Category: Cosmos

Primordial Dramas and Present Easy-Breathing

Our Solar System has changed dramatically over the aeons since the planets accreted/collapsed out of the initial nebula. The Sun both got brighter in overall output, but has dimmed in its extreme UV brightness (EUV) and solar-wind levels, with dramatic consequences for the atmospheres of the terrestrial planets & giant planet-sized moons. A good review article:

Atmospheric Escape and Evolution of Terrestrial Planets
and Satellites Space Sci Rev (2008) 139: 399–436, DOI 10.1007/s11214-008-9413-5

…available at one of the co-authors, R.E.Johnson’s, webpage. EUV absorption in the very uppermost atmosphere, the exosphere, can drive the temperatures there to extremely high levels. This is due to the nature of EUV interactions with the very widely separated atoms and ions of the exosphere. Most of the atmosphere is well mixed, due to interparticle collisions, but in the exosphere the atoms rarely collide. Instead they can be struck by highly energetic photons, like EUV, and retain that energy, equivalent to thousands of degrees. This puffs the exosphere up even further and makes it easier for the atmosphere to escape into space, causing potentially several times the present day atmospheric masses to be driven off.

Another suite of processes produce what’s called non-thermal escape basically via energy transfer from the solar-wind to the upper atmosphere. Such processes can be very complicated to model and simulate, and can often only be properly understood by direct measurement thanks to long-term space-probe missions. Finally another possible atmospheric escape process is via direct blow-off via impacts. This isn’t happening in the present day at appreciable levels – fortunately – but is believed to have been important on smaller bodies like Mars and the large Gas Giant moons. Volatiles can also be accreted via this mechanism – the difference lies in the speed of the incoming impactor. Too fast and the incoming material blows away into space, taking some of the surface with it.

Some surprising masses of primordial atmosphere can be lost via these mechanisms, reshaping the body in question irrevocably. Some plausible changes – Venus lost an ocean, Earth lost excess hydrogen, Mars lost its primordial warming blanket of CO2, the Galileans lost Titan-like atmospheres and Titan lost several times its present day nitrogen atmosphere. And, just possibly, Earth owes its ocean to accretion via comets. At least some of it, almost certainly.

The implications for exoplanetary systems are worth considering. A smaller planet in a red-dwarf habitable zone will experience a much higher impactor speed, due to its higher orbital velocity. But, contrariwise, will it experience more impactors? Our own impact flux depended heavily on the movements of the Gas Giants – a primordial Titanomachy, if you will, which pummelled the planets with gravitationally tossed proto-comets & asteroids. Red dwarf stars seem to produce fewer Gas Giants, at least of Jupiter/Saturn class sizes, and may well produce a less severe impact flux. Could that mean their terrestrial planets are deprived of cometary volatiles and thus desert planets?

That’s one possible example and no doubt more will be conceived as our understanding improves.

Dark Matter puzzle?

Astronomers Find Black Holes Do Not Absorb Dark Matter

The media produced breathless copy like the above, which comes from one of the more considered and sensible space science news-sites, Universe Today. The ‘headline’ was inspired by this paper…

An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes

…which does seriously challenge the naive model of dark matter in its “plain Dark Matter” form – i.e. responds to gravity and only interacts with other Dark Matter via annihilation reactions. But what if Dark Matter is more complicated? Some theories argue for other Dark Matter forces that it alone feels. If Dark Matter is “Shadow Matter”, which has a full suite of Standard Model forces, but in mirror reflection to Normal Matter, then Dark Matter is subject to “dark light”, its own kind of electromagnetic forces. Remember all varieties of proposed Dark Matter feel gravity and a central galactic black-hole is going to be a black hole in either the Normal Matter or Shadow Matter ‘universes’. But there’s more Shadow Matter than Normal Matter and, due to differences in Big Bang Nucleosynthesis, the ratio of hydrogen’ to helium’ is lower than the Normal Matter H/He ratio. The Shadow Universe began old, with a higher metallicity driven opacity in its star-forming gases. That means in the Shadow Universe the Galaxies never condensed into flat disks because supernova blew them into huge hot bubbles, surrounding Normal Matter galaxies as the observed Dark Matter haloes to the present day. Thus Shadow Quasars, and their black hole engines, blew away any excess central density in the Shadow galaxies and the central black holes were starved of Dark Matter, as the new study observes.

