Why I think Mars One is a really stupid notion

I posted last week about the silliness of trying to colonise Mars on a one-way basis, unless you’re sending Justin Bieber.

Sure, most colonists here on Earth made the trip one-way. But Earth’s way more hospitable. Even Roanoke. You can breathe the air, for a start.

Artists’ impression of the Orion EFT-1 mission. NASA, public domain. Eventually, Orion may be part of the system that takes us to Mars – and brings us back.

Mars – that’s another planet. It has red skies and blue sunsets, temperatures that make Antarctica look summery, and surface air pressure about 0.6% that of Earth, though that’s academic because it’s mostly carbon dioxide anyway. Mars also has no magnetic field, which means the surface is irradiated from space. Then there’s the dirt, which the Phoenix lander found was saturated with naturally-formed perchlorates. Know what perchlorate is? Rocket fuel. It’s nasty stuff, it’s toxic, and the chances of keeping the habitat clear of it after a few EVA’s seems low.

The biggest problem is that nobody’s been there yet. There’s bound to be a curve ball we don’t know about. It’ll be discovered the hard way.

That was the Apollo experience forty years ago. It turned out lunar dust is abrasive and insidious. As early as Apollo 12, astronauts found dust in the seals when they re-donned their suits for a second EVA – moon-walker Pete Conrad reported that ‘there’s no doubt in my mind that with a couple more EVA’s something could have ground to a halt’. All the later Apollo astronauts hit it; leak rates soared in the suits as dust worked its way into the sealing rings.

I think it’s safe to say something of equal practical difficulty will be discovered about Mars, one way or another. Not good if you’ve just arrived – permanently. Besides, what happens if someone gets needs a hospital now? Or is injured? Well, that’s a no-brainer. You can imagine the colony consisting of a cluster of grounded Dragons with a row of graves next to it.

Cut-away of the modified Apollo/SIVB ‘wet lab’ configuration for the 1973-74 Venus flyby. NASA, public domain, via Wikipedia.

Mars One plan to send more missions every two years, each with four colonists to join the happy bunch. If they’re alive. My money says they won’t be. This is Scott of the Antarctic territory – high-tech for the day (Scott even had motorised tractors) but still gimcrack.

The main reason we’ve not gone there yet, despite space agencies making serious plans since the 1960s, is cost. Manned interplanetary fly-bys were (just) within reach of the hardware built for the Moon landings – and until the Apollo Applications Programme was slashed to just Skylab, NASA was looking at a manned Venus flyby for 1973-74, using Apollo hardware.

Composite panorama of Mars. NASA, public domain.

Unfortunately, stopping at the destination, landing on it, and all the rest was another matter. It was easy to accelerate an Apollo CSM and habitat module into a free-return Venus or Mars trajectory; no further fuel was needed, it’d whip past the target at interplanetary velocities, and the CM could aerobrake to a safe landing on Earth. But stopping at the destination, landing and then returning home? In rocketry – whether chemical or nuclear-thermal (NERVA), the two technologies available until recently, mass-ratios are critical.

Mass ratio is the difference in mass between an empty and fuelled rocket at all times, and fuel takes fuel to accelerate it. It’s a calculation of sharply diminishing returns, and the upshot for NASA and other Mars mission planners in the twentieth century was that a practical manned landing mission was going to (a) require a colossal amount of fuel, and (b) would still transit by low-energy Hohmann orbit requiring a 256 day flight each way, meaning more life support, which meant more fuel (see what I mean?).

Some plans looked to refuel the system from Martian resources, but that had challenges of its own. Either way, the biggest challenge in all Mars mission schemes was the first step, lifting the Mars ship off Earth into a parking orbit. No single rocket could do that in one go, meaning multiple launches and assembly in orbit, raising cost and complexity still further. With figures in tens and hundreds of billions of dollars being bandied about, and no real public enthusiasm for space after Apollo, it’s small wonder governments were daunted.

