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  • At Wired, Matt Simon explores the remarkably wrong-headed theory of the 19th century US that "rain follows the plough."

  • These National Geographic photos of the unexplored lakes in Angola that feed the Okavango are remarkable.

  • Rachel Brown examines billy burr, the Colorado hermit whose collection of decades of climate data is invaluable.

  • Universe Today notes a new study confirming the existence of Tau Ceti e and f, potentially habitable rocky exoplanets just 12 light years away.

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  • Centauri Dreams considers the prospects for habitable worlds at Tau Ceti considering the composition of planets and the star's evolution over time, considers the need for consistent observation in SETI programs, looks at possibly detectably volcanic 55 Cancri e, wonders if Fermi bubbles are detectable, considers stellar drift in the context of expanding interstellar civilizations, and looks at exoplanets with circular orbits.

  • The Dragon's Gaze notes that Kapteyn's Star apparently does not support habitable-zone exoplanets, suggests that the superdense atmosphere of even a Venus analog could be eroded fairly quickly by a red dwarf, wonders if the G2 cloud at the galactic centre is a planetary embryo, wonders if water-rich asteroids have been detected impacting a white dwarf, and considers methane exoplanets.

  • The Dragon's Tales wonders if the geysers of Enceladus feeds the E ring of Saturn, looks at thermal anomalies on Enceladus, imagines ways to detect Europa's tides by space probe flybys, and compares the arroyos of Mars and Earth.

  • The Planetary Society Blog notes how radio astronomy can be contaminated by Earthly pollution, notes the society's recent lightsail launch, and looks at Ceres.

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The Dragon's Gaze linked to an interesting speculative paper about the planets of Tau Ceti. A nearby solar analog known to have multiple planets, this star has a different elemental composition from our own sun. What consequences would this have for planets made from Tau Ceti's primordial protoplanetary disk?

{\tau} Ceti (HD10700), a G8 dwarf with solar mass of 0.78, is a close (3.65 pc) sun-like star where 5 possibly terrestrial planet candidates (minimum masses of 2, 3.1, 3.5, 4.3, and 6.7 Earth masses) have recently been discovered. We report abundances of 23 elements using spectra from the MIKE spectrograph on Magellan. Using stellar models with the abundances determined here, we calculate the position of the classical habitable zone with time. At the current best fit age, 7.63 Gy, up to two planets (e and f) may be in the habitable zone, depending on atmospheric properties. The Mg/Si ratio of the star is found to be 1.78, which is much greater than for Earth (about 1.2). With a system that has such an excess of Mg to Si ratio it is possible that the mineralogical make-up of planets around {\tau} Ceti could be significantly different from that of Earth, with possible oversaturation of MgO, resulting in an increase in the content of olivine and ferropericlase compared with Earth. The increase in MgO would have a drastic impact on the rheology of the mantles of the planets around {\tau} Ceti.
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  • The Burgh Diaspora points to articles discussing Germany's ongoing demographic issues.

  • Crooked Timber's John Quiggin meditates on the rapid urbanization of China.

  • Daniel Drezner expects somewhat more out of the recent Iranian election of a moderate president than of North Korea's latest diplomatic moves.

  • The Dragon's Tales' Will Baird shares the news that none of the planets discovered orbiting Tau Ceti are likely to be habitable, e being Venus-like and f closer to Mars. There's still space for a low-mass planet orbiting between e and f, though, right?

  • Geocurrents criticizes the recently publicized linguistics thesis claiming that languages which have ejective consonants are likely to have evolved in mountainous areas, where these sharp sounds are suited to area with low air pressure.

  • Marginal Revolution's Tyler Cowen agrees now with Dani Rodrik's long-staning critique of Turkish politics this past decade as undemocratic.

  • The New APPS Blog notes the blemishing of Erdogan's record in Turkey and mass protests in Brazil's Sao Paulo over public transit.

  • The Power and the Money's Noel Maurer wonders if the Colombian-American alliance might worsen Colombia's insurgencies.

  • Peter Rukavina shares the GIS numbers of Prince Edward Island, the geographical coordinates of a box encompassing the island province.

  • Torontoist notes that Toronto saw the first pay-TV show, a 1961 Bob Newhart special.

  • The Volokh Conspiracy notes the imprisonment in Egypt of a Muslim cleric convicted of offending Christians.

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There have been many mentions of past appearances of worlds of Tau Ceti in science fiction, but so far as I know, few have have brought up Arizona-based science fiction writer Michael McCollum's 1992 The Sails of Tau Ceti.

