Posts Tagged ‘Rosetta Mission’

On Friday (30 September 2016) the European Space Agency’s Rosetta mission ended by crashing the space probe into comet 67P. This was done deliberately. With the comet moving further and further from the Sun, Rosetta’s solar panels were getting to the point where they could not supply enough power to the spacecraft to operate its instruments. Mission scientists had to choose between putting Rosetta into hibernation, with the risk that the probe would not wake up properly when it next came near enough to the Sun, or to deliberately crash the probe into the comet and gain some extra science. They chose to do the latter.


On Friday (30 September 2016) the highly successful Rosetta mission came to a dramatic end when the space probe was deliberately crashed into the surface of comet 67P.

As Rosetta gently approached the surface of comet 67P (remember, the gravity of the comet is so weak that the fastest that it “fell” was only about 1 metre per second) it took pictures in ever increasing detail. The last image it took is shown above, when the probe was only some 20 metres from the surface.

Rosetta has been a hugely successful mission, and it will take scientists many years to analyse all the data which it and Philae have returned to us. I have blogged about Rosetta before, here, here, here and here.

Some of the most important findings so far are

  • that comet 67P is spongy, with about 70% of its volume being empty space
  • complex organic molecules have been found on the comet’s surface, supporting the theory that the building blocks of life on Earth may have been brought by comets
  • the composition of the water jets emanating from comet 67P was found to be different to water on Earth. This seems to contradict the idea that water on Earth was brought here by comets

There are thousands of images and spectra taken by Rosetta, so there is far more science to come in the future. But, perhaps Rosetta’s greatest success was the way in which the mission captured the public imagination. Surely Rosetta will be just the first mission that we send to orbit and land on a comet.

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Last night (Monday the 24th of August) I went to a public lecture about the Rosetta mission
at the National Museum of Wales in Cardiff. The lecture was given by Mark McCaughrean, who is senior science advisor at the European Space Agency (ESA) and, if I’m correct, also either heads up or is very senior in their public outreach efforts. It was one of the best public lectures I’ve ever attended, and in writing that statement I am trying to figure out how many public lectures I have actually attended. In addition to having given probably over 100 public lectures myself, I have probably attended some 150-200 public lectures given by others in the last 40-odd years.

The opening slide of Mark Mcxxx's public lecture about the Rosetta mission at the National Museum of Wales

The opening slide of Mark McCaughrean public lecture about the Rosetta mission at the National Museum of Wales

In addition to learning a lot about the Rosetta mission (I will blog about some of what I learnt next week), the lecture got me thinking about what makes a good public lecture. I have also been thinking about this the last few days because my book on the Cosmic Microwave Background has been reviewed by Physics World (the magazine of the Institute of Physics), and that review will apparently appear in their October magazine. But, the reviewer shared with me some of her observations about the book, and one point she raised is that she felt I was inconsistent in my level of explanations in the book. What she meant was that there are some things I explain so that complete novices can follow my arguments, but other things where more of a physics/astronomy background would be necessary to follow that I am saying.

This is a valid point, and it shows the quandary I was in when trying to decide at what level to pitch the book. My primary audience was that I hoped the book will be used by undergraduates in the Disunited Kingdom and graduate students in the United States as a background text to any course they may be doing on the early Universe. But, in the back of my mind, I also had the interested lay-reader in mind, which is why I explained some things at a level for them. What I probably ended up doing was falling between two stools, and that is not always good in communicating science to the public.

Last night’s lecture by Mark did a wonderful job, as it seemed to me that he was able to keep it at a level that (hopefully) everyone could understand, but at the same time there was some specialist information in there for professional astronomers to give them (and me) the impression that we too had learnt something. This is a difficult tightrope to walk, but Mark did it very well.

