I can only wonder what Miguel de Cervantes Saavedra would have thought of the idea that a distant star would one day be named for him. I wonder, too, what the Spanish novelist (1547-1616) would have made of the idea that planets circled other stars, and that planets around the star named for him would have names taken from his most famous work, Don Quixote. Maybe the great character of the book’s title, obsessed with tales of chivalry, would have been unhinged enough to take things like other solar systems in stride.
We have the NameExoWorlds contest to thank for these speculations. The contest, organized by the International Astronomical Union (IAU) gave the public the opportunity to choose the names of selected stars and planets. The star named for Cervantes is mu Arae (HD 160691), a G-class star about fifty light years out in the constellation Ara (the Altar). Here we’ve found three gas giant planets comparable to Jupiter as well as a ‘super-Earth.’ And frankly, as a reader who agrees with Schopenhauer that Don Quixote is one of the world’s great novels, I am delighted with what the public has chosen, at least for this star.
Image: Portrait of Miguel de Cervantes y Saavedra (1547-1615), by the artist Juan de Jauregui y Aguilar (circa 1583-1641). Credit: Bridgeman Art Library.
For mu Arae b becomes Quijote, while mu Arae c is Dulcinea. The system is rounded out with Rocinante (mu Arae d) and Sancho (mu Arae e). Names as enchanting as these, with roots in classic literature, are likely to stick. When the voting finished at the end of October, the IAU had received 573,242 votes, which went toward naming 14 host stars and 31 exoplanets. Names were submitted from astronomy organizations in 45 countries, everything from amateur astronomy clubs to universities and planetariums, drawn from a wild variety of sources.
Take Thestias, the planet depicted in the image below. The grandfather of Pollux, Thestias orbits the star of the same name (Pollux, already named, needs no further designation). In Greek mythology, Pollux and Castor were twin brothers known as the Dioscuri who became transformed at death into the constellation Gemini. The winning name came from SkyNet, an astronomy project based at the International Centre for Radio Astronomy Research (ICRAR) in Perth, Australia. The group, which includes over 200,000 volunteers globally, arrived at the submission by an internal vote, drawing on the idea of volunteer Rich Matthews.
Image: Artist’s impression of Thestias around its star Pollux. Credit: NASA/ESA and G. Bacon (STScI).
If mu Arae taps the late European Renaissance for its inspiration, 47 Ursae Majoris (46 light years out) draws on Thai folklore. The star receives the name Chalawan, while 47 Ursae Majoris b becomes Taphao Thong and 47 Ursae Majoris c is Taphao Kaew, these being two sisters in the story of a mythological crocodile king. The star upsilon Andromedae (an F-class star 44 light years away) becomes Titawin, a point of contact in Morocco between Spaniards and Arabs after the 8th Century. The planets upsilon Andromedae b, c and d become Saffar, Samh and Majriti, names drawn from astronomers and mathematicians notable in 11th Century Spain.
I think some of these names will last, but I’m not at all sure why the IAU chose to put out a call for new names for epsilon Eridani, at 10.5 light years one of the closest stars and a familiar name to generations of science fiction readers. I’m OK with giving epsilon Eridani b the name AEgir, which is drawn from Norse mythology (he was husband to Ran, the goddess of the sea), but changing the star epsilon Eridani to Ran is just not going to work, the original name being too widely circulated. It’s as odd as if we named the three Centauri stars anything other than their designation, the point being that by wide use, the designation and the name are one.
18 Delphini gets tagged Musica (lovely!), while its planet 18 Delphini b is now the wisely chosen Arion, a Greek musician whose tunes attracted the dolphins who saved him at sea. It’s also heartening to see the 55 Cancri planets named for great figures in astronomy including Galileo and Brahe, while the star itself becomes Copernicus. But is Poltergeist going to survive as the name of one of the pulsar planets (PSR 1257+12 c)? How about Spe for 14 Andromedae b?
My cavils aside, I love the idea of pulling the public into the naming of planets because we live in a world undergoing an unprecedented expansion of consciousness skyward. The great voyages of discovery have nothing on what we are doing now, pushing away from Sol to find planets at ever smaller and more Earth-like scale as we begin, in the tiniest way, the process of mapping the planetary systems of a galaxy of 200 billion stars. Ultimately, naming exoplanets will by necessity become an ad hoc process, to be resorted to as needed, because the number of planets will dwarf our lexicons. But we’re still getting used to that idea, and the NameExoWorlds contest has been a delightful way to bring visibility to the question.
