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...

Are there large moons -- perhaps Earth-sized or even bigger -- around gas giant planets in habitable zones somewhere in the Milky Way? It’s a wonderful thought given how it multiplies the opportunities for life to find a foothold even in systems much different from our own. Centauri Dreams regular Andrew Tribick recently passed along a new paper that addresses the question in an interesting way, by modeling moon formation and orbital evolution under widely varying conditions of circumplanetary disk composition and evolution. We’re entering new terrain from this site’s perspective, because I can’t recall going deeply into circumplanetary disks before, at least not in the exoplanet context. But Marco Cilibrasi (Università di Pisa, Italy) and colleagues take us through the necessary background issues. We have two primary models for giant planet formation inside a protoplanetary disk, one being core accretion, when collision and coagulation occurs among dust particles to build up a...

A new project called Exoplanets in Transits and their Atmospheres (ExTrA) has been set in motion at the European Southern Observatory’s site at La Silla (Chile). Funded by the European Research Council and the French Agence National de la Recherche, ExTrA’s three 0.6-metre telescopes will be operated remotely from Grenoble, France. This is an exoplanet transit effort centered around finding and characterizing Earth-sized planets orbiting M-dwarf stars. Not an easy task from the ground, as lead researcher Xavier Bonfils makes clear, though if you’re going to attempt it, northern Chile offers optimum conditions: “La Silla was selected as the home of the telescopes because of the site’s excellent atmospheric conditions. The kind of light we are observing — near-infrared — is very easily absorbed by Earth’s atmosphere, so we required the driest and darkest conditions possible. La Silla is a perfect match to our specifications.” To do its work, ExTrA weds spectroscopic information to...

The wrong initial assumption can easily lead anyone down a blind alley. The problem comes across loud and clear in new work from Marc Kuchner (NASA GSFC) and colleagues, which Kuchner presented at the recent meeting of the American Astronomical Society in Washington. At issue is the matter of the disks of gas and dust around young stars, in many of which we can find patterns such as rings, arcs and spirals that suggest the formation of planets. But are such patterns sure indicators or merely suggestions? Kuchner's team has been looking at the question for several years now, presenting in a 2013 paper the possibility that a phenomenon called photoelectric instability (PeI) can explain the narrow rings we see in some disk systems. PeI happens when high-energy ultraviolet light strikes dust and ice grains, stripping away electrons. The electrons then strike and heat gas in the disk, causing gas pressure to increase and more dust to be trapped. Rings can form that begin to oscillate,...

As Centauri Dreams readers know, I always keep an eye on the K2 mission, the rejuvenated Kepler effort to find exoplanets with a spacecraft that had originally examined 145,000 stars in Cygnus and Lyra. Now working with different fields of view, K2 has examined a surprisingly large number of stars, some 287,309, according to this Caltech news release. Digging around a bit, I discovered that each 80-day campaign brings in data on anywhere from 13,000 to 28,000 targets, all released to the public within three months of the end of the campaign. In the paper we'll discuss today, this influx is referred to as a 'deluge of data.' Our datasets just continue to grow in a time of exploration that seems unprecedented in scientific history. I've heard it compared to the explosion in knowledge of microorganisms after their detection by van Leeuwenhoek in the 17th Century, though of course it also conjures up thoughts of early exploratory voyages as humans pushed into hitherto unknown terrain....

Although I carry on about upcoming observatories on the ground and in space, I never want to ignore the continuing contribution of the Hubble telescope to our understanding of planet and star formation. As witness the latest deep survey made by team lead Massimo Robberto (Space Telescope Institute) and colleagues, which used the instrument to study small, faint objects in the Orion Nebula. At a relatively close 1,350 light years from Sol, the nebula is something of a proving ground for star formation, and now one that is yielding data on small stars indeed. Identifying some 1,200 candidate reddish stars, the survey tapped Hubble's infrared capabilities to extract 17 candidate brown dwarf companions to red dwarf stars, one brown dwarf pair and one brown dwarf with a planetary companion. We also learn that a planetary mass companion to a red dwarf has turned up as well as, interestingly enough, a planet-mass companion to another planet, the duo orbiting each other in the absence of a...

To understand why Beta Pictoris is receiving so much attention among astronomers, particularly those specializing in exoplanets, you have only to consider a few parameters. This is a young star, perhaps 25 million years old, one with a well observed circumstellar disk, the first actually imaged around another star. We not only have a large gas giant in orbit here, but also evidence of cometary activity as seen in spectral data. ? Pic is also relatively nearby at 64 light years. Image: This composite image represents the close environment of Beta Pictoris as seen in near infrared light. This very faint environment is revealed after a careful subtraction of the much brighter stellar halo. The outer part of the image shows the reflected light on the dust disc, as observed in 1996 with the ADONIS instrument on ESO's 3.6 m telescope; the inner part is the innermost part of the system, as seen at 3.6 microns with NACO on the Very Large Telescope. The newly detected source is more than 1000...