SPARCS is the name of a CubeSat-based space mission out of Arizona State University, the acronym standing for Star-Planet Activity Research CubeSat, with astronomer Evgenya Shkolnik as principal investigator. The idea here is to look at ultraviolet flare activity on M-dwarf stars, a wavelength about which we could do with a great deal more information. The plan is to target specific stars that will be observed continuously over at least one complete stellar rotation, which could be anything from five to forty-five days. That this is a good idea is borne out by what we are learning about GJ 887, also known as Lacaille 9352 and known to be orbited by at least two planets. Located in the southern constellation of Piscis Austrinus, the star has the fourth highest known proper motion, with parallax measurements indicating it is a bit less than 11 light years from the Sun. It is one of the brightest M-dwarfs in our sky. When TESS (Transiting Exoplanet Survey Satellite) fixed its gaze on GJ...

The boundary between planet and star is hard enough to pin down without thinking of some recently discovered brown dwarfs that are cool enough to approach Earth temperatures. Yet worlds/stars like these are among the haul assembled by volunteers working data for Backyard Worlds: Planet 9, a citizen science project whose latest findings include 95 cool brown dwarfs in the Sun's neighborhood, as reported in the Astrophysical Journal. Despite a determined search, we've yet to find such an object closer than the nearest stars at Alpha Centauri. But 23 light years out -- the distance of the closest of these brown dwarfs -- is definitely close in galactic terms, and most of the brown dwarfs tracked in the new work are between 30 and 60 light years from Earth. That makes sense, for objects like these are faint enough that identifying them at greater range is all but impossible. The data used in the brown dwarf collection come from a range of observatories including W. M. Keck, Mont...

When it comes to detecting life on planets around other stars, my guess is that what will initially appear to be a life signature will quickly become controversial. We might, for example, find ozone in an exoplanet atmosphere with a space telescope like HabEX (Habitable Exoplanet Observatory). That would lead to hyperbolic news stories, to be sure, but ozone can happen when nitrogen and oxygen are exposed to ultraviolet light. The presence of ozone makes no definitive statement about life. In fact, definitive statements about life may take more than a few decades to achieve. If ozone seems like a good catch, that's because it implies oxygen, which makes us think of photosynthesis, but oxygen itself is hardly infallible as a biosignature. Oxygen-rich atmospheres can be completely abiotic, with UV from the host star breaking down carbon dioxide. For that matter, an atmosphere rich in water vapor can produce oxygen and hydrogen through the effects of UV radiation. Better, then, to look...

The exoplanet K2-25b, a young world in the Hyades cluster orbiting an M-dwarf star, raises intriguing questions. We’d like to know how it formed, for K2-25b is much more dense than we would expect for a world slightly smaller than Neptune. Planets in a range between Earth and Neptune seem to be common around other stars, although we have none in our Solar System unless we make an interesting discovery about putative Planet 9. But let lead author Gudmundur Stefánsson (Princeton University) point out the unusual nature of K2-25b:: “The planet is dense for its size and age, in contrast to other young, sub-Neptune-sized planets that orbit close to their host star. Usually these worlds are observed to have low densities — and some even have extended evaporating atmospheres. K2-25b, with the measurements in hand, seems to have a dense core, either rocky or water-rich, with a thin envelope.” Image: New detailed observations with NSF’s NOIRLab facilities reveal a young exoplanet, orbiting a...

Under other circumstances, the red dwarf TVLM 513-46546 would not cause a ripple in news coverage of exoplanets. What astronomers have found there is a planet of Saturn mass in a 221 day orbit, raising eyebrows only in that while planets are common around M-dwarfs, they are usually smaller, rocky worlds. But the TVLM 513-46546 story gains weight when we consider the methods used to find this planet, which have implications for studying system architectures around many stars as we refine our techniques and new instruments come online. The star in question is 35 light years from Earth, and we've found the planet through astrometry, a method that tracks a star's position in the sky to an extreme precision and detects the minute variation in motion caused by the gravitational effect of the planet. If this sounds a bit like radial velocity methods, the difference is that with astrometry we are measuring tiny changes in the stars position in the sky, as opposed to the Doppler shift of...

How many habitable planets should we expect in the average stellar system? One sounds like a good number to me, even an optimistic one. But it’s a tough question because we don’t exactly know what an ‘average’ stellar system is, there being such a wide range currently being discovered. There was a time less than a century ago when the idea that there might be three habitable planets -- i.e., habitable by humans -- in the Solar System was current. Imagine Venus as something like French Polynesia, or maybe what was then the Belgian Congo. Imagine Mars with a thicker atmosphere and ancient seas, Edgar Rice Burroughs territory. Today we think of multiple habitability here in the Solar System as perhaps including ocean life under the ice of the moons of giant planets, but we’ve ruled out anything a human could walk around on in relative comfort. The question of what makes our Solar System able to support just one planet in the human habitability range bothered Stephen Kane (UC-Riverside)...