Planets that transit across their star as seen from Earth allow us to use transmission spectroscopy to study their atmospheres. The idea is straightforward: Even though we can’t see the planet at optical wavelengths, we can examine the starlight that travels through its outer atmosphere during the transit. Each atmosphere leaves its own signature, and the atmospheres of some of the ‘hot Jupiters’ thus far studied have raised questions. Why do some of these worlds have less water than our models of their atmospheres would predict? Is this an indication that such planets formed in protoplanetary disks that were depleted of water?
A new study brings us some answers by going to work on eight hot Jupiters (WASP-6b, WASP-12b, WASP-17b, WASP-19b, WASP-31b, WASP-39b, HAT-P-1b and HAT-P-12b) using the Hubble Space Telescope. The worlds chosen here offer a wide range of temperature, surface gravity, mass and radii. All eight were observed at optical wavelengths using Hubble’s Space Telescope Imaging Spectrograph (STIS) instrument, while two of them (WASP-31b and HAT-P-1b) were also observed in the near infrared with Hubble’s Wide Field Camera 3.
But lead author David Sing (University of Exeter) and team did not stop there. The Hubble survey was bolstered by infrared data from the Spitzer Space Telescope, and the work folded in data from both HST and Spitzer on two of the most widely studied hot Jupiters, HD 209458b and HD 189733b. Although we’re only dealing with ten worlds, this turns out to be the largest spectroscopic catalog of exoplanet atmospheres yet assembled.
What we learn is that these planets show a continuum from completely clear to cloudy atmospheres. It turns out that the difference between a planet’s radius as measured at optical and infrared wavelengths allows us to distinguish between the two types. A cloudy planet shows up larger in visible light than it does in the infrared — at the latter wavelengths, we are looking deeper into the atmosphere. The paper notes the significance of this finding:
We find that the difference between the planetary radius measured at optical and infrared wavelengths is an effective metric for distinguishing different atmosphere types. The difference correlates with the spectral strength of water, so that strong water absorption lines are seen in clear-atmosphere planets and the weakest features are associated with clouds and hazes. This result strongly suggests that primordial water depletion during formation is unlikely and that clouds and hazes are the cause of weaker spectral signatures.
In other words, the clouds are the culprit, and ‘dry’ hot Jupiters are not depleted in water.
Image: This image shows an artist’s impression of the 10 hot Jupiter exoplanets studied by astronomer David Sing and his colleagues using the Hubble and Spitzer space telescopes. From top left to lower left, these planets are WASP-12b, WASP-6b, WASP-31b, WASP-39b, HD 189733b, HAT-P-12b, WASP-17b, WASP-19b, HAT-P-1b and HD 209458b. Credit: NASA, ESA, D. Sing (University of Exeter).
A couple of things to note in the image. The colors are vivid but as this Hubblesite news release explains, they are purely for illustrative purposes. We have little data on the color of any of these worlds with the exception of HD 189733b, sometimes called the ‘blue planet.’ The cloud patterns shown here are also theoretical, based largely on what we see on Jupiter.
An interesting difference between hot Jupiters and brown dwarfs emerges in this paper. With the latter, which can have temperatures similar to hot Jupiters, we can go from warmer, cloudy L-class dwarfs to cooler T-dwarfs whose atmospheres are inferred to be clear — the paper calls this sequence ‘well defined.’ In contrast, hot Jupiters do not show a strong relationship between temperature and cloud formation, at least based on this sample, where both cloudy and not cloudy planets appear throughout the temperature range studied. The authors speculate on the difference:
We suggest that the difference between hot Jupiters and brown dwarfs is due to the vertical temperature structure of hot-Jupiter atmospheres. Hot Jupiters have very much steeper pressure-temperature profiles compared to isolated brown dwarfs, owing to the strong incident stellar flux heating the top of the planetary atmosphere… Since cloud condensation curves run nearly parallel to hot-Jupiter profiles, a relatively small temperature shift (about 100K) could easily move a cloud base by a factor of tens or hundreds in pressure, in or out of the visible atmosphere.
Moreover, some hot Jupiters are likely to have cloud materials that are cold-trapped deep within the atmosphere, and thus out of the range we can detect. The paper adds that hot Jupiters show a wider range of gravities and metallicities than brown dwarfs, factors that play a role in atmospheric circulation and condensation as well as temperature. As we learn more about how to distinguish between clear and cloudy atmospheres, we’ll strengthen our ability to focus on worlds with clear skies whose chemical abundances can be studied in greater detail.
