An Epic Adventure in Space: Rosetta's Journey and Discovery
I want to take you to Rosetta (The Rosetta Comet Probe is an unmanned spaceship program organized by the European Space Agency whose main mission is to explore the mystery of the origin of the solar system 4.6 billion years ago and whether comets "provided" Earth with the water and organic material necessary for life. Go on an epic adventure. Escorting the probe to land on a comet has been my passion for the past two years. In order to achieve this, I need to explain to you something about the origin of the solar system.
Let's go back 4.5 billion years, there was a cloud full of gas and dust. At the center of this cloud, our sun forms and burns there. At the same time, objects that we now call planets, comets, and asteroids formed. Subsequently, according to the theory, when the Earth formed and the temperature began to drop a little, the comet greatly affected the Earth and delivered water to the Earth. They may also have transported complex organic material to Earth, which may have induced the emergence of life. You can compare this process to completing a 250-piece puzzle instead of completing a 2,000-piece puzzle. Then, large planets like Jupiter and Saturn, which weren't where they are today, interacted through gravity and cleaned up the entire interior of the solar system, and the objects we now call comets ended up in a place called the Kuiper Belt, which is a collection zone of celestial bodies outside neptune's orbit. Sometimes these objects collide with each other, and gravitational shifts occur, and Jupiter's gravity then pulls them back into the solar system. Then they become comets that we see in the sky.
It's important to note that during this period, for 4.5 billion years, these comets have been sitting outside the solar system and have never changed — a deep, frozen version of the solar system. In the air, they look like this. We know them through their tails. There are actually two tails here. One is a dust tail, blown out by the sun. The other is the ion tail, which is the charged particle, which is influenced by the magnetic field of the solar system, and they can see the wisdom hair, and the wisdom nucleus, which is so small that it is almost invisible, but you have to remember that in the case of Rosetta, the spacecraft was on that central pixel. We are only 20, 30, 40 kilometers away from this comet. So what are the key points? Comets contain primordial material from the formation of the solar system, so they are ideal objects for studying the composition that emerged at the time of the origin of Earth and life. Comets are also likely to have brought with them the elements that triggered the origin of life.
In 1983, the European Space Agency began the long-term Horizon 2000 program (ESA was originally introduced in 1984 and intended to cover 1995-2007). There were four main "cornerstone" missions, the Rosetta Mission was the last), which included a foundation project, a mission to visit comets. At the same time, a small mission to visit comets, the Giotto you see here, was launched, and in 1986, its fleet of other spacecraft flew through Halley's Comet. The results of that mission made it clear that comets were ideal objects for studying the solar system. Thus, in 1993, the Rosetta mission was approved, initially it was set to launch in 2003, but was later cancelled due to problems with the Ariane rocket. However, our PR department, full of enthusiasm, has made 1,000 Delft blue porcelain plates and printed those wrong comet names. So I haven't bought any porcelain since. This is the positive side. After all the problems were solved, Rosetta left Earth in 2004 and flew to the re-selected comet, Comet Chulyumov Gracimenko. The comet was chosen because, first, you had to be able to get to where it was, and secondly, it didn't stay in the solar system for long. This particular comet entered the solar system in 1959. It was the first time it came to the solar system after being deflected by Jupiter, because it was close enough to the sun to change. So this is a very new comet. Rosetta has made many historic breakthroughs. It was the first artificial satellite to enter the comet's orbit and accompanied the comet through its entire solar system journey — reaching the shortest perihelion.
Then leave the solar system again. This is the first time a spacecraft has landed on a comet. We actually used some comet orbiting technology on Rosetta that wouldn't normally be used on other spacecraft. Usually, if you look at the sky, you will know the direction and coordinates. But in this case, that wasn't enough. We navigate by looking at landmarks on comets. We identify those features—pebbles, craters—and then we know we're in that region on the comet. Of course, this is also the first spacecraft to use solar cells to fly into Jupiter's orbit. This sounds more than a feat, as the technology of radioisotope thermoelectric motors was not yet available in Europe at the time, so there was no choice at the time.
But these solar panels are huge. This is one of its flanks. These are not diminutive people who have been deliberately chosen. They are normal people like you and me. We have two such wings, 65 square meters. Then, of course, as we fly towards the comet, you'll find that flying a 65-square-meter sail towards an exhausting object isn't always a convenient option. How did we get to this comet? Because we have to go to a very distant place — to accomplish rosetta's scientific goals.
