A Bit More Detail

Assorted Personal Notations, Essays, and Other Jottings

Posts Tagged ‘gliese 581

[BLOG] Some Friday links

  • Antipope Charlie Stross argues that the publishing industry, beset by consolidations, is trying unsuccessfully to move from an artisan model of literary production to something new. Would that something new could be found and made to work.
  • The Dragon’s Gaze links to a paper that tries to model the atmosphere and climate of the exoplanet Gliese 581g, potentially Earth-like but tidally locked.
  • The Dragon’s Tales reports on the ongoing events in Ukraine.
  • Geocurrents’ Martin Lewis maps the political divides of the south India state of Kerala onto caste and religious boundaries.
  • Language Log links to a paper analyzing big data in linguistics.
  • Languages of the World’s Asya Perelstvaig notes that California is exceptionally diverse language-wise.
  • Lawyers, Guns and Money’s Erik Loomis notes that the ability of journalist Nicholas Kristof to be fooled by an alleged anti-prostitution activist in Cambodia prone to making things up fits in a long Progressive history of being easily fooled about things Progressives care about..
  • Torontoist introduces the new Fort York branch of the Toronto library system.
  • Towleroad’s David Mixner interviews GLBT activists in Italy about their challenges.
  • The Volokh Conspiracy’s Eugene Volokh notes, in discussing the underemployment of many minorities at Google relative to their shares of the American population, the ways in which Asians are assimilated to the white majority, at least rhetorically.
  • Window on Eurasia links to a Russian journalist’s analysis of the consequences of Russia’s annexation of Crimea. It’s bad for Russia internationally, he concludes, but a good way for the state to consolidate its control domestically.

[BLOG] Some Thursday links

  • The Big Picture shares photos of young Russian military cadets training.
  • blogTO has a transcript of one of Ford’s most recent reported rants.
  • Centauri Dreams and D-Brief both note that the giant exoplanet Beta Pictoris b apparently has an eight-hour day.
  • Crooked Timber’s John Quiggin, focusing on Australia, discusses right-wing tribalism.
  • The Dragon’s Gaze links to a paper examining various possibilities for orbits of planets in the Gliese 581 system.
  • The Dragon’s Tales links to a proposal (with pictures) for a Io volcano observer space probe.
  • Eastern Approaches notes the continuing deterioration of eastern Ukraine.
  • Geocurrents’ Martin Lewis comments on the geographical illiteracy of the United States and of a very bad Pakistani school atlas.
  • Joe. My. God. notes that, today, Brunei is implementing full sharia law.
  • Lawyers, Guns and Money notes an Australian proposal to outlaw civil society-led boycotts.
  • Marginal Revolution links to a poll suggesting Americans don’t care about income inequality.
  • The Planetary Society Weblog’s Emily Lakdawalla notes that we’re getting closer to figuring out which Kuiper belt dwarf planet is larger, Pluto or Eris.
  • The Tin Man explains why he prefers Twitter to Facebook. (The former feels more free-form, less of a gated community.)
  • Window on Eurasia notes that responsibility for recent increases in birth rates in Russia can’t be assigned entirely, or even mostly, to the Russian government.