The paper is Sing et al., “A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion,” published online in Nature 14 December 2015 (abstract).
I think you’ll find Jon Lomberg’s new essay in Slate as interesting as I do. We Need a World Cup for SETI uses a familiar figure at many sports events — the guy in the stands holding up a Biblical reference on a poster — to dig into a far more interesting issue. How does one go about maximizing visibility? The guy with the sign knows how to do it and if we think about his methods, we can better understand SETI.
For as we think about radio and optical SETI, we’re usually looking for signals that have been intentionally sent. Here we run into the particularly tricky business of trying to understand the thinking of an alien being, but there are certain principles that may apply to any civilization trying to send out a beacon-like message. The message needs to be short, cheap, easy to find, and in a place where it’s likely to be seen. So what kind of beacon is this going to be?
We’ve discussed ‘Benford beacons’ in these pages before (see, among others in the archive, Detecting a ‘Funeral Pyre’ Beacon). A beacon announcing little more than ‘We Are Here’ could be used to attract the attention of any receiving culture, after which we (the receivers) would apply our resources to looking harder at the source. But from the standpoint of efficiency and economy, a brief, bright beacon is best. James and Gregory Benford have addressed the matter in two key papers cited at the end of this essay. Let me quote a brief bit of one:
No technology available in the near-term will allow us to deliver powerful signals every minute of the day over a span of multiple epochs… But we might be able to make a beacon that works more efficiently, by targeting only those star systems where life seems most likely, and then pinging them each in turn, repeating the cycle every few months or so. Presumably, if a curious civilization caught one transmission, it would train its telescopes on that exact spot until the next part of the beacon’s message arrived. This more sensible approach—a sort of Energy Star specification for SETI—would save enough power to keep the beacon running for millions of years.
The Benfords bring useful synergies to bear on the matter. Jim is a plasma physicist — he knows all about beaming — while Greg is both physicist and science fiction author, a man who has speculated for decades on the workings of extraterrestrial civilizations. Jim’s son Dominic, also active in the beacon work, is a physicist at NASA GSFC. Beacons like the Benfords are suggesting are different from the kind of directed beacon SETI has long looked for, one that demands intense focus on stars in the hopes of finding continually broadcasting signals. A Benford beacon puts out a signal we would perceive as intermittent, a brief pulse.
Image: What kind of signal to look for amidst 200 billion stars? Credit: Center for Planetary Science.
The Long Stare
You can see that this puts the premium on what SETI people call ‘dwell times,’ i.e., the time we look at a particular target. In his Slate essay, Lomberg points out that there is a major timing issue here. Just how long would a beacon like this take before it repeated?
If you ever detect a possible beacon, you have to remain on target long enough for it to repeat—and who knows how long you have to wait? For an ancient and long-lived society, with perspectives far longer than our 10,000-year civilization, that might be a long time. Their notion of patience might be very different from ours. They’re aliens, after all. Of one thing I am sure: Any brief, potentially artificial signal should be closely watched for a repeat. A new approach to SETI could involve unbroken observation of some of the special directions on the sky.
Given that open question, we still need to maximize the possibilities, and I think Lomberg is right in emphasizing a strategy of constant listening. How to do this? Paul Shuch, the canny and deeply dedicated executive director of the SETI League, has long advocated getting away from what he calls ‘soda straw’ SETI, in which we perform a deep study of a target for only a short period of time before moving on. Instead, Shuch backs attempts like Project Argus, the SETI League’s microwave SETI effort aimed at providing continuous, full-sky coverage.
The notion here is to deploy and coordinate about 5000 small radio telescopes around the world, an attempt to provide continuous monitoring of the sky in real time. A station for Project Argus is not a huge dish but an amateur installation fully capable of detecting a Benford beacon’s transient signal if it should occur. In terms of cost, such a site has more in common with amateur radio than with Arecibo-style astronomy. It could be built for no more than a few thousand dollars and, depending on the builder, perhaps for less.
Image: H. Paul Shuch, N6TX, uses the SETI Horn of Plenty antenna for portable operations when away from his Project Argus station FN11lh. The horn, which fits in the back of a minivan, is ideal for classroom demonstrations, exhibiting +20 dBi of gain at 1.4 GHz. Credit: SETI League.
