Category: Sol Space

Interplanetary flight, Planets, Moons, ‘Roids and Comets – plus dust

Cryovolcanism on Charon and Beyond…

LPSC 38 2007 Cryovolcanism on Charon.

(With thanks to Paul Gilster for asking Cryovolcanism on Charon? over at Centauri Dreams )

Who would’ve expected liquid water out around Neptune and beyond? Not on the surface of any object, of course. That’d be stretching physics just a bit too much. Underground. Deep under an insulating blanket of ices and dust. But how deep? Just how big does an object have to be to keep a liquid mantle of (probably) ammonia-water sloshing around? According to the study above as low as 600 km in radius is enough. That means a multitude of Dark Abyssal Oceans exist in the swarm of Dwarf Planets astronomers estimate to exist in the Edgeworth-Kuiper Belt, the Scattered Disk and probably the Oort Cloud too.

Is surface water in liquid form really so crazy though? A deep hydrogen/helium atmosphere probably got captured by anything bigger than Mars in the Outer System as the Gas Giants were forming. In theory such an atmosphere could keep the heat in quite efficiently. But just how much geothermal heat would the planet need to be putting out? Too cold and the planet’s atmosphere will start condensing in its outer reaches, causing runaway collapse of the hydrogen into vast, COLD seas of the stuff. That’s a plus if the deuterium freezes out, but the protium doesn’t – but it’s not the sort of sea I want. So, I’d expect, the planet will need to be hotter than hydrogen’s critical point, 33 K. That means the internal heat-flow outwards is comparable to Earth’s roughly 80 mW/m2 (a temperature of 34.46 K in absence of solar heating) which may be feasible if it’s mostly rock. Ice would dilute things too much. A binary object with a high eccentricity might also be warmed to sufficient levels by tidal heating too.

The lesson is to not rule anything out. We don’t know that much yet.

Late in the PreCambrian…

Explosive growth of life on Earth fueled by early greening of planet.

Explosive growth of life on Earth fueled by early greening of planet.

Was ancient Earth a green planet?.

Earth formed a Super-Continent, Rodinia, c. 1 Gya. Perhaps its emergence from beneath the waves encouraged plant-life to invade, because it did invade en masse and, perhaps, led to the collapse of the old methane greenhouse of the Proterozoic.

Once the Earth greened, then the stage was set for animals…

Dawn of the Animals: Solving Darwin’s Dilemma

…though it’s possible the animals encouraged the oxygen change that swept the world and, apparently, locked up the planet in glaciers a couple of times before animal fossils grew large and numerous.

Curious. Do all worlds spawn animal life in the same way? Is oxygen the secret ingredient? There are reasons to answer… ‘Maybe, yes.’

Greater Longevity for Planets with Life?

Caltech Scientists Predict Greater Longevity for Planets with Life – Caltech.

The paper is:

“Atmospheric pressure as a natural regulator of the climate of a terrestrial planet with biosphere,” by King-Fai Li, Kaveh Pahlevan, Joseph L. Kirschvink, and Yuk L. Yung

…and its abtract is here at the “Proceedings of the National Academy of Sciences.” The chief researcher is King-Fai Li, whose publications page is here and well worth a LOOK…

Basically the pressure of an atmosphere enhances the IR-absorbing spread of carbon dioxide molecules, which is how they trap heat so efficiently on Venus, and apparently how a miniscule 380 ppm of CO2 on Earth plays such a key-role on Earth, but 950,000 ppm on Mars isn’t so effective. If the total nitrogen – some 78% of the atmosphere – declined with the rise in solar insolation, then Earth’s average temperature would remain more stable over the next 2.3 billion years compared with previous models (eg. Lovelock or Caldeira & Kasting.) By the end of that period, when a runaway greenhouse finally kicks in, the surface pressure has dropped to ~0.1 of today. So just how ‘habitable’ Earth remains is a different question. Over such a long-span then life would no doubt adapt, but a luckless Time-Traveller might be a tad short of breath.

Another atmospheric processes guru involved in the paper is Joe Kirschvink, whose webpage is a rewarding visit for all who want to dig deeper. He has papers online about Enceladus and the ALH84001 Martian meteorite which maybe had microfossils.

A Miss is as Good as a Mile… Part 1

JPL Small-Body Database Browser.

21 metre wide space-rock 2009 KR21 whizzed past the Earth and Moon at a distance of 285,000 and 150,000 km respectively on June 1st. If it had been but 0.0019 AU or 0.001 AU closer to either, then it would’ve collided. The relative velocity was 12.87 km/s and 13.87 km/s respectively, so it would’ve been a decent collision speed after acceleration in the gravity field of either.

