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...

We just looked at how gravitational microlensing can be used to analyze the mass of a star, giving us a method beyond the mass-luminosity relationship to make the call. And we're going to be hearing a lot more about microlensing, especially in exoplanet research, as we move into the era of the Nancy Grace Roman Space Telescope (formerly WFIRST), which is scheduled to launch in 2027. A major goal for the instrument is the expected discovery of exoplanets by the thousands using microlensing. That's quite a jump - I believe the current number is less than 100. For while radial velocity and transit methods have served us well in establishing a catalog of exoplanets that now tops 5000, gravitational microlensing has advantages over both. When a stellar system occludes a background star, the lensing of the latter's light can tell us much about the planets that orbit the foreground object. Whereas radial velocity and transits work best when a planet is in an orbit close to its star,...

It’s not easy teasing out information about a tiny red dwarf star, even when it’s the closest star to the Sun. Robert Thorburn Ayton Innes (1861-1933), a Scottish astronomer, found Proxima using a blink comparator in 1915, noting a proper motion similar to Alpha Centauri (4.87” per year), with Proxima about two degrees away from the binary. Finding out whether the new star was actually closer than Centauri A and B involved a competition with a man with a similarly august name, Joan George Erardus Gijsbertus Voûte, a Dutch astronomer working in South Africa. Voûte’s parallax figures were more accurate, but Innes didn’t wait for debate, and proclaimed the star’s proximity, naming it Proxima Centaurus. The back and forth over parallax and the subsequent careers of both Innes and Voûte make for interesting reading. I wrote both astronomers up back in 2013 in Finding Proxima Centauri, but I’ll send you to my source for that article, Ian Glass (South African Astronomical Observatory), who...

Are there limits on how big a moon can be to orbit a given planet? All we have to work with, in the absence of confirmed exomoons, are the satellites of our Solar System’s planets, and here we see what appears to be a correlation between a planet’s mass and the mass of its moons. At least up to a point – we’ll get to that point in a moment. But consider: As Vera Dobos (University of Groningen, Netherlands) and colleagues point out in a recent paper for Monthly Notices of the Royal Astronomical Society, if we’re talking about moons forming in the circumplanetary disk around the young Sun, the total mass is on the order of 10-4Mp. Here Mp is the mass of the planet. A planet with 10 times Jupiter’s mass, given this figure, could have a moon as large as a third of Earth’s mass, and so far observational evidence supports the idea that moons can form regularly in such disks. There is no reason to believe we won’t find exomoons by the billions throughout the galaxy. Image: The University of...

A liquid water-defined habitable zone is a way of establishing parameters for life as we know it around other stars, and with this in mind, scientists study the amount of stellar radiation a planet receives as one factor in making the assessment. But of course, not everything in a habitable zone is necessarily habitable, as our decidedly uninhabitable Moon makes all too clear. Atmospheric factors and tectonic activity, for example, have to be weighed as we try to learn what the actual temperature at the surface would be. We're learning as we go about other contributing factors. A problem of lesser visibility in the literature, though perhaps just as crucial, is whether a given planet can stay habitable on timescales of billions of years. This is where an interesting new paper from Cayman Unterborn (Southwest Research Institute) and colleagues enters the mix. A key question in the view of these researchers is whether carbon dioxide, the greenhouse gas whose ebb and flow on our world...

What to make of a Jupiter-class planet that orbits its host star at a distance of 13.8 billion kilometers? This is well over twice the distance of Pluto from the Sun, out past the boundaries of what in our system is known as the Kuiper Belt. Moreover, this is a young world still in the process of formation. At nine Jupiter masses, it's hard to explain through conventional modeling, which sees gas giants growing through core accretion, steadily adding mass through progressive accumulation of circumstellar materials. Core accretion makes sense and seems to explain typical planet formation, with the primordial cloud around an infant star dense in dust grains that can accumulate into larger and larger objects, eventually growing into planetesimals and emerging as worlds. But the new planet - AB Aurigae b - shouldn't be there if core accretion were the only way to produce a planet. At these distances from the star, core accretion would take far longer than the age of the system to produce...

Exoplanet science can look forward to a rash of discoveries involving gravitational microlensing. Consider: In 2023, the European Space Agency will launch Euclid, which although not designed as an exoplanet mission per se, will carry a wide-field infrared array capable of high resolution. ESA is considering an exoplanet microlensing survey for Euclid, which will be able to study the galactic bulge for up to 30 days twice per year, perhaps timed for the end of the craft’s cosmology program. Look toward crowded galactic center long enough and you just may see a star in the galaxy's disk move in front of a background star located much further away in that dense bulge. The result: The lensing phenomenon predicted by Einstein, with the light of the background star magnified by the intervening star. If that star has a planet, it's one we can detect even if it's relatively small, and even if it's widely spaced from its star. For its part, NASA plans to launch the Roman space telescope by...