And yes, the famous “Wow Signal,” a one-off detection via Ohio State’s Big Ear radio telescope in 1977, does seem to fit the model of a Benford beacon, in being powerful, brief, and never seen again. How should we look for the next “Wow Signal”? Science fiction author David Brin backs the Project Argus idea in The Search for Extraterrestrial Intelligence (SETI) and Whether to Send “Messages” (METI):
Clearly SETI would benefit from a supplementary system that covers the Earth, searching continuously and broadly for pings that are sent by ETCs narrowly. That system would be ready to detect and pounce upon any new Wow Signals and automatically net-notify larger telescopes to zoom quickly on the source. Not a competitor with classic SETI, this second layer could serve as an ideal alert-generating system, filling a glaring deficit in the current approach.
An Expanded Project Argus
In Greek mythology, Argus was a giant whose epithet “all seeing” (panoptes) spawned depictions of him with multiple eyes. Argus always had a few eyes open, thus becoming the perfect watchman. Can we find a way to maximize the potential of Project Argus?
For while the endeavor is loaded with promise and benefits from the skills and energies of people like Shuch, it has been unable to reach anything like the needed 5000 stations for continuous coverage. This is why a comment by the above-quoted David Brin on a SETI-oriented mailing list recently caught my eye. Brin notes that even as ‘soda straw’ SETI continues, we have the option of energizing the Project Argus idea. We already see wealthy people like Paul Allen and Yuri Milner becoming deeply involved in SETI. What if we could find a similar figure to create a Project Argus kit?
The idea here would be to take the building of a home receiving station for SETI out of the realm of sophisticated electronic technology and into into a turn-key kit that could be purchased for several hundred dollars and simply attached to a basic backyard dish. Like SETI@Home, a Web-based collection system could be used to track the ongoing datastream. A global system for transient detections like this is the kind of network that could find a Benford beacon.
Image: My friend Mike Gingell, KN4BS, shows off his two dishes, 12 and 10 feet in diameter, used for radio astronomy, satellite TV, and of course SETI. I’m sorry to say that Mike passed away last year, but he remained fascinated by SETI prospects until the end. Credit: Mike Gingell / SETI League.
We need to keep an eye on the possibilities that can emerge from private funding and the work of skilled amateur radio astronomers. But we also need to grow the numbers of those who have the means to participate. An updated version of Project Argus could supplement and extend the original, taking what began as a superb idea for engineers working with home equipment into the realm of everyday users with a yen to use digital tools to explore SETI’s possibilities. Make the kit cheap enough and straightforward to operate and the transient detection system we need emerges, an approach to SETI that widens our capabilities even as traditional SETI continues.
The papers are Benford, “Messaging with Cost Optimized Interstellar Beacons,” Astrobiology Vol. 10(5) (June, 2010), pp. 475-490 (preprint) and “Searching for Cost Optimized Interstellar Beacons,” Astrobiology Vol. 10(5) (June, 2010), pp. 491-498 (preprint). Paul Shuch’s Searching for Extraterrestrial Intelligence: SETI Past, Present, and Future (Springer, 2011) is an essential resource on SETI issues.
The Dawn spacecraft has reached its final orbital altitude, closing to within 385 kilometers of the asteroid (and yes, I really should start calling Ceres a ‘dwarf planet’ consistently — working on it). We have no observations from this distance yet, but that process begins within days, and should give us images with a resolution of 35 meters per pixel, along with a wealth of data from the craft’s scientific package.
Like New Horizons, Dawn makes history every time it returns observations of places we haven’t seen before, or surface features we’re seeing at higher resolution as the orbit lowers. Unlike New Horizons, Dawn is an orbiter, which makes me long for the idea of a Pluto orbiter, even though New Horizons has amply demonstrated how useful and powerful a flyby mission can be. An orbiter lets you complete the mapping process so essential to making a new world tangible, while there are parts of Pluto that our flyby couldn’t make out at highest resolution.
I found the temperatures Dawn recorded at Ceres a bit startling. The 180 K (-93 °C) on the low side seems about right, but I hadn’t expected equatorial temperatures to reach as high as 240 K (-33 °C), which is a temperature I can recall experiencing several times in Iowa during an unusually tough winter. This JPL news release notes that temperatures at and near Ceres’ equator are too high to support surface ice for long periods, as explained in new work published in Nature to which we now turn.
