of these transits from the bottom. If you realize which star it’s, and you realize roughly the correct time, you realize you are able to do a ground-based observing marketing campaign to detect extra transits, after which that tightens up the, the orbit and cuts down on the uncertainty. You don’t need JWST a star and notice that it was, you have been truly hours off the time of the transit. 

Host: Ugh, heartbreak! Eric, what was your large leap? 

Dr. Mamajek: I don’t know if there was a lot large leaps as, as, you realize, there’s a number of steps and alternatives, and I’m grateful for these. I used to be an undergraduate at Penn State, and I used to be in a position to work on radio astronomy tasks and spectrograph lab tasks with Eric Feigelson and Larry Ramsey, professors at Penn State. Those have been nice alternatives. I used to be in a position to do a grasp’s in Australia and a Ph.D. in Arizona. 

In Australia, one of many issues that actually shook me, that made me notice there’s simply numerous discoveries on the market to be made was shortly after I arrived in Australia for my masters, the info that I used to be analyzing revealed a there was a brand new star cluster inside 100 parsecs, which I discovered superb. Like, how was this missed? This is the Eta Chamaeleontis cluster, a brand new group of about five-or-10-million-year-old stars within the constellation Chamaeleon. 

And I discovered that incredible that new objects that close by might be discovered within the knowledge units. And the trick was combining X-ray knowledge with astrometry, and hastily, you see this group of X-ray emitting stars shut collectively on the sky co-moving. So, that changed into a number of papers. I began engaged on, you realize, younger stars and protoplanetary discs and particles discs, after which brown dwarfs. I went to University of Arizona, and began collaborating with a few of my colleagues. Matt Kenworthy has been a longtime collaborator of mine. It’s changed into tasks and now involving imaging planets round star, younger stars and, and transits, discovering attention-grabbing objects transiting stars. 

So, I’d say the opposite one was J1407 b, it was this ringed object that we printed round 2010. That was a very bizarre object, one thing about an astronomical unit in dimension, however had very advanced ring construction, much like Saturn’s rings. We nonetheless don’t know what that object is. It’s some sort of sub-stellar object that has a very difficult ring construction round it. It’s in all probability a rogue planet. It doesn’t seem like orbiting its star proper now, in any other case we’d have detected it.

So, there’s been some, there’s been some attention-grabbing discoveries alongside the way in which, and so they’ve changed into attention-grabbing instructions for future tasks. 

Host: This has been fascinating. Thanks for sharing every little thing about exoplanets and all of your work. Thank you, Eric.

Dr. Mamajek Hey, thanks! 

Host: That wraps up one other episode of Small Steps, Giant Leaps. For extra on Dr. Mamajek and NASA’s exoplanet analysis, go to nasa.gov/podcast and click on on Small Steps, Giant Leaps. There’ll you’ll find a full transcript of all our episodes together with hyperlinks to the matters talked about right now. You also can take a look at our different podcasts like Houston, We Have a Podcast, Curious Universe, and Universo Curioso de la NASA. As at all times, thanks for listening.

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