In October 1997, the six ton CassiniInterstellar probeWas launched to flySaturnTrack.This is the last large spacecraft for interplanetary exploration in the 20th century.
There are 17 countries participating in the Cassini program, which is the largest since mankind entered the space ageinternational co-operationOne of the topics.Cassini has a diameter of 3 meters, a height of 7 meters, and a weight of 6.4 tons. It carries 27 kinds of the most advanced scientific instruments and equipment.[1]
400 years ago,ItalyscientistGalileostayHuman historyFor the first time, the telescope was aimed at the stars in the sky, pushing the ancient astronomy into a new era.When Galileo observed Saturn with a telescope, he found that there were things like human ears on both sides of the circular surface of Saturn.In 1659,NetherlandsAfter more detailed observation, scientist Huygens determined that,SaturnThese two things like ears are actually connected, which is a flat circle around Saturn.
Cassini was born in Italy, and later came to France to serve asObservatoire de Paris The first director.In 1675, he wasSaturn's ringsDuring observation, it was found that there was a dark gap in the middle of the halo, which divided the halo into internal and external parts.Later, astronomers called this gapCassini circular seam。
October 18, 1989, the United States and EuropeCooperative launchHas“Galileo”Space probe。On December 7, 1995, "Galileo" entered the orbit around Jupiter, and began to carry out research on Jupiter and its four major satellitesscientific research。It was Galileo who discovered these fourJupiter satellite。The space probe was named "Galileo" in memory of Galileo's discovery.
Inspired by the success of Galileo, the United States and Europe further cooperated to develop a space probe to Saturn, and to commemorateCassiniFound that yearSaturn's ringsThe space probe was named Cassini.
There are 17 countries participating in the "Cassini" Saturn exploration program, which is the most exciting large-scale space exploration program since mankind entered the space ageinternational co-operationOne of the topics.Cassini is 3 meters in diameter, 7 meters high, 6.4 tons in weight, and carries 27 kinds of the most advanced scientific instruments and equipment.Cassini also carried one of Saturn's largest moonstitanDetector named“Huygens”。
Name Source
Giovanni Domenico Cassini (1625 – 1712), astronomer.Born in Perrinaldo, Italy, on June 8, 1625, died in France on September 14, 1712Paris。
Cassini made many contributions to astronomy in his life, including the discovery of four moons of Saturn-Rhea（Rhea）、Iapetus（Iapetus）、Enceladus(Dione) andEnceladusTethys also observed the rotation of Mars, Jupiter and the structure of Saturn's ring. In 1666, he measured MarsRotation period24 hours and 40 minutes (error about 3 minutes);The first Jupiter was announced in 1668Calendar。Discovered in 1679Saturn's ringsA hidden seam in the middle - rear scale“Cassini circular seam”（Cassini's Division）。Since 1683, he has systematically observed and studiedEcliptic light(zodiacal light) is the first person who systematically observed and studied zodiacal light.
In addition, he also calculated the distance between the earth and Mars, and accurately calculated the distance between the earth and the sun.
Exploration course
The Cassini was launched at 16:43 Beijing time on October 15, 1997.If you only rely on the rocket thrust to fly directly to Saturn, and ask it to do so in seven yearsInward flightTo Saturn, the fuel used must not be less than 70 tons.However, man has not yet been able to build rockets that can carry so much fuel.Therefore, Cassini adopted“Galileo”In a similar way, the gravity of the planetGravitational slingshot effectTo speed up.
After the launch of Cassini, it first flew 284 kilometers away from Venus in April 1998, accelerating by the gravity of Venus.After that, it goes aroundsunlightIn June 1999, it once again flew 600 kilometers away from Venus, gaining the second acceleration of Venus' gravity.In August of the same year, Cassini flew 1171 kilometers away from the earth and was accelerated again by the gravity of the earth.
Cassini left the earth for the second time before flying to the outer layer of the solar system.In December 2000, it was in the distance ofStar ApproximationFlying at 10 million kilometers, the acceleration of Jupiter's gravity was obtained.At this time, its speed exceeded 30 kilometers per second.Then it flew to Saturn, its destination.
The distance from Saturn to the earth is less than 1.3 billion kilometers at the nearest time and 1.6 billion kilometers at the farthest time. However, Cassini has taken the above circuitous flight route, and its journey to Saturn is up to 3.5 billion kilometers.However, sharpening the knife does not delay the firewood cutting, so the flight time has not increased, and the fuel has been greatly saved.
CassiniSpace probeAfter six years and eight months, 3.5 billion kilometersspace travelAfter that, at 12:12 on July 1, 2004, Beijing Time, we successfully entered the orbit as plannedSaturnThe rotating orbit started a 4-year scientific investigation of Saturn's atmosphere, halo and satellite.
