Source: Image courtesy K. Churyumov

The photo above was taken by Klim Churyumov on 21st September 1969 using a big telescope in Kazakstan whilst on a comet hunting expedition with one of his researchers, Svetlana Gerasimenko. It is of course our friend comet 67/P Churyumov-Gerasimenko and this was our first glimpse of it when it was discovered by these two astronomers. They had no idea of course that 45 years later we would be sending a robot spacecraft to orbit and then land on it.

The European Space Agency have funded a short film that explores how important the Rosetta mission might be to us, the human race, in the future. It is a bit dramatic for my personal taste, but still good. Watch it on a big screen with the volume up if you can and press the enlarge button on the video controls at the bottom right of the video below:



So far, Rosetta has been an amazing success. Just like the guy says in the film, all sorts of things could have gone wrong before it arrived at the comet but amazingly they haven’t. It isn’t just about what we have learnt already and what we might learn over the next year whilst the mission continues. It is also about the fact that we’ve had the ambition and bravery to actually do something so difficult and get this far.

How old is our planet, Earth? It’s old. Really old. Mind-staggeringly, head-hurtingly old. In a minute I will give you one useful number that will help you understand how old and how all the rest of history fits into the picture.

Before I do that lets talk about big numbers. What is the biggest number you can imagine? I can imagine 10 things with no problem at all. 100. Yep, easy. 1000? There were nearly 1000 people at my senior school so I can think of that number. How about 100 schools like that put together, so 100 000? Its possible to think of that. Ten of those is 1 000 000 - one million. I stop there. That is about the limit of what I can imagine but that is good enough for now.

So imagine those numbers in terms of years. I don’t know about you, but for me that is a bit harder. I’ve lived for 41 years so even 100 years is a long time. 1000 years ago we know our country was in Saxon times just before the Normans invaded in 1066. 10 000 years ago we are beyond written human history so we don’t have stories from those times about what people were doing then. 1 million years seems like an incredibly long time to think of, doesn’t it?

Well our magic number is four thousand five hundred and forty. 4540. Because the Earth is around 4540 of those 1 million years old! But 4540 is a simple number and it will be very helpful to remember when later on we talk about fossils and dinosaurs and such like.

The picture at the top of this post shows how some people talk about time in the Earth’s long lifetime. These four really long periods of time are called eons. There are other ways of describing the Earth’s many ages and we will talk about them another time. The start and end of these ages can be said to have happened so many millions of years ago, which can be written MYA. So for example the beginning of the Phanezoic eon, the eon we are living in now, began 542 million years ago or 542MYA. This is the age where the first plant and animal fossils were found - before that there were probably only tiny microscopic bacteria and viruses that lived on our planet. You’ll see from the picture that plants and animals came quite late on the scene in Earth’s lifetime.

How do we know how old the Earth is? There are a number of different ways we know but I’ll tell you one way that you’ll understand if you’ve read my other posts about what stuff is made of. There is a type of metal in some of the rocks in the Earth called Uranium. Like all materials it is made of lego-brick like atoms. Uranium atoms are a bit unstable, but only a bit. From time to time one atom will suddenly change into another one - a lead atom. Lead is a metal too and in very old houses water pipes used to be made of it. Actually it changes into a misfit isotope lead atom not a regular normal one. It doesn’t happen very often. In fact if you took a lump of uranium of any size it would take 700 million years for half of the atoms in that lump to turn to lead. By measuring how much misfit lead isotope is in meteorites and moon rock - which we think were made at the same time as the Earth - then we can work backwards and know when that rock was made. So far all the rocks we have tested point to a number about 4500 million years.

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Image courtesy of ESA

In my rush to tell you all about the Rosetta mission and update you on it’s progress I forgot to tell you why the European Space Agency (ESA) are chasing a comet in the first place.

Comets are special because they were made at the same time that the other parts of the solar system were made - the Sun and the planets - but since that time, out in deep space, nothing much has happened to them. Our comet 67/P has been circling the Sun far far away in the Oort cloud until some time ago something bumped it and then it fell towards the Sun ending up travelling in a much shorter elliptical loop where we first noticed it in 1969. Despite the change in path, it is still the same lump of rock and ice that it always was since the beginning of the solar system. What is it made of? That is the question that Rosetta and Philae are going to find out. It is the first time we’ve had the chance to land on the surface of one of these ancient bits of our solar system and touch it and smell it. Up until now we’ve only seen comets from Earth or from shorter a distance away from a space mission. Never before have we been this close.

There are eleven measuring machines on the main Rosetta orbiter spacecraft and ten on Philae, the lander. Each of them was built by different teams of people in Europe and the information from each will go back to these same teams during the mission. Have a look at the ESA web page here to see what each of them does.

There is also a question that the Rosetta mission may help to answer; where did the water on Earth come from? A long way back near the beginning of the solar system lots of big rocks and chunks of ice that later became planets, asteroids and comets flew around bashing into each other. Where do you think the craters on the Moon came from? Probably most of the big ones were created around this time called the Late Heavy Bombardment. No one is quite sure why it took place but we have good evidence it really happened. Some people think that a lot of the water on our planet also arrived around this time from icy comets hitting the Earth. How could we ever know if that is really true? How about landing on an ancient comet now and finding out what type of water is in it?