[BLOG] Some Saturday links

  • Centauri Dreams has a guest post from Jason Wright talking about using infrared telescopes to pick up waste heat from extraterrestrial civilizations.
  • Cody Delistraty opposes a boycott of the Sochi Olympics, notwithstanding Russia’s human rights issues, on the grounds that the Olympics have essentially no relationship to whatever country is hosting them at the present.
  • The Dragon’s Tales links to reports on plans for a future united Africa.
  • The Dragon’s Gaze reports that apparently close-orbiting binaries–stars within 20 AU of each other, like Alpha Centauri–are bad for planetary formation, and comments on the discovery of brown dwarfs near multiple stars including fabled Gliese 581.
  • Eastern Approaches reports on the disarray at Sochi.
  • Amitai Etzioni argues that the United States and China should be clear on their red lines regarding Taiwan.
  • Far Outliers reports on the United States’ constitution of an intelligence service from nothing in the First World War.
  • Language Hat notes a proposal to give Russian official status in Austria-Hungary to defuse pan-Slavism, and observes how language clues within the Bible give hints as to authorship.
  • Language Log notes the creative use of different scripts and languages in Taiwanese product advertising.
  • Lawyers, Guns and Money notes the role of Sochi in the final suppression and expulsion of the Circassians by the Russian Empire.
  • Marginal Revolution notes the huge economic problems of Puerto Rico: shrinking economy, emigrating workforce, growing debt … The disinterest of young Germans in apprenticeships is also noted.
  • The Planetary Society Blog’s Emily Lakdawalla reports that the world can’t communicate with the returning ICE/ISEE3 probe because it no longer has the technology to do so.
  • The Power and the Money’s Noel Maurer argues that Argentine currency controls which make imports increasingly unaffordable are soon going to have to fail.
  • Discover‘s Seriously Science notes a study claiming that fish can use tools.
  • Steve Munro quite dislikes false savings on TTC expenditures claimed by, most recently, the Toronto Star.
  • Understanding Society’s Daniel Little takes a look at social science takes on the Chinese revolution, examining first Lucien Bianco’s early study then Theda Skocpol’s comparative study contrasting French and Russian revolutions.
  • Window on Eurasia notes that the rise of Islam is the North Caucasus is partly a consequence of Arab-funded global networks, comments on the role of Crimean Tatars in keeping Crimea for Ukraine, notes that some Russians would like to start revising borders across the post-Soviet region, and observes that many Russians are surprisingly OK with Finland’s Second World War leader Mannerheim.
  • Zero Geography notes a paper commenting on uneven geographies of user-generated content.

[LINK] “On Debris Disks and Super-Earths”

Gliese 581, a dim red dwarf star some 22 light years away noteworthy for hosting two planets which could conceivably support Earth-like environments, and 61 Virginis, a Sun-like yellow dwarf star 28 light years away supporting three close-orbiting superterrestrial planets, are noteworthy for hosting only relatively low-mass planets but relatively dense Kuiper belts, disks of icy debris orbiting distantly from the star. Synthesizing two papers, Centauri Dreams’ Paul Gilster wonders if there might be an actual correlation at work.

[W]e have interesting new work from the European Space Agency’s Herschel space observatory announcing that Gl 581, along with the G-class star 61 Vir, another nearby planetary system, shows the the signature of cold dust at -200 degrees Celsius.

It’s an abundant signature, too, meaning that both these systems must have ten times the number of comets found in our own Solar System’s Kuiper Belt. The two papers on this work grow out of a program called, fittingly, DEBRIS (Disc Emission via a Bias-free Reconnaissance in the Infrared/Sub-mm). What the researchers working these data are suggesting is that the lack of a large gas giant in the two systems may relate to the dense debris cloud. Instead of an era of heavy bombardment triggered by gas giants disrupting the Kuiper Belt, as occurred in our system, these stars may have experienced a much gentler inflow of volatiles.

[. . .]

An older star like Gl 581 would have had two billion years or so for a substantial amount of water to be delivered to the inner system and, of course, to any potentially habitable worlds that reside there. What we now believe about the planets circling Gl 581 is that they have masses between 2 and 15 times that of the Earth, all located within 0.22 AU of the star, while the debris disk extends from 25 AU to 60 AU. A Neptune-class world further out, however, is a possibility. The researchers believe the large amount of dust Herschel has detected must be the result of cometary collisions, which could be triggered by a planet — perhaps about as large as the close-in planets — orbiting near the debris disk.

So we are looking at larger debris disks around systems where there is no Jupiter-class planet, and far less dense disks around stars where large gas giants are found.

Written by Randy McDonald

November 29, 2012 at 4:59 am

[LINK] “Gl 581: The Case for Habitable Planets”

News late last month of the reconfirmation of the existence of Gliese 581 g, a hypothesized planet orbiting a red dwarf star 21 light years away that, by virtue of its size and the amount of radiation received from its sun, is the most Earth-like world discovered yet, was examined in a recent Centauri Dreams post.

Not long ago, while making a presentation about possible destinations for an interstellar probe, I called Gl 581d the most likely candidate for habitability yet discovered among nearby stars. I knew the planet was problematic, perhaps too far on the outer edge of the habitable zone to be a realistic candidate, although this seems to depend on a variety of factors including atmospheric modeling. But what I had really been pondering in deciding whether or not to include Gl 581d in the talk was whether its purported sister world, Gl 581g, should be brought into play.

