Month: March 2007

ER1470 Reconsidered…

In 1972 Richard Leakey and his team discovered a curious skull, now catalogued as ER1470, and dated it to c. 2.6 million years ago. Leakey reconstructed it as a flat-faced, large-brained hominid and called it Homo habilis, though his co-worker Alan Walker doubted it was flat-faced, or even Homo [see The Wisdom of Bones by Walker and his wife Pat Shipman.] Now it seems Walker was on to something. Dr. Timothy Bromage has used the known developmental sequence of all mammal skeletons, especially the skull, to show that ER 1470 was reconstructed incorrectly, as reported by his University, NYU…
Man’s Earliest Direct Ancestors Looked More Apelike Than Previously Believed …though the title is slightly misleading as there’s some doubt about ER1470’s ancestral status.

Bromage presented his findings at the IADR meeting (March 23-27) in a poster, available here (warning 8.8 megabyte pdf) which is very interesting. The new ER1470 is much more apelike and has a brain capacity of just 526(+/-49) cc, versus the ~ 750 cc of Leakey’s original reconstruction. The new value is much the same as the lighter-built ER1813 skull, 510 cc, compared here with the old reconstruction of ER1470.

BTW fossil hominids have odd sounding catalogue numbers, but what “ER” means is the location of the find, East Rudolph (i.e. Lake Rudolph in Eastern Africa.)

Hiatus

Study looms and blogging is eating into my assignment writing time, so expect very sporadic writings for a few months.

One thing before I go is a topic Paul Gilster from Centauri Dreams mentioned – the hazards for an interstellar high-speed fly-by from interplanetary dust. Daedalus, for example, was to fly through Barnard’s Star’s system at 12.2 % of lightspeed, which gives a massive energy punch to any dust impacts. So I quantified the hazard – in the Sun’s Inner System interplanetary dust masses about 10^16 kg. If every bit was 1 mm cubes, density ~ 2, then the dust masses 2 x 10^-6 kg each, making for about 5 x 10^21 specks of dust. Sounds like a lot, but the volume of the inner 2 AU of the Solar System is 4/3*pi*(3.0E+11 m)^3 = 1.13 x 10^35 cubic metres – 22.6 trillion cubic metres per speck. That’s a cube 28.3 km on a side per speck.

If Daedalus is 50 metres wide (that’s its dust-shield) then it punches a 2 AU long, 50 m wide hole through the dust and encounters about 26 dust specks – each one packing a punch of 1.33 gigajoules (a few kilos of TNT) which isn’t fun, but blown into plasma by the precursor shielding cloud it’s a survivable dose of energy, heating the beryllium shield to about 1000 K. The Daedalus sub-probes are much smaller and probably have a 50/50 chance of an encounter, but they have precursor shield systems too.

For interest sake I also looked at some figures on mass in the Oort Cloud which Robert Zubrin uses in “Entering Space” – his results are seriously in error. He describes the Oort as containing 100 km cometoids about 10 AU apart – sounds spacious, but the Oort is 100,000 AU in radius, thus he’s describing 10^12 cometoids at 100 km in size. Then 1000 times more (i.e. 10^15) 10 km cometoids 1 AU apart each, then 1000 times that number of 1 km comets just 0.1 AU apart… and so on down to 10 cm chunks just 1,500 km apart. 7 orders of magnitude, giving a total mass of 7 x 10^30 kg (3.5 solar masses!) for comets of 500 kg/m^3 density.

That’s ridiculous! Long period comet orbits wouldn’t be anything like stable, or long period with that much mass out there. In actual fact the total mass is usually quoted as 40 – 30 Earth masses – about 30,000 times less than Zubrin’s wild figures. Fortunately for us, or else we’d have a sky full of comets all the time and mass extinctions every ~ 3,000 years. The real Oort Cloud is very wide open spaces…

Ok. Bye for now!

Alpha Centauri Rising

Tonight the Two Pointers and the Southern Cross were rising not long after sunset – have missed them in the sky. I always look wistfully at Alpha Centauri – the Brightest Pointer – and think it’s only a cosmic stone’s throw away… all 40 trillion kilometres of a throw *sigh*

Back on Topic

Multi-bounce laser-sails

Crowlspace is chiefly about spaceflight and cosmic things, but the Tomb stuff has popped up, so I felt compelled to write. Back to the central topic now… a new idea has arisen for pushing things around with lasers – why not recycle the laser beam itself? This idea was recently discussed at Centauri Dreams and references a paper by Robert Metzger and Geoff Landis, which looks at an Earth-Mars mission using multiple-reflection.