One of Cassini's missions is to detect Saturn's rings.Although it is a newcomer, the orbit entry process itself is an excellent opportunity to be the closest to Saturn in the expected 4-year exploration operation. When it is closest to the top of Saturn's surface cloud layer, it is only about 20000 kilometers away.Scientists will not miss this opportunity to explore Saturn's rings, so they arranged to pass through Saturn's rings twice during its orbit entry.
Cassini crosses Saturn's ring from the gap between F and G rings.This ring slit is the widest one in Saturn's rings, with a width of 30000 kilometers.There may still be some particles in the circumferential seam."Cassini" passes through the annular gap. If there are particles hitting its vital parts or carrying scientific instruments, it may cause very bad consequences.For this reason, the Cassini is crossingSaturn's ringsBefore, first adjust the posture, turn 180 degrees, turn the 4-meter diameter dish antenna that was originally located at the tail towards the earth to the forward direction, and become a "shield" against particles in the circumferential cracks.
At 9:11, the Cassini adjusted its posture.At 10:08, it began to cross the halo from below;At 10:11, it reached the top of the halo and successfully pierced.Then, it turns back and makes the jet pipe of the engine face forward, so as to form deceleration resistance after ignition.At 10:21, the Cassini turned again successfully;At 10:36, the engine ignited and the Cassini began to decelerate.Under the action of Saturn's gravity, the decelerated Cassini turns aroundBig bendAnd gradually enter into the predetermined running track.
At 12:12, the engine of the Cassini stalled.At this time, it has completely transferred from the original route to Saturn to the orbit around Saturn.Then, it began to compare Saturn andSaturn's ringsCarry out close detection, including usingMagnetometerMeasure the strength and direction of Saturn's magnetic field, detect the size of particles and the thickness of the ring when passing through the ring, and estimate the composition, temperature and structure of the ring.
At 13:32, the Cassini adjusted its posture again;At 13:58, it crossed the halo again and returned from above to below.Then, it turns the dish antenna toward the earth and enters normalrunning state 。
During the four years of circling Saturn, Cassini has taken a close look at the panorama of Saturn and made a comprehensive survey of Saturn and its many satellites.
Cassini has been taking comprehensive and complete pictures of the Saturn family since January 2004.Camera carried by Cassini, BihubbleSpace telescopeThe performance of similar cameras on is better.
Before entering orbit, on June 11, 2004, itIapetusThe survey was carried out and extremely clear pictures of the satellite were taken.Titan is the farthest satellite of Saturn, with a radius of 110 kilometers. Scientists suspect that it is a satellite captured by Saturnasteroid。Cassini passed 2000 kilometers away from it, and its mass and density were measured.
On February 17, 2005, the Cassini will leaveEnceladus1179 kilometers away, and on March 9 of the same year, it was 499 kilometers away.Enceladus has a radius of 250 kilometers, and its surface is very bright, reflecting almost 100% of the sun's light.Scientists suspect that its surface is a smooth ice layer. Cassini will detect its magnetic field to determine whether there is saline water under its surface.
From April to September in 2005, the orbit of Cassini will change fromSaturn equatorThe face changes to an angle of 22 degrees with this planeSaturn's ringsAnd the atmosphere to further explore the structure of the ring, the material particles that make up the ring and the physical properties of Saturn's atmosphere.
From September to November 2005, the Cassini will approach one by oneEnceladus、Rhea、TitanandEnceladusAnd observe them respectively.Titan has a radius of 560 kilometers, and Rhea has a radius of 870 kilometers. Their appearance is very similar to our moonCrater。Titan is located intitanAndIapetusIt is irregular in shape, with the longest diameter of 175 kilometers, much like an asteroid.Titan has a radius of 530 kilometers, and its density is the same as that of water. It is likely to be an ice ball.
From July 2006 to July 2007, Cassini will systematically monitor and photograph Saturn, Saturn's rings, SaturnMagnetosphereImage of.From July to September 2007, it will take another image of Saturn and its family, and on September 10 to about 1000 kilometers away from IapetusIapetusObserve.The radius of Iapetus is 720 kilometers. One side of its surface is very dark, but the other side is close to white, which is very strange.
From October 2007 to July 2008, Cassini will further increase the angle between its orbit and Saturn's equatorial plane to 75.6 degrees.In this way, Cassini can better observe Saturn's halo, measure the magnetic field and particles far away from the equatorial plane of Saturn, monitor the polar regions of Saturn and observeSaturn auroraPhenomenon.In the meantime, on December 3, 2007 and March 12, 2008, it will approachEpimetheus, observed the satellite 6190 km and 995 km away from Eleven Titan respectively.
