Category: Starflight

All matters interstellar

Did Gaia birth Selene?

How did the Moon get here? Charles Darwin’s grandson, George, theorised that the Moon was spun off from the Earth, leaving a gaping hole we now know as the Pacific. Others theorised the Moon was captured from an independent orbit, or that the Earth and Moon somehow formed together.

Then in 1975, after Apollo and the first round of science results from studying Moon rocks, William Hartmann and colleagues proposed that the Moon was brutally bashed off the Earth by another planet. Since then this theory has come to dominate the debate, and has been refined, with the impactor being dubbed “Theia”. But there’s a problem. Theia had to impact the proto-Earth (call her “Gaia”) with almost no energy excess – in other words it didn’t ram the Earth, but merely fell into its gravity well.

Another puzzle is just how the various isotopic balances of the two, Earth and Moon, became so alike after such violent smashing together – according to the simulations the Moon accreted out of mantle material from Theia, not from Gaia. Yet the two are near identical. A sore puzzle indeed, implying they formed together at the same radial distance from the Sun.

Finally, for the two to form in the same region of space and for Theia to collide at such low energy, then she must have formed as a co-orbital of the other. In Gaia’s L4 or L5 point what become Theia formed, then the orbital arrangement destabilised when Theia’s mass exceeded about 1/24th of Gaia… but it had to accumulate something more like 1/10th of Gaia’s mass before the two collided. How did it survive an unstable orbital arrangement for so long?

How to reconcile the two? According to the work of Rob de Meijer, an ex-nuclear engineer now a nuclear geophysicist, and Wim van Westrenen, experimental geochemist, the solution comes from within Gaia. According to isotopic balances of various rare earth metals, the Core Mantle Boundary formed within 30 million years of Gaia forming. At this point in time natural radioactives – uranium 235 & 238, thorium 232, and plutonium 244, were present at much higher levels than the present day. A massive fast-breeder style runaway reaction occurred which vaporised a vast bubble of mantle material. This rose rapidly, as per Archimedes principle, and flung immense amounts of mantle rock and vapour into space, out to 100,000 kilometres. The debris mostly went into orbit and formed a heavy ring around the Earth which congealed into the Moon, with perhaps an extra Mini-Moon or two that eventually fell back. The theory is detailed in a Cosmos Magazine article from August 2008, but which has just gone online for all to discuss.

According to the study by de Meijer and van Westrenen the proto-Earth object had a spin of 2.3 hours, but once the Moon was expelled a large fraction of the angular momentum was transferred to it by tidal forces. This would have occurred pretty rapidly in the early stages as a semi-molten Earth would’ve allow a massive whole-body tidal response, rather than the much lower oceanic response that has dominated tidal dissipation to the present day. Once the Moon had moved out to ~200,000 km the response would’ve slowed and followed the more sedate tidal dissipation regime recorded in tidal rythmites through-out the Archean, Proterozoic and Phanerozoic geological record.

Speculations:

  • Did Venus birth Mercury? Venus is somewhat enriched in actinides (i.e. uranium and thorium and kin) relative to Earth, so a “Big Bang” there would’ve been *BIG*.
  • Was the bang given more *OOMPH* by variable speed of light, as per Louise Riofrio’s Variable-Cee cosmology? The Sun was potentially warmer due to higher c, so could the energy have been higher from uranium fission.

    • Only time will tell.

    ERRATUM
    Contrary to my opinion Venus isn’t enriched in Uranium & Thorium – data from Venera 8 showed enrichment, but this was anomalous compared to all the other landers that have since followed, Veneras and Vegas. Apparently Magellan’s SAR imaging data shows us that Venera 8 landed on a volcanic outflow rather different to all the other lander sites, so the observed enrichment is peculiar to that location, not Venus.

Carnival of Space #81

Yep, it’s up at Tiny Mantras… diverse as always. Check out David Portree’s Altair VI and his two-part post on Phil Bono’s MarsGlider of 1960 (and Part 2) which landed, in some other Universe, in 1971.

Not at the Carnival, but worth a look is Murray Leinster’s 1946 (!) SF story that prefigured the Internet: A Logic Named Joe… he called it so well, even if his singular invention of the computer didn’t happen.

