"A brief meeting between a human and a pentapod businessbeing.
The pentapods are an alien race from GDW's classic roleplaying game 2300AD. Amphibious, radially symmetric, bioengineered and somewhat non-individual, they are definitely not people dressed up in funny suits. But they understand trade."
Planet formation models suggest that small planets are regularly flung from their solar systems by close encounters with neighboring gas giants. The giants’ gavitational fields create an interplanetary slingshot effect, sending smaller planets on unstable orbits that quickly leave their star behind.
Prior to ejection, some of those planets could conceivably be like Earth, with continents, oceans and biospheres. A new model suggests that submarine aliens on such a planet could have a chance at survival.
“We originally started with the question, what if you turned off the sun?” said University of Chicago geophysicist Dorian Abbot, co-author of a paper submitted to Astrophysical Journal Letters and pre-published Feb. 5 on arXiv.org.
Along with fellow University of Chicago astrophysicist Eric Switzer, Abbot ran the numbers to see if an ocean could stay liquid without heat from a star. They called their rogue world a Steppenwolf planet, “since any life in this strange habitat would exist like a lone wolf wandering the galactic steppe.”
The pair assumed the planet was between 0.1 and 10 times Earth’s mass, with a similar amount of water and rock. Once the planet fled its warm, nurturing star, the ocean would start to freeze. But leftover heat from the planet’s formation and decaying radioactive elements in the rock could keep the ocean warm beneath a shell of ice. As long as the planet could keep the ice from freezing all the way to the core, the ocean should be safe.
[. . .]
In a slightly more bizarre twist, the Switzer and Abbot imagined the Steppenwolf planet with volcanoes spewing carbon dioxide into the atmosphere. The gas would freeze and fall as snow almost immediately, covering the world with an insulating blanket of dry ice. In that case, planets as small as 0.3 times the mass of Earth could keep a liquid ocean.
![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif){kind=small}
james_nicoll's blog (among other places), started up a very interesting thread. How many people would be necessary to keep our high-tech civilization running?Around 1900, it took the effort of about 20-30% of a nation's work-force to provide food for everybody; and another 30-50% working in factories to produce clothing, machinery, and processed materials like bricks and billets of pig iron. Today, we only need 0.5-1% of the work force to feed everyone, and another 1-4% working in industry to produce the basics — but the microspecialities have exploded, to the extent that a lot of our needs seem to require a trans-national economy to provide. There are only two vendors of wide-body airliners on any scale today, Boeing and Airbus, and both of them are effectively multinational consortia (more than half the components of the Boeing 787 Dreamliner are produced overseas, and shipped to Seattle for final assembly). There seems to only be room for one vendor of super-Jumbo airliners — if Boeing and Airbus tried to exploit that niche simultaneously, they'd both starve — so they appear to be avoiding conflict in that (and some other) area(s). And so on.
So. I ask: how many people does it take, as a minimum, to maintain our current level of technological civilization?
I'd put an upper bound of about one billion on the range, because that encompasses basically the entire population of NAFTA and the EU, with Japan, Taiwan, and the industrial enterprise zones of China thrown in for good measure. (While China is significant, more than half of its population is still agrarian, hence not providing inputs to this system).
I'd put a lower bound of 100 million on the range, too. The specialities required for a civil aviation sector alone may well run to half a million people; let's not underestimate the needs of raw material extraction and processing (from crude oil to yttrium and lanthanum), of a higher education/research sector to keep training the people we need in order to replenish small pools of working expertise, and so on. Hypothetically, we may only need 500 people in one particular niche, but that means training 20 of them a year to keep the pool going, plus future trainers, and an allowance for wastage and drop-outs by people who made a bad career choice. Higher education accounts for 1.8-3% of gross spending in the developed world, with primary and secondary education taking a whopping chunk on top of that (if you spent 10 years in a school with a staff:pupil ratio of 1:10, then you soaked up a person-year of time; there may be more labour going into pre-university education than goes into agriculture and industry combined).
[Astronomer Scott]Gaudi’s team has concluded that about fifteen percent of the stars in the galaxy are orbited by planetary systems like our own, meaning they have several gas giants in the outer part of the solar system. That fifteen percent is telling. “Solar systems like our own are not rare,” says Gaudi, “but we’re not in a majority, either.” Microlensing is useful for this kind of study because the method does a good job at picking up giant planets far from their primary star, a more difficult task with Doppler methods.
Working with colleague Andrew Gould, Gaudi used four years of MicroFUN data and folded in a statistical analysis based on ‘robust assumptions’ and the earlier work of both men. It turns out that MicroFUN in that period of time has revealed precisely one solar system with two gas giants in roughly the configuration of Jupiter and Saturn. Statistically, if every star had a solar system like ours, we should have found about six such systems by now. The slow discovery rate implies only a small number of systems have our configuration, no more than about fifteen percent.
[. . .]
[G]iven the number of stars in the galaxy, even narrowing the odds down to fifteen percent leaves several hundred million systems that could resemble ours. Nor should we assume that a system necessarily has to mimic our own for life to develop within it. Nonetheless, this is an intriguing result that reinforces our sense that extrasolar planetary systems come in a surprising variety, one we learn more about with every new detection.