Steven Vogt (UC-Santa Cruz) and colleagues were getting ready to distribute their new paper making a further case for a super-Earth in the habitable zone, one that seemed to be ideally placed for liquid water to exist on the surface. Bring that into the discussion?

I decided against it, because the controversy over this world continues and Centauri Dreams seems a better venue than a short public talk to get into the details. Let’s begin here, then, with Michel Mayor and the Geneva team, who had already identified four planets in the system, including Gl 581c, itself a target of speculation about whether or not it might be in the habitable zone. But Gl 581c looks to be too hot to support life, leading to the renewed interest in Gl 581d. This work was accomplished using data from the HARPS spectrograph on ESO’s 3.6m La Silla instrument.

What Vogt and team did in 2010 was to combine the earlier HARPS data with 122 additional measurements made using the HIRES spectrometer at the Keck Observatory on Mauna Kea. It was from this combined dataset that Vogt drew evidence of two new planets: Gl 581f (with an orbital period of 433 days) and Gl 581g, with a period of 36.5 days. It wasn’t long after this that Francesco Pepe (Observatoire de Genève) added another 60 HARPS measurements to the earlier ones and announced his team could not confirm the presence of either of the two worlds Vogt had found. In his new paper, Vogt’s team questions whether Gl 581f or Gl 581g would have been detectable using the 179-point HARPS data set on its own.

I’m moving through the details here quickly — the paper is available on the arXiv site and I encourage you to look at it. But new work by Thierry Forveille (Institut de Planetologie et d’Astrophysique de Grenoble) added another full observing season of HARPS data and still found no trace of Gl 581f or Gl 581g. It’s this set of expanded HARPS radial velocity data that Vogt’s new paper goes to work on, and it reaches a significantly different conclusion (F11 in the excerpt below refers to Forveille’s paper):

… we have shown in the present work that the F11 Keplerian solution is dramatically unstable over a wide range of starting conditions, and is thus untenable. F11’s conclusion of there being only four planets in the system was based on this unphysical model and can thus be discounted. Furthermore, the data points that were apparently omitted from the F11 analysis were dropped solely based on deviation from their 4-planet model, thus unfairly and specifically suppressing evidence for any additional planets in the system.

Things are, as you can see, heating up. What Vogt is talking about is that his simulations of the Forveille Keplerian models — with the Gl 581 planets in eccentric rather than circular orbits — showed that these orbits were unstable. This is important because Forveille used the Keplerian model in assessing the likelihood of the existence of Gl 581f and Gl 581g. In fact, among 4000 eccentric orbit simulations, not one survived beyond 200,000 years, with only 24 surviving for at least 20,000 years. All 4000 simulations ended with a collision between the two inner planets. By contrast, all 4000 simulations based on circular orbits turn out to be stable for at least 100,000 years.

Using stable, circular orbits for its modeling, Vogt’s team sees a fifth planet (V10 below refers to Vogt’s 2010 paper):

Contrary to F11’s conclusions, we find that the full 240-point HARPS data set, when properly modeled with self-consistent stable orbits, by and of itself actually offers confirmative support for a fifth periodic signal in this system near 32-33 days, and is consistent with the possibility of having been detected as GJ 581g at its 36-day yearly alias period by V10. The residuals periodograms both of our interacting and non-interacting fits and of the F11 four-planet circular fit reveal distinct peaks near 32 days and 190 days. Both of these residuals peaks are largely simultaneously accounted for by adding a fifth planet at 32.1 days to the system.

According to Vogt, we wind up with a planet with minimum mass of 2.2 times that of Earth orbiting at 0.13 AU, “solidly in the star’s classical liquid water Habitable Zone.” That, at least, is what the data analysis produces if we assume circular orbits of the four known planets and work out the reasons for the further perturbations that Vogt’s team sees as evidence for a fifth planet. Vogt believes a 5-planet model with all circular orbits trumps a 4-planet model with eccentric planetary orbits, but adds that it may take time and further data to give a definitive answer.


