We know about an extremely interesting planet around Proxima Centauri, and there are even plans afoot (Breakthrough Starshot) to get probes into the Alpha Centauri system later in this century. But last April, when Breakthrough Initiatives held a conference at Stanford to talk about this and numerous other matters, the question of what we could see came up. For in Alpha Centauri, we're dealing with three stars that are closer to us than any other. If there are planets around Centauri A and/or Centauri B, are there ways we could image them? This gets interesting in the context of Project Blue, a consortium of space organizations looking into exoplanetary imaging technologies. This morning Project Blue drew on the work of some of those present at Stanford, launching a campaign to fund a telescope that could obtain the first image of an Earth-like planet outside our Solar System, perhaps by as early as the end of the decade. The idea here is to ignite a Kickstarter effort aimed at...

Our knowledge of protoplanetary disks around young stars is deepening. This morning we have news of three recently examined disks, each with features of interest because we know so little about how such disks evolve. What we do know is that planets are spawned from the gas and dust we find within them, as we see in the disk below discovered using the SPHERE instrument on the European Southern Observatory's Very Large Telescope in Chile. Image: A team of astronomers observed the planetary disc surrounding the star RX J1615, which lies in the constellation of Scorpius, 600 light-years from Earth. The observations show a complex system of concentric rings surrounding the young star, forming a shape resembling a titanic version of the rings that encircle Saturn. Such an intricate sculpting of rings in a protoplanetary disc has only been imaged a handful of times before. Credit: ESO, J. de Boer et al. The comparison with Saturn is not amiss, for this is a complex system of concentric...

The three Alpha Centauri stars get more and more interesting as we begin to discover planets around them, and the hope of finding planets in the habitable zone around Centauri A or B continues to drive research. Alpha Centauri could be thought of as a close binary with a distant companion, since we're still not absolutely sure whether Proxima Centauri is gravitationally bound to the system. Learning more about binary systems, in any case, is interesting in itself but also may open windows into our nearest stellar neighbors. Thus the discovery of planets in the binary system HD 87646 draws my attention. Here we have a primary star, HD 87646A, about 12 percent more massive than the Sun that is some 22 AU away from another star, HD 87646B, the latter about 10 percent less massive than the Sun. Translated into local terms, that would be something like having another star at about the distance Uranus is in our Solar system. Image: The HD 87646 system, seen here in adaptive optic imaging...

Seasonal change on our planet is relatively moderate because the Earth has a small axial tilt. Just how that situation arose makes for interesting speculation, and a series of scientific papers that have been augmented by a new analysis in Nature from Matija ?uk (SETI Institute) and Sarah Stewart (UC-Davis). Working with colleagues at Harvard and the University of Maryland, the scientists have created computer simulations showing that the early Earth experienced a day as short as two hours, and had a highly tilted spin axis. How we get from there to here is the question, and it’s one that ?uk and company answer by examining the collision that spawned Earth’s Moon. The impact theory sees the Moon forming from the debris of the collision between an infant Earth and a Mars-sized protoplanet. It was ?uk and Stewart who suggested some four years ago that following the ‘Big Whack,’ the Earth’s rotation period was closer to two hours than the five that earlier work had suggested. The Moon...

Just how do gas giant planets form? A team of researchers at ETH Zürich, working with both the University of Zürich and the University of Bern, has developed the most fine-grained and instructive computer simulations yet to help us understand the process. Using the Piz Daint supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano, ETH Zürich postdoc Judit Szulágyi and Lucio Mayer (University of Zürich) can now show clear and observable differences between the two formation processes under study by theorists. The core accretion model begins with a massive solid core that is large enough to pull in gas from the protoplanetary disk and maintain it. The gravitational instability theory, on the other hand, presumes a massive enough disk around the young host star that spiral arms form in the disk in which gravitational collapse can occur around material that has begun to clump there. The simulations demonstrate that with either formation mechanism, a circumplanetary...