The stars beyond Sol have been ciphers for all of human history - for almost all of the time that science fiction has been written, Earth's intrepid explorers might find anything under other suns.
This decade might see this change a bit. NASA's Kepler telescope, launched last March on a multi-year mission to discover strange new worlds, has been hard at work, and on Monday details were released of the five new exoplanets detected by its efforts. All five of the newfound planets are hot worlds, orbiting extremely close to their parent stars, and only one is smaller than Jupiter. Going back to the discovery of Bellerophon in 1995, many of the exoplanets so far detected have been such "Hot Jupiters." Kepler is poised to change that, with its sensitive instruments said to be capable of detecting Earth-mass planets orbiting other stars. Not only that - in the near future, telescopes may well be able to detect individual moons orbiting these gas giants. Presumably, only the exotic properties of the mass relays will prevent Kepler from detecting them as well.
While this is great news to me, as a scientifictionist it poses a problem for the immediate future. Back in 1940, spaceflight itself was widely considered a fool's dream - whether or not Mars had canals and Venus jungles, if the writers of the time were concerned about accuracy, for all they knew it might have been a hundred years until they were proven wrong or right either way. I feel like I'm in a similar place now as to when Larry Niven wrote and sold The Coldest Place in 1964, written when the leading consensus was that Mercury was tidally locked, a consensus that was only broken by radar mapping - and after The Coldest Place had been bought, but before it was published.
[. . .]
Kepler, if successful, will revolutionize our understanding of the interstellar neighborhood. In ten years, maybe we'll know that a planet of Tau Ceti or a moon of a gas giant at 55 Cancri has an oxygen-nitrogen atmosphere and liquid water. We wouldn't be speculating blind anymore.
John Hearnshaw (University of Canterbury, Christchurch) reports in a recent post on Cosmic Diary that the university’s Mt. John Observatory has begun a program to search for Earth-mass planets around Centauri A and B. Although the observatory is heavily invested in microlensing technologies (working with the Microlensing Observations in Astrophysics collaboration), the new efforts will put radial velocity methods to work using the Hercules spectrograph.
The program is a joint effort with Stuart Barnes at the Anglo-Australian Observatory and Mike Endl at the University of Texas (Austin). And as Hearnshaw notes, the problem is a formidable one, given that an Earth-mass planet in the habitable zone around Centauri A creates a ‘wobble’ of only 10 cm/s (slightly larger for the less massive Centauri B). Yet the observatory is banking on Hearnshaw’s statement that 30,000 spectra of Centauri A or B over three years can detect a habitable zone ‘Earth.’
The habitable zone around Centauri A should be found at about 1.2 AU, while 0.75 AU is calculated for Centauri B. What else do we know about the primary Centauri stars? Earlier work has demonstrated that no gas giants as massive as Jupiter can exist there — Doppler studies would have found them by now. But the case for Earth-mass planets remains open.
We know that Alpha Centauri “A” has a dominant pulsation period that’s about 5 minutes, just like the sun. I’m not really worried about periodic variations of minutes. We’ll be able to average right over that kind of noise. But no one knows whether or not there are long period variations in “A” or “B”. We do know that “A” is probably not as stable as “B”. People have measured pulsation periods in “A”, and in general we find that more massive stars have more active atmospheres. So yeah, I agree that “B” is a better bet. And if you told me that I could only observe one star, I’d choose B. But we’re studying both stars. And it turns out that this strategy of looking at both stars is pretty critical in ensuring a solid set of data.
Astronomers have discovered hundreds of Jupiter-like planets in our galaxy. However, a handful of the planets found orbiting distant stars are more Earth-sized. This gives hope to astrobiologists, who think we are more likely to find life on rocky planets with liquid water.
The rocky planets found so far are actually more massive than our own. Dimitar Sasselov, professor of astronomy at Harvard University, coined the term "Super-Earths" to reflect their mass rather than any superior qualities.
But Sasselov says that these planets – which range from about 2 to 10 Earth masses – could be superior to the Earth when it comes to sustaining life.
[. . .]
The fear today is that too much carbon dioxide in the atmosphere will lead to global warming. Yet too little carbon dioxide in the atmosphere would make Earth a much colder place, and the photosynthetic plants and algae that rely on CO2 would perish. The demise of these oxygen-producing organisms would leave us all gasping for breath.
According to Sasselov, Earth's mass helps keeps tectonics in action. The more massive a planet, the hotter its interior. Tectonic plates slide on a layer of molten rock beneath the crust called the mantle. Convective currents within the mantle push the plates around. For smaller planets like Mars, the interior is not hot enough to drive tectonics.
Super Earths, with a larger and hotter interior, would have a thinner planetary crust placed under more stress. This probably would result in faster tectonics, as well as more earthquakes, volcanism, and other geologic upheavals. In fact, Sasselov says the plate tectonics on Super Earths may be so rapid that mountains and ocean trenches wouldn't have much time to develop before the surface was again recycled.
![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
branchandrootdancing_serpent
