Here’s a thought that puts a different spin on exoplanet studies. The speaker is Darryl Seligman (Cornell University): "The comets and asteroids in the solar system have arguably taught us more about planet formation than what we've learned from the actual planets in the solar system. I think that the interstellar comets could arguably tell us more about extrasolar planets than the extrasolar planets we are trying to get measurements of today." Seligman’s comment plays into the growing interest in interstellar objects that drift into our Solar System like 1/I ‘Oumuamua and 2/I Borisov. These may be the initial members of what is actually a large class of debris from other stars that we are only now learning how to detect. Among the many things we have yet to refine in our understanding of ‘Oumuamua is its actual size. Projections of 115 by 111 by 19 meters are deduced from its brightness and the changes produced by its apparently tumbling motion. The interstellar interloper is too...

The problem with Alpha Centauri is that the system is too close. I don’t refer to its 4.3 light year distance from Sol, which makes these stars targets for future interstellar probes, but rather the distance of the two primary stars, Centauri A and B, from each other. The G-class Centauri A and K-class Centauri B orbit a common barycenter that takes them from a maximum of 35.6 AU to 11.2 AU during the roughly 80 year orbital period. That puts their average distance from each other at 23 AU. So the average orbital distance here is a bit further than Uranus’ orbit of the Sun, while the closest approach takes the two stars almost as close as the Sun and Saturn. Habitable zone orbits are possible around both stars, making for interesting scenarios indeed, but finding out just how the system is populated with planets is not easy. We’ve learned a great deal about Proxima Centauri’s planets, but teasing out a planetary signature from our data on Centauri A and B has been frustrating despite...

The presence of water in the circumstellar disk of V883 Orionis, a protostar in Orion some 1300 light years out, is not in itself surprising. Water in interstellar space is known to form as ice on dust grains in molecular clouds, and clouds of this nature collapse to form young stars. We would expect that water would be found in the emerging circumstellar disk. What new work with data from the Atacama Large Millimeter/submillimeter Array (ALMA) shows is that such water remains unchanged as young star systems evolve, a chain of growth from protostar to protoplanetary disk and eventually planets and water-carrying comets. John Tobin, an astronomer at the National Science Foundation’s National Radio Astronomy Observatory (NRAO), is lead author on the paper on this work: “We can think of the path of water through the Universe as a trail. We know what the endpoints look like, which are water on planets and in comets, but we wanted to trace that trail back to the origins of water. Before...

If there is a Planet Nine out there, I assume we’ll find it soon. That would be a welcome development, in that it would imply the Solar System isn’t quite as odd as it sometimes seems to be. We see super-Earths – and current thinking seems to be that this is what Planet Nine must be – in other stellar systems, in great numbers in fact. So it would stand to reason that early in its evolution our system produced a super-Earth, one that was presumably nudged into a distant, eccentric orbit by gravitational interactions. The gap in size between Earth and the next planet up in scale is wide. Neptune is 17 times more massive than our planet, and four times its radius. Gas giant migration surely played a role in the outcome, and when considering stellar system architectures, it’s noteworthy as well that all that real estate between Mars and Jupiter seems to demand something more than asteroidal debris. To make sense of such issues, Stephen Kane (University of California, Riverside) has run...

We’re beginning to learn how common planets are around stars of various types, but M-dwarfs get special attention given their role in future astrobiological studies. As I’ve just been talking about CARMENES, the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs program, I’ll fold in today’s news about their release of 20,000 observations covering more than 300 stars, for we can mine some data here about planet occurrence rates. 59 new planets turn up in the spectroscopic data gathered at the Calar Alto Observatory in Span, with about 12 thought to be in the habitable zone of their star. I’ll await with interest our friend Andrew LePage’s assessment. His habitable zone examinations serve as a highly useful reality check. I mentioned spectrographic data above. The CARMENES instruments are built for optical as well as near-infrared studies, and have been used to explore nearby red dwarfs and their possible planets since...

Let’s look at a second red dwarf planet in this small series on such, this one being Wolf 1069b. I want to mention it partly because of the prior post on K2-415b, where we had the good fortune to be dealing with a transiting world around an M-dwarf that should be useful in future atmospheric characterization efforts. Wolf 1069b, by contrast, was found by radial velocity methods, and I’m less interested in whether or not it’s in a ‘habitable’ orbit than in the system architecture here, which raises questions. This work, recounted in a recent paper in Astronomy & Astrophysics, describes a planet that is not just Earth-sized, as is K2-415b, but roughly equivalent to Earth in mass, making a future search for biosignatures interesting once we have the capability of collecting photons directly from the planet. If the planet has an atmosphere, argue the authors of the paper, its surface temperature could reach 13 degrees Celsius, certainly a comfortable temperature for liquid water. A...

