A Bit More Detail

• Ryan Anderson at anthro{dendum} looks at the unnatural history of the beach in California, here.


• Architectuul looks at the architectural imaginings of Iraqi Shero Bahradar, here.


• Bad Astronomy looks at gas-rich galaxy NGC 3242.


• James Bow announces his new novel The Night Girl, an urban fantasy set in an alternate Toronto with an author panel discussion scheduled for the Lillian H. Smith Library on the 28th.


• Centauri Dreams looks at the indirect evidence for an exomoon orbiting WASP-49b, a possible Io analogue detected through its ejected sodium.


• Crooked Timber considers the plight of holders of foreign passports in the UK after Brexit.


• The Crux notes that astronomers are still debating the nature of galaxy GC1052-DF2, oddly lacking in dark matter.


• D-Brief notes how, in different scientific fields, the deaths of prominent scientists can help progress.


• Bruce Dorminey notes how NASA and the ESA are considering sample-return missions to Ceres.


• Andrew LePage at Drew Ex Machina looks at the first test flights of the NASA Mercury program.


• The Dragon's Tales looks at how Japan is considering building ASAT weapons.


• Andrew LePage at Drew Ex Machina looks at the first test flights of the NASA Mercury program.


• Far Outliers looks how the anti-malarial drug quinine played a key role in allowing Europeans to survive Africa.


• At In Media Res, Russell Arben Fox considers grace and climate change.


• io9 reports on how Jonathan Frakes had anxiety attacks over his return as Riker on Star Trek: Picard.


• JSTOR Daily reports on the threatened banana.


• Language Log looks at the language of Hong Kong protesters.


• Erik Loomis at Lawyers, Guns and Money notes how a new version of The Last of the Mohicans perpetuates Native American erasure.


• Marginal Revolution notes how East Germany remains alienated.


• Neuroskeptic looks at the participant-observer effect in fMRI subjects.


• The NYR Daily reports on a documentary looking at the India of Modi.


• Corey S. Powell writes at Out There about Neptune.


• The Planetary Society Blog examines the atmosphere of Venus, something almost literally oceanic in its nature.


• Noel Maurer at The Power and the Money considers how Greenland might be incorporated into the United States.


• Rocky Planet notes how Earth is unique down to the level of its component minerals.


• The Russian Demographics Blog considers biopolitical conservatism in Poland and Russia.


• Starts With a Bang's Ethan Siegel considers if LIGO has made a detection that might reveal the nonexistence of the theorized mass gap between neutron stars and black holes.


• Frank Jacobs at Strange Maps looks at Marchetti's constant: People in cities, it seems, simply do not want to commute for a time longer than half an hour.


• Understanding Society's Daniel Little looks at how the US Chemical Safety Board works.


• Window on Eurasia reports on how Muslims in the Russian Far North fare.


• Arnold Zwicky looks at cannons and canons.

In the "Grand Tack" (GT) scenario for the young solar system, Jupiter formed beyond 3.5 AU from the Sun and migrated as close as 1.5 AU until it encountered an orbital resonance with Saturn. Both planets then supposedly migrated outward for several 105 yr, with Jupiter ending up at ~5 AU. The initial conditions of the GT and the timing between Jupiter's migration and the formation of the Galilean satellites remain unexplored. We study the formation of Ganymede and Callisto, both of which consist of ~50% water and rock, respectively, in the GT scenario. We examine why they lack dense atmospheres, while Titan is surrounded by a thick nitrogen envelope. We model an axially symmetric circumplanetary disk (CPD) in hydrostatic equilibrium around Jupiter. The CPD is warmed by viscous heating, Jupiter's luminosity, accretional heating, and the Sun. The position of the water ice line in the CPD, which is crucial for the formation of massive moons, is computed at various solar distances. We assess the loss of Galilean atmospheres due to high-energy radiation from the young Sun. Ganymede and Callisto cannot have accreted their water during Jupiter's supposed GT, because its CPD (if still active) was too warm to host ices and much smaller than Ganymede's contemporary orbit. From a thermal perspective, the Galilean moons might have had significant atmospheres, but these would probably have been eroded during the GT in < 105 yr by solar XUV radiation. Jupiter and the Galilean moons formed beyond 4.5 (+/-0.5) AU and prior to the proposed GT. Thereafter, Jupiter's CPD would have been dry, and delayed accretion of planetesimals should have created water-rich Io and Europa. While Galilean atmospheres would have been lost during the GT, Titan would have formed after Saturn's own tack, because Saturn still accreted substantially for ~106 yr after its closest solar approach, ending up at about 7 AU.

• 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.

Astronomer Mike Brown and his colleague Kevin Hand might be suffering from “Pump Handle Phobia,” as radio personality Garrison Keillor calls it, where those afflicted just can’t resist putting their tongues on something frozen to see if it will stick. But Brown and Hand are doing it all in the name of science, and they may have found the best evidence yet that Europa has a liquid water ocean beneath its icy surface. Better yet, that vast subsurface ocean may actually shoot up to Europa’s surface, on occasion.

[. . .]

“We now have evidence that Europa’s ocean is not isolated—that the ocean and the surface talk to each other and exchange chemicals,” said Brown, who is an astronomer and professor of planetary astronomy at Caltech. “That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”

“The surface ice is providing us a window into that potentially habitable ocean below,” said Hand, deputy chief scientist for solar system exploration at JPL.

[. . .]

Salts were detected in the Galileo data – “Not ‘salt’ as in the sodium chloride of your table salt,” Brown wrote in his blog, “Mike Brown’s Planets,” “but more generically ‘salts’ as in ‘things that dissolve in water and stick around when the water evaporates.’”

