h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Like me, you may be watching with interest the news reports of that probe landing on the comet, codenamed 67P. At the time of writing, it appears to have landed safely, although it looks like it bounced a couple of times first. If so, I'm looking forward to seeing what the thing's going to do next.

This project has been going for over 20 years, I understand. I guess at the outset they wouldn't have known a lot about the comet they were going to land on. It's only in recent years that we've seen it to be a giant rotating knobbly thing - from one angle it looks like a rubber duck, but I think it's a perfect potato shape. This must have caused an immense amount of replanning, but it seems that their design of this washing-machine-sized craft has been able to cope with all the new complexities they have discovered along the way. Even if the mission achieves little more, it must be seen as a huge triumph for the scientists and engineers involved.

If there's one thing I'd like to ask our h2g2 astronomical experts, it's the claim that comets may once have brought water, and hence the conditions for life to planet Earth in its distant past. How much water can a comet hold? Is it really enough to fill all of Earth's oceans?

The latest news is that the probe landed in the shadow of a cliff, so its solar panels are inoperative. Its batteries will run out tomorrow, so they're desperately trying to do as much science as possible in the limited time available.

I believe that there are hundreds of tons of water asteroids crashing into the Earth every day. These mainly strike the oceans.

Don't tell me they're having problems with Cliff and the Shadows?

Radio 4 this morning had an introduction from the Clangers children TV programme as part of the hype around this probe. Apparently Justin whatever-he's-called is obsessed with the Clangers.

The thing about the water in these asteroids, wouldn't it more likely become so hot on entry and become water vapour and rain?

That thing about water asteroids is fascinating (maybe you could write an entry on it?)

http://www.smithsonianmag.com/science-nature/how-did-water-come-to-earth-72037248/?no-ist

It makes me want to do the maths about how much water we would have needed delivered daily by asteroid since the Earth cooled - in order to fill our oceans?

(any takers?)

I've actually been to ESA in Darmstadt, in case anyone's interested.

F56786?thread=8293955

(Icy and I are the only ones in that thread!)

I thought the latest news was that this comet was really an alien spaceship, and it's talking to us?

That is incredibly sad, that it is in shadow and can't recharge itself. Will it come out of shadow, or does the comet keep the same aspect to the sun?

Sure, they have achieved more than any previous shot already, but they had the potential for a lot more.

[Amy P]

Let's keep our fingers crossed.They might come up with some plan for moving it.

"When a meteor enters the atmosphere friction causes ablation of its surface (i.e. it burns up). If the meteor is small (fist-sized) it vaporizes before hitting the ground. If larger it survives to impact on the ground, although it will be reduced in size during entry into the atmosphere. About 25 million meteors enter the Earth's atmosphere every day (duck!). Most burn up and about 1 million kilograms of dust per day settles to the Earth's surface."

http://abyss.uoregon.edu/~js/ast121/lectures/lec18.html

So, yes, space debris does hit the Earth's atmosphere, but it has to be fairly big in order to "crash into the oceans." Friction form the atmosphere whittles the size down considerably.

Philae is not doomed yet. It does still get sun exposure for 1.5 hours a day rather than the 5-6 they were expecting. They could put it in sleep mode and wait until it gets nearer to the sun and gets more sunlight. Or, when they get more info about the lander's exact position they could make some attempts to alter its position (although I did hear that they may have screwed it down already, so maybe not).

Oh, also I followed the landing live(ish) via XKCD, an excellent, stick figure based web comic. Here is an archive of all 142 updated pages he posted during the event.


http://xkcd1446.org/#0 You can use the right arrow key to step through it.

At 5:00 today Philae's twitter feed announced that they successfully rotated the lander by 35° allowing it to get much more sun exposure.

And here was me wondering if they'd be sending up mirrors or diamond-studded satellites to reflect light down on to the right side of the comet....

Philae has shut down now. Managed to send back some important info though and may have got some samples. I did wonder how they were going to get the samples back to at first but apparently the equipment to analyse it is all on board, although I reckon they'll need to recharge the batteries to do that.

I don't believe comets brought Earth's water, in fact I think it's a miracle this planet is just right in every way for humans and animals, and supplies all our needs. Who or what supplied the miracle remains a mystery to be resolved. For the moment I'll go along with the journey, whatever you want to call it, and play the game.

GB

Miracle or no miracle, the more we see of the rest of the universe the clearer it is that this planet is truly paradise, and the only paradise we can reasonably hope to encounter. And what are we doing to it?

Pressure of population

The Earth still has some amazing stuff. It would take some doing to ruin *all* of it, but some folks are giving it a shot anyway.