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...