Icy Planet Bonanza

Seems Edgeworth-Kuiper Belts are more common than regular star-systems, at least around A stars…

Universe may abound with icy planets (from COSMOS magazine.)

…A stars are like Sirius A and Fomalhaut (stellar celebrity with a planet now spotted by the HST), substantially brighter than the Sun, not heavy enough to get dramatic and go SuperNova. Instead they race through the Main Sequence and become Red Giants in less than a billion years. So while the belts of Icy Planets are currently chilled, eventually they will melt down and become rather nice for a few million years before their stars sputter out.

The Cost of SETI & METI

The Search for ExtraTerrestrial Intelligence and Messaging ExtraTerrestrial Intelligence are about 50 years old as a proper scientific endeavour – the first published paper was in 1958 and the first SETI was in 1960. But the Search has come up empty handed. However before we conclude ETIs are rare to non-existent we should ask ourselves if we’re conducting the Search in a reasonable manner? Have we considered the best strategy? Or has SETI been driven by wishful thinking divorced from economics?

Twin brothers James & Gregory Benford, plus Dominic Benford, have argued that Searching and Messaging driven by cost considerations (in a very general sense) won’t look anything like the hoped for (and unseen) Great Blindingly Obvious beacons, and will look a lot like the brief flashes of radio-energy seen so far…

Cost Optimized Interstellar Beacons: SETI
Cost Optimized Interstellar Beacons: METI

…following the current work on the Galactic Habitable Zone, and the Extra-Galactic Cosmic-Ray Periodic Death Scenario, the authors argue that searching and messaging should focus on the Galactic Core and stick to the Galactic Plane. This also reduces the total energy needed and increases the odds of a message finding a receiver.

Forming Planets: part1

The Gemini telescope has spotted a possible planet around another star… First Picture of Likely Planet around Sun-like Star …though its mass range and orbit are extreme for it to be called a planet. Firstly it masses somewhere between 7 to 12 Jupiter masses (8 being the most likely), so it’s close to the deuterium-burning mass of 13 Jupiters, which some see as the natural line between ‘planet’ and ‘brown-dwarf’. Still it’s not burning deuterium or anything else, so a “planet” is a reasonable box to put it in.

But it’s also 330 AU from its primary (see this table) and that’s rather far out for a planet proper to form. Anthony Whitworth and colleagues have developed a model that quite efficiently makes such objects… Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs …and also showed, as much as an SPH model can, that nothing much forms via disk-instability closer than 40 AU… Can giant planets form by gravitational fragmentation of discs?

That does seem like a natural division – planets form via core accretion within 40 AU, brown-dwarfs via gravitational instability further out. Except forming planets via core accretion is yet to jump the very important hurdle from dust to planetesimals. After that everything works, but the small details are still recalcitrant to the best efforts of the theorists! Andrew Youdin gives a lecture on the current problems facing theorists like himself… From Dust to Planetesimals

Carnival of Space: Week #68 …star-travel won’t be easy

Welcome to the Carnival of Space, brought to you this week by Crowlspace and the never-tiring efforts of Fraser Cain and Universe Today. First cab off the rank is musings by Paul Gilster (Centauri Dreams) who ponders the difficulty of interstellar travel as depicted by Robert Frisbee who brings us the 160 million ton antimatter powered starship (see this old “Discover” magazine piece Star Trek for more details.) “Crowlspace” also covers Frisbee’s rather gloomy prognostications here… Antimatter Ain’t What it Used to Be

Also on theme Brian Wang’s Next Big Future gives another viewpoint on the difficulty of antimatter rocketry and the relative ease of leaving the engines at home and riding a beam… Interstellar Prospects

Next Nancy Houser of A Mars Odyssey ponders the dangerously variable magnetic field of the Earth… A Newly Found Dent in Earth’s Protective Bubble…. Dr.Ian O’Neill puzzles over the folly of media hyping of a radio detection of the Galactic Core… No, An Alien Radio Signal Has Not Been Detected.