Those of us fascinated by dim red stars find these to be exhilarating days indeed. The buzz over Proxima b continues, as well it should, given the fact that this provocative planet orbits the nearest star. We also have detections like the three small planets around TRAPPIST-1, another red dwarf that is just under 40 light years out in the constellation Aquarius. These are small stars indeed, just 8 percent the mass of the Sun in the case of the latter, while Proxima Centauri is about 10 times less massive (and 500 times less luminous) than the Sun. But just what might we find on planets like these? A new paper from Yann Alibert and Willy Benz (University of Bern) drills down into their composition. The researchers' goal is to study planet formation, with a focus on planets orbiting within 0.1 AU, a range that includes the habitable zone for such stars. While a forthcoming paper will look at the formation process of these planets in greater detail, the present work studies planetary...

First light for the European Extremely Large Telescope (E-ELT) is scheduled for 2024, a useful fact given that a few years later, we may be able to use the instrument in a gravitational lensing opportunity involving Alpha Centauri. Specifically, Centauri A is expected to align with the star 2MASS 14392160-6049528, thought to be a red giant or supergiant and far more distant than Alpha Centauri. This will create an event that not just the E-ELT but other instruments, like the GRAVITY instrument on the Very Large Telescope Interferometer (VLTI), will be able to study -- GRAVITY is capable of extremely high accuracy astrometry. A team of French astronomers led by Pierre Kervella (CNRS/Universidad de Chile) is behind this new study, which involved fine-tuning our knowledge of the trajectories of Centauri A and B. Remember that we see gravitational lensing when a massive object like a star distorts the spacetime around it, so that light from the more distant object must follow a curved...

Determining the age of a star is not easy, but one way of proceeding with at least some degree of confidence is to identify the star as a member of a stellar association. Here we’re talking about a loose cluster of stars of a common origin. Over time, the stars have begun to separate, but they still move together through space. It was the Armenian astronomer Viktor Ambartsumian, the founder of the Byurakan Observatory, who discovered the nature of these associations and demonstrated that they were composed of relatively young groups of stars. Stellar associations, or young moving groups (YMGs), provide an outstanding place to study the evolution of protoplanetary disks around young stars, for all associated stars have a similar age. Indeed, their galactic motion can be traced back to their place of origin. Another benefit: Exoplanets in such infant systems are often still hot, well within the capabilities of our near-infrared direct imaging techniques. Many direct imaging and disk...

Spotting planets a long way from their stars is no easy proposition when you’re using radial velocity methods. The idea is to track the minute movement of the star as it is affected by an orbiting planet, which shows up as a Doppler shift in the data. What we’re actually seeing is the star and planet orbiting the center of gravity, an indirect method of detection that observes not the planet itself but the effects of the planet as it produces this variation in radial velocity. The first exoplanets were detected this way, and the method has continued to produce new discoveries. But as a planet’s distance from its star increases, radial velocity becomes tricky to use. Now observation times become extended as the planet completes its longer orbit. We face the same issue with the transit method, which charts the drop in brightness as a planet moves across the face of its star as seen from Earth. Here, too, planets in distant orbits around their star are hard to detect because of the...

We’ve seen circumstellar disks around numerous stars, significant because it is from such disks that planets are formed, and we would like to know a good deal more about how this process works. Now we have word of planet-forming disks around several low-mass objects that fit into the brown dwarf range, and one small star about a tenth the mass of the Sun. With the brown dwarfs, we’re working with objects small enough to be at the boundary between planet and star. The work is led by Anne Boucher (Université de Montréal), whose team drew photometric data from the Two-Micron All-Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE) mission, allowing the detection of the objects at infrared wavelengths. Boucher notes the strong attraction such objects hold for astronomers: “Finding disks in low-mass systems is really interesting to us, because objects that exist at the lower limit of what defines a star and that still have disks that indicate planet formation can tell us...