Thus the new study isn’t telling us that Dark Matter is somehow immune to Black Holes, which is utterly contrary to the gravitational justification for Dark Matter in the first place. Instead Dark Matter is more complex than the simple variety invoked as the minimal working hypothesis. There’s much more to learn about the Shadow Universe than we first thought – surely that’s got to be a good thing?

Odds & Ends News 14-2-2010

Happy Valentine’s Day to all you loveable Blog-ghosts who read this page.

I’ve been working on the dynamics of laser pushed reflectors – i.e. super-reflectors which can ‘reuse’ the beam thousands of times before it is absorbed and lost as heat. The concept was AFAIK originally discussed by Robert Metzger & Geoff Landis, but Young K. Bae has used it experimentally in a mock-up of a low-power position system for space-vehicles. Ignoring relativity, for now, and staying at close range to minimise diffraction loses, the final velocity over a range from Xo to X is pretty easily solved as…

v = sqrt[2.E/m*ln(X/Xo)]

…but then integrating, care of the Online Integrator from Wolfram’s Mathematica, to find the trip-time produces this horror…

t = 2.X.F{sqrt[ln(X/Xo)]}.sqrt[m/2E]

…F{…} is Dawson’s Function or Integral which is related to the Error Function that produces the Bell Curve. In otherwords there’s no easy way of computing the rotten thing.

Trawlling the Web produces some interesting finds, courtesy of the University of Arizona Press, a whole book online by Carl Sagan & James Pollack (both sadly deceased), Planetary Engineering ,which covers all the big questions of remaking the planets. Cool.

Sagan was a heavy-hitter in astrobiology & SETI – he worked on even while battling his ultimately fatal cancer and produced this paper, one of his last…

Scintillation-induced Intermittency in SETI

…which covers the fade & amplify effect that interstellar plasma can have on radio signals. Thus we might occasionally receive a signal from much further away, thanks to random drifts of plasma in the intervening void. Makes it very hard to get a repeat performance from such signal sources and the full implications are discussed here by his co-writer…

Now You See Them, Now You Don’t

…on his web-site (John Lazio’s page.)

Mentioned by the 1997 paper is an earlier SETI results paper, by Paul Horowitz & Sagan (again) from 1993…
Five years of Project META – an all-sky narrow-band radio search for extraterrestrial signals
…which reports a tantalising set of signals. Benford3 reference the paper in their duology…

Searching for Cost Optimized Interstellar Beacons

Messaging with Cost Optimized Interstellar Beacons

…which are deserving of a more detailed discussion next time.

God of the Goofs

Theology and theodicy are fraught with pitfalls and surprises. Amateur theology even more so. Here’s a review that is a case in point…

A caring God would not have designed us like this

…discussing a review of a new book, Inside the Human Genome: A case for non-intelligent design by John C. Avise, which argues the genome is such a demonic mess that it had no Designer. The reviewer makes the interesting point – perhaps we have a moral imperative to then fix the mess.

But what of the Designer? With a hat-tip to Anne Rice I wrote this…

Perhaps the Designer intended for biochemical Life to remain as ‘immortal’ archea & eubacteria, and was taken by surprise when they ganged together, made eukaryotes, then sex & death at the same time. After a billion years of watching the carnage S/He decided “enough is enough” and chose to intervene by developing an Intelligent Watchmaker who could fix the biosphere… but we’re just not finished yet. The Designer is still struggling with how to handle “junk memes” and is working on new software to upgrade us to Humanity 2.0…

As believeable as any religion, just more up-to-date.

…tongue firmly in cheek, but the point is that perhaps God didn’t know how the world would turn out – until it turned out this way. Even a “god outside time” has to let events occur to foreknow them, else they’re all being directly orchestrated by god and any “freedom” and “free-will”, as well as any evil and sin, is written into the Script of the cosmos, and God really is just a mask for the Devil. So even a God outside time must be surprised, from time to time, but eternally surprised.

And why should we be surprised by that fact? A number of mathematical arguments imply that knowledge, even perfect knowledge, of a system is only possible by letting that system ‘run’ when it is past a certain level of complexity. God took a cosmic risk when S/He created space-time and all else that followed.