I want to mention the recent confirmation of K2-415b because this world falls into an interesting category: Planets with major implications for studying their atmospheres. Orbiting an M5V M-dwarf every 4.018 days at a distance of 0.027 AU, this is not a planet with any likelihood for life. Far from it, given an equilibrium temperature expected to be in the range of 400 K (the equivalent figure for Earth is 255 K). And although it’s roughly Earth-sized, K2-415b turns out to be at least three times more massive. What this planet has going for it, though, is that it transits a low mass star, and at 70 light years, it’s close. Consider: If we want to take advantage of transmission spectroscopy to study light being filtered through the planetary atmosphere during ingress and egress from the transit, nearby M-dwarf systems make ideal targets. Their habitable zones are close in, so we get frequent transits around small stars. But the number of Earth-sized transiting worlds around nearby...

LHS 475b, a planet whose diameter is all but identical to Earth's, makes news not so much because of what it is but because of what it tells us about studying the atmospheres of small rocky worlds. Credit for the confirmation of this planet goes to the NIRSpec (Near-Infrared Spectrograph) instrument aboard the James Webb Space Telescope, and LHS 475b marks the telescope’s first exoplanet catch. Data from the Transiting Exoplanet Survey Satellite (TESS) were sufficient to point scientists toward this system for a closer look. JWST confirmed the planet after only two transits. Based on this detection, the Webb telescope is going to live up to expectations about its capabilities in exoplanet work. NIRSpec is a European Space Agency contribution to the JWST mission, and a major one, as the instrument’s multi-object spectroscopy mode is able to obtain spectra of up to 100 objects simultaneously, a capability that maximizes JWST observing time. No other spectrograph in space can do this,...

Although I often see the exoplanet WASP-39b referred to as a ‘hot Saturn,’ and sometimes a ‘hot Jupiter,’ the terms don’t really compute. This is a world closer to Saturn than Jupiter in mass, but with a radius somewhat larger than that of Jupiter. Hugging its G-class primary in a seven million kilometer orbit, it completes a circuit every four days. The system is about 700 light years from us in Virgo, and to my mind WASP-39b is a salutary reminder that we can carry analogies to the Solar System only so far. Because we have nothing in our system that remotely compares to WASP-39b. Let’s celebrate the fact that in this exoplanet we have the opportunity to study a different kind of planet, and remind ourselves of how many worlds we’re finding that are not represented by our own familiar categories. I imagine one day we'll have more descriptive names for what we now call, by analogy, 'super-Earths' and 'sub-Neptunes' as well. I've seen WASP-39b referred to in the literature as a...

From the standpoint of producing interesting life, K-dwarf stars look intriguing. Our G-class Sun is warm and cozy, but its lifetime is only about 10 billion years, while K-dwarfs (we can also call them orange dwarfs) can last up to 45 billion years. That's plenty of time for evolution to work its magic, and while G-stars make up only about 6 or 7 percent of the stars in the galaxy, K-dwarfs account for three times that amount. We have about a thousand K-dwarfs within 100 light years of the Solar System. When Edward Guinan (Villanova University) and colleague Scott Engle studied K-dwarfs in a project called "GoldiloKs," they measured the age, rotation rate, and X-ray and far-ultraviolet radiation in a sampling of mostly cool G and K stars (see Orange Dwarfs: 'Goldilocks' Stars for Life?). Their work took in a number of K-stars hosting planets, including the intriguing Kepler-442, which has a rocky planet in the habitable zone. Kepler-442b is where we'd like it to be in terms of...

I’m interested in a new paper on planet formation, not only for its conclusions but its methodology. What Amy Bonsor (University of Cambridge) and colleagues are drawing from their data is how quickly planets can form. We’ve looked numerous times in these pages at core accretion models that explain the emergence of rocky worlds and gravitational instability models that may offer a way of producing a gas giant. But how long after the formation of the circumstellar disk do these classes of planets actually appear? A planet like the Earth poses fewer challenges than a Jupiter or Saturn. Small particles run into each other within the gas and dust disk surrounding the young star, assembling planets and other debris through a process of clumping that eventually forms planetesimals that themselves interact and collide. Thus core accretion: The planet ‘grows’ in ways that are readily modeled and can be observed in disks around other stars. But the gas giants still pose problems. Core...

Are we overlooking a potential biosignature? A new study makes the case that nitrous oxide could be a valuable indicator of life on other worlds, and one that can be detected with current and future instrumentation. In today’s essay, Don Wilkins takes a close look at the paper. A retired aerospace engineer with thirty-five years experience in designing, developing, testing, manufacturing and deploying avionics, Don tells me he has been an avid supporter of space flight and exploration all the way back to the days of Project Mercury. Based in St. Louis, where he is an adjunct instructor of electronics at Washington University, Don holds twelve patents and is involved with the university’s efforts at increasing participation in science, technology, engineering, and math. by Don Wilkins Biosignatures, specific signals produced by life, are the focus of intense study within the astronomical community. Gases such as nitrogen (N2), oxygen and methane are sought in planetary atmospheres as...

I hadn’t intended to return to habitability around red dwarf stars quite this soon, but on Saturday I read a new paper from Anna Childs (Northwestern University) and Mario Livio (STScI), the gist of which is that a potential challenge to life on such worlds is the lack of stable asteroid belts. This would affect the ability to deliver asteroids to a planetary surface in the late stages of planet formation. I’m interested in this because it points to different planetary system architectures around M-dwarfs than we’re likely to find around other classes of star. What do observations show so far? You’ll recall that last week we looked at M-dwarf planet habitability in the context of water delivery, again involving the question of early impacts. In that paper, Tadahiro Kimura and Masahiro Ikoma found a separate mechanism to produce the needed water enrichment, while Childs and Livio, working with Rebecca Martin (UNLV) ponder a different question. Their concern is that red dwarf planets...