Michael McCollum, The Sails of Tau Ceti

I read the book again wanting to really like it. McCollum was a very active hard SF writer in the 1980s and 1990s, at least from my young perspective as I bought interesting-looking new titles in used book stores on Prince Edward Island. His bibliography in his German Wikipedia article is extensive. (Curiously, the article has no English-language counterpart.)

The ideas behind The Sails of Tau Ceti is certainly audacious. Centuries after the mysterious nova destroyed Tau Ceti that 25th of August, 2001, the inhabitants of our industrialized solar system detect a light sail craft apparently pushed into interstellar flight by the light of the nova. Starhopper, the first prototype starship, is repurposed to intercept the craft before it enters our solar system. Carrying, among others, the software engineer Tory Bronson, they rendezvous with the craft only to discover that it is a crewed vehicle, an O'Neill-type habitat housing tens of thousands of hexapodal Phelans fleeing the ruin of their home system and seeking succor in ours. Bronson is convinced to represent the refugees and their case to humanity.

What's the secret? )

A minor kibbitz. The Phelans are noted as sending ships not only to our solar system but to Epsilon Eridani, Epsilon Indi, and Alpha Centauri, in other words the three closest Sun-like stars to our own planetary system other than lost Tau Ceti. Looking at the Internet Stellar Database, the Phelans had other options: Omicron 2 Eridani, or 40 Eridani, is closer to Tau Ceti than Epsilon Indi (10.2 light years versus 11.5), while 82 Eridani is just two thousand astronomical units further from Tau Ceti than Sol (both roughly 11.9 light years from the Phelans' home system). Especially if the pre-nova Phelans were aware of humanity through our radio pollution and uncertain about our attitudes towards alien refugees, in-universe wouldn't the Phelans have explored other, potentially safer, options. (I'm guessing that the data on the location of Sun-like stars in the neighbourhood of Tau Ceti that's a simple Google search in 2013 was more problematic 21 years ago.)

Good ideas, but nothing compelling. )
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A large part of me wants to making the posting of maps of planetary systems a daily feature. I'll satisfy myself by reposting the below map, drawn up by the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo of the orbits of the five worlds discovered orbiting nearby Tau Ceti (Sol Station, Wikipedia), after Wednesday's remarkable announcement. It turns out that a dense cloud of debris in-system might mean a planet would get heavily bombarded with cosmic detritus, but certainly doesn't mean planets won't form in the first place.

Chart of the Tau Ceti system

This came with this press release authored by Abel Mendez Torres, who made the point that Tau Ceti e (orbiting just inside the inner edge of the habitable zone, makred in blue) and Tau Ceti f (the outermost planet, orbiting just inside the outer edge of the habitable zone) are only marginally habitable.

Tau Ceti e doesn't look very promising.

The planet Tau Ceti e orbits close to the inner edge of the habitable zone. It receives about 60% more light than Earth from the Sun making it a hot planet probably only habitable to simple thermophilic (heat-loving) life. Its mean global surface temperature should be near 70°C assuming a similar terrestrial atmosphere. However, it is likely that superterran planets have much denser and heat trapping atmospheres and Tau Ceti e might be instead dominated by a strong greenhouse effect making it more likely a super-Venus than a super-Earth. Without any knowledge of its atmosphere we are not able to tell if it is a mildly hot planet tolerable for simply life forms or a very hot non habitable Venus-like world. Tau Ceti e has an Earth Similarity Index of 0.77 assuming a more terrestrial-like atmosphere.

Tau Ceti f, now, might well be more promising.

The planet Tau Ceti f orbits close to the outer edge of the habitable zone. It only receives about 27% the light of Earth from the Sun making it a cold planet probably only habitable to simple psychrophilic (cold-loving) life. Its mean global surface temperature should be near -40°C assuming a similar terrestrial atmosphere. However, it is likely that as Tau Ceti e, it is also dominated by a strong greenhouse effect making it even acceptable for complex life, which requires temperatures from 0°C to 50°C. Without any knowledge of its atmosphere we are not able to tell if it is a frozen Mars-like planet tolerable for simply life forms or even an Earth-like world. Tau Ceti [f] has an Earth Similarity Index of 0.71 assuming a more terrestrial-like atmosphere.