Apparently ultra-reflective surfaces for a given frequency are now feasible – we’re talking 99.99995% of all the energy of a beam being bounced off the surface. That’s enough to allow many thousands of bounces of the beam itself, between laser and target, thus boosting the effective momentum transferred by the beam’s energy. It takes 150 MJ to give a 1 Newton impulse to a perfect mirror, but if the beam could be bounced 20,000 times, losing a bit of energy as heat each time, then the effective force multiplies about 10,000-fold. Of course the effective path-length goes up 20,000-fold, so the acceleration distance has to be pretty short too before the diffraction limit spreads the beam out too much.

In the Metzger/Landis example the boost is assumed to be 1,000-fold and the diffraction-limit gives a boost range of 210,000 km for acceleration at 0.33 m/s^2, boosting the laser-sail/payload of 20 tons to 12 km/s. That’s enough for an Earth-Mars transit in 96 days, which is pretty respectable. The energy cost works out at $240/kg, supplied by a couple of reactors at Earth and Mars. There’s no reason why nuclear reactors are required as Landis himself has posited designs for 3 GW (in-space power) Solar Power Satellites that mass a mere 1,300 tons. With 70% efficient concentrator solar cells the mass is halved, and for just a GW of power the mass drops to a mere 200 tons. Lighter than a GW reactor, unless it’s an open-cycle gas-core reactor, which by itself would make a good rocket.

A 10 ton payload may not sound like much, but it’s 1/3 what the Shuttle laboriously hauls into orbit when fully loaded. A lot of payloads launched fast would make the system worthwhile, and that’s the main point. Also payloads boosted into near-Hohmann transfer orbits requiring a mere 4 km/s could mass 90 tons over the same boost distance and that’s serious payload on an interplanetary trajectory.

Jesus Tomb… or Otherwise

Well the Tomb has sunk like a lead balloon and leading the charge has been other archaeologists – basically the people involved in the Jesus Tomb have overstated the case for its contents as the mortal remains of JC and kin. Fair enough. Do a Web-search and you’ll find plenty of arguments about the Tomb, which is interesting by itself. I think the most telling argument is the recent revelation that the James Ossuary was photographed in 1976 before the Talpiot Tomb itself was discovered in 1980. So it can’t be the putative missing ossuary, thus knocking one support out from under Jacobovici and Cameron’s case. Another problem is that the name identified as “Yeshua” could equally be “Hanun” as the inscription is hard to read. This kind of militates against their central claim, that it’s Jesus’s family – Marys and Josephs are a dime a dozen in First Century Jewish family plots.

Oh well. It was a nice prospect while it lasted – archaeological proof of a mortal Jesus. Now we’re left with two competing faith claims – that dead people don’t rise, and that God raised Jesus on the Third Day. The latter seems more an act of faith than the former, but it’s hard to refute the claim that JC was reported to have left his tomb empty by his closest friends and followers. All the textual evidence tells us that the tomb discovery was followed by apparitions of the Risen Christ – though the nature, number and location varies from Gospel to Gospel.

I’ve already said that I think the tomb was found emptied, but it took time for the Risen Christ to be believed – Mark and Matthew make this pretty clear, since both locate the apparitions squarely in Galilee. Luke and John are more problematic for my view, but both are rather at odds with the first two Gospels. Why the disparity? And why does John feature a major appearance to Peter, and his old business partners, in the Sea of Galilee when Luke doesn’t if they’re drawing on the same source events?

Yet having said that I have my doubts about the skeptical case for a dead Christ too. Chief amongst my “doubts” is the enigma that is the Shroud of Turin – which recently has been proven somewhat older than the 1988 radiocarbon dating first implied. Apparently the samples for the dating had all been taken from a Medieval patch – the rest of the cloth itself is much older, as measured, albeit roughly, by a biochemical clock related to the aging of the fabric.

The Shroud itself proves that a dead man was in it, but why it became associated with JC is because of the unique wounds the Shroud Man bears – multiple lacerations to the forehead (i.e. Crown of Thorns) and the bleeding wound in his side. Plenty of other people had been crucified and scourged by the Romans – also seen on the Shroud Man – but the extra abuse of the victim is surely unique. But if the Shroud Man is JC then why isn’t the Shroud mentioned as an amazing sign in the Gospels?

Isn’t it?