Audience participation time - the audience had to jump 4cm in the air to simulate the acceleration felt by Philae when landing on comet 67/P

Audience participation time – the audience had to jump 4cm in the air to simulate the acceleration felt by Philae when landing on comet 67/P

This is what I try to do in my own public lectures, but I doubt I do it as well as Mark did last night. Whether I’m talking to school groups, astronomical societies, on the radio or TV or lecturing on a cruise, I always try to make sure that I don’t lose any of my audience in the first three quarters or so of the lecture by keeping things as simple as possible. At the same time, I always try to make sure that there is some information in the lecture (maybe some 25% of it) which will be news to even a professional in the field, as even in a public lecture you may have professionals in the audience. This was the case, for example, in lectures I gave on the cruise I did in South America in March – one of my regular attendees had worked at NASA JPL and he and I would have long chats after each lecture where he would quiz me further, or impart some information that I did not know about.

Last night, Mark had a perfect mixture of videos, cartoons, animations, humour and exciting information, and it was all delivered in a relaxed and humorous way. As I say, one of the best public lectures I have ever attended.

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I thought I would give a brief update on some of the results that have been trickling through from the Philae lander, which I blogged about here. The news has tended to concentrate on the fact that the lander had to power-down after some 60 hours because the solar panels were not getting enough sunlight, which might lead people to think that the Philae mission was not a success. But, in fact, it achieved nearly all of its core science goals, something the media have sadly largely ignored.

The reason the solar panels are not getting enough sunlight is because the lander is stuck in what appears to be a deep chasm, and so is only getting just over 1 hour of sunlight a day instead of the 6-hours that it should have got. When it landed, Philae bounced and ended up in an unfortunate location on the surface up against a “wall”. However, the saying that “every cloud has a silver lining” is true in this case for one of the instruments on-board Philae, namely an instrument called ‘Ptolemy’.

This instrument has been trying to analyse the composition of the surface of the comet. When the Philae lander bounced it threw up material from the surface, and Ptolemy was able to analyse this cloud of surface material, making its job probably easier than had this bounce not happened. What it has found in that cometary surface material is fascinating, clear signs of complex carbon molecules, the building blocks of life.

An image of Philae taken by the Rosetta spaceprobe

An image of Philae taken by the Rosetta spaceprobe

This does not mean that comets brought life to Earth, although it does not rule it out either. But, it does show that such complex carbon-based molecules, essential building blocks of life, are present on objects like comets. Philae has conducted a number of other experiments in its brief 60-hour time on the comet’s surface, and the results from those experiments are under analysis. Scientists who have worked on Philae are also hopeful that the lander will wake back up as the comet gets closer to the Sun, as the solar panels may start getting more sunlight. We shall have to wait and see, but we also need to remember that Philae was just part of the much larger Rosetta mission, and Rosetta will carry on studying the comet for about another year covering the time it will get closest to the Sun and then start its journey back to the outer Solar system.

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Yesterday (Wednesday the 12th of November) the European Space Agency (ESA) successfully landed a tiny space-probe called Philae on to the surface of a comet. This is a remarkable achievement, and one which has clearly captured the imagination of the public and was the top story on the news here in the Disunited Kingdom yesterday. I was on the BBC talking about this just before 8am, with Philae detaching from its mother ship Rosetta just over half an hour later, at 08:35 UTC.

This remarkable photograph was taken of Philae by Rosetta’s cameras as Philae descended towards the surface of the comet. You can see in the photograph that Philae has deployed its landing legs, but unfortunately just before its release from Rosetta it was realised that a thruster on top of the washing-machine sized lander was not working. They decided to drop it anyway.

A remarkable photograph of Philae taken by its mother-ship Rosetta as it drops towards the comet. The photograph clearly shows that Philae has deployed its landing legs.

A remarkable photograph of Philae taken by its mother-ship Rosetta as it drops towards the comet. The photograph clearly shows that Philae has deployed its landing legs.