Written by Randy McDonald

August 3, 2012 at 3:00 am

[LINK] Two Centauri Dreams notes on the search for extraterrestrial intelligence

The two latest posts at Centauri Dreams, both by Paul Gilster, examines the search for extraterrestrial intelligence and the impact of new techniques and technologies. What’s possible?

The first is “Is our civilization detectable?”. The new Square Kilometre Array, a collection of hundreds of small radio telescopes scattered across the Southern Hemisphere–South Africa, Australia, New Zealand–will be very sensitive. Could it pick up signals from a civilization like ours?

People sometimes assume that stray signals would be easily snared at interstellar distances, but we’re learning that it would take a mammoth installation to make such a catch. The film Contact, made from Sagan’s novel of the same name, uses the wonderful device of a broadcast returned to us, a transmission from the 1936 Olympics in Berlin. Receiving such a signal parroted back to us would surely flag the detection of an extraterrestrial civilization and cause researchers to begin the necessary work to look for embedded information inside it.

The people behind the Square Kilometer Array talk about the ability of this instrument, once its vast telescopic resources are in place and connected to powerful computing facilities, to pick up something as weak as the extraterrestrial equivalent of an airport radar around another star. It’s a fantastic prospect, implying our ability to add a new layer to our existing SETI investigations. Is it possible that instead of scanning the skies for beacons, we might simply begin to pick up the extraneous signals of a civilization going about its daily life? The goal is energizing, but hearing claims about extraterrestrial detections always makes me uneasy.

Back in late 2010, James Benford discussed leakage radiation at a meeting of the Royal Society in Britain, asking whether the kind of installations we currently have on Earth could detect signals this weak if sent from a nearby star. It turns out a typical radio telescope like the Parkes instrument in Australia, if located near Alpha Centauri, would not be able to detect our TV transmissions at all. Benford pointed out that signal information is transmitted in bands on each side of the central frequency and that broadcast antennae aim their transmitted power mostly toward the surface. Signals that get into space are not coherent and are unlikely to be noted.

The second, “All Quiet Around Gliese 581”, reports on the results of a proof-of-concept scan of this nearby red dwarf star and its planets.

We’ve been considering the possibilities growing out of the Square Kilometer Array for SETI purposes, prompting a number of readers, Adam Crowl being the first, to send along a new paper on using Very Long Baseline Interferometry in a targeted SETI search. Hayden Rampadarath and colleagues at the International Centre for Radio Astronomy Research (Perth, Australia) intend the paper to be a foundational document for the use of VLBI in future SETI projects including those at the SKA. The results show great promise for the technique.

With VLBI, combining signals from multiple telescopes allows us to emulate a single instrument the size of the maximum separation between the telescopes, which could be hundreds to thousands of kilometers. Interestingly, there has been little application of VLBI techniques in SETI, although the SETI-Italia project using the VLBI Medicina telescope is active and the SETI Institute has been studying interferometric techniques at frequencies between 1200 and 1750 MHz. What Rampadarath and colleagues have done is to target the widely studied red dwarf Gliese 581, using observations at 1230-1544 MHz made with the Australian Long Baseline Array, which includes three radio telescopes spaced widely in New South Wales.

It’s a good choice of target because Gliese 581 is a multi-planet system with at least one planet that looks to be on the edge of the habitable zone. With Kepler’s investigations of thousands of planetary candidates ongoing, we’re beginning to pick out high-value targets like this, defined as planets where liquid water could exist on the surface and life might arise. Gl 581 is not one of the Kepler worlds, but it does present us in the form of Gl581d with a super-Earth with an orbital period of 83 days that according to at least one recent study may offer habitable conditions. The existence of another possible habitable zone planet, Gl581g, now appears unlikely.

The Perth team observed Gl581 for eight hours using the stations of the Long Baseline Array. The result: 200 narrow-band and 22 broadband candidate signals were examined, most or all of which are thought to have been caused by Australian space to Earth geostationary satellites. No evidence for signals from the region of Gl581 emerges. The result is hardly a surprise, but the good news is that this pilot study demonstrates that Very Long Baseline Interferometry makes what the authors call ‘an ideal technique for targeted SETI.’

Written by Randy McDonald

June 2, 2012 at 3:01 am