On August 17, 2015, it was the fifth time that the detector passedEnceladusThe surface is 474 kilometers away from the satellite.[2]
After nearly 20 years away from Earth, the probe officially entered the "grand finale" of the mission on April 26, 2017, crossing between Saturn and Saturn's ring for the first time, and observing Saturn closely.
Pic. 2 Cassini Falls into Saturn
On September 15, 2017 Beijing time, the Cassini Saturn probe was about to run out of fuel, and scientists controlled it to crash into Saturn. At 19:55 Beijing time, Cassini lost contact with the Earth, and it entered the atmosphere of Saturn and burned as part of Saturn.This is the end of Cassini's mission.
In January 2019, American researchers used the latest data sent back by the Cassini Saturn probe to calculate that the duration of the day on Saturn was 10 hours, 33 minutes and 38 seconds, which was about 6 minutes shorter than the measurement value more than 20 years ago.[3]
Equipment composition
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CassiniPlasmaSpectrometer (CAPS): used to detect Saturn'sthe ionosphereAnd magnetic field.
Figure 3
Cosmic dustAngstromAnalyzer(CDA): It is used to detect cosmic dust near Saturn.Composite infrared spectrometer (CIRS): used to measure the temperature and composition of the measured object.
Cassini carried the Huygens sub detector, which was filled with liquid methanetitanLog in onHuygens worked on Titan for 24 hours, focusing on detecting possible signs of life on TitanTitan is the planet that scientists believe is the most likely to have life in the solar system except EarthIt is Saturn's largest "moon", calledTitan。
Exploration task
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overview
With“Cassini”The spacecraft successfully entered the orbit of Saturn, the second in the solar systemMegaplanetsFor the first time, a man-made "satellite" has been added around.The Cassini exploration is considered to be the most complicated interplanetary exploration program implemented so far. Its close observation for at least four years will not only deepen scientists' understanding of Saturn, but also help to uncover the secrets of the formation of the Earth and life.
Run around
Fig. 4 Titan may have underground ocean
According to the plan, Cassini will "get close" to Saturn's seven satellites 52 times in the course of 76 weeks around Saturn in the next four years.Among them, Saturn's largest satellite -——titanThe detection of is particularly desirable.Cassini has flown over Titan's surface for about 950 kilometers 45 times in four years, and plans to drop the Huygens probe on this satellite.Scientists believe that humans maytitanFind clues on how the Earth forms an environment conducive to the growth of life.
HuygensThe detector officially disengaged on December 24, 2004 (Christmas Eve)“Cassini”The moon Titan began its four million kilometer journey to Titan.After a long journey of 20 days, the probe passed through the outer atmosphere of Titan on January 14, 2005 and launchedparachuteLanded, and carried out two and a half hours of scientific exploration on Titan (because of the limited energy carried by itself).The results of the exploration will be transmitted back to the scientists on earth through Cassini.The Huygens probe is the firstMoonOne other thanNatural satelliteMan made detector landing on the ground.
Rich in nitrogen
Among the major planets and their satellites in the solar system, only the Earth andTitan's atmosphereIt is rich in nitrogen.It is speculated that there may be a large number of methane likehydrocarbon。Scientists say,titanThere may be many compounds refrigerated on the earth, and some similar compounds may have existed on the earth before the birth of life.Some scientists even believe that“Cassini”And the Huygens exploration results will show that Titan will be more similar to the early Earth than the current Earth.
Those involved in this exploration planEuropean Space AgencyScientists let.Pierre.Lebreton said: "In a sense, Cassini and Huygens are like time machines, taking us to explore a world that we have never seen before. That world is like our earth 4.5 billion years ago."
according toSina TechnologyNews On July 2, 2012 Beijing time, according to the website of NASA, the latest news from the Cassini probedata displayTitan, Saturn's largest moon, may have a liquid water layer under its icy surface.Cassini is still working hard to send us information about distant planets.
hotspot issues
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Not landing on Saturn
Q: Cassini's plan is to fly around Saturn. Why didn't it land on Saturn.
A: Because Saturn itself is a "balloon".itsatmosphereIt is tens of thousands of kilometers thick and has a small core.Since there is no land on the surface, the spaceship cannot land.Even if it reaches Saturn, the spacecraft may be crushed and burned by its huge pressure.
Although it won't go deep this timeSaturns atmosphere The Huygens probe carried by the spacecraft will land on Saturn's largest satellite——titan。Titan is similar to the icy earth 4 billion years ago, and it can surprise us.