It would’ve entered Earth’s atmosphere at 17 km/s and probably burst quite high in the air from aerodynamic forces, liberating about 168 kilotons of TNT equivalent energy… quite a bang indeed. On the Moon it would’ve struck at 14.07 km/s and exploded with 114 kilotons, digging a decent hole and producing a brief flash that some amateur could spot with a patiently watching automated telescope.

That assumes it’s low density porous space-rock with an average density of water at ~60% porosity. If it was more compact iron/nickel then the explosive punch would be about 8 times higher – a megaton explosion on Earth and the Moon. Iron/nickel meteorites are mechanically very strong and impact the surface with most of their space-velocity intact.

But what if it was something stranger? One possibility is that a significant number of Shadow Matter meteoroids exist. But what is ‘Shadow Matter’ you ask?

see Part 2

Lord Kelvin | On the Age of the Sun’s Heat

Lord Kelvin | On the Age of the Sun’s Heat.

William Thomson was one of the giants of 19th Century physics, playing an important role in all the major innovations of that crowded Century – thermodynamics, electricity, telegraph and geology. Not everything he proclaimed the verdict of physics on was found to be the way he had assumed, but he pushed physical insight to its limits. Famously he is apocryphally said to have claimed physics was over in about 1900 – though no source can ever be found where he says something so short-sighted. He’s also said to have disbelieved x-rays, though what isn’t mentioned is he became a firm supporter of Roentgen’s work after getting his own hand x-rayed. Experiment trumped theory for William Thomson, Lord Kelvin.

Infamously he challenged Charles Darwin over the age of the Earth. But Thomson was correct, within the limits of knowledge of the day, that the Earth couldn’t be as internally warm nor the Sun as bright for as long as Darwin and the geologists wanted… unless both were internally different to what was inferred. Sure enough, heat transport within the Earth proved more complicated than simple heat conduction. Convection of the mantle changes the thermal profile, so that below a certain depth the rate of change in temperature declines at a much slower rate with depth. Similarly the Sun is chiefly powered by a source other than the gravitational contraction that Thomson had invoked – nuclear fusion. But none of Thomson’s work on the Sun – or the Earth – was invalidated, merely extended. A newly forming star is powered by gravitational contraction energy until its core becomes sufficiently dense and hot to initiate proton-proton fusion. And the Earth’s thermal profile is much as Thomson described until it reaches a depth where the mantle softens enough to convect.

So, rightly, Thomson is remembered for his foundational work in thermodynamics and for his principled work in applying new physical insights as they became established. We owe the first successful Trans-Atlantic telegraph cables to him too. Quite an amazing life really.

The Night Land (I)

The Night Land by William Hope Hodgson – Project Gutenberg.

A seriously creepy tale, by dint of the setting in time and space. “The Night Land” is millions of years in the future, after the Sun has become too cold to be visible to human eyes. Life on Earth has been preserved in a vast ravine a hundred miles deep into the mantle, warmed and powered by volcanism. Humanity struggles on, preserved against the “Night Land”, in the Last Redoubt, which is a huge pyramidal Arcology, several miles square on its base and projecting eight miles into the endless night. It is threatened by weird creatures, chiefly vastly old and patient “Watchers” and darker (!) forces of spiritual evil. Billennia before, it’s revealed, humans had experimented in space-time and let in “Things” – spiritual lifeforms that predate on human minds/souls.

The basic tale I’ll save for next time, but for now I wanted to examine the physics. Basically we’re talking about the Kelvin-Helmholtz timescale for the Sun’s contraction and its powering by gravitational potential energy being converted into heat energy. Essentially every mass falling into another mass will release energy and the total energy represented by all the mass of an object falling together into its current configuration is its binding energy.

Back in the 19th Century the only energy source known powerful enough to keep the Sun shining for millions of years was gravitational energy. But there was a problem – the Sun’s present configuration represented a binding energy of 18.75 million years of sunshine at present levels. Allowing for unknowns about the insides of the Sun, the total lifespan to date of the Sun was less than 100 million years and probably less than 30 million years.

That produced two problems. Firstly, geology seemed to imply Earth was at least 100 million years old and probably much older. Secondly, it meant that without a continuing infall of mass on to the Sun, it would grow cold and go out within a few million years.