Conceptual art of Philip Bono’s colossal ROMBUS booster in Mars orbit: Mars Excursion Module backs away ready for landing. Public domain, NASA.

My take – which is far from original to me – is don’t try going to Mars now. Focus on building a space-to-space propulsion system that offers better impulse than chemical or nuclear-thermal motors. Do that and the 256-day trans-Mars cruise – which is what drives the scale and risk of the mission, including problems with radiation doses in deep space – goes away. One promising option is the Variable Specific Impulse Magnetoplasma Rocket (VASIMIR), a high-powered ion drive that might do the trick if it works as envisaged. Another is the FDR (Fusion Driven Rocket). Current projections suggest Earth-Mars transit times as low as 30 days.

Of course, if your drive won’t light when you need it to slow down, you’re on a one-way trip out of the solar system. But hey…

Maybe we should send Justin Bieber on that first VASIMIR mission, just in case…

Copyright © Matthew Wright 2015

Yes – a Kiwi might go to Mars, but I still wish it was Justin Bieber

A New Zealander’s reached the short-list of 100 possible candidates for the one-way Mars One mission proposed for 2025-26 by Dutch entrepreneur Bas Lansdorp, co-founder of the project.

Personally I’d have preferred they despatched Justin Bieber and left it at that. But the presence of a Kiwi isn’t bad given that the original long-list ran to 202,586 individuals.

Conceptual artwork by Pat Rawlings of a Mars mission rendezvous from 1995. NASA, public domain, via Wikipedia.

Still, I can’t quite believe the plan. Settlers will be lobbed to Mars in batches of four, inside modified Space-X Dragon capsules. They’ll land, build a habitat based on inflatable modules and several Dragons, and remain there for the rest of their lives. Kind of like Robinson Crusoe, but with all of it beamed back to us for our – well, I hesitate to use the word under these circumstance. Entertainment.

I doubt that the show will run for many seasons. The development timing for the mission seems optimistic – a point I am not alone in observing. There have been a wide range of practical objections raised by engineers at MIT. But apart from that, nobody’s been to Mars before. Sure, we’ve despatched over 50 robots, 7 of which are still operational. But that doesn’t reduce the challenges involved in keeping humans alive in a hostile environment for their natural lives, and I figure from the Apollo experience that there’ll be curve balls along the way.

Those challenges will begin as soon as the colonists are cruising to Mars, a 256 day journey jammed into a 10-cubic metre metal can along – eventually – with 256 days worth of their wastes. Think about it. Popeye lived in a garbage can. The first Mars colonists? Well, they’re going to live in a commode. Hazards (apart from launch-day waste bags bursting on Day 255) include staying fit in micro-gravity and radiation flux. That last is the killer. The trans-Mars radiation environment was measured by the Curiosity rover, en route, and turned out to be – on that trip anyway – 300 millisieverts, the equivalent of 15 years’ worth of the exposure allowed to nuclear power plant workers. A typical airport X-ray scan, for comparison, delivers 0.25 millisieverts.

I suppose the heightened risk of cancer isn’t really an issue, given their life expectancy on Mars (68 days, according to MIT). Though if the sun flares – well, that’ll be too bad. (‘My goodness, what a lovely blue glow. Nice tan.’)

A large solar flare observed on 8 September 2010 by NASA’s Solar Dynamics Observatory. Public Domain, NASA.

Unfortunately the radiation problem continues on the surface of Mars. The planet lacks a magnetic field like Earth’s and its atmosphere is thin, meaning radiation is a threat even after you’ve landed. The answer is to bury yourself under Martian dirt, but Space One’s plans don’t seem to include that. There also a possible problem – which we’ll look at next time – with the nature of that dirt.

Whether the intrepid colonists will get away is entirely another matter. Apart from the hilariously optimistic timetable, the project relies on a modified version of Space-X’s Dragon, which has yet to be human-rated. And then there’s funding, which I understand will come from media coverage. But I suspect the likely barrier will be regulatory. These people will be flying inexorably and certainly to their deaths, and odds are on it will be before the natural end of their lives. Will the nation that hosts the launch permit that?

