How likely are we to find a definitive biosignature once we begin analyzing the atmospheres of nearby rocky exoplanets? We have some ideal candidates, after all, with stars like TRAPPIST-1 yielding not one but three potentially life-bearing worlds. The first thing we'll have to find out is whether any of these planets actually have atmospheres, and what their composition may be. 'Habitable zone' is a fluid concept, and that's not just a reference to liquid water on the surface. A relatively dry terrestrial planet, one with little surface water and not a lot of water vapor in the atmosphere, might avoid a runaway greenhouse and manage to stay habitable in an orbit closer to a G-class star than Earth. A planet with an atmosphere dominated by hydrogen could maintain warm temperatures even at 10 AU and beyond. So we'll need to find out what any exoplanet atmosphere is made of, and weigh that against its orbital position near its star. Image: An extended habitable zone that captures some...

Video presentations from the recent Tennessee Valley Interstellar Workshop are beginning to appear online. It's welcome news for those of us who believe all conferences should be available this way, and a chance for Centauri Dreams readers to home in on particular presentations of interest. I published my Closing Remarks at TVIW right after the meeting and will watch with interest as the complete 2017 videos now become available. There are a number of these I'd like to see again. All of this gets me by round-about way to Project Blue, the ongoing attempt to construct a small space telescope capable of directly imaging an Earth-like planet around Centauri A or B, if one is indeed there. For the other talk I gave at TVIW 2017 (not yet online) had to do with biosignatures, and the question of whether we had the capability of detecting one in the near future with the kind of missions now approved and being prepared for launch. This was delivered as part of a presentation and panel...

An object called A/2017 U1, whether it is an asteroid or a comet, is drawing attention because it seems to be an interstellar wanderer. Discovered on October 19 by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, the object was quickly submitted to the Minor Planet Center by Rob Weryk (University of Hawaii Institute for Astronomy, IFA). Weryk was subsequently able to identify the object in Pan-STARRS imagery from the previous night. Image: This animation shows the path of A/2017 U1, which is an asteroid -- or perhaps a comet -- as it passed through our inner solar system in September and October 2017. From analysis of its motion, scientists calculate that it probably originated from outside our Solar System. Credit: NASA/JPL-Caltech. Thus a nightly search for near-Earth objects may have uncovered an object whose origins lie much further away. A/2017 U1 is about 400 meters in diameter and on a highly unusual trajectory, one that fits neither an asteroid or comet from...

Just how do you go about building a 'super-Earth'? One possibility may be emerging in the study of young debris disk systems with thin, bright outer rings made up of comet-like bodies. Three examples are under scrutiny in work discussed at the recent American Astronomical Society's Division for Planetary Sciences meeting in Provo, Utah. Here, Carey Lisse (JHU/APL) described his team's results in studying the stars Fomalhaut, HD 32297 and HR 4796A. What the scientists are finding is that dense rings of comets can become a construction zone for planets of super-Earth size. The makeup of the material in these ring systems varies, from two that are rich in ice (Fomalhaut and HD 32297) to one that is depleted in ice but rich in carbon (HR 4796A). Take a look at the image below, showing the ring surrounding HR 4796A, and you'll see how strikingly tight the band of dust around this relatively young stellar system is. Image: Gemini Planet Imager observations reveal a complex pattern of...