Sub-Neptune planets are going to be occupying scientists for a long time. They’re the most common type of planet yet discovered, and they have no counterpart in our own Solar System. The media buzz about K2-18b that we looked at last time focused solely on the possibility of a biosignature detection. But this world, and another that I’ll discuss in just a moment, have a significance that can’t be confined to life. Because whether or not what is happening in the atmosphere of K2-18b is a true biosignature, the presence of a transiting sub-Neptune relatively close to the Sun offers immense advantages in studying the atmosphere and composition of this entire category. Are these ‘ hycean’ worlds with global oceans beneath an atmosphere largely made up of hydrogen? It’s a possibility, but it appears that not all sub-Neptunes are the same. Helpfully, we have another nearby transiting sub-Neptune, a world known as TOI-270 d, which at 73 light years is even closer than K2-18b, and has in...

As teams of researchers begin to detect molecules that could indicate the presence of life in the atmospheres of exoplanets, controversies will emerge. In the early stages, the method will be transmission spectroscopy, in which light from the star passes through the planet’s atmosphere as it transits the host. From the resulting spectra various deductions may be drawn. Thus oxygen (O₂), ozone (O₃), methane (CH₄), or nitrous oxide (N₂O) would be interesting, particularly in out of equilibrium situations where a particular gas would need to be replenished to continue to exist. While we continue with the painstaking work of identifying potential biological markers -- and there will be many -- new findings will invariably become provocations to find abiotic explanations for them. Thus the recent flurry over K2-18b, a large (2.6 times Earth’s radius) sub-Neptune that, if not entirely gaseous, may be an example of what we are learning to call ‘hycean’ worlds. The term stands for...

The thought of a planet orbiting a Sun-like star began to obsess me as a boy, when I realized how different all the planets in our Solar System were from each other. Clearly there were no civilizations on any planet but our own, at least around the Sun. But if Alpha Centauri had planets, then maybe one of them was more or less where Earth was in relation to its star. Meaning a benign climate, liquid water, and who knew, a flourishing culture of intelligent beings. So ran my thinking as a teenager, but then other questions began to arise. Was Alpha Centauri Sun-like? Therein hangs a tale. As I began to read astronomy texts and realized how complicated the system was, the picture changed. Two stars and perhaps three, depending on how you viewed Proxima, were on offer here. ‘Sun-like’ seemed to imply a single star with stable orbits around it, but surely two stars as close as Centauri A and B would disrupt any worlds trying to form there. Later we would learn that stable orbits are...

In astronomy, the first thing you see may be the least typical. A case in point: ‘Hot Jupiters.’ A few prescient souls, among them Buzz Aldrin and John Barnes in their novel Encounter with Tiber, speculated about gas giants that survived incredibly tight orbits around their star, and when asked about this in the 1990s, Greg Matloff ran the numbers and confirmed to his surprise that there was a theoretical case for their existence. Let me quote Matloff on this: Although I was initially very skeptical since then-standard models of solar system formation seemed to rule out such a possibility, I searched through the literature and located the appropriate equation (Jastrow and Rasool, 1965)….To my amazement, Buzz was correct. The planet’s atmosphere is stable for billions of years. Since I was at the time working as a consultant and adjunct professor, I did not challenge the existing physical paradigm by submitting my results to a mainstream journal. Since “Hot Jupiters” were discovered...

The problem of flares in red dwarf planetary systems is stark. With their habitable zones relatively near to the star, planets that might support life are exposed to huge outbursts of particles and radiation that can strip their atmospheres. We can see that in nearby M-dwarfs like Proxima Centauri, which is extremely active not only in visible light but also in radio and millimeter wavelengths. New work at the Atacama Large Millimeter/submillimeter Array (ALMA) digs into the millimeter-wavelength activity. The results do nothing to ease the concern that systems like this may be barren of life. Small M-dwarf stars are a problem because they operate through convection as energy from fusion at the core is transferred to the surface. A convective structure is one in which hot material from below moves constantly upward, a process that can be likened to what we see in a boiling cauldron of water. Larger stars like the Sun show a mix of radiative transfer – photons being absorbed and...

