A living world around another star will not be an easy catch, no matter how sophisticated the coming generation of space- and ground-based telescopes turns out to be. It’s one thing to develop the tools to begin probing an exoplanet atmosphere, but quite another to be able to say with any degree of confidence that the result we see is the result of biology. When we do begin picking up an interesting gas like methane, we’ll need to evaluate the finding against other atmospheric constituents, and the arguments will fly about non-biological sources for what might be a biosignature. This is going to begin playing out as the James Webb Space Telescope turns its eye on exoplanets, and methane is the one potential sign of life that should be within its range. We know that oxygen, ozone, methane and carbon dioxide are produced through biological activity on Earth, and we also know that each can be produced in the absence of life. The simultaneous presence of such gases is what would intrigue...

Why is it so difficult to detect planets around Alpha Centauri? Proxima Centauri is one thing; we’ve found interesting worlds there, though this small, dim star has been a tough target, examined through decades of steadily improving equipment. But Centauri A and B, the G-class and K-class central binary here, have proven impenetrable. Given that we’ve found over 4500 planets around other stars, why the problem here? Proximity turns out to be a challenge in itself. Centauri A and B are in an orbit around a common barycenter, angled such that the light from one will contaminate the search around the other. It’s a 79-year orbit, with the distance between A and B varying from 35.6 AU to 11.2. You can think of them as, at their furthest, separated by the Sun’s distance from Pluto (roughly), and at their closest, by about the distance to Saturn. The good news is that we have a window from 2022 to 2035 in which, even as our observing tools continue to improve, the parameters of that orbit...

I always keep an eye on the Phase I and Phase II studies in the pipeline at the NASA Innovative Advanced Concepts (NIAC) program. The goal is to support ideas in their early stages, with the 2022 awards going out to 17 different researchers to the tune of a combined $5.1 million. Of these, 12 are Phase I studies, which deliver $175,000 for a nine-month period, while the five Phase II awards go to $600,000 over two years. We looked at one of the Phase I studies, Jason Benkoski's solar-thermal engine and shield concept, in the last post. Today we go hunting exoplanets with a starshade. This particular iteration of the starshade concept is called Hybrid Observatory for Earth-like Exoplanets (HOEE), as proposed by John Mather (NASA GSFC). Here the idea is to leverage the resources of the huge ground-based telescopes that should define the next generation of such instruments - the Giant Magellan Telescope, the Extremely Large Telescope, etc. - by using a starshade to block the glare of...

The apparent discovery of a new planet around Proxima Centauri moves what would have been today’s post (on laser-thermal interstellar propulsion concepts) to early next week. Although not yet confirmed, the data analysis on what will be called Proxima Centauri d seems strong, in the hands of João Faria (Instituto de Astrofísica e Ciências do Espaço, Portugal) and colleagues. The work has just been published in Astronomy & Astrophysics. It’s good to hear that Faria describes Proxima Centauri as being “within reach of further study and future exploration.” That last bit, of course, is a nod to the fact that this is the nearest star to the Sun, and while 4.2 light years is its own kind of immensity, any future interstellar probe will naturally focus either here or on Centauri A and B. Years are short on Proxima d – the putative planet circles Proxima every five days. That’s a tenth of Mercury’s distance from the Sun, closer to the star than to the inner edge of the habitable zone....

It would explain a lot if two recent discoveries involving 'mini-Neptunes' turned out to be representative of what happens to their entire class. For Michael Zhang (Caltech) and colleagues, in two just published papers, have found that mini-Neptunes can lose gas to their parent star, possibly indicating their transformation into a 'super-Earth.' If such changes are common, then we have a path to get from a dense but Neptune-like world to a super-Earth, a planet roughly 1.6 times the size of the Earth and part of a category of worlds we do not see represented in our Solar System. As we drill down toward finding smaller worlds, we've been finding a lot of mini-Neptunes as well as super-Earths, with the former two to four times the size of the Earth. Thus we have a bimodal gap in exoplanet observation. Where are the worlds between 1.6 and 2-4 times the size of Earth? The new work examines two mini-Neptunes around the TESS object TOI 560, located about a hundred light-years from Earth,...