The first problem is another tale, but the second inspired SF for several decades after Lord Kelvin first posed it in the 1860s. H.G.Wells visited an Earth orbitting a Sun grown cold in his “The Time Machine”, mentioning the infall of both Mercury and Venus which kept the Sun glowing hot for a bit longer. In 30 million years from his own time, his Time Traveller sees a huge red Sun over a chilled Earth which is facing its Final Winter. The Sun hasn’t grown huge like it is imagined to in present day astrophysics – instead Earth has slowly spiralled in towards it. And it is only shining like a red-hot ember, albeit a gigantic one, that’s rapidly losing its warmth.

By 1912, in William Hope Hodgson’s tale, the discovery of radioactivity was giving some geologists hope that the interior of the Earth would remain warm, but no one was too sure about the Sun and the other stars. Einstein’s work on the interconversion of mass and energy hadn’t filtered through to most fictioneers or astrophysicists, though very soon people would be talking about powering the Sun through annihilation of mass. But Hodgson doesn’t show any awareness of this, though he does indicate knowledge of speculations about non-Euclidean geometry with his “Doorways of the Night”, akin to the modern-day ‘wormhole’.

In an earlier tale Hodgson has a character visit the very end of the Cosmos as the corpse of the Sun itself collides with the “Central Star” – a speculation of the 19th Century that eventually gravity would bring everything together, at least in this “Island Universe”. But that fate is for much later than “The Night Land”…

Iron and Oxygen: A Tale

The Iron Record Of Earth’s Oxygen / Science News.

Oxygen and iron can both exist in aqueous solution, but not together in great quantities. Instead they form insoluble oxides that precipitate out i.e. they make rust! Earth’s oceans haven’t always been as iron poor nor as oxygen rich as they are today. For about 2 billion years – from about 4.4 Gya to 2.3 Gya – they were full of dissolved iron and short on oxygen. As the Science News article, linked to above, reports new research is giving us deeper insights into the “Great Oxygenation Event” of that post-Archean, early Paleo-Proterozoic Era. For example, about 2.316 Gya enough oxygen had built up to form an ozone layer, fundamentally changing the prospects for life ever since.

Geological understanding is built on applying what we know of present day processes to past events – a maxim usually put as “the Present is the Key to the Past”. One present day key-to-the-past is an oxygen-poor lake in Indonesia. Its surface waters are oxygenated, but short on nutrients, then below ~120 metres the water is full of dissolved iron, no oxygen and alive with “photoferrotrophs” – bacteria that use photosynthesis to get energy from oxidising dissolved iron. They live by rusting the iron in the deep lake waters. A feature of the early days of oxygen’s rise are “Banded Iron Formations”, BIFs, from which most of the world’s commercial sources of iron/steel are derived. Basically BIFs are huge rust deposits and the “photoferrotrophs” of the Archean/Paleo-Proterozoic seem to be partially responsible.

What a strange, and humbling, debt we owe to such obscure bacteria. Their metabolic wastes are the ruddy feedstock of the first stage of manufacturing many of modern day industry and construction’s products. The steel skeletons of the Colossii of a modern City come from bacterial chemistry concentrating iron oxides over millennia. And frequently BIFs show a banding effect, now believed to have been caused by seasonal chemistry changes – more rust deposited in warm weather, more silica in cold. But the BIFs keep many more mysteries that geologists have yet to tease out of them…

Brightside of Meteorite bombardment & Junk DNA

Meteorite bombardment may have made Earth more habitable, says study.

Saved by Junk DNA.

The Origin of Life on Earth is a puzzle that biologists, biochemists, physicists and geologists – to name a few – have chewed on over the past 150 years since Darwin opened up the conceptual doors and let in the refreshing light of natural selection. One related question is just when was Earth first inhabited and habitable. The first study above seems to indicate that both Mars and Earth were made more clement by that last gasp of accretion, the Late Heavy Bombardment, which pounded the Inner Planets some 4.0-3.9 billion years ago.

How so? The infalling meteorites released both water and carbon dioxide, thus wetting & warming both planets, perhaps sufficiently for liquid water to remain stable on the open surface. Prior to that event, water may well have been mostly frozen. There’s good reason to think that the process of making long-chains of biomolecules, an important step before ‘Life’ itself, was via concentration of smaller sub-units within ice. Tiny channels of unfrozen liquid become increasingly concentrated in solutes as watery solutions freeze, providing an accelerated reaction environment for polymerisation. In such conditions even quite short pieces of RNA become capable of ‘ligation’, the fusing of RNA sub-units into longer chains.