The Bad Astronomer blogs at “Discover” magazine on why telescopes haven’t been used to disprove the “Moon Hoax” claims… Moon hoax: why not use telescopes to look at the landers? (as if astronomers don’t have better things to look at anyway!)

Dr. Bruce Cordell of 21st Century Waves draws on the the Lewis and Clark expedition (almost as arduous as a trip to Mars) to get perspective on current space exploration hopes… 10 Lessons Lewis & Clark Teach Us About the Human Future in Space.

From Out of the Cradle just in time for back to school (in the Northern Hemisphere that is), Ken Murphy reviews the new ‘Kids to Space Mission Plans’ designed for teachers and homeschoolers who want to add some space-themed activities to their classrooms… Take an Educational Field Trip to the Solar System. Wish I’d had that 6 months ago 😉

Darnell Clayton’s Colony Worlds poses a pungent conundrum for interplanetary colonisation… Living Off World May Stink … our dreams of humanity expanding throughout our native star system may ultimately come to naught, due to the simple fact that living off world may irritate one of our key bodily members, also known as the nose.

This week David Portree’s Altair VI promotes a new facility for public and professional researchers he’s just opened at the US Geological Survey Flagstaff Science Center:

We Have Liftoff

He also looks at a novel approach to Mars sample collection put forward by Alan Stern in 1989.

Mars Tethered Sample Return (1989)

Ray Villard’s Cosmic Ray asks if arguing over Pluto’s status as a “real” planet is worth the hype… Spirited Pluto Battle, But a Great Debate? Once upon a time there were only 7, including the Sun and Moon. How things change!

OTOH Emily Lakdawalla argues maybe anything studied by “Planetary Scientists” should be called a “planet”… Things that probably won’t ever be called planets, but maybe they should

Simostronomy (Mike Simonsen) looks closer at the good news and the bad news out of a recent cosmogony simulation… Planets – Good News, Bad News …which found only 1 solar system like ours out of 100 simulations. Terrestrial planets form easily it seems, but not in solar systems like our Solar System.

New & Noteworthy at the LPI Library gives us an update on recently available Astrophysics related resources, including the new Portal to the Universe.

The Phoenix Mars Polar Lander spied frost for the first time this week… Phoenix Sees First Frost …courtesy of The Meridiani Journal.

Ian Musgrave, the Astroblogger says Kopf Hoch! Raise your heads people and Look! I did and I saw Venus and Mercury together at sunset yesterday.

Stuart Atkinson, of Cumbrian Sky gives us… Narnia Mars

Bruce Irving’s Music of the Spheres looks back on the Earth from deep space… Distant Mirrors (and Cribsheets)

Aloha Carnival! Says A Babe in the Universe, Louise Riofrio. Last week the Cassini spacecraft made a close flyby of Saturn’s mysterious moon Enceladus: Enceladus Flyby …Cassini was able to localise sources of the water geysers erupting from the South Pole. More heat comes from this little moon than can be produced by tidal
forces or radioactive decay. Louise speculates about other causes, even a Black Hole.

And that’s it for this week! Enjoy, be enlightened and (if you’re in the USA) vote for the right person to lead the Spacewards Vanguard… whoever that might be 😉

Antimatter ain’t what it used to be…

Antimatter annihilation propels the most memorable SF starship of all – the USS Enterprise – between the stars at FTL speeds by powering the manipulation of “subspace”. But what can real matter annihilation do? A naive view would claim an antimatter drive is a photon rocket with an exhaust velocity of lightspeed. The problem with that is that antimatter and matter turn into some seriously nasty gamma-rays. And nothing known can reflect a mega-electron volt gamma-ray. Is antimatter annihilation a hopeless cause then?