It's four times the distance from Earth to the Sun — and a speed we can't reach with the normal fuel of a spacecraft. Because we have to carry six times the weight of the spacecraft itself. So how do you do that? At a very low altitude, about a few thousand kilometers, when passing through a planet, using the pulling effect and elastic force of gravity, you will directly get the same speed around the sun as that planet. We have tried many times. On Earth, on Mars, and then on Earth twice, we also flew by two asteroids, Lutecia and Stans. By 2011, we were too far away from the sun.
But if this spacecraft has a problem, we can't save it at all, so we go into hibernation. All but one timer, all the instruments were turned off.
What you see in white here is its trajectory, and its trajectory. You can see this circle from the beginning, this white line,
We could get more and more ellipses, and eventually we got closer to the comet in May 2014, and then we had to start doing rendezvous deceleration. On the way, we flew over Earth and took some photos to test our camera. It was the moon rising on the other side of the earth, and this is what we now call a selfie, and by the way, the word "selfie" didn't exist at that time. This was taken on Mars by a comet infrared and visible light analyzer camera. It was a camera on the lander, and it looked like it was underneath the solar panels, and you could see Mars and the solar panels in the distance. When we were awakened from hibernation in January 2014, we began to move forward and reached a distance of 2 million kilometers from this comet in May. However, the speed of this spacecraft is too fast. We're 2,800 kilometers ahead of the comet, so we need to brake. We had to do 8 decelerations, and as you can see, some of them are really big. Our first deceleration required reducing the speed by hundreds of kilometers per hour, in fact the process took 7 hours and consumed 218 kilograms of fuel, which was also a frightening 7 hours.
Because in 2007, there was a leak in rosetta's propulsion system and we had to turn off a break,away from it, so the propulsion system was operating under pressure beyond its design capacity. Then we reached the vicinity of this comet, which was the first photograph we saw.
The comet's true rotation period is 12.5 hours, so it's accelerated, but you guys can definitely understand what our line dynamics engineers think, and it's not an easy landing. We used to fantasize that it was some kind of thing
Something shaped like a potato that is easy to land. At that time, we threw a glimmer of hope:
Maybe it's flatter. But this is not the case, and its surface is still very rough. So we had to make the choice: we had to map the object with all the details we had collected, because we had to find a flat land with a diameter of 500 meters. Why 500 meters? This is the error we made when we landed the probe. So we took immediate action and mapped the surface of the comet. We used a technique called photometric inclination. Take advantage of the shadows cast by the sun. There is such a rock on the surface of the comet, and the sun shines down from above. Through the shadows, we use our brains to immediately roughly judge the shape of this rock. You can use a computer to make up a program like that, and then cover the whole comet.
You can draw a topography of its surface. To do this, we start flying along a special trajectory from August. First, fly along a triangle with a side length of 100 kilometers at a distance of 100 kilometers, then change the side length of the triangle to 50 kilometers, and then repeat the whole process. At that time, we had already observed the comet from all angles, and we could use this technique to map the entire surface of the comet. Now, it's time to choose a landing site. All we had to do was to map the comet's topography within 60 days to find a final landing site.
We don't have more time. By contrast, on average, a mission on Mars takes hundreds of scientists years to find a landing site. But we only have 60 days, that's all. We finally chose a landing site and had Rosetta's instructions to send Philae ready. (In 2004, Europe launched Rosetta, which carried Philae to the universe, and then Philae landed, but lost contact with Rosetta, in this vast universe, they waited for news from each other...) Thankfully, Rosetta finally found Philae. The premise, though, is that Rosetta is in the right position in the air and aims at the comet because the lander is passive. It needs to be pushed out and fly towards a comet. Rosetta had to turn around so that its camera could face it and communicate with it as it flew away. The entire landing process took 7 hours. A simple calculation: if rosetta's speed error is 1 centimeter per second, and 7 hours is 25,000 seconds, that means that the error when the lander landed on the comet was 252 meters. So we have to accurate Rosetta's speed error to less than 1 centimeter per second, and its position in space 500 million kilometers away from Earth, the error should be accurate to less than 100 meters. That's not an easy task.