A circumbinary planet is one that orbits two stars, and to date we haven't found many of them. Word of a new detection comes from an event observed back in 2007 during a microlensing study called OGLE -- Optical Gravitational Lensing Experiment. OGLE is a Polish undertaking designed to study dark matter using gravitational microlensing, but while dark matter remains as dark as ever, the project has been able to deliver useful findings on distant exoplanets. A number of groups specializing in gravitational microlensing also contributed to this analysis. These are observation efforts not as well known to the public as Kepler or Gaia, but they're doing exceptional work: MOA (Microlensing Observations in Astrophysics); MicroFUN (Microlensing Follow-Up Network); PLANET (Probing Lensing Anomalies NETwork); and Robonet. Subsequent Hubble Telescope data were then applied to the analysis, confirming the discovery. Image: This artist's illustration shows a gas giant planet circling a pair of...

Proxima Centauri b, that highly interesting world around the nearest star, is about 0.05 AU out from its primary. The figure leaps out to anyone new to red dwarf stars, because it's so very close to the star itself, well within the orbit of Mercury in our own system. But these are small, dim stars compared to our Sun, and hugging the star is essential to remain in the habitable zone. That also makes for very short years -- Proxima b completes an orbit every 11.2 days. Guillem Anglada-Escudé and colleagues reminded us in the discovery paper that among the many things we have to ask about this planet is whether or not it has a strong magnetic field. Because Proxima Centauri is known for flare activity, not to mention 400 times the X-ray flux the Earth receives. A magnetic field could help the planet hang on to its atmosphere, but just how strong would it need to be? Like any M-dwarf planet, then, Proxima b seems vulnerable. This thinking has ramifications much closer to home. We...

TRAPPIST continues to be my favorite astrophysical acronym. Standing for Transiting Planets and Planetesimals Small Telescope, the acronym flags a robotic instrument at the La Silla Observatory in Chile that is operated by the the Institut d'Astrophysique et Géophysique (University of Liège, Belgium) in cooperation with the Geneva Observatory. The name is a nod to the branch of the Cistercian order of monks called Trappists, whose beer is world-renowned and closely associated with Belgium itself (although also brewed in the Netherlands and a few other countries). A jolly telescope indeed. You'll recall TRAPPIST-1 as the far more approachable term for the red dwarf star 2MASS J23062928-0502285, a bit over 39 light years away in the direction of the constellation Aquarius. A 2016 paper in Nature announced three rocky planets orbiting the star, one of which could conceivably be in its habitable zone, where liquid water can exist on the surface. Now we have a helpful follow-up...

Alpha Centauri A and B, the two primary stars of the Alpha Centauri threesome, orbit a common center of gravity, with an average separation of 23.7 AU. But bear in mind that this average covers wider ground. The separation can close to about 11 AU or widen to as far as 36 AU. I bring these distances up because it's an open question whether there are planets around either of these stars. The possibility exists that we might find planets around both, and of course we already know of that interesting planet circling nearby Proxima Centauri. Do we have examples of close binaries in which we find a planet around each star? Until late August, the closest known binary system with planets orbiting both individual stars showed a separation of 1000 AU. But now we have the twin stars HD 133131A and HD 133131B. Around the former we have two planets, one whose minimum mass is about 1.5 times Jupiter's mass, the other with a minimum of about half Jupiter's mass. The second star hosts a planet of...

Meeting people I've written about is always a pleasure at gatherings of the interstellar-minded, and I was delighted to run into Victoria Meadows (University of Washington) in the lobby of our hotel on the final day of the Breakthrough Starshot meetings. Rory Barnes is a colleague of Meadows at UW and recently described the research underway at the Virtual Planetary Laboratory there, at which Meadows is the director. Barnes' essay Opportunities and Obstacles for Life on Proxima b appeared as a guest post on the Pale Red Dot site. I wished I had time to discuss Proxima with Meadows, but our meeting was brief as everyone dispersed for dinner. What Meadows and fellow researchers Giada Arney, Edward Schwieterman and Rodrigo Luger are doing is to produce computer models through which they can study Proxima b's habitability, based on everything from the planet's orbit to the characteristics of not just its host star, but the nearby stars Centauri A and B. Out of this come conclusions about...

