You can blame H. G. Wells' The Time Machine for my interest in the Earth's far future. That swollen red Sun at the end of the novel created vivid 'end of the world' scenarios for me as a boy, and later I would learn that outer planets or moons around a G-class star might turn habitable once it became a red giant. But it would only be in the last few years that I learned how robust the investigations into white dwarf systems -- the fate of a red giant -- have become, and now we're finding out not only that such stars can retain planets, but can conceivably create new ones through an emerging disk packed with the pulverized dust of remnant materials like asteroids. Image: This artist's concept shows a white dwarf debris disk. Credit: NASA/JPL-Caltech. Jordan Steckloff (Planetary Science Institute, Tucson) has just published a short paper on the matter, looking at how white dwarf debris disks emerge. The disks seem to form only after ten to twenty million years following the end of the...

Back in the 1990s, when the first exoplanet detections were made, the best possible targets for radial velocity searches were what we now call 'hot Jupiters.' Radial velocity looks at the Doppler shift of light as a star moves first towards us, then away, tugged by the invisible planet. A massive Jupiter in a tight orbit tugged maximally, and quite often, because its orbit could be measured in mere days or weeks. It was purely selection effect, but it seemed that such planets were common, until we began to discover just how many other kinds of worlds were out there. Outer-system Jupiters like ours are a different problem. A gas giant in a multi-year orbit produces a radial velocity signature that is far smaller and dependent upon long analysis. Thus, early numbers on the existence of gas giants in the Jupiter or Saturn class and similarly far from their host star are just beginning to emerge as exoplanet science matures. We'll be learning more -- a lot more -- but tentative findings...

Laboratory work on Earth is, as we saw yesterday, leading to hypotheses about how planets form and the effect of these processes on subsequent life. Whether in our own outer Solar System or orbiting other stars, planets in the 'ice giant' category, like Uranus and Neptune, remain mysterious, with Voyager 2's flybys of the latter the only missions that have gone near them. We also know that sub-Neptune planets are common, many of these doubtless sharing the characteristics of their larger namesake. Thus recent experiments probing ice giant interiors catch my eye this morning. Involving an international team of collaborators, the work looks at the interactions between water and rock that we would expect to find in the extreme conditions inside an ice giant. Planets like Uranus and Neptune are thought to house most of their mass in a deep water layer, a dense fluid overlaying a rocky core, a sharp departure from terrestrial worlds. What happens at that interface is ripe for examination....

While a planet's position in the habitable zone is thought critical for the development of life like ourselves, new work out of Rice University suggests an equally significant factor in planetary growth. Working at a high-pressure laboratory at the university, Damanveer Grewal and Rajdeep Dasgupta have explored how planets capture and retain key volatiles like nitrogen, carbon and water as they form The team used nitrogen as a proxy for volatile distribution in a range of simulated protoplanets. Two processes are under study here, the first being the accretion of material in the circumstellar disk into a protoplanet, and the rate at which it proceeds. The second is differentiation, as the protoplanet separates into layers ranging from a metallic core to a silicate shell and, finally, an atmospheric envelope. The interplay between these processes is found to determine which volatiles the subsequent planet retains. Most of the nitrogen is found to escape into the atmosphere during...

Is there any chance we may one day find technosignatures around the nearest stars? If we were to detect such, on a planet, say, orbiting Alpha Centauri B, that would seem to indicate that civilizations are to be found around a high percentage of G- and K-class stars. Brian Lacki (UC-Berkeley) examined the question from all angles at the recent Breakthrough Discuss, raising some interesting issues about the implications of technosignatures, and the assumptions we bring to the search for them. We’re starting to consider a wide range of technosignatures rather than just focusing on Dysonian shells around entire stars. Other kinds of megastructure are possible, some perhaps so exotic we wouldn’t be sure how they operated or what they were for. Atmospheres could throw technosignatures by revealing industrial activity along with their potential biosignatures. We could conceivably detect power beaming directed at interstellar spacecraft or even an infrastructure within a particular stellar...