Still, let’s suppose there are no legislative barriers. And let’s say the colonists get to Mars without their hair falling out or the waste bags bursting and filling the cabin with – well, let’s not go there. Let’s say they land safely. Suddenly they’re on Mars. Forever. What now? And what about those curve-balls?

More next week.

Copyright © Matthew Wright 2015

Searching for that elusive exo-Earth

In the nearly 20 years since Michel Mayer and Didier Queloz confirmed the first known exoplanet around 51 Pegasi, the number of known exoplanets has risen to over 1860 – and there are more to come. The Kepler space telescope, before being hobbled by mechanical failure, created a massive database of planet candidates orbiting the 150,000 stars it looked at – some 4,175 in fact – which are still being checked. Eight new planets were confirmed just last week.

We can be sure there are a lot more out there. Kepler scanned just 0.28 percent of the sky in the direction of Draco, out to 3000 light years. In that patch, it could only detect planets whose orbits cross the disk of their star from our viewpoint. Other planetary systems, tilted at different angles, aren’t detectable by the transit method. But they will be there. And now the hot question – how many planets are like Earth?

Exo-Earth. A picture I made. Apart from fractal artefacts, does anybody notice what’s wrong?

Astronomers have found a few planets Earth-sized and below – including two of last week’s confirmations. Some are in the ‘Goldilocks’ orbit where the star’s warmth would allow liquid water to flow on a planetary surface. Though bear in mind that an observer using Kepler to scan our solar system would classify Venus as “Earth-sized” in the habitable zone. The problem is that transit-detection gives us diameter and orbital period, hence mass and density of the planet (and of its parent star). But it doesn’t give visual data – we can’t do spectroscopy on the atmosphere, for instance, though that’s possible with other techniques, and some data has been fielded about planetary atmospheres.

However, it’s only a matter of time (and money) before instruments are able to pick up more data from subtle fluctuations of stellar light. A photon here, a photon there – literally. From that, we’ll learn about planetary colour, atmospheric composition (via changes to starlight passing through it). Maybe we’ll learn whether any have large moons, if the orbit of that moon is in line with the star. Though I wonder. We’re looking for another Earth – but who says our world has been replicated?

Neptune. A picture I made with my trusty Celestia installation (cool, free science software).

One of the types we’ve found is the ‘hot Neptune’ – a world maybe twice the diameter of Earth with eight or more times the mass. About 19.3 percent of exoplanets found so far fall into this category, as opposed to 5.3 percent of Earth-sized worlds. They also orbit relatively closely to their stars. This is largely a function of technical limits – we can detect the bigger worlds more easily, and picking up the orbits of worlds that are distant from their stars requires years-long observations. So these proportions will likely change. But for the moment that’s where the data points.

Close to its primary, such worlds could be water planets, rather than the ice giants we have in our solar system. Maybe these ‘exo-Neptunes’ define ‘normal’. Or maybe every world is unique – product of many variables, obeying the same laws of physics but emerging in variations defined by subtle differences in composition, size, ambient temperature, and so on. Check out Jupiter’s biggest moons – all different, all formed in the same place at the same time.

The realities of physics mean we won’t travel to these exo-worlds any time soon. Or later (and yes, I know about the ‘Alcubierre drive’). But it’s fun to speculate…and I have a question. Suppose we found another Earth and arrived, en masse. Do you think we’d ruin it, the way we’re making a good job of ruining the Earth we’ve got? Just wondering…

Copyright © Matthew Wright 2015

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Zero gravity day is a total hoax. Email me on 5 Jan to say I’m right.

On 4 January 2015, due to a supposed planetary alignment, Jupiter and Pluto are apparently going to overwhelm Earth’s surface gravity and so allow us to float like the astronauts on the space station.