Exactly how astrophysicists model entire stellar systems through computer simulations has always struck me as something akin to magic. Of course, the same thought applies to any computational methods that involve interactions between huge numbers of objects, from molecular dynamics to plasma physics. My amazement is the result of my own inability to work within any programming language whatsoever. The work I’m looking at this morning investigates planet formation within protoplanetary disks. It reminds me again just how complex so-called N-body simulations have to be. Two scientists from Rice University – Sho Shibata and Andre Izidoro – have been investigating how super-Earths and mini-Neptunes form. That means simulating the formation of planets by studying the gravitational interactions of a vast number of objects. N-body simulations can predict the results of such interactions in systems as complex as protoplanetary disks, and can model formation scenarios from the collisions of...

I’ve been digging into NASA’s Small Spacecraft Strategic Plan out of continuing interest in missions that take advantage of miniaturization to do things once consigned to large-scale craft. And I was intrigued to learn about the small spacecraft deployed on Apollo 15 and 16, two units developed by TRW in a series called Particles and Fields Subsatellites. Each weighed 35 kilograms and was powered by six solar panels and rechargeable batteries. The midget satellites were deployed from the Apollo Command and Service Module via a spring-loaded container giving the units a four foot-per-second velocity. Apollo 15’s operated for six months before an electronics failure ended the venture. The Apollo 16 subsatellite crashed on the lunar surface 34 days into its mission after completing 424 orbits. Here I thought I knew Apollo history backwards and forwards and I had never run into anything about these craft. It turns out that smallsats – usually cited as spacecraft with weight up to 180...

Some 900 light years away in the constellation Puppis, the planet WASP-121b is proving an interesting test case as we probe ever deeper into exoplanetary atmospheres. As has been the case with so many early atmosphere studies, WASP-121b, also known as Tylos, is a hot-Jupiter, with a year lasting about thirty Earth hours, in a vise-like tidal lock that leaves one side always facing the star, the other away. What we gain in two new studies of this world is an unprecedented map of the atmosphere’s structure. At stake here is a 3D look into what goes on as differing air flows move from one side of the planet to the other. A jet stream moves material around its equator, but there is a separate flow at lower altitudes that pumps gas from the hottest regions to the dark side. “This kind of climate has never been seen before on any planet,” says Julia Victoria Seidel (European Southern Observatory), lead author of a paper that appears today in Nature. Seidel points out that we have nothing...

Someone asked me the other day what it would take to surprise me. In other words, given the deluge of data coming in from all kinds of observatories, what one bit of news would set me back on my heels? That took some reflection. Would it surprise me, my interlocutor persisted, if SETI fails to find another civilization in my lifetime? The answer to that is no, because I approach SETI without expectations. My guess is that intelligence in the universe is rare, but it’s only a hunch. How could it be anything else? So no, continuing silence via SETI does not surprise me. And while a confirmed signal would be fascinating news, I can’t say it would truly surprise me either. I can work out scenarios where civilizations much older than ours do become known. Some surprises, of course, are bigger than others. Volcanoes on Io were a surprise back in the Voyager days, and geysers on Enceladus were not exactly expected, but I’m talking here about an all but metaphysical surprise. And I think I...

What catches your eye in this description of an exoplanetary system? Start with a ‘hot Jupiter,’ with a radius 0.87 times that of our Jupiter and an orbit of 7.1 days. This is WASP-132b, confirmed in 2016, and first discovered through the labors of the Wide-Angle Search for Planets program. Subsequent confirmation came through the CORALIE spectrograph installed on the Euler telescope at the European Southern Observatory’s La Silla site. This world orbits a K-class star 403 light years out in Lupus. The CORALIE measurements gave hints of another giant planet in a long period orbit. The system came still further into focus in 2021, when observations from TESS (Transiting Exoplanet Survey Satellite) showed a transiting super-Earth with a diameter of 1.8 Earth radii in a tight orbit of 1.01 days. The mass of the planet, as measured by the HARPS spectrograph at La Silla, is six times that of Earth. So we have both a hot-Jupiter and a super-Earth hugging the star, along with an outer gas...

