What is it we are looking for when we probe nearby planetary systems? Certainly the search for life elsewhere compels us to find planets like our own around stars much like the Sun. But surely our goal isn't restricted to finding duplicate Earths, if indeed they exist. A larger goal would be to find life on planets unlike the Earth -- perhaps around stars much different from the Sun -- which would give us some idea how common living systems are in the galaxy. And beyond that? The ultimate goal is simply to find out what is out there. That takes in outcomes as different as widespread microbial life, perhaps leading to more complex forms, and barren worlds in which life never emerged. A galaxy filled with life vs. a galaxy in which life is rare offers us two striking outcomes. We ignore preconceptions to find out which is true. Flaring Red Stars Let's try to put Proxima Centauri's recent flare, discussed yesterday, in context. Events like this highlight our doubts about the viability...

News of a major stellar flare from Proxima Centauri is interesting because flares like these are problematic for habitability. Moreover, this one may tell us something about the nature of the planetary system around this star, making us rethink previous evidence for dust belts there. But back to the habitability question. Can red dwarf stars sustain life in a habitable zone much closer to the primary than in our own Solar System, when they are subject to such violent outbursts? What we learn in a new paper from Meredith MacGregor and Alycia Weinberger (Carnegie Institution for Science) is that the flare at its peak on March 24, 2017 was 10 times brighter than the largest flares our G-class Sun produces at similar wavelengths (1.3 mm). Image: The brightness of Proxima Centauri as observed by ALMA over the two minutes of the event on March 24, 2017. The massive stellar flare is shown in red, with the smaller earlier flare in orange, and the enhanced emission surrounding the flare that...

At the last Tennessee Valley Interstellar Workshop, I was part of a session on biosignatures in exoplanet atmospheres that highlighted how careful we have to be before declaring we have found life. Given that, as Alex Tolley points out below, our own planet has been in its current state of oxygenation for a scant 12 percent of its existence, shouldn't our methods include life detection in as wide a variety of atmospheres as possible? A Centauri Dreams regular, Alex addresses the question by looking at new work on chemical disequilibrium and its relation to biosignature detection. The author (with Brian McConnell) of A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach (Springer, 2016), Alex is a lecturer in biology at the University of California. Just how close are we to an unambiguous biosignature detection, and on what kind of world will we find it? by Alex Tolley Image: Archaean or early Proterozoic Earth showing stromatolites in the foreground. Credit: Peter...

Between Kepler and the ensuing K2 mission, we’ve had quite a haul of exoplanets. Kepler data have been used to confirm 2341 exoplanets, with NASA declaring 30 of these as being less than twice Earth-size and in the habitable zone. K2 has landed 307 confirmed worlds of its own. K2 offers a different viewing strategy than Kepler’s fixed view of over 150,000 stars. While the transit method is still at work, K2 pursues a series of observing campaigns, its fields of view distributed around the ecliptic plane, and with photometric precision approaching the original. Why the relationship with the ecliptic? Remember that what turned Kepler into K2 was the failure of two reaction wheels, the second failing less than a year after the first. Working in the ecliptic plane minimizes the torque produced by solar wind pressure, thus minimizing pointing drift and allowing the spacecraft to be controlled by its thrusters and remaining two reaction wheels. Each K2 campaign is limited to about 80 days...

Yesterday we saw that, by pushing the Hubble telescope to its limits, we could make a call about three of the TRAPPIST-1 planets -- d, e and f -- and one possibility for their respective atmospheres. The Hubble data rule out puffy atmospheres rich in hydrogen for these three (TRAPPIST-1 g needs more work before a definitive call can be made there). This is a useful finding, for hydrogen is a greenhouse gas that can heat planets close to their star beyond our usual norms for habitability. Set out deeper in a stellar system, we can think of Neptune, a gaseous world far different from the kind of rocky, terrestrial-class planets most likely to produce surface water. So on balance, the Hubble work, while not telling us anything more about potential atmospheres in this system, does rule out the Neptune scenario. That leaves open the question of whether future instruments will find more compact atmospheres. The James Webb Space Telescope should be able to probe these worlds, perhaps...

This week offers two interesting papers about the TRAPPIST-1 planets, one from Hubble data looking at the question of hydrogen in potential planetary atmospheres, the other drawing on data from the European Southern Observatory's Paranal facility as well as the Spitzer and Kepler space-based instruments. We'll look at the Hubble work this morning and move on to the second paper tomorrow. Both offer meaty stuff to dig into, for we're beginning to characterize these seven planets, which form a unique laboratory for the study of red dwarf systems. Published in Nature Astronomy, the Hubble results screen four of the TRAPPIST-1 planets -- d, e, f and g -- to study their potential atmospheres in the infrared, using Hubble's Wide Field Camera 3 in data collected from December 2016 to January 2017. The data allow us to rule out a cloud-free hydrogen-rich atmosphere on three of these worlds, while TRAPPIST-1g needs further observation before a hydrogen atmosphere can be conclusively excluded....

I was pleased to be a guest on David Livingston's The Space Show last week. David's questions are always well chosen, as were those of the listeners who participated in the show, and we spoke broadly about the interstellar effort and what it will take to eventually get human technologies to the stars. The show is now available in David's archives. I suspect that if David and I had spoken a couple of days later, the topic would have gotten around to gravitational microlensing, and specifically, the news about planets in other galaxies. On the surface, the story seems sensational. In our own galaxy, we can use radial velocity and transit studies on stars, but here our working distances are constrained by our method. The original Kepler field of view in Cygnus, Lyra and Draco, for example, contained stars ranging from 600 to 3000 light years out -- get beyond 3000 light years and transits are not detectable. Image: The Sun is about 25,000 light years from the center of the galaxy, about...