The planet candidate KOI-456.04 strikes me as significant not so much because of the similarity of its orbit with that of Earth (a 378 day orbital period around a star much like the Sun), but because of the methods used to identify its possible presence. Make no mistake, this is still very much a planet candidate, as co-authors René Heller and Michael Hippke are at pains to explain, noting that systematic measurement errors cannot be ruled out, though they estimate an 85 percent likelihood that it is there. We don’t have many examples of small planets potentially in the habitable zone of a star like ours, and this is what has received the most media attention. So let’s look at this aspect of the story quickly, because I want to move past it. If this candidate is confirmed, it looks to be less than twice the radius of the Earth, receiving about 93 percent of Earth’s insolation from its star. Make assumptions about its atmosphere and you can arrive at a surface temperature averaging...

Selection is going to be a key issue for future ground- and space-based observatories. Given lengthy observing times for targets of high interest, we have to know how to cull from our exoplanet catalog those specific worlds that can tell us the most about life in the universe. Recently, Ramses Ramirez (Earth-Life Science Institute, Tokyo Institute of Technology) went to work on the question of habitable zones for complex life, which are narrower than the classic habitable zone defined by the potential for water on the surface. In today's essay, Alex Tolley looks at Ramirez' recent paper, which examines the question in relation to the solubility of gases in lipid membranes. What emerges in this work is a constrained habitable zone suited to complex life, with limits Alex explores. The model has interesting ramifications right here in the Solar System, but it also points the way toward constraining the list of planets upon which we'll apply our emerging tools for atmospheric...

55 Cancri e is a confirmed planet, and thus a departure from our topic of the last two days, which was the act of exoplanet confirmation as regards Proxima Centauri b and c, the latter still in need of further work before it can be considered confirmed. But 55 Cancri e has its uses in offering a tight orbit around a Sun-like star that can be detected using the transit method. That was just what was needed for ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics), a technology demonstration mission involving a tiny CubeSat. Sara Seager (MIT) has been at the heart of the investigation of CubeSats as exoplanet research platforms. I think the idea is brilliant. If we want to mount the most effective search of nearby Sun-like stars for Earth analogs, multiple telescopes must be in use. CubeSats are cheap. Why not launch a fleet of them, each with the task of monitoring a single star at a time. Launched in 2017, ASTERIA was the prototype, a nanosatellite equipped with...

Hard on the heels of the confirmation of Proxima Centauri b, we get news of Proxima c, which has now been analyzed in new work by Fritz Benedict (McDonald Observatory, University of Texas at Austin). Benedict has presented his findings at the ongoing virtual meeting of the American Astronomical Society, which ends today. The work follows up and lends weight to the discovery of Proxima c announced earlier this year by a team led by Mario Damasso of Italy's National Institute for Astrophysics (INAF), which had used radial velocity methods to observe the star. We need further work, however, to say that Proxima c has been confirmed, as Dr. Benedict explained in an email this morning. But first, let's straighten out a question of identity. Yesterday, when discussing the confirmation of habitable zone world Proxima b, we talked about a second signal in data culled by the ESPRESSO spectrograph. If the second ESPRESSO signal does turn out to be a planet, it will be a third Proxima Centauri...

I’ve always liked the image of Proxima Centauri b that the ESO’s Martin Kornmesser has conjured directly below, and have used it in a couple of previous articles about the planet. Indeed, you’ll see it propagated widely when the topic comes up. But like all of these exoplanet artist impressions, it’s made up of educated guesses, as it has to be. We don’t even know, for example, whether the world we see here even has an atmosphere, as depicted. Whether or not it does is important because it affects the possibilities for life around the star nearest to our own. Twenty times closer to its star than the Earth is to the Sun, Proxima b nonetheless receives roughly the same energy, meaning we could have surface temperatures there that would support liquid water on the surface. But the planet also receives 400 times more X-rays than the Earth, which leads the University of Geneva’s Christophe Lovis to ask: “Is there an atmosphere that protects the planet from these deadly rays? And if this...

Studying the atmospheres of exoplanets is a process that is fairly well along, especially when it comes to hot Jupiters. Here we have a massive target so close to its star that, when a transit occurs, we can look at the star's light filtering through the atmosphere of the planet. Even so, clouds are a problem because they prevent accurate readings of atmospheric composition below the upper cloud layers. Aerosols -- suspended solid particles or droplets in a gas -- are common, range widely in composition, and make studying a planet's atmosphere harder. We'd like to learn more about which aerosols are where and in what kind of conditions, for we have a useful database of planets to work with. Over 70 exoplanets currently have transmission spectra available. A wide range of cloud types, many of them exotic indeed, have been proposed by astronomers to explain what they are seeing. Imagine clouds of sapphire, or rubies, which is essentially what we get with aerosols of aluminum oxides...

You would think that the orbits of planets would align closely with the spin of their star, since they emerged from the same primordial disk. Many planets do just that, and in our own system, the orbits of the planets are aligned within 6 degrees of the Sun's rotation. But the numerous cases of star-planet orbital misalignment around other stars cause us to question whether these systems formed out of alignment or were influenced by later perturbations. A massive companion in a wide orbit could do the trick, and other mechanisms to tilt the orbital or spin axes are discussed in the literature. To examine the question, the Rossiter-McLaughlin effect comes into play. Discovered by studying binary stars, the effect is named after the two University of Michigan graduate students who figured it out back in the 1920s. They realized that as a star rotates, part of it seems to be coming toward the observer, creating a blueshift, while the other side seems to be moving away, producing a...