Anybody see a monolith go by? A picture I made with my trusty Celestia installation – cool, free science software.

It is, of course, total bollocks, not least because the idea began life as an April Fools day joke in 1976, and the exact same hoax did the rounds this time last year. But I’m fascinated by the fact that such an idea can gain traction in the first place.

The sole bodies in the solar system that have human-perceptible effect on Earth are the Moon and the Sun, which cause tides. Even if Jupiter’s effect on us was more than the 0.000037% of Earth surface gravity that it actually is, the only way it could cause us to perceive gravity as ‘nullified’ would be if Earth was somehow a fixed object, nailed down to something else that Jupiter wasn’t pulling on. In other words, if we humans were affected and the Earth wasn’t. As matters stand, the Earth is pulled along with us by other astronomical bodies.

As for the ‘alignment’, Pluto has a mass 0.002 times that of the Earth, or thereabouts (more soon, when New Horizons checks it out). Jupiter’s mass is 317 times that of Earth. Even if they were the same distance from us, Jupiter’s pull is so huge by comparison that Pluto can be discounted. But wait, it’s worse. In December 2014, Pluto was 5.03 billion kilometres from Earth. Jupiter was 739 million kilometres. Gravitational pull operates according to the inverse square law, meaning that if distance doubles, pull drops by a power of two; so even if they were pulling together, which they’re not, Pluto’s pull is so insignificant I won’t even bother doing the math.

And don’t get me started about what ‘zero gravity’ means, versus ‘free fall’, which is what actually gives the impression of ‘floating’ in space.

But hey, who am I to argue the point? We all know that in reality the only way to avert disaster is if you send me all your money. Now. In unmarked bills…

Copyright © Matthew Wright 2015

Orion’s first flight is good news – but can NASA sell the space dream?

I checked the latest space news on Saturday with bated breath. NASA had a lot riding on this week’s Orion flight. In a climate of limited budgets and little real public enthusiasm, failure wasn’t an option.

Artists’ impression of the Orion EFT-1 mission. NASA, public domain.

The problem is where Orion goes next. By Cold War standards ambitions are vague; a couple more test flights, fly around the Moon or go to a captured asteroid by 2021-25, and then on to Mars some stage in the 2030s….eventually. Maybe. Both these aims and the time-frame stand at odds with Apollo-era determination when goals, budgets, public support and intent all meshed. I wouldn’t be surprised if Orion flounders before it gets much further, purely because of that mushiness vs public apathy vs budgetary realities.

Which is a pity, because it’s a good spacecraft and the flight on Saturday demonstrated – after two tragic ‘private enterprise’ failures – that the Apollo-era NASA ‘business model’, which rested on private contractors and commercial suppliers – still works. Rocket science is just that – it’s risky, difficult, and stretches materials science. Cutting corners, private-enterprise style, may save money. But when it comes to spaceflight there’s no room for error.

EFT-1 Orion being prepared to flight atop a Delta 4 Heavy. NASA, public domain.

The other point is that Orion is not – as some critics suggest – a retrograde step. Sure, Orion looks like a 1960s capsule. But it isn’t – it’s stuffed with twenty-first century tech. Don’t be fooled by its 2002-era PowerPC 750FX-based computers, either; space computer hardware has to be well proven and rugged. If it fails at the wrong moment, you die. Armstrong and Aldrin’s Raytheon AGC fly-by-wire computer partly crashed when they were descending to the Moon in 1969. But not totally – and it was safe to land.

What’s driving the illusion of Orion being ‘retrograde’, I think, is that we’re conditioned to imagine space ‘progress’ as ‘advance’ from one-shot cone-shaped ‘capsules’, to multi-use winged spaceplanes designed to fly, literally, into space. They were the future, way back when. Except they weren’t. The problem is that the laws of physics don’t co-operate. Mass is everything in spaceflight – dry mass to fuel mass ratio, in particular. The Shuttle orbiter had to lug a LOT of mass into orbit that was useless up there – wings, tail, landing gear, hydraulics, heat shield and so forth. Dead loss for your fuel budget. And that’s apart from the risks of strapping the spaceplane to the side of its booster.

