Whether or not life can emerge on the planets of red dwarf stars remains an unknown, though upcoming technologies should help us learn more through the study of planetary atmospheres. Tidal locking always comes up in such discussions, an issue I always thought to be fairly recent, but now I learn that it has quite a pedigree. In a new paper from Rory Barnes, I learn that astronomers in the late 19th Century had concluded (erroneously) that Venus was tidally locked, and there followed a debate about the impact of synchronous rotation on surface conditions. As witness astronomer N. W. Mumford, who in 1909 questioned whether tidal friction wouldn't reduce half of Venus to a desert and annihilate all life there. Or E. V. Heward, who speculated that life could emerge on Venus despite tidal lock, and wrote in a 1903 issue of MacMillan's Magazine: ...that between the two separate regions of perpetual night and day there must lie a wide zone of subdued rose-flushed twilight, where the...

I'm not much for changing the meaning of words. True, languages always change, some at a faster clip than others (contrast Elizabethan English with today's, though modern Icelandic is structurally very similar to the Old Norse of the sagas). But I love words and prefer to let linguistic variety evolve rather than be decreed. Even so, I get what Elizabeth Tasker is doing when she makes the case for exoplanet hunters to do away with the term 'habitable zone.' In a comment to Nature Astronomy, Tasker (JAXA) and quite a few colleagues point out just how misleading 'habitable zone' can be, given that when we find a new exoplanet, we usually only know the size of the planet (perhaps through radius, as in a transit study, or through minimum mass for radial velocity), and the amount of radiation the planet receives from its star. From such facts we can infer whether we're dealing with a gas giant or a rocky world. This is hardly enough on which to base a claim of habitability, but it gets...

The new work on Tau Ceti, which analyzes radial velocity data showing four planets there, looks to be a step forward in this workhouse method for planetary detection. With radial velocity, we're analyzing tiny variations in the movement of a star as it is affected by the planets around it. These are tiny signals, and the new Tau Ceti paper discusses working with variations as low as 30 centimeters per second. It's a good number, but we'll want better -- to detect a true Earth analog around a Sun-like star, we need to get this number into the 10 cm/s range. The planets detected in this work all come in at less than four Earth masses, and two of them are getting attention because they are located near the inner and outer edges of the habitable zone respectively. Tau Ceti has always drawn our attention, being relatively close (12 light years) and a solitary G-class Sun-like star. No wonder it and Epsilon Eridani were the two targets Frank Drake chose for Project Ozma when he launched...

If life can arise around red dwarf stars, you would think TRAPPIST-1 would be the place to look. Home to seven planets, this ultracool M8V dwarf star about 40 light years away in Aquarius has been around for a long time. The age range in a new study on the matter goes from 5.4 billion years up to almost ten billion years. And we have more than one habitable zone planet to look at. Adam Burgasser (UC-San Diego) and Eric Mamajek (JPL) are behind the age calculations, which appear in a paper that has been accepted at The Astrophysical Journal. We have no idea how long it takes life to emerge, having only one example to work with, but it's encouraging that we find evidence for it very early in Earth's history, dating back some 3.8 billion years. But we also have much to learn about habitability around red dwarfs in general. Image: This illustration shows what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credit: NASA/JPL-Caltech. [PG note...

We're beginning to find stratospheres on planets around other stars. A new study based at NASA Ames has looked closely at WASP-121b, a 'hot Jupiter' in its most extreme form. This is a planet about 1.2 times as massive as Jupiter, but with a radius almost twice Jupiter's. The puffy world orbits its star in a scant 1.3 days (Jupiter, by contrast, circles the Sun every twelve years). As you would imagine, temperatures on WASP-121b are extreme, reaching 2500 degrees Celsius, which is enough to cause some metals to boil. A stratosphere is simply a layer within an atmosphere where temperature increases with higher altitudes. Exactly how do scientists determine whether a planet fully 900 light years from Earth has such a layer? The answer is in the signature of hot water molecules, observed here by examining how these molecules in WASP-121b's atmosphere react to specific wavelengths of light. The researchers used spectroscopic data from the Hubble instrument to make the call, knowing that...