Maria Cristina De Sanctis (National Institute of Astrophysics, Rome) and colleagues tell us in one of the two new papers that Dawn has turned up evidence for clays that are rich in ammonia on Ceres, using data gathered by the spacecraft’s visible and infrared mapping spectrometer. I hearken back to those temperatures because Ceres is too warm to support surface ammonia ice, but ammoniated compounds (ammonia molecules combining with other minerals) could be stable. Finding these tells us that Ceres may not have formed in the main asteroid belt.
“The presence of ammonia-bearing species suggests that Ceres is composed of material accreted in an environment where ammonia and nitrogen were abundant,” says De Sanctis. “Consequently, we think that this material originated in the outer cold solar system.”
The other possibility: The dwarf planet formed about where it is today but drew in materials from the outer system that had formed near the orbit of Neptune. Another interesting finding: Although carbonaceous chondrites (meteorites rich in carbon) are thought to be similar to Ceres in composition, the data do not match at all wavelengths. Ceres shows absorption bands in its reflected light that match up with the ammoniated minerals described above. Moreover, Ceres shows water content as high as 30 percent, while carbonaceous chondrites normally weigh in at 15 to 20 percent bulk water content, possibly indicating accretion from volatile-rich material.
Image: Dwarf planet Ceres is shown in these false-color renderings, which highlight differences in surface materials. Images from NASA’s Dawn spacecraft were used to create a movie of Ceres rotating, followed by a flyover view of Occator Crater, home of Ceres’ brightest area. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.
Resolving the Bright Spots
While we began seeing a small number of unusual bright spots on Ceres as Dawn approached, it turns out that close study reveals more than 130 areas of unusual brightness, most of them associated with impact craters. The second paper in Nature is the work of Andreas Nathues (Max Planck Institute for Solar System Research, Göttingen) and colleagues. Here we learn that the bright material is consistent with hexahydrite, which is a type of magnesium sulfate. What the paper argues is that the bright spots are areas rich in salt that were left behind when water ice sublimated long ago, having been brought to the surface by an impact.
Image: This representation of Ceres’ Occator Crater in false colors shows differences in the surface composition. Red corresponds to a wavelength range around 0.97 micrometers (near infrared), green to a wavelength range around 0.75 micrometers (red, visible light) and blue to a wavelength range of around 0.44 micrometers (blue, visible light). Occator measures about 90 kilometers wide. Scientists use false color to examine differences in surface materials. The color blue on Ceres is generally associated with bright material, found in more than 130 locations, and seems to be consistent with salts, such as sulfates. It is likely that silicate materials are also present. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.
That, of course, backs up the idea that we’re dealing with a subsurface layer of salty water ice, an idea supported by the global nature of the bright spots. The Occator crater contains the brightest material found on Ceres, and it also appears to be one of the youngest surface features, with an age of about 78 million years. Remarkably, what appears to be a diffuse haze can be seen filling the floor of the crater at certain times of day.
The haze appears to be absent at dawn and dusk, while it can be seen at local noon, making Ceres, in the view of the study authors, something like a comet, where water vapor when warmed can lift particles of dust and residual ice off the surface. The Herschel space observatory reported water vapor at Ceres in 2014, a finding consistent with these observations. Remember, however, that we’re still waiting on the unambiguous detection of water ice on Ceres, so the story of the Occator haze will require more data and further analysis.
The papers are Nathues et al., “Sublimation in bright spots on (1) Ceres,” Nature 528 (10 December 2015), 237-240 (abstract) and De Sanctis et al., “Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres,” Nature 528 (10 December 2015), 241-244 (abstract).
Two papers have appeared on the arXiv server suggesting hitherto undiscovered objects in the outer Solar System (thanks to Centauri Dreams reader Stevo Darkly for the pointer). Both papers use data harvested by the Atacama Large millimeter/submillimeter array (ALMA), an interferometer of radio telescopes in Chile’s northern high desert. Here some 66 12-meter and 7-meter radio telescopes work the sky at millimeter and submillimeter wavelengths, with targets that have ranged from galactic dust in the early universe to magnetic fields near a supermassive black hole.
ALMA’s uses closer to home are made clear in the new papers, which demonstrate that this array can be a major tool in helping us probe the outer system well into the Oort Cloud. In the first paper, the researchers draw on three periods of observation with ALMA to detect point-like emissions at different positions in two of the periods. The two emissions are thought to be the same source, considering what the authors call “the negligible probability of having identified two independent highly variable background sources.” Assuming a single source, the team dubs the object Gna, noting that it was not visible in the third observing period 42 days later.