Orion recovered off California after the flight, 4 December 2014. NASA, public domain.

For anything beyond low-earth orbit, you need a vehicle that lacks the encumbrance of aircraft-style flight hardware – but which can still make an aero-braked descent to Earth, because it’s not practical to carry the fuel you need to slow down by rocket. Ideally the spacecraft also has to generate a certain amount of aerodynamic lift, both to steer the descent and to reduce deceleration forces on the crew. The resulting shape is specific, and Apollo, Orion, the Boeing CST-100 and Chelomei’s 1970s-Soviet era VA re-entry capsule all use virtually the same truncated cone design. McDonnell Douglas’ Gemini, Space X’s Dragon, the Soyuz and Shenzhou offer only minor variations on the theme.

Apollo vs Orion. NASA, public domain.

Orion, in short, is a recognition of the physics of rocket-propelled spaceflight. Budgets permitting, the 2020s should bring a flurry of similar spacecraft into low-earth orbit – Space X’s Dragon and Boeing’s CST-100, servicing the space station. The Russians (hopefully) will be in on the mix with their late-generation Soyuz. And there’s the Chinese manned programme.

Cut-away of the modified Apollo/SIVB for the 1973-74 Venus flyby. NASA, public domain.

Beyond that, Orion will be on hand to fly to the Moon, a nearby asteroid, and eventually Mars. Orion will not, of course, fly by itself on long-duration missions. It’s good for 21 days in space – enough for an Apollo-type jaunt around the Moon – but for longer flights it’ll be docked to a habitat module. This mirrors the 1968 plan to send astronauts on a Venus flyby using Apollo hardware – the crew would have spent most of the 396 day flight inside a modified S-IVB stage, using the CSM only for the launch and re-entry phases.

Artist’s impression of Orion with propulsion and small habitat module for an asteroid mission. NASA, public domain.

Orion, similarly, will be docked with various habitats and propulsion stages depending on mission. The whole stack will become the ‘interplanetary spacecraft’. But all this assumes budget and enthusiasm, among other things (‘other things’ includes finding ways of dealing with radiation, of which more some other time). Bottom line is that state-run space efforts can be killed with the stroke of a political pen.

Perhaps the biggest challenge, then, will be re-selling the excitement of the space dream to a wider public, both in the US and beyond. And this, I think, is where the focus needs to be for the foreseeable future. Space flight is, after all, one of the greatest ventures in the history of the world.

Copyright © Matthew Wright 2014

The really annoying thing about time travel stories

I’ve always wanted to invent a time machine so I could whip back in time to stop Hitler before he did anything evil. Of course there are a couple of problems. First is I’d be joining the back of a LOOONG queue. The other is that our friend Albert Einstein tells us it’s impossible.

But even if a time machine could be built, nobody’s really figured out what it entails. Here’s the deal.

The Horsehead nebula, Barnard 33, as seen by Hubble. Wonderful, wonderful imagery.

Science fiction is rife with stories about time travel, variously either as social commentary, H. G. Wells style, or as cautionary tales – witness Ray Bradbury’s wonderful A Sound of Thunder. Invent a time machine, go back in time and change the past – and you’d better watch out.

Of course, if things change so you don’t exist, then you can’t have invented the time machine. Which means you didn’t go back in time. Therefore you do exist, so you did invent the time machine and… Yah.

Or there’s Harry Harrison’s hilarious Technicolour Time Machine, about a movie maker who uses a time machine to cut production costs on his period drama by going back to the actual period. What I’m getting at is that there’s a gaping great hole in all of this. And it’s an obvious one.

Suppose you COULD time travel. Suppose you’d built a machine to do it. You decide to whip back twelve hours. And promptly choke to death in the vacuum of deep space.

