In Stephen Baxter’s novel Ark (Gollancz, 2009), a starship launched by an Earth in crisis reaches a planet in the 82 Eridani system, an ‘Earth II’ that turns out to have major problems. Whereas Earth has an obliquity, or tilt relative to its orbital axis, of about 23.5 degrees, the second ‘Earth’ offers up a whopping 90 degree obliquity. Would a planet like this, given what must be extreme seasonality, be remotely habitable? The crew discusses the problem as they watch a computerized display showing Earth II and its star. The planet’s rotation axis is depicted as a splinter pushed through its bulk, one that points almost directly at the star. But as the planet rotates, the axis keeps pointing at the same direction in space. After half a year, the planet’s north pole is in darkness, its south pole in light. One of Baxter’s characters explains the consequences: “Every part of the planet except an equatorial strip will suffer months of perpetual darkness, months of perpetual light. Away...

The definition of a habitable zone is under constant refinement, an important line of research as we choose which exoplanets to focus on in our search for life. Centauri Dreams regular Alex Tolley today looks at the question as it involves the presence of methane. With planetary warming already known to vary depending on the spectral type of the host star, we now learn that the presence of methane can produce thermal inversions and surface cooling on M-star exoplanets, impacting the outer limits of the habitable zone. The work of Ramses Ramirez (Tokyo Institute of Technology) and Lisa Kaltenegger (Carl Sagan Institute, Cornell University), the paper also suggests a possible biosignature near the outer habitable zone edge of hotter stars, one of several results that Alex explores in today's essay. by Alex Tolley Alien world - still from 2001: A Space Odyssey. Credit: Metro-Goldwyn-Mayer (MGM) As noted in previous posts on biosignatures, especially in regards to life prior to...

Looking for biological products in planetary atmospheres is how we'll first study exoplanetary life, assuming it exists. The tools for characterizing atmospheres have already developed to the point that we are examining the gases surrounding some 'hot Jupiters,' and even talking about the movement of clouds -- exoplanet meteorology -- on giant worlds. The hope is that TESS will find targets that we can then investigate with new space telescopes. The way forward is exciting, but my guess is that as we start looking into the atmospheres of transiting planets around nearby red dwarfs, the most accessible targets in the near future, we're going to find ourselves awash in controversy. Did we just find oxygen? Maybe we're on the way to a biosignature detection, but then again, ultraviolet radiation can break down atmospheric water to produce oxygen. For that matter, UV can split carbon dioxide molecules. What about methane? Abiotic methane from geothermal activity on the surface could...

Scientists have been saying for some time now that helium should be readily detectable in the atmospheres of gas giant planets -- after all, this is the second-most common element in the universe, and we know it is plentiful at Jupiter and Saturn. The problem has been how to detect it, an issue which this morning's story brings into sharp relief. At the University of Exeter (UK), Jessica Spake has put data from the Hubble telescope's Wide Field Camera 3 to good use, finding an abundance of helium in the upper atmosphere. The planet in question is the puffy WASP-107b, and this marks the first helium detection of the inert gas on an exoplanet. Some 200 light years from Earth in the constellation Virgo, WASP-107b shows little similarity to anything in our own Solar System. It was discovered in 2017 and is one of the lowest density planets yet found, a world that, although roughly the same size as Jupiter, has only 12 percent of its mass. In a tight six-day orbit around its K-class...

Scaling up our space telescopes calls for new thinking. Consider this: The Hubble telescope has a primary mirror of 2.4 meters. The James Webb Space Telescope takes us to 6.5 meters. But as we begin to get results from missions like TESS and JWST (assuming the latter gets off safely), we're going to need much more to see our most interesting targets. Imagine what could be done with a 30-meter space telescope, and ponder the challenge of constructing it. This is what Cornell University's Dmitry Savransky has been doing, developing a NIAC study that looks at modular design and self-assembly in space. Savransky's notions take me back to a much earlier era, when people like Bob Forward talked about massive structures in space that dwarf any engineering project we've yet attempted. Forward saw these projects -- his vast Fresnel lens between the orbits of Saturn and Uranus 1000 kilometers in diameter, for example -- as ultimately achievable, but his primary concern was to be sure the...

Avi Loeb's always interesting work has recently taken us into the realm of target selection for exoplanet surveys. Where should we be putting our time and money in the search for life elsewhere, and what can we do to maximize both the credibility of the investigation and the funding that it demands? These sound like pedestrian matters compared to the excitement of discovery -- finding Proxima b was a lot more exciting than watching any congressional committee debate over NASA's priorities. But Proxima Centauri b, that fascinating world around the nearest star, fits neatly into this narrative, for reasons that contrast nicely with its own nearest neighbors, Centauri A and B. The Centauri stars are an obvious target, and one that Loeb has devoted considerable time to assessing, given his deep involvement with Breakthrough Starshot's study of a mission there. If we find planets around Centauri A or B, are they our priority? Just where does Proxima b fit in? And what of fascinating...