OK that sounds an odd thing to say. What do I mean what type of water? Well, water, like all things, as we know from earlier blog posts, is made of lego brick-like atoms. What I haven’t said before is that water has misfit atoms in a very small number of molecules. Think of them as lego bricks that are the wrong colour for their normal type. We call these misfit molecules isotopes. Water has two different types of misfit. We know how common they are in our water on Earth - have a look at the picture above - but we also know that they can be present in different amounts in water from other parts of the solar system. So that is what I mean by type of water - the amount of isotopes give water from different sources their own different fingerprint, if you want to call it that. If the water on comet 67/P has the same proportion of misfit isotopes that would be another clue to suggest that our water on Earth originally came from comets crashing into it. If it does not, that’s not a problem, it helps us to look in other places for where it might have come from instead. Our water may have come from asteroids in the past, from the rocks that made up the early Earth, or from early plants or bacteria living much before the dinosaurs.

So as well as being an amazing thing to do in and of itself, landing on this comet may also give us another clue as to where our own water originally came from.

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Source: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Since I wrote to you about the Rosetta space mission a few things have happened that I wanted to tell you about. When I first mentioned the comet to you in August, the spacecraft was about 100km away from comet 67/P - the same distance from Luton to Coventry - but now, a few weeks later, it is only 10km away. It is exactly on schedule as was planned when it blasted off from Earth ten and a half years ago.

In less than 3 weeks the small robot landing craft, called Philae, will set off from the main Rosetta spaceship and land on the surface of the comet - the first time that the human race has ever attempted to do this. We have only just properly seen the comet after Rosetta got close enough to start taking good photos of it and so up until now the people at the European Space Agency (ESA) who are running the mission weren’t sure where the lander was going to touch down. For the past few weeks they have been looking at the surface of the comet to try to find a place that is both a good spot to land safely but also interesting enough to bother going there at all and now they have, a place called site J.

You will remember that comet 67/P is a funny shape - a bit like a rubber duck. Site J is on the ‘head’ of the two lumps of the comet. If Site J doesn’t work out during the landing then ESA have a back up landing site called Site C on the other lump, the ‘body’ of the rubber duck. The photo at the top of the blog shows where site J is on the comet and the photo below this paragraph shows a close up of it taken when Rosetta was 30km away from it a few days ago. Click on it to make it nice and big.

Source: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Of course Site J is a bit of a dull name for a place that is going to make history and so ESA have started a competition for people to give the place a better and more interesting name. Want to have a go? Then follow this link and send them your suggestion.  You have a few more days before the competition closes on 22nd October.

By the way, as you know, I normally try to create the photos and drawings I use on my blog posts myself. When I’m talking about a comet deep in space that is of course very hard to do but instead I’ve used photos that ESA have been taking using the cameras on Rosetta and then putting on their website, www.esa.int. I’ve used the full sized images they have published so make sure you click on all of them to see them in greater detail. Remember, these are not works of art or imaginary drawings made up by special effects people, they are photos of a real space object that has come from far outside our solar system. If you have a moment go and have a look at more fantastic photos on their website. Here is a photo Rosetta took of itself, with the comet in the background, a few days ago:

Source: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Philae will land on the comet on 12th November. I’ll try to remember to give you another news report around then.

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A few weeks ago I wrote to you about how everything was made of tiny little lego-brick-like atoms. Later, I wrote about how some things, like gold and diamonds, are made up of the same type of atom-brick. But like most toys made from of lego bricks, most things in reality are made up of many different types of atom joined together not just one type.

Like lego, atoms can be made to join with other atoms to make bigger and more complicated shaped bricks. These bigger bricks are known as molecules. It is this fact that makes the world around us full of very different types of stuff. Although the whole universe, that we know of so far, is made up of just 98 types of atom you can build very different types of things by joining them together in different ways and different arrangements. It is worth saying that although they are bigger than atoms, molecules are still very very small things indeed. Even the big complicated ones.

The above picture shows six lego brick molecules that I made up in my head using just four types of lego brick. It didn’t take me very long to do. Have a go yourself if you have some lego or other building blocks at home. Make some models of molecules and see how easy it is to come up with new shapes using only a few types of brick.

A good example of a very simple and small molecule is water. It is made of one type of atom brick joined up with two types of another. One drop of water contains huge numbers of these molecules rubbing against and sliding around each other. It just so happens that this combination and arrangement of atom bricks makes stuff that is wet in warm weather but frozen solid when it’s cold and that can turn into vapour when it gets very hot, such as in a kettle.

For an example of a much more complicated molecule that contains lots of different types of atom bricks you need look no further than your own hair and finger nails. Much of these parts of you is built from molecules of something called keratin. One molecule of keratin is made of more than 4000 atoms stuck together in a long spiral shape. These molecules stick to each other to make very long, strong chains. If water is just like three Lego bricks of two different types joined together then this molecule is like the Lego Star Wars Death Star - made of lots of bricks of lots of different types. The Death Star model has 3803 bricks to be exact so a keratin molecule has even more parts than that. Even so, it is still very small because atoms are incredibly tiny things indeed.

Because they are all sorts of shapes and sizes each type of molecule acts differently to others. This is why millions of water molecules together in a glass of water are see-through and liquid but lots of keratin molecules create tough bendy stuff like your nails.

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