Philae descended very slowly towards Comet 67P. A common misconception seems to be that the comet does not have any gravity, but this is not true. It does, but its gravity is very very weak. Philae has a mass of 100kg, but on the surface of the comet this would feel more like a few grams. If you were on the surface of Comet 67P and you were to jump gently upwards, you would probably not return back to the surface, so weak is its gravity. This photograph was taken by Philae as it slowly descended towards the surface.

A photograph of Comet 67P as Philae descended towards its surface. This was taken from about 3km away.

A photograph of Comet 67P as Philae descended towards its surface. This was taken from about 3km away.

ESA finally reported that Philae had landed soon after 16:00 UTC, and here is a screen capture of the robot’s Twitter feed (@Philae2014). As you can see from the announcement of its landing, it also says that the harpoons did not fire. These were designed to secure the robot to the surface.

A screen capture from Philae's Twitter feed

A screen capture from Philae’s Twitter feed

As of my writing this on Thursday morning, we still do not know how securely Philae is on the surface of the comet. The latest reports are saying that Philae bounced a few times, but that it is now stationary on the surface. My understanding is that ESA are now trying to decide whether to fire the harpoons to secure it better to the surface. The danger of doing this is by firing them Philae will be sent in the opposite direction, ie. away from the surface, due to Newton’s 3rd law (to every action there is an equal and opposite reaction). If the harpoons manage to get a grip on the comet then firing them is not a risk, as then the motors can winch Philae back to the surface. But, if they fail to grip, Philae may float away from the surface not to return.

Whether ESA gets Philae secured to the surface or not, this landing has still been a remarkable success. Many of the instruments on Philae are working and taking data, and of course we also need to remember that the Philae landing was just a part of a larger mission for Rosetta. Rosetta will stay in orbit about Comet 67P and observe and study it up close as it passes at its closest to the Sun, and is scheduled to continue sending us data until December 2015.

So, whether Philae does manage to get a firm grip on the comet or not, let us remember that this is one of the greatest achievements in our history of space exploration – to land a robotic probe onto the surface of a comet which is hurtling through space some 500 million km away from Earth. Well done ESA!

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Yesterday (Monday the 20th of January 2014), at 10am (Universal Time) the European Space Agency’s (ESA) space probe Rosetta woke itself up from a 30-month hibernation. Over the next several months Rosetta will travel towards the comet 67P/Churyumov-Gerasimenko, with a planned rendezvous with the comet in August. The rendezvous includes, for the first time, trying to land a probe (called Philae) on the surface of a comet, which is scheduled to happen in November. This is to analyse the comet’s composition and tell us about the nature of the early Solar System. The mission will also monitor the changes which happen to the comet as it gets closer to the Sun on its journey into the inner Solar System.

Comet 67P/Churyumov-Gerasimenko was discovered in 1969. Tracing back its orbital properties, we have found that prior to 1959 it had a different orbit, but its orbit was altered by the gravitational effect of Jupiter. Its current orbit gives it an orbital period of nearly 6.5 years, and it will reach perihelion (closest approach to the Sun) on the 13th of August 2015, when it will come to within 1.25 AUs (about 188 million kms) of the Sun.

The story as covered by the BBC

The story as covered by the BBC

This is one of the ESA’s most ambitious missions. Rosetta was launched way back in 2004, and is currently out near the orbit of Jupiter, some 800 million km from the Earth. It was decided in June 2011 to put the space probe to sleep to save on power, as its solar panels were picking up so little light from the Sun.

A summary of the Rosetta mission.

A summary of the Rosetta mission.

Although Rosetta was scheduled to wake up at 10am UT, the signal that the space probe had successfully woken up was not received back on Earth until 18:16 UT. The faint signal was received by a 70-metre radio dish in California operated by NASA as part of its deep space network.

Analysing the composition of comets is one of the few ways we have to learn about the nature of the early Solar System. In addition, some scientists have argued that many of the complex organic molecules necessary for life were brought to the Earth by comets. It also seems likely that the Earth’s water was brought to our planet by comets, so understanding comets’ composition may be vital in unravelling the mystery of how life got started here on Earth.

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