Small M-dwarf stars, the most common type of star in the galaxy, are likely to be the primary target for our early investigations of habitable planets. The small size of these stars and the significant transit depth this allows when an Earth-mass planet crosses their surface as seen from Earth mean that atmospheric analysis by ground- and space-based telescopes should be feasible via transmission spectroscopy. Recent studies have shown that the James Webb Space Telescope has the precision to at least partially characterize the atmospheres of Earth-class planets around some M-dwarfs. Soon-to-be commissioned ground-based extremely large telescopes will likewise play a role as we examine nearby transiting systems. But M-dwarfs make challenging homes for life, if indeed it can exist there. In addition to flare activity, we also have to reckon with the presence of water. Too much of it could suppress weathering in the geochemical carbon cycle, but too little does not allow for the...

When it comes to planetary habitability, it is all too easy to let our assumptions slide past without review. It's a danger to be avoided if we want to understand what may distinguish various types of habitable worlds. That's the implication of a presentation at the recent Europlanet Science Congress (EPSC), which finished its work on September 23 at the Palacio de Congresos de Granada (Spain). Tilman Spohn (International Space Science Institute) and Dennis Höning (Potsdam Institute for Climate Impact Research) have been investigating the ratio of land to ocean and the evolution of biospheres. The assumptions the duo are examining revolve around the kind of habitable world our Earth represents. Our planet draws on solar energy through continents balanced against large oceans that produce abundant rainfall. Would a given exoplanet have similar geological properties? According to the scientists, it is a balance between the emergence of continents and the volcanism and continental...

The discovery of a super-Earth around the M-dwarf Ross 508 gives us an interesting new world close to, if not sometimes within, the inner edge of the star’s habitable zone. This is noteworthy not simply because of the inherent interest of the planet, but because the method used to detect it was Doppler spectroscopy. In other words, radial velocity methods in which we study shifts in the spectrum of the star are here being applied to a late M-dwarf that emits most of its energies in the near-infrared (NIR). I usually think about transits in relation to M-dwarf planets, because our space-based observatories, from CoRoT to Kepler and now TESS, have demonstrated the power of these techniques in finding exoplanets. M-dwarfs are made to order for transits because they’re small enough to offer deep transits – the signature of the planet in the star’s lightcurve is more pronounced than a transit across a larger star. From a radial velocity perspective, planets in an M-dwarf habitable zone...

So let’s get to work with the James Webb Space Telescope. Those dazzling first images received a gratifying degree of media attention, and even my most space-agnostic neighbors were asking me about what exactly they were looking at. For those of us who track exoplanet research, it’s gratifying to see how quickly JWST has begun to yield results on planets around other stars. Thus WASP-96 b, 1150 light years out in the southern constellation Phoenix, a lightweight puffball planet scorched by its star. Maybe 'lightweight' isn’t the best word. Jupiter is roughly 320 Earth masses, and WASP-96b weighs in at less than half that, but its tight orbit (0.04 AU, or almost ten times closer to its Sun-like star than Mercury) has puffed its diameter up to 1.2 times that of Jupiter. This is a 3.5-day orbit producing temperatures above 800 ?. As you would imagine, this transiting world is made to order for analysis of its atmosphere. To follow JWST's future work, we’ll need to start learning new...

It’s hard to imagine what the field of exoplanet discovery will look like in a hundred years. Just as difficult as it is to imagine what might happen if we do get to a ‘singularity’ in machine intelligence beyond which we humans can’t venture. Will the study of other stellar systems become largely a matter of computers analyzing data acquired by AI, with human operators standing by only in case of equipment failure? Or will the human eye for pattern and detail so evident in many current citizen science projects always be needed to help us piece together what the machines find? I wonder this when I read about the effort going into teasing new data out of older observations, as we saw recently in VASCO, a project to study old astronomical photographic plates looking for possible technosignatures. And I suspect we’ll always need human/machine collaboration to draw maximum knowledge out of our data. Today let’s look at how useful software tools are illuminating what we’ve already learned...

Let's catch up with white dwarfs, a kind of star that may spawn planetary systems of its own. For I've just found another case of archival data being put to good use in the form of a study of a white dwarf system called G238-44. Here, the data come from the Hubble instrument (specifically, its Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph), the Far Ultraviolet Spectroscopic Explorer (FUSE), and the Keck Observatory's High Resolution Echelle Spectrometer (HIRES) in Hawaii. What astronomers presented at a recent AAS conference is a picture of a system severely disrupted by its star's transition to white dwarf status. Moreover, this is a star in the process of accretion with a distinct twist from earlier such discoveries. For the white dwarf - the remnant left behind after the system's star went through its red giant phase - is actively drawing rocky and metallic material as well as ices from the debris of the disrupted system. These are the stuff of planet...