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...