Several analyses say otherwise. Robert Frisbee studied the concept a bit more closely for NASA…

Systems-Level Modeling of a Beam-Core Matter-Antimatter Annihilation Propulsion System (Robert H. Frisbee)

ADVANCED PROPULSION FOR THE XXISt CENTURY (Robert H. Frisbee)

HOW TO BUILD AN ANTIMATTER ROCKET FOR INTERSTELLAR MISSIONS

…basically concluding that building the thing was possible, but the performance somewhat poorer than first imagined. So much energy is lost as gamma rays that the effective exhaust velocity he computed was 0.33 c. That’s way, way above the piddling 0.01-0.05 c hoped for from fission or fusion reactions, but a long way from ideal. A major problem was storing the antimatter – very cold anti-hydrogen ice could be levitated due to the residual magnetic field of hydrogen (and anti-hydrogen) molecules, but the storage density had to be very low, maybe 1/10th the density of hydrogen ice (itself just 75 kg/cu.metre.) Another problem was cooling off systems exposed to the gamma-rays produced by the engine. Frisbee’s starship design is very narrow, and very, very long. But he believed a transit speed of 0.25 c was feasible, and allowed a return mission design.

A slightly poorer performance, just 0.2083 c, was derived by Ulrich Walter in his text Astronautics (from Google book preview.) Not bad, but no one is likely to be powering to near lightspeed with any reasonable amount of antimatter. At least with normal matter structures.

Hans Moravec speculated on an interesting material over 20 years ago… Higgsinium …which is composed of heavy, charged supersymmetric versions of the Higgs boson (still undiscovered.) If such could be made in sufficient amounts it could be used as a gamma-ray reflecting material and enable true antimatter/matter photon rockets. However such SUSY particles have yet to be observed – maybe they exist, maybe they don’t. Once the Large Hadron Collider has obliterated enough particles in the TeV range of energies we may well know. Watch this Space for an update in ~2 years.

300+ Exoplanets…

A milestone was crossed, with relatively little fan-fare, just today… there’s now, officially, over 300 exoplanets

Extra-Solar Planets Catalog… 303 Known Exoplanets

…and there’s five new Super-Earths – exoplanets over Earth’s mass. None have known radii so we’ve no idea if they’re rocky or icy or gas, but they’re not as big as the Gas Giants that have dominated discoveries thus far. A hopeful trend towards Earth-like planets, we can hope.

At this point in time it’s just not worth speculating what they’re like. At most we can tell how much sunlight they receive from their primaries, but not much else can be said. Will they be greenhouse wastelands? Planetary steam-baths? Hyperactively volcanic, or tectonically locked in place? Coated in thousands of kilometres of hot ice? Or something utterly unexpected?

All I can say… Watch the Skies!

Gliese 436c

A new super-Earth has been announced around M-dwarf Gliese 436…

Scientists Find Smallest Exoplanet

…now the radius quoted is ~ 1.5 Earth radii. Different mixes of silicates and iron give slightly different indexes (0.272-0.268) for a power-law fit to the mass-radius curve – in this case lets take the average ~0.27, which means the planet is ~ 1.544 Earth radii. Seems the media was listening, which is unusual for a space-science story. Surface gravity would be 2.1 gee so it’s not a long-term habitable planet, but alright for visits in exoskeletons. Just 30 light-years away, so a laser-sail could reach it in ~ 100 years at 0.3 c.

Could humans get there? Another recent news item is further results from earlier studies on H2S gas induced suspended animation (SA) in mice… Rotten egg gas to Save Mars Mission …though that item doesn’t discuss further possibilities of inducing the effect via its metabolites so there’s no direct poisoning via the hydrogen sulphide itself. The research is still too basic to say what the effect on humans will be. Mice are a good start.

Let’s imagine – say the SA effect is like time-slowdown that some writers have imagined. What would that imply? Perhaps a crew could be augmented by smart AI that responds to circumstances faster than the ~ 100-fold slower crew. And what would 1 subjective year be like in induced torpor? Could muscles be used at all, or would that be too fast? Imagine crew in power-chairs controlled purely by (very slow) thoughts, with robotic arms. A normal speed person would be witness to some very strange effects, and would be a blurry figure to a time-slow crew person.

Would you go, if you could? Or some place closer, like Alpha Centauri B’s putative rocky world? That would be at least 30 years round-trip at 0.3 c. Would you risk being cut-off from the rest of humanity for so long? Good telecommunications, via laser, would allow you to keep track, but you wouldn’t be able to contribute to it without a multiyear time-lag. Could you stand the separation? Could you tolerate the same faces nearby for +30 years?