So what exactly do we have here? If gravitationally bound, the object would be at a distance between 12 and 25 AU, most likely a Centaur with a semi-major axis between Jupiter and Neptune, though a large one, in the range of 220-800 kilometers depending on distance and albedo. The authors note that the location of the field of view (close to the galactic plane toward the star W Aquilae) may explain why the object was not seen sooner despite its size.
But there is another possibility, that Gna is unbound. “In that case,” write the authors, “the most exciting possibility is that we have observed a planetary body or brown dwarf in the outer reaches of the Oort cloud.” Which leads to recent WISE studies that found no evidence of a Saturn-class object out as far as 28000 AU, or of a Jupiter out to 82000 AU, while a Jupiter-sized brown dwarf could be excluded out to 26000 AU at the locations previously suggested by John Matese and Daniel Whitmire. The latter have argued that a large planetary body in the Oort would explain the seemingly clustered orbits of many comets.
Could Gna be that object? The paper notes the WISE data in reference to the new findings, stating that a submillimeter flux of 3 mJy at a distance of 5000-50000 AU would point to an object that has retained residual heat or generates emission of its own. It would not, in other words, absorb enough sunlight to display the measured flux. As the paper notes:
This would imply a large planet or brown dwarf and could be reconciled with the Jupiter sized brown dwarf or Saturn/Neptune size planetary limits provided by WISE (Luhman 2014), if Gna is located around or beyond ? 20000 AU.
But the high proper motion seen here seems to rule out anything beyond about 4000 AU. While unable to exclude a large gravitationally unbound body within 4000 AU, the authors think it most likely that Gna is a bound Centaur in retrograde orbit, currently between 12 and 25 AU out and with a size of 220-880 kilometers.
But we’re not through with ALMA just yet. Another set of ALMA observations ten months apart (2014-2015) by the same research team has revealed a point source that appears to share the proper motion of Alpha Centauri A and B. Is there an Alpha Centauri D? Apparently not, for at the distance of the Centauri stars, the measurements would correspond to an M2-class dwarf, a star bright enough to be clearly visible. If there were an Alpha Centauri D, we would have seen it by now.
Instead, the authors make the case that the object is a Trans Neptunian Object (TNO). From the paper:
For reasons of sensitivity (or rather, lack thereof), TNOs on highly eccentric orbits have traditionally been firstly detected when close to their perihelia. Further away, there would have remained unseen… However, a sizable population of such bodies is expected to exist at large distances from the Sun. It is clear, therefore, that ALMA with its high submm sensitivity provides presently the only existing means to detect TNOs far from their perihelia, where temperatures are merely some tens of Kelvin. There must be a vast reservoir of objects between, say, roughly 100 and 1000 AU, of which we hitherto have seen only a tiny fraction.
Image: An illustration of the relative sizes, albedos and colors of some of the largest known TNOs. Credit: Wikimedia Commons. Licensed under CC BY-SA 3.0.
Just what kind of an object would this be? The paper continues:
We argue that the object is most likely part of the solar system, in prograde motion, albeit at a distance too far to be detectable at other wavelengths, viz. an ETNO [Extreme Trans Neptunian Object] (? 100 AU), a hypothesized Super-Earth (? 300 AU) or a super-cool brown dwarf (? 20 000 AU).
From an ETNO to a brown dwarf is quite a range, highlighting how much we still don’t know. So we can’t say we’ve found the large perturber discussed by Matese and Whitmire, but we do have interesting work on new objects, one of which could conceivably fit the description. It will take a lot of work to learn more about the new ALMA objects, but we’re finding out how the array can fine-tune our capabilities in probing out into the Oort Cloud. If such perturbers exist, we’re going to turn them up sooner or later as we continue to map the system’s farthest depths.
The paper on Gna is Vlemmings et al., “The serendipitous discovery of a possible new solar system object with ALMA,” submitted to Astronomy & Astrophysics (preprint). The paper on the point source near Alpha Centauri in the sky is Liseau et al., “A new submm source within a few arcseconds of ? Centauri: ALMA discovers the most distant object of the solar system,” submitted to Astronomy & Astrophysics (preprint). Eric Berger offers a highly skeptical take on this work here.
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
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