Given our recent discussion of exomoon candidate Kepler-1708 b-i, a possible moon 2.6 times the mass of Earth orbiting a gas giant, I want to be sure to work in Miki Nakajima’s work on how moons form. Nakajima (University of Rochester) is first author of the paper describing this work. It’s a significant contribution because it points to a way to refine the target list for exomoon searches, one that may help us better understand where to look as we begin to flesh out a catalog of these objects.. And flesh it out we will, as the precedent of the rapidly growing exoplanet count makes clear. What I want to do today is consider how we’ve thus far proceeded. You’ll recall that when David Kipping and team performed their deep analysis of the data leading to Kepler-1708 b-i, they chose gas giants on orbits with a period of 400 days or more, so-called ‘cool worlds’ more like Jupiter than the ‘hot Jupiters’ found so frequently in early exoplanet studies. The method produced a strong candidate...

Half a century ago, we were wondering if other stars had planets, and although we assumed so, there was always the possibility that planets were rare. Now we know that they’re all over the place. In fact, recent research out of Katholieke Universiteit Leuven in Belgium suggests that under certain circumstances, planets can form around stars that are going through their death throes, beginning the transition from red giant to white dwarf. The new work homes in on certain binary stars, and therein hangs a tale. After a red giant star has gone through the stage of helium burning at its core, it is referred to as an asymptotic giant branch star (AGB), on a path that takes it through a period of expansion and cooling prior to its becoming a white dwarf. These expanding stars lose mass as the result of stellar wind, up to 50 to 70 percent of the total mass of the star. The result: An extended envelope of material collecting around the object that will become a planetary nebula, a glowing...

We started finding a lot of 'hot Jupiters' in the early days of planet hunting simply because, although their existence was not widely predicted, they were the most likely planetary types to trigger our radial velocity detection methods. These star-hugging worlds produced a Doppler signal that readily showed the effects of planet on star, while smaller worlds, and planets farther out in their orbits, remained undetected. David Kipping (Columbia University) uses hot Jupiters as an analogy when describing his own indefatigable work hunting exomoons. We already have one of these - Kepler-1625 b-i - but it remains problematic and unconfirmed. If this turned out to be the first in a string of exomoons, we might well expect all the early finds to be large moons simply because using transit methods, these would be the easiest to detect. Kepler-1625 b-i is problematic because the data could be showing the effects of other planets in its system. If real, it would be a moon far larger than any...

Using machine learning to provide an algorithmic approach to the abundant data generated by the Transiting Exoplanet Survey Satellite (TESS) has proven unusually productive. I'm looking at an odd object called TIC 400799224, as described in a new paper in The Astronomical Journal from Brian Powell (NASA GSFC) and team, a source that displays a sudden drop in brightness - 25% in a matter of four hours - followed by a series of brightness variations. What's going on here? We're looking at something that will have to be added to a small catalog of orbiting objects that emit dust; seven of these are presented in the paper, including this latest one. The first to turn up was KIC 12557548, whose discovery paper in 2012 argued that the object was a disintegrating planet emitting a dust cloud, a model that was improved in subsequent analyses. K2-22b, discovered in 2015, showed similar features, with varying transit depths and shapes, although no signs of gas absorption.. In fact, the objects...

As we begin the New Year, I want to be sure to catch up with the recent announcement of a discovery regarding 'rogue' planets, those interesting worlds that orbit no central star but wander through interstellar space alone (or, conceivably, with moons). Conceivably ejected from their host stars through gravitational interactions (more on this in a moment), such planets become interstellar targets in their own right, as given the numbers now being suggested, there may be rogue planets near the Solar System. Image: Rogue planets are elusive cosmic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of astronomers, using data from several European Southern Observatory (ESO) telescopes and other facilities, have just discovered at least 70 new rogue planets in our galaxy. This is the largest group of rogue planets ever discovered, an important step towards...