Arrive at Saturn
Q: Man has landed on the moon and plans to march to Mars.Is it possible for us humans to reach Saturn?
Answer: It is impossible and unnecessary for humans to go to Saturn, because Saturn is not a solid planet.Of course, the plan of sending astronauts to Saturn to fly and observe around it is possible and will come true sooner or later, but there are still many unsolvable problems:
First,flight timeToo long, what about the daily life of astronauts?
Second, as mentioned above, the spacecraft cannot land on Saturn.
Third, the Cassini probe bought a "one-way ticket" and could never return to the earth. For astronauts, safe return is the first priority.
Strange sailing route
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General
According to the principle of gravitational boosting, scientists designed a path for Cassini to SaturnWisdom curveThe uniqueness of this wisdom curve lies in: first, it did not fly directly to Saturn, but first ran inward to the sky over Venus;Secondly, it circled the earth several times before aiming at Saturn. The whole journey reached 3.52 billion kilometers, more than 2.5 times the actual distance between the earth and Saturn.Its flight path is a rotating curve, which is severalhyperbolaInterceptThe combination of looks likeField snailSpiral on the back.[4]
boost
The first Venus gravity boost time: April 26, 1998
Boost height: 337km
Speed before boost: 37.2 km/s
Speed after boosting: 40.9 km/s
Gravitational boosting speed: 3.7 km/s
Venus's second gravitational boost time: June 24, 1999
Boost height: 598 km
Speed before boost: 39.2km/s
Speed after boost: 42.3 km/s
Gravitational boosting speed: 3.1 km/s
(The following is flying against the direction of the solar gravitational field, and the speed is becoming slower)
On October 15, 1997, Cassini was launched and flew away from the earth's gravity to space at a speed of 12.4 km/s.However, Cassini did not aim at the orbit of Saturn far from the sun. Instead, it went in the opposite directionEarth revolutionThe inner side of the orbit flew away, and it turned out that it was going to Venus for help.Venus is the closest planet to the Earth, with an average distance of about 41.5 million kilometers. It is the most suitable first station for the probe to borrow power.
The launch time of Cassini has also been carefully arranged so that it can meet Venus at the right time and at the right angle to borrow the gravity of Venus.Cassini will pass after launchHohmann transfer orbit It happens to fly over Venus, and when it flies over Venus, it is also in the northeast direction of the sun (from the Earth), so that Cassini can take advantage of the power and fly towards the outside of the solar system.
Fly to Venus
When Cassini was launched on October 15, 1997, Venus was just on the other side of the sun opposite to the earth (this is called "Shanghe"). When Cassini left the earth, the speed was about 26 km/s (the speed of the probe after leaving the earth was based on the sunFrame of reference(calculated) flew to the orbit of Venus. As it was flying along the direction of the solar gravitational field, the speed of Cassini was gradually accelerating, and finally reached about 37 km/s.
The first time Venus borrows power
On April 26, 1998, Cassini passed Venus for the first time 300 kilometers above Venus, gaining an acceleration of 3.7 kilometers per second.Increase its speed from 37.2 km/s to 40.9 km/s.In addition, the reason why Cassini is so close to Venus is that it wants to obtain a larger turning angle from this gravitational boost of Venus. Generally speaking, the turning angle generated when it slowly flies over a planet near is much larger than that generated when it quickly flies over in the distance.When Cassini flew out of the gravity range of Venus, not only its speed increased, but also its flight direction was changed by the gravity of Venus, and it flew to the outside of the solar system.
The second time Venus borrows power
After Cassini passed Venus, the increased speed can support it to fly awaysunlightMore distant orbits, but Venus's gravity is too small, and Cassini cannot use a single gravitational boost to send itself to a higher planetary orbit, so when Cassini flew toEarth orbitBetween the orbit of Mars, the speed gradually increasesSlower, was pulled back to the inside by the sun's gravity again, and returned to the orbit of Venus again on June 24, 1999, and was accelerated again by the gravity of Venus.
Return to the Earth for help
In the precise calculation of scientists, maybe this is not enough to support the arrival of Cassiniouter planetAs a result, Cassini's next target is Earth and Jupiter.Therefore, before the second borrowing, we should calculate the Hohmann transfer orbit between Venus and the Earth, and also calculate the Hohmann transfer orbit of Cassini from the Earth to Jupiter.In this way, we can borrow from Venus to the Earth and then to Jupiter without any difference.