OK, so it’s not a time machine, but this is what one SHOULD look like. Nikolai Tesla, being spectacular with AC electricity (he’s reading a book, centre left). Public domain, from http://www.sciencebuzz.org/ blog/monument-nearly-forgotten-genius-sought

What gives? The problem is that everything in space is moving. Earth is rotating. Earth also moves around the Sun, which itself is orbiting the galaxy, which itself is moving as part of the Local Group, and so forth. We don’t notice or even think about it because we’re moving with the Earth. If we take Earth as our reference point, it’s fixed relative to us. And that leads us to imagine that  time machines are NOT moving through space – Wells, in particular, was quite explicit that his time machine was fixed and time moved around it.

But actually, a time machine that did this – that stayed ‘still’ relative to Earth would have to move through space, because Earth is moving.

Let’s reverse that for a moment. What say your time machine doesn’t move in space at all. You move back and forth through time, but your absolute spatial position is fixed. Not relative to Earth, but relative to the universe.

You leave your lab and leap back 12 hours. Earth won’t be there – it won’t have arrived. Leap forward 12 hours – same thing, only Earth’s moved away. If you’ve only moved a few seconds, you might find yourself plunging from a great height (aaaargh!). Or buried deep in the Earth (choke).

So for a compelling time-machine story you need to have a machine that not only travels anywhere in time, but also anywhere in space. And, of course, any relative dimensions associated with both. That’s right. A machine that travels anywhere through time and relative dimensions in space.

Heeeeeey, wait a minute…

Copyright © Matthew Wright 2014

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Why this week’s comet landing is way better than celebrity butt-fests

This week’s landing on Comet 67P/Churyumov-Gerasimenko was a landmark in space history – not because the comet apparently bore a passing resemblance to the Kardashian backside that was competing for place in the news, but because surface gravity on 67P is about one millionth Earth’s. You don’t land so much as drift in and try like hell to stay there.

Potential landing sites on the double-lobed Comet 67P/Churyumov-Gerasimenko. Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Add to that the fact that the cometary surface is like a rugged boulder-field and you have a recipe for Ultimate Challenge. That’s what made the landing so risky – and why ESA’s Philae lander was equipped with harpoons, ice-screws, and a down-firing thruster. When they failed, Philae landed on the comet, then bounced a kilometre back into space before the comet’s lazy gravity pulled it back. It was also a funny sort of bounce because the comet isn’t a sphere – it’s more like a dumb-bell. When Philae came down a second time, it bounced again before eventually settling.

For me the three-bounce landing (at 15:34, 17:25 and 17:32 GMT on 12 November) has a wow factor well beyond landing on a comet for the first time e-v-a-h. It’s also about gravity – and that means it’s about Einstein, one of my favourite physicists. Let me explain. Gravity doesn’t just cause celebrity butt-sag, after a while. It’s also why the comet’s where it is today. Fact is that 67P/Churyumov-Gerasimenko experienced a gravitationally-driven orbit change in 1959, when an encounter with Jupiter dropped its perehelion (closest approach to the Sun) from 2.7 to 1.3 astronomical units, giving the comet its current 6.45 year period. That’s why it’s where it is now.

Gravity is also how ESA got the probe to the comet. It was boosted, during a decade-long journey, by gravity assist manoeuvres, swing-bys of Earth and Mars that exploited space-time curvatures around the planets to accelerate the probe (three times) and decelerate it (once), without burning a single gram of fuel.

Ain’t physics neat. So just what is gravity? This looks like a stupid question. Actually, it isn’t.

Rosetta’s long odyssey to the comet – with slingshot gravity boosts from Earth and a de-boost from Mars. NASA, public domain.