It's worth noting that there is a very large gap between e at ~0.55 AU and f at ~1.35 AU. Might there be other planets, smaller planets, squarely in Tau Ceti's habitable zone? (0.7 AU seems to be the right distance.)
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News that the yellow dwarf star Tau Ceti (Sol Station, Wikipedia) apparently possesses a family of five planets was widely syndicated, since this solitary yellow dwarf star--much like our own sun--has been an object of considerable interest today. Tau Ceti has been the subject of considerable speculation as to the possible existence of planets in orbit, and of life on these planets, for at least a half-century.

I like the overview of the discovery provided at Scientific American.

Astronomers have detected five possible alien planets circling the star Tau Ceti, which is less than 12 light-years from Earth — a mere stone's throw in the cosmic scheme of things. One of the newfound worlds appears to orbit in Tau Ceti's habitable zone, a range of distances from a star where liquid water can exist on a planet's surface.

With a minimum mass just 4.3 times that of Earth, this potential planet would be the smallest yet found in the habitable zone of a sun-like star if it's confirmed, researchers said.

"This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets," study co-author Steve Vogt, of the University of California, Santa Cruz, said in a statement. "They are everywhere, even right next door."

The five planet candidates are all relatively small, with minimum masses ranging from 2 to 6.6 times that of Earth. The possibly habitable world, which completes one lap around Tau Ceti every 168 days, is unlikely to be a rocky planet like Earth, researchers said.

"It is impossible to tell the composition, but I do not consider this particular planet to be very likely to have a rocky surface," lead author Mikko Tuomi, of the University of Hertfordshire in England, told SPACE.com via email. "It might be a 'water world,' but at the moment it's anybody's guess."

Universe Today's Nancy Atkinson goes into more detail about Tau Ceti's background and the methodology of the study.

Tau Ceti has long been a target of both detailed astronomical study and hopeful science fiction, since it is among one of the 20 closest stars to Earth. It is also easily visible to the naked eye and can be seen from both the Northern and Southern Hemisphere. During the 1960′s, Project Ozma, led by SETI’s Frank Drake, probed Tau Ceti for signs of life by studying interstellar radio waves with the Green Bank radio telescope. Science fiction authors like Robert Heinlein, Isaac Asimov and Frank Herbert used Tau Ceti as destinations and focal points in their books.

Scientists know this star has a dusty debris disk at least 10 times more massive than our solar system’s Kuiper Belt, and it has been observed long enough that no planets larger than Jupiter have been found.

An international team of astronomers from the United Kingdom, Chile, United States, and Australia, combined more than six-thousand observations from the UCLES spectrograph on the Anglo-Australian Telescope, the HIRES spectrograph on the Keck Telescope, and reanalysis of spectra taken with the HARPS spectrograph available through the European Southern Observatory public archive.

Using new techniques, the team found a method to detect signals half the size of previous observations, greatly improving the sensitivity of searches for small planets.

“We pioneered new data modeling techniques by adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches,” said lead author Mikko Tuomi of the University of Hertfordshire. “This significantly improved our noise modeling techniques and increased our ability to find low-mass planets.”

The paper is "Signals embedded in the radial velocity noise Periodic variations in the τ Ceti velocities", also available here.

The question of whether any of these world are habitable is open to question. At one extreme, Enzo, in the comments at Centauri Dreams' post, suggests that Tau Ceti e--the planet most likely to support Earth-like conditions--orbits Tau Ceti too closely to avoid overheating. At the other, a press release from the University of Puerto Rico at Arecibo's Planetary Habitability Laboratory suggests that Tau Ceti f, the outermost planet discovered, might be barely within the habitable zone.
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My favourite roleplaying game setting is 2300AD. A hard science-fiction setting with a very active fan base that I still participate in, it starts off as an alternate history where France stayed neutral in a Third World War fought by the rest of NATO with China against the Warsaw Pact, and accordingly ended up in a position to dominate the post-war world. The Earth greened again, civilization was restored, and in the 22nd century the French developed the stutterwarp drive which opened up the stars to humanity, notiwthstanding its peculiar limitations.

A faster-than-light device called the Stutterwarp Drive allows mankind to achieve practical travel between planetary systems. Ships can usually reach a speed of 3.5 light years per day; the real limitation of the Stutterwarp drive is that it can only propel a ship up to a maximum of 7.7 light years before it needs to enter a gravity well and discharge lethal radiation that would otherwise kill the crew. Because ships need to reach a world within this distance, the effect of this limitation is the creation of lanes along which travel and commerce are conducted and along which wars are fought, the Arms mentioned above.

