On September 15, 2017 (July 25, 2017 in the lunar calendar), the Saturn probe Cassini self-destructed after completing a 20-year fantasy journey. The National Space Administration (NASA) spacecraft Cassini (Cassini) ended its 20-year space journey on September 15, 2017 and crashed on Saturn. Scientists say Cassini taught us almost everything we have learned so far about Saturn and revolutionized our understanding of life elsewhere in the solar system. The Cassini mission cost a total of US$3.9 billion and was carried out by scientists from 27 countries. After sailing 7.9 billion kilometers, it exhausted rocket fuel as expected and crashed into Saturn's atmosphere at a speed of more than 120,000 kilometers per hour. "This spacecraft has lost signal and I hope everyone will be deeply proud of the amazing achievements of this mission," Metz, head of the Cassini program at NASA's Jet Propulsion Laboratory, told colleagues in the control room. Cassini sent its final signal to Earth as planned, and then crashed into Saturn, the farthest planet visible to people on Earth with the naked eye. Scientists planned for it to crash because they did not want to damage Saturn's other two oceanic moons, Titan and Enceladus. The ocean may contain life, and scientists hope it will remain original and be left for future exploration. The last flyby of Titan on September 11, Cassini was named after the Italian astronomer Cassini who discovered four moons of Saturn. It was launched in 1997 and entered Saturn's orbit in 2004. In December of the same year, the probe "Huygens" was sent to Saturn's largest moon Titan, and has orbited Saturn nearly 300 times so far. Cassini's enhanced color photo of Saturn's rings After Cassini's mission, Cassini made many major discoveries, including the liquid methane sea on Titan and the underground ocean on Enceladus. Zuboqin, deputy director of NASA's science missions, said: "Cassini's discovery of the oceans of Titan and Enceladus changed everything and deeply shook our view of where life might exist outside Earth." Cassini probe's final confession: Human friends, when you see this line, my life has already entered the countdown. I, Cassini, NASA's last flagship deep-space exploration project in many years, has entered the final battle after orbiting Saturn for 13 years: burning the last bit of energy and doing everything possible to get close to mysterious territory that has never been explored before: exploring Saturn's rings, Saturn's atmosphere and outer structures. If everything was ideal, I would hit Saturn on September 15 (Eastern Time) and completely burn myself, but before then, even a little accidental collision would be enough to end my 20-year-old life prematurely. It doesn't matter. For an interstellar probe, being able to work at this age is enough. If you have never heard of my name, please allow me to introduce myself a little. My full name is Cassini-Huygens. Cassini-Huygens are two scientists in the 17th century. Italian scientist Cassini discovered the ring seam of Saturn. His name is used to name my main probe. Dutch scientist Huygens discovered Titan. His name is used to name my little brother, the Titan landing probe Huygens, which I carried. The latter landed on Titan on January 14, 2005, and the earth received the first image of Titan. In the 1980s, some scientists from NASA and ESA proposed to jointly explore Saturn and Titan. In the process of turning this idea into reality, there were rounds of "wars", including political games between superpowers and funding wars between allies, and then a series of battles such as academic status and environmental storms. If ESA and the Italian Space Agency had not taken the lead in funding, and NASA had strongly advised Congress not to do something as vulgar as skipping votes, the project might have died in a minute. A total of 17 countries have participated in the Saturn exploration program, which is one of the most exciting large-scale international cooperation projects since mankind entered the space age. After costing $3.2 billion, I finally formed: 3 meters in diameter, 7 meters high, weighing 6.4 tons, carrying 27 of the most advanced scientific instruments and equipment at the time. On October 15, 1997, I took my little brother Huygens and launched it from Cape Canaveral Air Force Base in the United States. In April 1998, I flew 284 kilometers away from Venus and used Venus 'gravity to accelerate. After that, I circled the sun and flew 600 kilometers away from Venus again in June 1999, obtaining the second acceleration of Venus 'gravity. In August of the same year, I flew 1171 kilometers away from the earth, used the gravity of my parent star to accelerate for the third time, and officially flew to the outer layer of the solar system. Two years later, in December 2000, I flew about 