Warming White Dwarfs with Dark Matter

Two recent arXiv preprints discuss capture of Dark Matter and limits on its self-annihilation inside white dwarfs…

Capture of Inelastic Dark Matter in White Dwarves

Inelastic Dark Matter As An Efficient Fuel For Compact Stars

…the first discusses limits for inelastic Dark Matter capture inside the white dwarfs of globular cluster M4, while the second discusses capture in general. PhysicsWorld.com has a commentary news-piece on the limits and the putative inelastic DM signal from the DAMA/LIBRA experiment… Warm white dwarfs could reveal ‘inelastic’ dark matter …and mentions white dwarfs maintaining an even 7000 K temperature, rather than cooling towards ~3000 K (what the coolest WDs radiate at.)

What does that mean, in the long term, I wondered? Consider the average white dwarf, which is about 0.7 solar masses and about 0.0093 solar radii. Call it 0.01 size of the Sun. At 7000 K each square metre is radiating x2.15 times the Sun’s 5780 K, thus the white dwarf is putting out about 0.0002 Solar luminosities – i.e. about 5000 white dwarfs would equal the Sun. Since the galaxy is expected to evolve to a state of being either white dwarfs or brown, then there will be about ~20 million solar luminosities worth of Dark Matter annihilation energy radiating from them until the Dark Matter runs out some time between 1019 – 1020 years from now.

The SETI implications are interesting – does it imply that civilizations with an extremely long-view will ultimately move into residence around white dwarfs? Such would live ~1-10 million times longer than red-dwarf based societies, which is quite impressive. Of course a mere 1020 years is nothing compared to eternity…

In Ages Long Ago II…

Nick Lane is a prolific writer and has some very interesting pieces available at “New Scientist” as well as his own web-pages. Very readable work from a biochemist. Here’s a sampler from “New Scientist”…

The Big O …not orgasm, but Oxygen and its variations through geological time. During the Carboniferous it was 35% of the atmosphere (just 21% today), yet a few million years later it was just 12% at the end of the Permian. How did Life respond?

Has the mystery of sex been explained at last? …why do we have sex when some animals get along without it just fine? Or do they? The old explanation is that sex helps defend against external parasites… BUT that doesn’t quite work. What about genomic ‘parasites’?

What’s the point of being warm-blooded? …maintaining a high, constant body temperature is what burns most of our calories in a day, and that’s true for almost all mammals and birds. Why the waste heat? Why not burn slower like our reptilian ancestors?

Was our oldest ancestor a proton-powered rock? …Think ‘Chemiosmosis’ and you’ll get the idea. The LUCA (Last Universal Common Ancestor) was a cell in a ‘rock’… read more for details and an engrossingly told story. A summary in 10 Steps is available too.

Finally, not from Nick Lane, is this ABC News item…

Cell’s Power Packs Came from Within

…which studies how mitochondria – the common energy factory of all eukaryotes – came to be converted from a free-living bacterium to energy centre. Apparently the transfer molecular machinery that shuttles materials from mitochondrion to host cell came together from diverse bacterial parts organised in those first eukaryotes, and the researchers recreated just how.

In Ages Long Ago…

Not the opener to “Voltron”, but the latest synthetic palaeo-news.

First, appropriately enough, the first tracks of the First Crawling Things…

Found: The first ever animal trails …reported by “New Scientist”, some rock-hounds have discovered 565 million year old anemone trails. Well… they look like anemone trails at least. Older ‘trackways’ are known, but they’re not obviously animal tracks since things like gas-bubbles under algal mats can leave similar markings. These are the real deal.

But why then? The Ediacaran/Vendian came just after the last Big Glaciation (Snowball Earth) and a multitude of squishy, shelly Things appeared and left fossils. Why not earlier?

The next news item answers that…

First breath: Earth’s billion-year struggle for oxygen …seems cyanobacteria, the oxygen-making variety, didn’t appear until c.2.7 billion years ago, took 300 myr to oxygenate the air, then collapsed during the subsequent Ice Age, caused by oxidation of the methane greenhouse of the time. The first series case of climate change due to Life’s by-products, perhaps. An earlier one might’ve been caused by the methanogens themselves, who warmed the Archean Earth.

After the end Archean Ice Age, the Earth languished in an epoch of smelly oceans – hydrogen sulphide and sulfate dominated – but finally something shifted, probably the Greening of Rodinia about 800 mya. This mass erosion event caused by lichens and terrestrial algaes, set the Earth for the Snowball Earth events and the subsequent explosion of animal Life. Or so the story goes as told by Nick Lane. Like all such Proterozoic Tales, there’s a lot we just don’t know.

The implications are interesting. Where did the oxygen making bacteria come from? Could they have drifted in from Venus as its oceans were wafted into the stratosphere and photolysed? That’s my pet theory – we’re all Venusians. Of course Panspermia implies all the suitable solar planets and moons are really one common biosphere.