Astrography--at least astrography as known in the late 1980s when 2300AD came out--makes the Arms look like this.

2300AD Starmap: Core and Arms

Alpha Centauri, 4.3 light years away, site of the prosperous world of Tirane is well within range of stutterwarp. Beta Canum Venaticorum (27.3 light years away) and Beta Comae Berenices (29.9 light years away) form the nucleus of a prosperous cluster of stars, the "French Arm," shown in light blue on the map above, colonized mainly by Europeans. Procyon (11.5 light years away) Tau Ceti (11.9 light years away), 40 Eridani (16.5 light years away), and Epsilon Indi (11.8 light years away) form the backbone of another cluster, the "Chinese Arm" (in dark blue), extensively colonized by Asian and Latin American powers with the addition of Canada and some local aliens, all under Manchurian hegemony, that's unfortunately much less accessible than the French Arm--these stars might be closer to Sol than the French Arm stars, but there just aren't any stars conveniently located to bridge the gap between the Chinese Arm and Sol. Finally, Mu Herculis (27.4 light years away) is one of the notable stars in the American Arm (in darkest blue), colonized by the Americans and Australians, but because of a lack of stars in sufficiently convenient locations the American Arm is self-contained. (Or, more accurately, it started off as being self-contained in the game, but that's another thing.)

It turns out that the star maps of the late 1980s were profoundly limited. In the game, despite nearly four centuries of technological development, only a few brown dwarfs have been found. In actuality, it looks like brown dwarfs are--if not commoner than red dwarfs, as theory predicts but observations seem to contradict--pretty common. One of these stars was just discovered lurking closer than Tau Ceti or Epsilon Eridani.

Astronomers have discovered the closest new star to us that’s been spotted in 63 years. Though “star” might be a stretch, depending upon whom you ask.

The new find, UGPS 0722-05, is less than 10 light years from here. But sky-watchers missed it for so long because it’s a brown dwarf, a member of the murky class of celestial objects that linger between gas giant planets and low-mass stars. Brown dwarfs have so little mass that they never get hot enough to sustain the nuclear fusion reactions that power stars like the sun. Still, they do shine, because they glow from the heat of their formation, then cool and fade [New Scientist]. This dwarf’s temperature is somewhere between 266 and 446 degrees Fahrenheit, making it the coldest scientists have even seen. With its minimal activity, the brown dwarf gives off just 0.000026 percent the amount of light that our sun does.

There are almost certainly going to be other, closer brown dwarfs found closer to our solar system, perhaps even closer than the Alpha Centauri stars. Rogue planets may be commoner yet, floating sun-less deep in interstellar space. Who knows what could lie in these barely hypothesized environments. One scientist thinks that a rogue planet could be a living world. But then, with so little known about even relatively well-understood bodies like Mars--for that matter, with so relatively little know about our own homeworld--making predictions might be jumping things a bit.

I really like maps. I like knowing where I am, where I have been, where I will be. I like knowing the grand sweep of things and the minute details. I write in order to bring out details to others, to learn about new things myself, and to know my world that much better. I liked orienteering in junior high school; I like urban exploration and travel now; I can only imagine the things I'll have a chance to experience in the future. I'm truly grateful that I'm one of the lucky minority of humans to live in this age, an era when we can map the dimmest stars at the same time that we can dissect our DNA for traces of unusual ancestors. Our maps are so finely detailed yet so vast, I can hardly believe it.
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Tau Ceti is a star some 11.9 light years away from our Solar System, one of the twenty closest star systems excluding undiscovered solitary brown dwarves. A solitary yellow dwarf--indeed, a prototype of this class of star--Tau Ceti has long featured prominently as a potential home for life, whether human colonial or indigenous. The fact that Tau Ceti is substantially older than our Sol does mean that it has fewer of the heavy elements needed to produce rocky worlds like our own, but conversely the age of the star gives life more time to develop. Tau Ceti seemed attractive.

This changed when astronomers discovered that Tau Ceti's Oort cometary cloud is ten times denser than Sol's. Even if everything was equal, this would suggest that any hypothetical rocky planets orbiting Tau Ceti would be substantially more likely to be targets of devastating cometary impacts. As [livejournal.com profile] james_nicoll has pointed out in two postings (1, 2), things are not equal, with two stars--UV Ceti and YZ Ceti--bordering on the fringes of Tau Ceti's Oort cloud, ready to nudge comets into collision courses with planets at a high frequency. Best look elsewhere for the aliens, it seems.
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