I have much more to say about the Breakthrough Starshot meetings, but last evening I decided to slow the pace a bit. I mentioned in my first report that the discovery of a planet around Proxima Centauri had woven through our San Francisco meetings, creating a bright thread of discussion that continued through all three days. We are also getting papers on Proxima’s planet that inform us more about its potential habitability. In the next couple of days, then, I want to go through some of these before returning soon to the broader issues of Starshot. I also have to admit that I am still transcribing some of my handwritten notes from San Francisco to get everything in synch with my laptop, a process that is taking longer than I intended, thanks to my murky handwriting... In any case, whether Proxima b is habitable or not would surely play a large role in any decisions about using it as Starshot’s initial target. So let’s remember what Guillem Anglada-Escudé and the Pale Red Dot team had...

A planet in the habitable zone around Proxima Centauri? The prospect dazzles the imagination, but then, I’ve been thinking about just that kind of planet for most of my life. Proxima Centauri is, after all, the closest star to our own, about 15000 AU from the primary Alpha Centauri stars (though thought to be moving with that system). A dim red dwarf, Proxima wasn’t discovered until 1915, but it quickly seized the imagination of science fiction writers who pondered what might exist around such a star. Murray Leinster’s story “Proxima Centauri” (1935) is a clanking, thudding tale but it still evokes a bit of the magic of one of the earliest fictional interstellar voyages. Image: This wide-field image shows the Milky Way stretching across the southern sky. The beautiful Carina Nebula (NGC 3372) is seen at the right of the image glowing in red. It is within this spiral arm of our Milky Way that the bright star cluster NGC 3603 resides. At the centre of the image is the constellation of...

I often work out my thoughts on the topics we discuss here while taking long walks. I try to get in five miles a day but more often it’s about three. In any case, these long, reflective walks identify me as the neighborhood eccentric, an identity that is confirmed by the things I write about. What’s interesting about that is that so many people have a genuine interest in the stars and how we might get there. Some of the best questions I’ve ever had have been from people whose interest is casual but persistent, and one good question usually leads to another. Hence I wasn’t surprised on yesterday's walk to find myself talking with a neighbor about exomoons and why we study them. After all, we have a Solar System in which moons are commonplace. Isn’t it perfectly obvious that different solar systems would have planets with moons? The answer is yes, but it also follows that things that seem perfectly obvious still have to be confirmed. But let’s unpack it a bit more than that. We’re...

It’s been a week for unusual planetary systems, and I’ll cap it off with Kepler-80, a star about 1100 light years away that features five planets in extraordinarily tight orbits. Such systems are now being referred to as STIPs (Systems with Tightly-spaced Planets), a nod to our apparently imperishable drive to create acronyms. Whatever we call them, though, systems like these make us realize that our own Solar System’s configuration is but one possibility in a sea of other outcomes. Yesterday’s post on ‘warm Jupiters’ is yet another confirmation of the thought. What we have in new work from Mariah MacDonald, Darin Ragozzine (Florida Institute of Technology) and colleagues is an analysis of transit timing variations (TTVs) of the planets around this star, all of which orbit inside 1/10 AU. Here the planets’ years are 1.0, 3.1, 4.6, 7.1 and 9.5 days, respectively, close enough that gravitational perturbations can create slight changes in transit times. Although the innermost planet has...

Where exactly do ‘hot Jupiters’ come from? I usually see explanations involving planetary migration for Jupiter-class objects with tight orbital periods of 10 days or less, the thinking being that such planets are too close to their host stars to have accumulated a Jovian-style gaseous envelope there. Migration explains their placement, with gas giants forming much further out in their planetary systems and then migrating disruptively inward to become hot Jupiters. Does the scenario work? Consider the hot Jupiter WASP-47b, which has two low-mass planets nearby in its system. WASP-47b is a problem because a migrating gas giant should have produced profound gravitational issues for small worlds in the inner system, likely ejecting them entirely. A new paper from Chelsea Huang and Yanqin Wu (University of Toronto), working with Amaury Triaud (University of Cambridge), tries to explain the dilemma posed by WASP-47b. The answer turns out to be that, according to Kepler data used by the...