In the ranks of exoplanets we can actually see, we can include the gas giant PDS 70b, a young world orbiting the K-dwarf PDS 70. Bear in mind that of the more than 4,000 exoplanets thus far catalogued, only about 15 have been directly imaged, an indication of how tricky this work is and how far we have to go as we contemplate imaging Earth-size planets and taking spectroscopic measurements of their atmospheres. The most recent PDS 70b work was performed with the Hubble instrument, and is to my knowledge the first direct detection of an exoplanet in the ultraviolet. About 370 light years from Earth, PDS 70 (also known as V1032 Centauri) is a T Tauri star, a class of variables less than 10 million years old; this one appears to be no more than 5 million years old, and its largest planet is still in the process of building mass. The star is known to host at least two actively forming planets within its circumstellar disk of gas and dust, although only the larger is apparent in these UV...

Because we've just looked at how a carbon cycle like Earth's may play out to allow habitability on other worlds, today's paper seems a natural segue. It involves geology and planet formation, though here we're less concerned with plate tectonics and feedback mechanisms than the composition of a planet's mantle. At the University of British Columbia - Okanagan, Brendan Dyck argues that the presence of iron is more important than a planet's location in the habitable zone in predicting habitability. We learn that planetary mantles become increasingly iron-rich with proximity to the snow-line. In the Solar System, Mercury, Earth and Mars show silicate-mantle iron content that increases with distance from the Sun. Each planet had different proportions of iron entering its core during the planet formation period. The differences between them are the result of how much of their iron is contained in the mantle versus the core, for each should have the same proportion of iron as the star they...

Earth's long-term carbon cycle is significant for life because it keeps carbon in transition, rather than allowing it to accumulate in its entirety in the atmosphere, or become completely absorbed in carbonate rocks. The feedback mechanism works over geological timescales to allow stable temperatures as CO2 cycles between Earth's mantle and the surface. As a result, we have carbon everywhere. 65,500 billion metric tons stored in rock complements the carbon found in the atmosphere and the oceans, as well as in surface features including vegetation and soil. It's a long-term cycle that can vary in the short term but be stabilizing over geological time-frames. The Sun has increased in luminosity substantially since Earth's formation, but the long-term carbon cycle is thought to be the key to maintaining temperatures on the surface suitable for life. Does it exist on other planets? It's an open question, as astronomer Mark Oosterloo (University of Groningen, The Netherlands) points out:...

Why the renewed focus on astrometry when it comes to Alpha Centauri (a theme we saw as well in the previous post on ALMA observations from the surface)? One problem we face with other detection methods is simply statistical: We can study planets, as via the Kepler mission, by their transits, but if we want to know about specific stars that are near us, we can’t assume a lucky alignment. Radial velocity requires no transits, but has yet to be pushed to the level of detecting Earth-mass planets at habitable-zone distances from stars like our own. This is why imaging is now very much in the mix, as is astrometry, and getting the latter into space in a dedicated mission has occupied a team at the University of Sydney led by Peter Tuthill for a number of years -- I remember hearing Tuthill describe the technology at Breakthrough Discuss in 2016. Out of this effort we get a concept called TOLIMAN, a space telescope that draws its title from Alpha Centauri B, whose medieval name in Arabic,...

When it comes to finding planets around Centauri A and B, the method that most intrigues me is astrometry. At the recent Breakthrough Discuss sessions, Rachel Akeson (Caltech/IPAC) made the case for using the technique with data from the Atacama Large Millimeter Array (ALMA). My interest is piqued by the fact that so few of the more than 4300 known exoplanets have been discovered using astrometry, although astronomers were able in 2002 to characterize the previously known Gliese 876 using the method. Before that, numerous reported detections of planets around other stars, some going back to the 18th Century, have proven to be incorrect. But we’re entering a new era. ESA’s Gaia mission, launched in 2013, is likely to return a large horde of planets using astrometry as it creates a three-dimensional map of star movement in the Milky Way. Dr. Akeson’s case for using ALMA to make detections on the ground is robust, despite the challenges the method presents. She points out that if we...