10 million kilometers away from Jupiter and gained acceleration from Jupiter's gravity. At this time, my speed exceeded 30 kilometers per second. From this moment on, I flew towards my destination, Saturn. In these four boosts, the calculation time and angle are all extremely good. No matter which link is even the slightest difference, I will miss Saturn a thousand miles. On the morning of July 1, 2004, Beijing time, seven years after I was launched, I finally flew to Saturn, became the first human probe to orbit Saturn, and officially started work. Originally, my planned mission cycle was 4 years. Due to my excellent performance, the mission was extended again and again until my 13th year of service. This is a minor miracle, because the energy levels required by an interstellar probe to be working and dormant are completely different. In 2010, scientists far away on earth calculated that I had less than 1% of my booster left, which meant that if I ran out of fuel, I might fly out of control, and they had to plan a decent retirement ceremony for me. As an interstellar probe that is about to run out of energy, there are two common ways to retire: one is to stay in the orbit of Saturn and drift quietly from then on; the other is to fly farther away, such as Neptune or simply fly out of the solar system. But as a soldier, I rejected these retirement plans. I hoped to burn the last of my heat and see what Saturn really looked like at the expense of crashing into Saturn's atmosphere. Of course, there was another very important factor in choosing such a tragic ending. In my previous 13 years of explorations, I observed that it was very likely that life or life-supporting environments were present on Enceladus and Titan. When I was launched, I did not undergo space quarantine, so it is very likely that I had Earth's microorganisms on me. If I accidentally crashed on Enceladus and Titan in the future, it would be a disaster for those who might exist. And if you burn yourself in Saturn's atmosphere, these possible life will be completely safe. In view of this, I set out towards my final goal without hesitation. Is Titan the second earth I found for mankind? Titan (Titan) is a key focus for Cassini, and it spends much longer on it than it does exploring Saturn. NASA's website describes Titan this way: "In many ways, it is one of the most Earth-like objects we have ever found. It has a thick atmosphere and is rich in organic matter. Titan is like Earth billions of years ago, still frozen and without oxygen in the atmosphere. Titan is also the only celestial body in the solar system with known liquid oceans and lakes on its surface, but its oceans and lakes are not water, but methane. Pseudo-color Titan ocean map produced from radar data: Blue represents the ocean, not the actual color. The most important discovery in Titan's atmosphere was the discovery of organic molecules with molecular weights of up to tens of thousands 1000 kilometers above the ground. Large organic molecules may be transitional products of the origin of life. In terms of evolutionary sequence, it can be said that Titan was the predecessor of the Earth. How life on earth originated? Early research believed that it originated in the ocean. Another view is that life on earth fell from the sky, that is, raw materials with living matter, such as meteorites, meteors, and comets, hit the earth and brought in from outer space, but the earth itself does not have such things. But the discovery of Titan gave a new revelation. The origin of life may also have occurred from the sky, but not from the outside, but in places high in the atmosphere. Large organic macromolecules are very heavy and will fall slowly, becoming larger and larger as they fall. In this magnificent finale, in this countdown to life, I will do my best to complete these tasks: after completing these 22 subductions, I will officially end my mission, and even as the atmosphere burns, I will try my best to transmit data to Earth until the signal finally disappears completely. There is an 84-minute time difference between Saturn's information and Earth. Friends, when you received the last piece of data I sent back, I had actually integrated with Saturn more than an hour ago. I have been calling Earth for 20 years please call me today. After arriving at Saturn in July 2004, I began exploring the secrets of Saturn and its 62 moons. During this period, I flew 7.9 billion kilometers in space, executed 250,000 instructions, flew by the moons of Saturn 162 times, took more than 450,000 photos, and discovered 7 new moons of Saturn. Based on this, my human friends published 3948 pages of scientific paper. Okay, after I called the earth countless times (Internet terms meaning support, cheer, encouragement), on September 15th, friends, please call me a Call.