[. . . N]ow, with data from the Keck Observatory, Brown and Hand have identified a spectroscopic feature on Europa’s surface that indicates the presence of a magnesium sulfate salt, a mineral called epsomite, that could have formed by oxidation of a mineral likely originating from the ocean below.

[. . .]

The magnesium sulfate appears to be generated by the irradiation of sulfur ejected from the Jovian moon Io and, the authors deduce, magnesium chloride salt originating from Europa’s ocean. Chlorides such as sodium and potassium chlorides, which are expected to be on the Europa surface, are in general not detectable because they have no clear infrared spectral features. But magnesium sulfate is detectable. The authors believe the composition of Europa’s ocean may closely resemble the salty ocean of Earth.

Though Saturn's largest moon, Titan, is a small, cold world orbiting on the outskirts of the solar system, it actually boasts many familiar features.

“Titan is fascinating because it has some surprising properties so similar to Earth,” said planetary scientist Oded Aharonson from the California Institute of Technology. “It has a liquid which erodes channels, an atmosphere, a hydrologic cycle, and many other parallels.”

Chief among Titan’s interesting qualities is that it's the only body other than Earth where liquids are known to flow in large concentrations on the surface. Because average temperatures there are -300 degrees Fahrenheit, these liquids are not water. Instead, hydrocarbons such as methane and ethane rain down from clouds, course over the landscape in rivers and eventually pour out into large lakes and seas.

The presence of liquids has sparked scientists’ imaginations. If Titan has so many Earth-like features, perhaps it possesses one more terrestrial trait: the presence of life. Native organisms on Titan would be an incredible discovery, showing that life may have formed more than once and suggesting it's common in the universe.

First, let's get the painfully obvious stuff out of the way: yes, Callisto is a bit on the bland side. It doesn't have an atmosphere, like Titan. It doesn' have volcanoes, like Io, or geysers, like Enceladus. It probably doesn't have a huge internal ocean of water like Europa. It's not part of a "double planet" like Charon. It doesn't have a magnetic field, like Ganymede. It's just a large, icy moon with a heavily cratered surface. So, yes, you could say that Callisto is less interesting than some other places.
Except that you'd be stupid to say that, because Callisto is actually pretty damn interesting.

Let's start with the most common misconception, which is that Callisto is "geologically dead". We're told that its surface is "saturated" with craters, so that any new crater would obliterate one or more old ones. Craters, nothing but craters. Right?

Wrong. Much of Callisto's surface is -- wait for it -- eroded. Yes, it's full of craters, but there are vast regions where the craters have been degraded to the point where you can hardly recognize them. All that's left are smooth, undulating basins with lumps or spires in the middle.

What's causing the erosion? Well, take a moment to consider how odd Callisto actually is. It's a large icy world that's relatively warm -- daytime surface temperatures get up to around 160 Kelvin, or about -170 Fahrenheit, and can peak at another 10 K higher than that at noon on the equator. That's actually pretty toasty for an ice moon. The other moons of Jupiter are all 30 or 40 degrees cooler than that. Callisto is warmer because it's dark -- it has a really low albedo. (Why? We're not sure. One guess is that radiolysis has broken down organic compounds, leaving a sooty residue.) Whatever the reason, Callisto is the warmest large icy body in the Solar System.

So Callisto gets warm enough that water ice can sublime. That's very different from, say, someplace like Titan. At Titan's 95 K, water ice is completely inert, dead as granite. But at 160 K? Water can actually have a vapor pressure. A very tiny vapor pressure, to be sure. But over geological time, many millions of years, water ice will slowly sublime away into the vacuum. The sharp edges of craters will gradually blur and then slump. Much of the vapor is lost to space, but some condenses as bright, reflective frost. That's what we're seeing when we look at Callisto... mostly dark stuff, but with gleaming shiny bright bits. So if you could walk around the surface of Callisto, it wouldn't look much like Earth's Moon, all gravel and sharp edges. Instead, most features would be rounded and soft-edged.

[. . .]

You'll still see a lot of people saying that Callisto's surface is "old", "ancient", or even "pristine". No. Even at the macro level, all those big craters have been softened by erosion, and the composition of the surface has been dramatically changed by radiolysis and the movement of volatiles. It's like the difference between a bright new shiny penny, and one that's old, worn down, and tarnished. And at the micro level, the scale of a human walking around, Callisto's surface has been completely transformed. It's not old at all.

And it's probably still evolving. Callisto's surface is being shaped by subtle, slow processes -- sublimation, condensation, radiolysis -- working over geologic time. These things aren't flashy. But they get results, and they're just as interesting as the faster and more blatant processes taking place on Io or Titan.

• Bad Astronomy's Phil Plait lets us know that T Pyxidis, a recurring nova star that might go supernova, isn't nearly close enough to kill us all.


• Global Sociology examines the very serious impact of the telenovela on all elements of popular culture but wonders how relevant it is to the North American soap opera experience.


• To commemorate Galileo's discovery of Jupiter's four planet-sized moons, Johnny Pez linked to four classic science-fiction short stories, each one set on a different moon. He also reports on the 1930s' race to ascend into the stratosphere.


• Marginal Revolution reports on a study of housing in India that suggests majority communities will respond more favourably to religious minorities if there's little residential segregation.


• Slap Upside the Head reports ona questionable Calgary Stampede marketing survey that asks respondents some homophobic questions.


• Spacing Toronto looks at Thistledown, a community long since assimilated into Toronto by the city's growth.


• Window on Eurasia considers whether Bonapartism--militarized and populist, but centralized and modernizing, on the model of Napoleon III--might be in Russia's future.