At some point, and probably soon, we're going to be able to identify planets around Alpha Centauri A and B, assuming they are there and of a size sufficient for our methods. We may even be able to image one. Already we have an extremely tentative candidate around Alpha Centauri A -- I hesitate even to call it a candidate, because this work is so preliminary -- which could be a 'warm Neptune' at about 1 AU. One of the pleasures of the recent Breakthrough Discuss meeting was to hear film director James Cameron on the matter. Cameron, after all, gave us Avatar, where a habitable moon around a gas giant in this system plays the key role. Despite his frequent protestations that he is not a scientist, Cameron was compelling. He's obviously well-enough versed in the science to know the terminology and the issues involved in the ongoing deep dive into the Alpha Centauri system, and he's done wonders in fixing the public's attention not only on its possibilities but also on presenting a...

I've been wanting to explore some of the observing campaigns for the Alpha Centauri system -- their approach, design and early results -- and we'll start that early next week. But let's home in first on an event within that system, a flare from Proxima Centauri that is fully 100 times more powerful than any flare ever detected from our own star. That Proxima was capable of major flares was already known in 2018 when, according to data from the Atacama Large Millimeter Array (ALMA), an earlier flare at millimeter wavelengths (233 GHz) was detected. It was an interesting moment, captured in a paper on the work in Astrophysical Journal Letters (citation below). Lead author Meredith MacGregor, an assistant professor at the Center for Astrophysics and Space Astronomy (CASA) and Department of Astrophysical and Planetary Sciences (APS) at the University of Colorado Boulder, also found it provocative. "We had never seen an M dwarf flare at millimeter wavelengths before 2018, so it was not...

What governs the size of a newly forming star as it emerges from the molecular cloud around it? The answer depends upon the ability of gravity to overcome internal pressure within the cloud, and that in turn depends upon exceeding what is known as the Jeans Mass, whose value will vary with the density of the gas and its temperature. Exceed the Jeans mass and runaway contraction begins, forming a star whose own processes of fusion will arrest the contraction. At the Max Planck Institute for Astronomy (Heidelberg), Hubert Klahr and colleagues have been working on a different kind of contraction, the processes within the protoplanetary disk around such young stars. Along with postdoc Andreas Schreiber, Klahr has come up with a type of Jeans Mass that can be applied to the formation of planetesimals. While stars in formation must overcome the pressure of their gas cloud, planetesimals work against turbulence within the gas and dust of a disk -- a critical mass is needed for the clump to...

The Nancy Grace Roman Space Telescope is the instrument until recently known as WFIRST (Wide-Field Infrared Survey Telescope), a fact I'll mention here for the last time just because there are so many articles about WFIRST in the archives. From now on, I'll just refer to the Roman Space Telescope, or RST. Given our focus on exoplanet research, we should keep in mind that the project's history has been heavily influenced by concepts for studying dark energy and the expansion history of the cosmos. The exoplanet component has grown, however, into a vital part of the mission, and now includes both gravitational microlensing and transit studies. We've discussed both methods frequently in these pages, so I'll just note that microlensing relies on the movement of a star and its accompanying planetary system in front of a background star, allowing the detection because of the resultant brightening of the background star's light. We're seeing the effects of the warping of spacetime caused by...

The circumstellar disks that give rise to planets occur in huge variety depending on the nature of star formation around them. Such disks form early as stars emerge, according to some recent work appearing within 10,000 years after the birth of the star. New work out of Leiden University in The Netherlands homes in on the environmental factors shaping the evolution of these disks, giving us a sense of how stellar systems differentiate as their planetary configurations form. The work, led by Francisca Concha-Ramírez, offers up a model of circumstellar disk formation in young star-forming regions. The formation model is a mathematical treatment that begins with the collapse of a giant molecular cloud and the subsequent formation of stars in a variety of masses, velocities and positions within a cluster. The disk formation model sets stellar evolution into motion at the same time as disk formation to study the interactions between the two as star-forming regions of varying densities...