Let me give you a quick overview of some of these scientific theories and instruments. I'm not going to go into all the details of the instruments so that you won't be confused, but I want to help you understand some of the concepts. We can detect gases, measure dusts, measure their shape and composition, there are magnetometers and so on with everything we need. It may not be much on its own, but look at those spikes. This is the day on the comet. You can see the effect of the sun on the evaporation of gas and the fact that comets are rotating. There's a point here, obviously, a lot of stuff comes out there, and it's heated by the sun and then cooled on the back. We can look at the density difference here. These are the gases and organic compounds that we have already measured. It's an impressive list, and there's going to be a lot more on it because we've taken more measurements. In fact, there's a conference in Houston, and the data will be shown at the meeting. We also measured dust particles.
It may not mean much to you, but scientists are thrilled when they see this. Two grains of dust: on the right they called it Boris, and they shot it with tantalum so that they could analyze it. We found sodium and magnesium. This also shows that this is the concentration of these two substances when the solar system first formed, so we know what material was present when the planet formed. Of course, one of the most important factors is imaging. One camera on the Rosetta— osiris camera — was shot, and that was actually the cover of the January 23, 2015 issue of Science magazine.
No one thought it would look like this. Big pebbles, rocks – it looks more like Yosemite's half-screen rock than anywhere else. We also saw something like this: a sand dune, and on the right-hand side, that looked like some wind-blown shadow. We've found these on Mars, but this comet doesn't have an atmosphere, so it's a bit difficult to create a shadow that's blown by the wind. It could be a local outflow, something rising and then falling. We don't know yet, so there's still a lot of investigation to do. The pictures it takes have two images of the same place. There is one and there is a pit in the middle. There was another sheet, and three streams of air erupted from the bottom of that pit. So that's what this comet is doing. Obviously, the bottom of these pits is the active area, which is also where the material evaporates into the air.
This comet has a very interesting crack in its neck. It is 1 km long and 2.5 m wide. Some people have suggested that in fact when we approach the sun, the comet might split in two, and then we have to make a choice, which half of the comet are we going to follow? The lander, too, carries a lot of instruments, except for some drilling devices, most of which are similar to those on spacecraft. Rosetta carries almost the same instrument as Rosetta because he wants to compare the material found in space to the comet. This is known as a "ground fact-finding survey". Images taken by Osiris cameras as they descend from the landing. The lander could be seen getting farther and farther away from rosetta. The lander's photographs taken 60 meters away are more than 60 meters above the surface of the comet. That big pebble is about 10 meters in diameter. The last photo we took before landing on the comet. You can see three enlarged images of the lander flying over the surface of the comet from the lower left corner of the figure to the middle. Then, at the top there is a contrast between before and after landing. The only problem is in the photos after landing
No lander appeared. But you look closely at the right-hand side of this image, and we see that the lander is still there.
But it was bounced off. It left the surface of the comet again. Now, it's a bit funny that in the design of the Rosetta,
It will carry a lander that can bounce. But because the cost was too high, I gave up. We've forgotten about it.
But the lander remembers. During the first rebound, on the magnetometer, you can see data from the x, y, and z coordinates. Halfway through, you can see a red line. This red line indicates that there is a change. What happened?
Apparently during the first bounce, one of the lander's legs hit the edge of a crater somewhere, and then the lander's rotational speed was changed. So we were lucky to be in the position we were in at the time. This is one of the iconic pictures taken by the Rosetta. It was an artificial object, one leg of the lander, standing on a comet. For me, this is what I've seen
One of the best space science photos. One of the tasks ahead is to find this lander. We know some information about where it should be. We haven't been able to find it yet, but the search continues, and we're trying to get the lander back to work. We listen carefully every day, hoping that between now and sometime in April, this lander will be back to work.
What we found on this comet is that this comet can float on water. It is half as dense as water. So while it looks like a big rock, it's not. We saw a 4-fold increase in its activity between June and August last year. As we get closer to the Sun, 100 kilograms of material will leave the comet every second: gas, dust, and so on. 100 million kilograms in 1 day.
Eventually, it was the day of landing. I'll never forget it – everyone went crazy, with 250 TV crews in Germany vying for coverage. While the BBC interviewed me, another TV station followed the staff who reported on me all day and also filmed my visit, which lasted all day. The Discovery Channel crew approached me as I left the monitoring room and asked the right questions, and I was in tears of excitement, and the feeling still lingered. In the month and a half since, I have tears in my eyes every time I think of the landing day, and that emotion still exists in my heart. I want to conclude today's talk with this picture of this comet.
1.Wikipedia encyclopedia
2. Astronomical terms
fy: chunhua zhang
Author: ted
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