Odds & Sods News, Australia Day 2010

Callisto & Ganymede, twin moons of Jupiter, yet so unalike. Why? Dr Amy Barr and Dr Robin Canup of the Southwest Research Institute (SwRI) believe the two moons diverged in their evolutionary paths about 3.8 million years ago, during the Late Heavy Bombardment. Here’s a scan of the news-pages…

Comets left their mark on Jovian moons …a good summary from Aunty.

SwRI researchers offer explanation for the differences between Ganymede and Callisto …from EurekaAlert, with original graphics from SwRI. Quick, condensed summary of this…

SwRI News release …with the pretty graphics on another page. Of course the real meat is in the paper…

Letter abstract

Nature Geoscience
Published online: 24 January 2010 | doi:10.1038/ngeo746

Origin of the Ganymede–Callisto dichotomy by impacts during the late heavy bombardment

Amy C. Barr1 & Robin M. Canup1

Top of page

Jupiter’s large moons Ganymede1, 2 and Callisto2, 3 are similar in size and composition. However, Ganymede has a tectonically evolved surface1 and a large rock/metal core2, whereas Callisto’s surface shows no sign of resurfacing3 and the separation of ice and rock in its interior seems incomplete2. These differences have been difficult to explain4, 5, 6, 7, 8, 9, 10, 11. Here we present geophysical models of impact-induced core formation to show that the Ganymede–Callisto dichotomy can be explained through differences in the energy received during a brief period of frequent planetary impacts about 700?million years after planet formation, termed the late heavy bombardment12, 13, 14, 15. We propose that during the late heavy bombardment, impacts would have been sufficiently energetic on Ganymede to lead to a complete separation of rock and ice, but not on Callisto. In our model, a dichotomy between Ganymede and Callisto that is consistent with observations is created if the planetesimal disk that supplied the cometary impactors during the late heavy bombardment is about 5–30 times the mass of the Earth. Our findings are consistent with estimates of a disk about 20 times the mass of the Earth as used in dynamical models that recreate the present-day architecture of the outer solar system and the lunar late heavy bombardment15, 16.
Top of page

1. Department of Space Studies; Center for Lunar Origin and Evolution, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA

Correspondence to: Amy C. Barr1 e-mail: amy@boulder.swri.edu

…all behind Nature’s Pay-per-View isn’t it? Ah well, the news summaries aren’t bad.

Amy & Robin’s homepages are…

Dr. Amy Barr

Dr. Robin Canup

…basically the model is that the higher energy and more frequent LHB impacts that Ganymede would’ve taken is why Ganymede is more differentiated than Callisto. Did that cause Ganymede to totally differentiate and produce the intrinsic magnetic field it has today? A future research question, I’d hazard.

Palaeo Cuteness News. Researchers have made a flying model of Microraptor to better understand its flight potential.
Microraptor model
…reported at Physorg News. The researchers are based in China and Kansas U, led by chief BANDit Larry Martin, and given a voice on NOVA…

KSU Link and Summary of NOVA episode

…BANDit? you say. The Birds-Are-Not-Dinosaurs (+its) are a small, but loud bunch of palaeo-ornithologists who think the bird-like dinosaurs are really birds. A long, long academic debate has swirled around a few key personalities, like Alan Feduccia and Larry Martin, about the dino-ness of birds and the birdy-ness of dinos. For an opposing view there’s the Dinosaur Mailing List bunch of Dino Docs who think the BANDits are splitting hairs.

Project Icarus

“Project Daedalus” now has a sequel, “Project Icarus”, which promises a smarter, better design…

http://www.icarusinterstellar.org/

…look for the Terms of Reference and see what’s planned to be discussed and thrashed out over the next 5 years.

Some very cool “Project Daedalus” artwork can be found on the “Icarus” website – plus some superb animations by Adrian Mann, whose own website is a treasure-trove of retro-space & ultra-modern designs…

This Is Rocket Science

Another inspiration piece is by Nathan Fowkes…

Project Daedalus Design Project 1994

…he presages “Icarus” by imagining the second “Daedalus” stage braking into orbit around Barnard’s Star to release its secondary probes and explore.

Joe Bergeron produced this gorgeous depiction back in 1999…

Bergeron Daedalus

…plus some kin of “Daedalus”…

Bussard Ramjet

Orion Nuclear Pulse Rocket