Gliese 486b is, in the words of astronomer Ben Montet, "the type of planet we'll be studying for the next 20 years." Montet (University of New South Wales) is excited about this hot super-Earth because it's the closest such planet we've found to our own Solar System, at about 26 light years away. That has implications for studying its atmosphere, if it has one, and by extension sharpening our techniques for atmospheric analysis of other nearby worlds. The goal we're moving toward is being able to examine smaller rocky planets for biosignatures. But we're not there yet, and what we have in Gliese 486b is an exoplanet that has now been identified as a prime target for future space- and ground-based instruments, one that, given its proximity, is an ideal next step to push our methods forward. The paper on this work shows that two techniques can be deployed here, the first being transmission spectroscopy, when this transiting world passes in front of its star and starlight filters...

The planets orbiting the young star TOI 451 should be useful for astronomers working on the evolution of atmospheres on young planets. This is a TESS find, three planets tracked through their transits and backed by observations from the now retired Spitzer Space Telescope, with follow-ups as well from Las Cumbres and the Perth Exoplanet Survey Telescope. TOI 451 (also known as CD-38 1467) is about 400 light years out in Eridanus, a star with 95% of the Sun's mass, some 12% smaller and rotating every 5.1 days. That rotation is interesting, as it's more than five times faster than our Sun rotates, a marker for a young star, and indeed, astronomers have ways of verifying that the star is only about 120 million years old. Here the Pisces-Eridanus stream, only discovered in 2019, becomes a helpful factor. A stream of stars forms out of gravitational interactions between our galaxy and a star cluster or dwarf galaxy, shoe-horning stars out of their original orbit to form an elongated flow....

We may or may not have imaged a planet around Alpha Centauri A, possibly a ‘warm Neptune’ at an orbital distance of roughly 1 AU, the distance between Earth and the Sun. Let’s quickly move to the caveat: This finding is not a verified planet, and may in fact be an exozodiacal disk detection or even a glitch within the equipment used to see it. But as the paper notes, the finding called C1 is “is not a known systematic artifact, and is consistent with being either a Neptune-to-Saturn-sized planet or an exozodiacal dust disk.“ So this is interesting. As it may be some time before we can make the call on C1, I want to emphasize the importance not so much of the possible planet but the method used to investigate it. For what the team behind a new paper in Nature Communications has revealed is a system for imaging in the mid-infrared, coupled with long observing times that can extend the capabilities of ground-based telescopes to capture planets in the habitable zone of other nearby...

Although it seems so long ago as to have been in another century (which it actually almost was), the first detection of an exoplanet atmosphere came in the discovery of sodium during a transit of the hot Jupiter HD 209458b in 2002. To achieve it, researchers led by David Charbonneau used the method called transmission spectroscopy, in which they analyzed light from the star as it passed through the atmosphere of the planet. Since then, numerous other compounds have been found in planetary atmospheres, including water, methane and carbon dioxide. Scientists also expect to find the absorption signatures of metallic compounds in hot Jupiters, and these have been detected in brown dwarfs as well as ultra-hot Jupiters. Now we have new work out of SRON Netherlands Institute for Space Research and the University of Groningen. Led by Marrick Braam, a team of astronomers has found evidence for chromium hydride (CrH) in the atmosphere of the planet WASP-31b, a hot Jupiter with a temperature of...

'Xallarap' is parallax spelled backward (at least it's not another acronym). And while I doubt the word will catch on in common parlance, the effect it stands for is going to be useful indeed for astronomers using the Nancy Grace Roman Space Telescope. This is WFIRST -- the Wide Field Infrared Survey Telescope -- under its new name, a fact I mention because I think this is the first time we've talked about the mission since the name change in 2020. Image: High-resolution illustration of the Roman spacecraft against a starry background. Credit: NASA's Goddard Space Flight Center. While a large part of its primary mission will be devoted to dark energy and the growth of structure in the cosmos, a significant part of the effort will be directed toward gravitational microlensing, which should uncover thousands of exoplanets. This is where the xallarap effect comes in. It's a way of drawing new data out of a microlensed event, so that while we can continue to observe planets around a...