Once RNA Life has given way to DNA Life what drives the evolution of ever longer strings of DNA and thus ever more complex Life? The second news piece is about evidence that so-called ‘Junk DNA’ – mostly repetitive segments of DNA with no obvious function – actually promotes faster evolution of organisms by altering the rate of gene mutation and gene expression. It seems the ‘Junk’ can make a gene’s DNA sequence more exposed and liable to change when the ‘Junk’ situated next to it has changed in length.

But there’s always a trade off. ‘Junk’ DNA is reduced in some organisms, very noticeably in birds, while it has immensely expanded in some organisms, like certain plants and slow-living creatures like amphibians and lungfish. One’s pace of life style has a distinct selective role on ‘Junk’ DNA’s quantity – fast-living reduces its presence, and perhaps its selective advantage. Birds need to rapidly churn out proteins from their DNA genes and operate at a higher blood temperature too. This might make the DNA more liable to change – birds are immensely speciose – without any ‘Junk’ DNA putting pressure on genes at all. Lungfish, and their kin, live ‘cold-blooded’ rather sedate lives, and carry around a large load of ‘Junk’ that ensures their DNA remains healthy, making the invasion of ‘DNA’ parasites, like viruses, much harder because the host DNA is already full of virus-like ‘Junk’.

What the Hell is a Polytrope?

polytrop.pdf (application/pdf Object).

This little pdf file covers some interesting properties of polytropes – but what’s a polytrope? Basically it’s a sphere of gas, or some other matter, governed by a particular equation of how the pressure and the density are related.

P = K.(rho)1+1/n

…(rho) being density, P is pressure, K is a constant, and n is the polytropic index.

This equation is used to create an expression for the structure of the sphere that is converted into a differential equation, the Lane-Embden equation, which then can be integrated. Polytropes of n = 3/2 are used to model brown dwarfs and planets, for example, while polytropes of n = 3 are used to model stars like the Sun. Both need to be computed numerically as closed form solutions only exist for n = 0, 1 & 5.

The paper referenced above derives an expression for the gravitational binding energy of a polytrope of arbitary index. And it’s surprisingly easy…

(Omega) = -[3/(5-n)]*GM2/R

…thus a sphere of constant density (n=0) is -(3/5)*GM2/R,
n=3/2 case is -(6/7)*GM2/R,
and n=3 case is -(3/2)*GM2/R. What that means is that the Sun has squeezed into it about 5/2 times the potential energy that you’d expect from the Kelvin-Helmholtz solar model. If its energy derived from gravitational contraction then it has about 50 million years stored up inside it in its current configuration.

A puzzle of stellar structure, prior to the breakthrough that was relativity and quantum mechanics, was what was stopping a star from collapsing forever? Nothing seemed strong enough to hold back the inexorable squeeze of a star’s own gravity.

Helium-burning Puzzler

The Triple-Alpha fusion process “burns” helium-4 into carbon-12 and powers stars on the Helium Main Sequence, the short-lived and bright After-Life of a star when it has exhausted its Core hydrogen and is reborn through the Phoenix-like pyre of the Red Giant Branch. A standard Triple-alpha process code, NACRE, reproduces the Red-Giant Branch neatly and has enjoyed a lot of support, but it is only approximate. This prompted Kazuyuki Ogata, Masataka Kan, and Masayasu Kamimura (OKK) to try to compute the Triple-alpha process over a range of relevant temperatures using more exact computational tools, thus producing a new temperature-reaction rate profile for the process. Now Aaron Dotter and Bill Paxton have given the new profile a test-run by using it to compute the evolution of low-mass stars, with surprising results… basically the ‘disappearance’ of the Red-Giant Branch (RGB) and an exceptionally long-lived, cooler Helium Main Sequence (HMS).

This is a seriously wrong result because the RGB and HMS are observationally very well circumscribed stages in stellar evolution – we would’ve noticed a cooler, longer HMS by ten times more stars actually in it, and we would’ve certainly have noticed a dearth of stars in the RGB. Looking deeper at the OKK profile the authors noticed it allowed a much earlier and cooler onset of helium burning at 30 million K rather than the NACRE derived 80 million K. This has dramatic consequences as helium burning is exquisitely sensitive to the temperature, which drives the RGB stage – basically the star is in a runaway nuclear reaction as its core collapses and heats up, ending only in the “Helium Flash”. The OKK profile still produces the Flash, but with a lower peak output and milder entry onto the HMS.

So the audience are now wondering: Can the discrepancy be resolved? Can theory and observation ever meet? Stay tuned…