The assumption that gas giant planets are unlikely around red dwarf stars is reasonable enough. A star perhaps 20 percent the mass of the Sun should have a smaller protoplanetary disk, meaning sufficient gas and dust to build a Jupiter-class world are lacking. The core accretion model (a gradual accumulation of material from the disk) is severely challenged. Moreover, these small stars are active in their extended youth, sending out frequent flares and strong stellar winds that should dissipate such a disk quickly. Gravitational instabilities within the disk are one possible alternative. Planet formation around such a star must be swift indeed, which accounts for estimates as low as 1 percent of such stars having a gas giant in the system. Exceptions like GJ 3512 b, discovered in 2019, do occur, and each is valuable. Here we have a giant planet, discovered through radial velocity methods, orbiting a star a scant 12 percent of the Sun’s mass. Or consider the star GJ 876, which has two...

HD 219134, an orange K-class star in Cassiopeia, is relatively close to the Sun (21 light years) and already known to have at least five planets, two of them being rocky super-Earths that can be tracked transiting their host. We know how significant the transit method has become thanks to the planet harvests of, for example, the Kepler mission and TESS, the Transiting Exoplanet Survey Satellite. It’s interesting to realize now that an entirely different kind of measurement based on stellar vibrations can also yield useful planet information. The work I’m looking at this morning comes out of the Keck Observatory on Mauna Kea (Hawaii), where the Keck Planet Finder (KFP) is being used to track HD 219134’s oscillations. The field of asteroseismology is a window into the interior of a star, allowing scientists to hear the frequencies at which individual stars resonate. That makes it possible to refine our readings on the mass of the star, and just as significantly, to determine its age...

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...