Last Friday’s post on K-dwarfs as home to what researchers have taken to calling ‘superhabitable’ worlds has caught the eye of Dave Moore, a long-time Centauri Dreams correspondent and author. Readers will recall his deep dives into habitability concepts in such essays as The “Habitability" of Worlds and Super Earths/Hycean Worlds, not to mention his work on SETI (see If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare). Dave sent this in as a comment but I asked him to post it at the top because it so directly addresses the topic of habitability prospects around K-dwarfs, based on a quick survey of known planetary systems. It's a back of the envelope overview, but one that implies habitable planets around stars like these may be more difficult to find than we think. by Dave Moore To see whether K dwarfs made a good target for habitable planets, I decided to look into the prevalence and type of planets around K dwarfs and got carried away looking at the specs for 500...

We think of Earth as our standard for habitability, and thus the goal of finding an ‘Earth 2.0’ is to identify living worlds like ours orbiting similar Sun-like stars. But maybe Earth isn’t the best standard. Are there ways planets can be more habitable than our own, and if so where would we find them? That’s the tantalizing question posed in a paper by Iva Vilović (Technische Universität Berlin), René Heller (Max-Planck-Institut für Sonnensystemforschung) and colleagues in Germany and India. Heller has previously worked this issue in a significant paper with John Armstrong (citation below); see as well The Best of All Possible Worlds, which ran here in 2020. The term for the kind of world we are looking for is ‘superhabitable,’ and the aim of this study is to extend the discussion of K-class stars as hosts by modeling the atmospheres we may find on planets there. While much attention has focused on M-class red dwarfs, the high degree of flare activity coupled with long pre-main...

Given our intense scrutiny of planets around other stars, I find it interesting how little we know even now about the history of our own Sun, and its varying effects on habitability. A chapter in an upcoming (wildly overpriced) Elsevier title called The Archean Earth is informative on the matter, especially insofar as it illuminates which issues most affect habitability and how the values for these vary over time. It’s also a fascinating look at changing conditions on Venus, Earth and Mars. We know a great deal about the three worlds from our local and planetary explorations, but all too little when it comes to explaining the evolution of their atmospheres and interior structures. But it’s important to dig into all this because as Stephen Kane, director of The Planetary Research Laboratory at UC-Riverside and colleagues point out, we seem to be looking at the end state of habitability on both Mars and Venus, meaning that our explorations of these worlds should yield insights into...

Over the weekend I learned about Joseph Haydn’s Symphony No. 47, unusual in that it offers up some of its treasures in perfect symmetry. Dubbed ‘The Palindrome,’ the symphony’s third movement, Minuetto e Trio, is crafted to play identically whether attacked normally – moving forward through the score – or backwards. You can check this out for yourself in this YouTube video, or on this non-auditory reference. The pleasure of unexpected symmetry is profound, and when seen through the eyes of our spacecraft, can be startling. Consider the storied star Vega. We see this system from our perspective at a very low inclination angle relative to its rotational axis, as if we were looking down from above the star’s pole. This face-on perspective is profoundly interesting when examined through our space-borne astronomical assets. In the image below, we get two views of Vega’s disk, from Hubble and then JWST. Image: The disk around Vega as seen by Hubble (left) and Webb (right). Hubble detects...

If you follow the fortunes of the stars closest to us, you know that Barnard’s Star has always excited interest, both because of its proximity to our system (about six light years) but also because of the early work on the star performed by Peter Van de Kamp at Sproul Observatory (Swarthmore College). That work, which ran until the early 1970s, initially appeared to show a Jupiter-class planet at the star but the results were later explained as instrumentation errors in Van de Kamp’s equipment. It was a cautionary tale, but credit the astronomer for working tirelessly using astrometry to attempt to validate a conclusion we now take for granted: There are planets around other stars. In 2018 we seemed to have a solid detection of a much different planet candidate via Guillem Anglada-Escudé (Queen Mary University, London) and Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain), indicating a super-Earth of 3.3 Earth masses in an orbit...