A living world around another star will not be an easy catch, no matter how sophisticated the coming generation of space- and ground-based telescopes turns out to be. It’s one thing to develop the tools to begin probing an exoplanet atmosphere, but quite another to be able to say with any degree of confidence that the result we see is the result of biology. When we do begin picking up an interesting gas like methane, we’ll need to evaluate the finding against other atmospheric constituents, and the arguments will fly about non-biological sources for what might be a biosignature. This is going to begin playing out as the James Webb Space Telescope turns its eye on exoplanets, and methane is the one potential sign of life that should be within its range. We know that oxygen, ozone, methane and carbon dioxide are produced through biological activity on Earth, and we also know that each can be produced in the absence of life. The simultaneous presence of such gases is what would intrigue...

Why is it so difficult to detect planets around Alpha Centauri? Proxima Centauri is one thing; we’ve found interesting worlds there, though this small, dim star has been a tough target, examined through decades of steadily improving equipment. But Centauri A and B, the G-class and K-class central binary here, have proven impenetrable. Given that we’ve found over 4500 planets around other stars, why the problem here? Proximity turns out to be a challenge in itself. Centauri A and B are in an orbit around a common barycenter, angled such that the light from one will contaminate the search around the other. It’s a 79-year orbit, with the distance between A and B varying from 35.6 AU to 11.2. You can think of them as, at their furthest, separated by the Sun’s distance from Pluto (roughly), and at their closest, by about the distance to Saturn. The good news is that we have a window from 2022 to 2035 in which, even as our observing tools continue to improve, the parameters of that orbit...

I always keep an eye on the Phase I and Phase II studies in the pipeline at the NASA Innovative Advanced Concepts (NIAC) program. The goal is to support ideas in their early stages, with the 2022 awards going out to 17 different researchers to the tune of a combined $5.1 million. Of these, 12 are Phase I studies, which deliver $175,000 for a nine-month period, while the five Phase II awards go to $600,000 over two years. We looked at one of the Phase I studies, Jason Benkoski's solar-thermal engine and shield concept, in the last post. Today we go hunting exoplanets with a starshade. This particular iteration of the starshade concept is called Hybrid Observatory for Earth-like Exoplanets (HOEE), as proposed by John Mather (NASA GSFC). Here the idea is to leverage the resources of the huge ground-based telescopes that should define the next generation of such instruments - the Giant Magellan Telescope, the Extremely Large Telescope, etc. - by using a starshade to block the glare of...

The apparent discovery of a new planet around Proxima Centauri moves what would have been today’s post (on laser-thermal interstellar propulsion concepts) to early next week. Although not yet confirmed, the data analysis on what will be called Proxima Centauri d seems strong, in the hands of João Faria (Instituto de Astrofísica e Ciências do Espaço, Portugal) and colleagues. The work has just been published in Astronomy & Astrophysics. It’s good to hear that Faria describes Proxima Centauri as being “within reach of further study and future exploration.” That last bit, of course, is a nod to the fact that this is the nearest star to the Sun, and while 4.2 light years is its own kind of immensity, any future interstellar probe will naturally focus either here or on Centauri A and B. Years are short on Proxima d – the putative planet circles Proxima every five days. That’s a tenth of Mercury’s distance from the Sun, closer to the star than to the inner edge of the habitable zone....

It would explain a lot if two recent discoveries involving 'mini-Neptunes' turned out to be representative of what happens to their entire class. For Michael Zhang (Caltech) and colleagues, in two just published papers, have found that mini-Neptunes can lose gas to their parent star, possibly indicating their transformation into a 'super-Earth.' If such changes are common, then we have a path to get from a dense but Neptune-like world to a super-Earth, a planet roughly 1.6 times the size of the Earth and part of a category of worlds we do not see represented in our Solar System. As we drill down toward finding smaller worlds, we've been finding a lot of mini-Neptunes as well as super-Earths, with the former two to four times the size of the Earth. Thus we have a bimodal gap in exoplanet observation. Where are the worlds between 1.6 and 2-4 times the size of Earth? The new work examines two mini-Neptunes around the TESS object TOI 560, located about a hundred light-years from Earth,...

Given our recent discussion of exomoon candidate Kepler-1708 b-i, a possible moon 2.6 times the mass of Earth orbiting a gas giant, I want to be sure to work in Miki Nakajima’s work on how moons form. Nakajima (University of Rochester) is first author of the paper describing this work. It’s a significant contribution because it points to a way to refine the target list for exomoon searches, one that may help us better understand where to look as we begin to flesh out a catalog of these objects.. And flesh it out we will, as the precedent of the rapidly growing exoplanet count makes clear. What I want to do today is consider how we’ve thus far proceeded. You’ll recall that when David Kipping and team performed their deep analysis of the data leading to Kepler-1708 b-i, they chose gas giants on orbits with a period of 400 days or more, so-called ‘cool worlds’ more like Jupiter than the ‘hot Jupiters’ found so frequently in early exoplanet studies. The method produced a strong candidate...