The day is not far off when we’ll be able to look at a small planet in the habitable zone of its star and detect basic features on its surface: water, ice, land. The era of the 30-meter extremely large telescope approaches, so this may even be possible from the ground, and large space telescopes will be up to the challenge as well (which is why things like aperture size and starshade prospects loom large in our discussions of current policy decisions). Consider this: On the Earth, while the atmosphere reflects a huge amount of light from the Sun, about half the total albedo at the poles comes from polar ice. It would be useful, then, to know more about the ice and land distribution that we might find on planets around other stars. This is the purpose of a new paper in the Planetary Science Journal recounting the creation of climate simulations designed to predict how surface ice will be distributed on Earth-like exoplanets. It’s a relatively simple model, the authors acknowledge, but...

It's no small matter to add 301 newly validated planets to an exoplanet tally already totalling 4,569. But it's even more interesting to learn that the new planets are drawn out of previously collected data, as analyzed by a deep neural network. The 'classifier' in question is called ExoMiner, describing machine learning methods that learn by examining large amounts of data. With the help of the NASA supercomputer called Pleiades, ExoMiner seems to be a wizard at separating actual planetary signatures from the false positives that plague researchers. ExoMiner is described in a paper slated for The Astrophysical Journal, where the results of an experimental study are presented, using data from the Kepler and K2 missions. The data give the machine learning tools plenty to work with, considering that Kepler observed 112,046 stars in its 115-degree square search field, identifying over 4000 candidates. More than 2300 of these have been confirmed. The Kepler extended mission K2 detected...

Discovered in 1915, Proxima Centauri has been a subject of considerable interest ever since, as you would expect of the star nearest to our own. But I had no idea research into planets around Proxima went all the way back to the 1930s. Nonetheless, a new paper from Emily Gilbert (University of Chicago) and colleagues mentions a 1938 attempt by Swedish astronomer Erik Holmberg to use astrometric methods to search for one or more Proxima planets. The abstract of the Holmberg paper (citation below) reads in part: Many parallax stars show periodic displacements. These effects probably are to be explained as perturbations caused by invisible companions. Since the amplitudes of the orbital motion are very small, the masses of the companions will generally be very small, too. Thus Proxima Centauri probably has a companion, the mass of which is only some few times larger than the mass of Jupiter. A preliminary investigation gives the result that 25% of the total number of parallax stars may...

We talked about the TOLIMAN mission last April, and the renewed interest in astrometry as the key to ferreting out possible planets around Alpha Centauri A and B. I was fortunate enough to hear Peter Tuthill (University of Sydney), who leads the team that has been developing the concept, rough out the idea at Breakthrough Discuss five years ago; Céline Bœhm (likewise at the University of Sydney) reported on more recent work at the virtual Breakthrough Discuss session this past spring. We now have an announcement from scientists involved that the space telescope mission will proceed. Eduardo Bendek (JPL) is a member of the TOLIMAN team: "Even for the very nearest bright stars in the night sky, finding planets is a huge technological challenge. Our TOLIMAN mission will launch a custom-designed space telescope that makes extremely fine measurements of the position of the star in the sky. If there is a planet orbiting the star, it will tug on the star betraying a tiny, but...

Circumbinary planets are those that orbit two stars, a small but growing category of worlds -- we've detected some 14 thus far, thanks to Kepler's good work, and that of the Transiting Exoplanet Survey Satellite (TESS). The latest entry, TIC 172900988, illustrates the particular challenge such planets represent. Transit photometry is a standard method for finding planets, detecting the now familiar drop in starlight as the planet moves between us and the surface of the host star. Kepler found thousands of exoplanets this way. But when two stars are involved, things get complicated. Image: The newly discovered planet, TIC 172900988b, is roughly the radius of Jupiter, and several times more massive, but it orbits its two stars in less than one year. This world is hot and unlike anything in our Solar System. Credit: PSI/Pamela L. Gay. Three transits are required to determine the orbital path of a planet. For us to make a detection, a circumbinary planet will have to transit both stars,...