Some years back I read a science fiction story in which the planet where the action took place orbited an F-class star. That was sufficiently odd to get my attention, and I began to pay attention to these stars, which represent on the order of 3 percent of all stars in the galaxy. Stars like our G-class Sun weigh in at about 7 percent, while the vast majority of stars are M-dwarfs, still our best chances for life detection because of the advantages they offer to our observing technologies, including deep transits and lower stellar brightness for direct imaging purposes. F-stars are intriguing despite the fact that they tend to be somewhat larger than the Sun (up to 1.4 times its mass) and also hotter (temperatures in the range of 6200-7200 K). Back in 2014, I looked at the work of Manfred Cuntz (University of Texas at Arlington), who had performed a study examining radiation levels in these stars and the damage that DNA would experience with an F-star in the sky at various stages of...

“What is this fascination of yours with small red stars?” a friend asked in a recent lunch encounter, having seen something I wrote a few years back about TRAPPIST-1 in one of his annual delvings into the site. “They’re nothing like the Sun, to quote Shakespeare, and anyway, even if they have planets, they can’t support life. Right?” Hmmm. The last question is about as open as a question can get. But my friend is on to something, at least in terms of the way most people think about exoplanets. My fascination with small red stars is precisely their difference from our familiar G-class star. An M-dwarf planet bearing life would be truly exotic, in an orbit lasting mere days rather than months (depending on the class of M-dwarf), and perhaps tidally locked, so inhabitants would see their star fixed in the sky. How science fictional can you get? And we certainly don’t have enough data to make the call on life around any of them. Let’s talk a minute about how we classify small red stars,...

Great observatories work together to stretch the boundaries of what is possible for each. Data from the Chandra X-ray Observatory were used in tandem with the James Webb Space Telescope, for example, to observe the death of a star as it was consumed by a black hole. JWST’s infrared look at this Tidal Disruption Event (TDE) helped show the structure of stellar debris in the accretion disk of the black hole, while Chandra charted the high-energy processes at play in the cataclysmic event. Or have a look at the image below, combining X-ray and infrared data from these two instruments along with the European Space Agency’s XMM-Newton, the Spitzer Space Telescope and optical data from Hubble and the European Southern Observatory's New Technology Telescope to study a range of targets. Image: Four composite images deliver dazzling views from NASA’s Chandra X-ray Observatory and James Webb Space Telescope of two galaxies, a nebula, and a star cluster. Each image combines Chandra’s X-rays — a...

Europa Clipper is scheduled to launch on October 10, with arrival at Jupiter in 2030. That will keep subsurface oceans on our minds as we tangle with the problems of analyzing water locked under kilometers of ice. Some moons, of course, help us out. Enceladus spews watery materials into space through cracks in its crust, making flybys through its geysers a possibility for snagging samples. Europa Clipper may find further evidence of the much less dramatic plume activity that has been spotted on Europa. Clipper’s SUrface Dust Analyzer (SUDA) would prove vital in such analysis. If cellular material is found in an ice grain snared from an orbital pass, would we be able to detect it? The answer may be found in laboratory work with a common bacteria that thrives in the waters off Alaska. As explained in new work out of the University of Washington and the Freie Universität Berlin, the bacterium Sphingopyxis alaskensis is made to order for such studies. It is smaller than Escherichia coli...

Just a few weeks ago I wrote about stellar interactions, taking note of a concept advanced by scientists including Ben Zuckerman and Greg Matloff that such stars would make for easier interstellar travel. After all, if a star in its rotation around the Milky Way closes to within half a light year of the Sun, it’s a more feasible destination than Alpha Centauri. Of course, you have to wait for the star to come around, and that takes time. Zuckerman (UCLA), working with Bradley Hansen, has written about the possibility that close encounters are when a civilization will attempt such voyages. I have a further idea along the lines of motion through the galaxy and its advantages to explorers, and it’s one that may not require tens of thousands of years of waiting. We’d like to get to another star system because we’re interested in the planets there, so what if an interstellar planet nudges into nearby space? I’ll ignore Oort Cloud perturbations and the rest to focus on a ‘rogue’ or...