The thing is, we think of gravity as a ‘force’. But actually, according to Einstein, it isn’t. We just perceive it as such. Here’s why. Science started looking at gravity in earnest when all-round super-geek Sir Isaac Newton worked out the math for the way gravity presented in everyday terms, which he published as part of his Philosophiæ Naturalis Principia Mathematica in 1687. His gravitational theory worked (and still works) well at everyday level – you could calculate how apples might fall, figure out planetary movements and so on (the key equation is    , which defines the force between two point-sources of defined mass.) Newton’s triumph came in 1838 when astronomers realised that Uranus wasn’t quite where it should have been, based on the tugs of the known planets. French mathematician Urbain Leverrier and British mathematician John Couch Adams, independently, reverse-engineered the data to pinpoint where an unknown planet should be – and sure enough, there it was. Neptune.

Albert Einstein lecturing in 1921 – after he’d published both the Special and General Theories of Relativity. Public domain, via Wikimedia Commons.

But as science began fielding more data, it became evident that Newton’s equations didn’t account for everything – which is where Albert Einstein comes in. His General Theory of Relativity, published in 1917, is actually a theory of gravity. General Relativity supersedes Newton’s theory and portrays gravity by a totally different paradigm. To Newton, gravity was a force associated with mass. To Einstein, gravity was not a force directly innate to mass, but a product of the distortion of space-time caused by mass/energy, which bent the otherwise straight paths of particles (‘wavicles’), including light.

The proof came in May 1919 when British astronomer Sir Arthur Eddington measured the position of Mercury during a solar eclipse. Mercury’s perehelion – the closest point to the Sun – precessed (moved) in ways Newton couldn’t account for. Einstein could – and the planet turned up at precisely the place general relativity predicted. Voila – general relativity empirically proven for the first time. I don’t expect that Einstein leaped around going ‘woohoo’, but I probably would have. And general relativity has been proven many, many times since, in many different ways – not least through the GPS system, which has to account for it in order to work, because space-time distortion also causes time dilation. (If you want to live longer, relative to people at sea level, live atop a mountain).

Einstein’s key field equation, as it eventually evolved, is  – which I am not going to explain other than to point out that it could be used to calculate the space-time distortion caused by the mass of, say, a Kardashian butt. This would be a hideous waste of brain-power, but at least means I’ve managed to put both Einstein’s field equation and a reference to society’s shallow obsession de jour in the same sentence. As an aside, I also think Einstein got things right in more ways than we know. I don’t say this idly.

Philae departing the Rosetta probe for its historic rendezvous with the comet. Taken by the orbiter’s OSIRIS camera. Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

One of the key things about both Newton and Einstein is that their theories treated clumps of particles – a mass such as the Earth for instance – as if the gravity originated in a mathematical point at the centre of the mass, even though the gravity (‘space-time distortion’) is produced by every particle within that mass. And that works perfectly at distance. But in detail an uneven distribution of mass –  a mountain range, for instance, or even a celebrity butt – can introduce local pertubations. Small – but calculable. It’s because of ‘mass concentrations’ that satellites we put around the Moon eventually crash, for instance.

Which brings me back to the science adventure on 67P/Churyumov-Gerasimenko, 28 light-minutes away outside the orbit of Mars. With a long-axis diameter of around 5 km and a composition of loose rocks held together by ices, 67P/Churyumov-Gerasimenko doesn’t have enough mass to bend space-time much. It has, in short, almost no gravity. Orbiting it, as Rosetta has been doing since 6 August, is more like a lazy drift around it. To land is more akin to docking than anything else. There’s not a lot to hold Philae ‘down’, and it doesn’t take much to bounce off. To that we have to add the dumb-bell shape of the comet’s nucleus, which produces complex (if gentle) space-time curvatures, meaning a ‘bounce’ on the comet isn’t going to be a simple parabola like a ‘bounce’ on Earth.

All of which underscores the tremendous technical achievement of the landing – bounces and all. The final lesson? Don’t bother with celebrity butt. Einstein and comets are FAR more interesting.

Copyright © Matthew Wright 2014