Although we’ve been talking this week about big telescopes, from extremely large designs like the Thirty Meter Telescope and the European Extremely Large Telescope to the space-based HabEx/LUVOIR descendant prioritized by Astro2020, small instruments continue to do interesting work around the edges. I just noticed a tiny one called the Star-Planet Activity Research CubeSat (SPARCS) that fills a gap in our study of M-dwarfs, those small stars whose flares are so problematic for habitability. Under development at Arizona State University, the space-based SPARCS is just halfway into its development phase, but let’s take a look at it in light of ongoing work on M-dwarf planets, because it bodes well for turning theories about flare activity into data that can firm up our understanding. The problem is that while theoretical studies delve into ultraviolet flaring on these stars, the longest intensive UV monitoring on an M-dwarf done thus far has been a thirty hour effort with the Hubble...

The surge of interest in white dwarfs continues. We've known for some time that these remnants of stars like the Sun, having been through the red giant phase and finally collapsing into a core about the size of the Earth, can reveal a great deal about objects that have fallen into them. That would be rocky material from planetary objects that once orbited the star, just as the planets of our Solar System orbit the Sun in our halcyon, pre-red-giant era. The study of atmospheric pollution in white dwarfs rests on the fact that white dwarfs that have cooled below 25,000 K have atmospheres of pure hydrogen or helium. Heavier elements sink rapidly to the stellar core at these temperatures, so the only source of elements higher than helium -- metals in astronomy parlance -- is through accretion of orbiting materials that cross the Roche limit and fall into the atmosphere. These contaminants of stellar atmospheres are now the subject of a new investigation led by astronomer Siyi Xu (NSF...

The idea that the composition of a star and its rocky planets are connected is a natural one. Both classes of object accrete material within a surrounding gas and dust environment, and thus we would expect a link between the two. Testing the hypothesis, researchers from three institutions -- the Instituto de Astrofísica e Ciências do Espaço (Portugal), the NCCR PlanetS project at the University of Bern, and the University of Zürich -- have confirmed the concept while fine-tuning the details. After all, we still have to explain iron-rich Mercury as an outlier in our own Solar System. Image: Mercury has an average density of 5430 kilograms per cubic meter, which is second only to Earth among all the planets. It is estimated that the planet Mercury, like Earth, has a ferrous core with a size equivalent to two-thirds to three-fourths that of the planet's overall radius. The core is believed to be composed of an iron-nickel alloy covered by a mantle and surface crust. Credit: NASA....

A gas giant similar to Jupiter, and with a somewhat similar orbit, revolves around a white dwarf located about 6500 light years out toward galactic center. As reported in a paper in Nature, this is an interesting finding because stars like the Sun eventually wind up as white dwarfs, so we have to wonder what kind of planets could survive a star’s red giant phase and continue to orbit the primary. If Earth one day is engulfed, will the gas giants survive? The new discovery implies that result, and marks the first confirmed planetary system that looks like what ours could become. Image: An artist’s rendition of a newly discovered Jupiter-like exoplanet orbiting a white dwarf. This system is evidence that planets can survive their host star’s explosive red giant phase, and is the first confirmed planetary system that serves as an analogue to the face of the Sun and Jupiter in our own Solar System. Credit: W. M. Keck Observatory/Adam Makarenko. Underlining just how faint white dwarfs are...

I was interested in yesterday's story about the two super-Earths around nearby M-dwarfs -- TOI-1634b and TOI-1685b -- partly because of the research that follows. In both cases there is the question of atmospheres. The two TESS planets are so numbingly close to their host stars that they may have lost their original hydrogen/helium atmospheres in favor of an atmosphere sustained by emissions from within. Hearteningly, we should be able to find out more with the James Webb Space Telescope, on which ride the hopes of so many exoplanet researchers. Today's system is the intriguing L 98-59, only 35 light years from Earth and possessed of at least four planets, with a fifth as yet unconfirmed. Here we have two rocky inner worlds, a possible ocean planet (L 98-59 d) and another likely rocky world to the inside of the habitable zone boundary. Perhaps within the habitable zone, if it exists, is L 98-59f, so this is a system to keep an eye on, an obvious candidate as a JWST target. At UC...