After the second flyby of Venus, two months later, Cassini flew over the earth on August 18, 1999. After gaining the acceleration of the earth's gravity, it finally left the earth and headed for the cold and dark layman aloneInterstellar space。In January 2000, it successfully passed through the thornyAsteroid belt。
Jupiter borrows
In December 2000, Cassini flew about 10 million kilometers away from Jupiter.Jupiter is too big. If the conditions are right, we will fly around itspacecraft, may fly away from the sun forever under its powerful boost.Therefore, for the Cassini to fly to Saturn, Jupiter's afterburner is absolutely indispensable.Finally, it flew to Saturn, its real destination.
Finally came to Saturn
On May 18, 2004, the gravity from Saturn exceeded that from the sun for the first time, and Cassini officially entered the Saturn system;On July 1, 2004, Cassini began its exciting "last jump" into the orbit of Saturn:field of gravitySaturn "captured" and plummeted. It launched the deceleration rocket and made the final critical deceleration, which lasted for 96.4 minutes.Subsequently, Cassini successfully entered the predetermined orbit, becoming the first SaturnArtificial satellite。
"Cassini" was precisely positioned during this long 7-year flight, and the orbit of Saturn entered was very close to the original planned orbit.Such a complex acceleration and flight route determines that at the moment of launch, the direction and force of launch should be calculated accurately, and the time and position of borrowing from Venus, Earth and Jupiter should be calculated at one time. The precise calculation of scientists is really impressive!Here, thanks to the luck of mankind, because any unexpected small stone in space may crush Cassini.[4]
Detection results
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overview
Figure 5 Cassini orbits Saturn. Different colors represent different years
According to NASAOfficial websiteIt was reported on October 17 that on October 15, 2012, NASA“Cassini”The 15th anniversary of the launch of the spaceship.Since its launch on October 15, 1997Interplanetary probeIt has traveled more than 3.8 billion miles (6.1 billion kilometers), enough to orbit the Earth 152, 000 times.In two flyoversVenus, Earth andJupiterLater, Cassini headed for Saturn and entered its orbit in 2004.So far, this probe has observed Saturn, its rings and satellites for eight years.
A team led by scientists from the Southwest Research Institute of the United States, using the data provided by NASA's Cassini probe, detected phosphorus, the key element of life, in the oceans of Enceladus, which exists in the form of phosphate.Relevant research papers were published in the journal Nature on June 14, 2023.[11]
Rhea
Ultra clear shooting of frozen surface
According to the United KingdomDaily MailReported on March 17, Figure 5 shows NASA“Cassini”Proximity of No. 1 detectorRheaThe original photograph taken when the surface is.From the picture, we can clearly see the frozen surface of Rhea, and millions of space rocks collide to form a largeMeteorite crater。When Cassini took these photos, it was about 1.2 billion kilometers away from the earth.
When Cassini reached 997 kilometers above the surface of Rhea, the rugged surface of Rhea was photographed.It is reported that Rhea isSaturnian system The second of 62 satellitesLarge satellite, with a diameter of 1500 kilometers.BiggesttitanIts volume is 3.5 times that of Rhea, and its emissivity is very good. There are a lot of ice materials on its surface, as well as many meteorite craters.It is reported that Rhea issolar systemThe inner meteorite is one of the planets with the most serious collision.
Rhea is composed of rocks and ice water,surface temperature Low, 218 below zerocentigradeTo minus 173 ℃Rock hardnessIt is larger than the earth.Besides measuring Rheagravitational fieldForceThe Cassini probe also searched for dust samples when flying over the satellite, so as to determine the level of small meteorites impacting its surface.
catch
Fig. 6 Venus surface
NASA's“Cassini”The spacecraft previously released this spectacular picture of Saturn, which was taken when it flew past Saturn's shadow.The camera faces Saturn and the sun, so the planet and its rings are backlit
This is often called "Earth'stwin brothers”The uniqueness of the planetportraitAccording to.This amazing picture of Venus captured by NASA's Cassini spacecraft shows that it is moving fromSaturn RingThrough.
Very far away from Saturn means Venus looks like a white dot in the picture, which is located at the top right of the picture.Although Venus hascarbon dioxideThe atmospheric temperature of the composition reaches nearly 900Fahrenheit degree(500 ℃), the surface pressure is 100 times that of the earth, but it is considered as the twin brother of our green home, because their size, mass, rock composition and orbit are almost the same.AndMercuryLike the Earth and Mars, Venus is a rocky "land" planet in the solar system that orbits relatively close to the sun.It is surrounded by a thick cloud of sulfuric acid, so it looks very bright.
Figure 7 Surface of Rhea
NASA said that this perspective is based onSaturn RingLook down at the dark side of Saturn's ring at an angle of about 17 degrees.This figure was used on November 10, 2012“Cassini”The wide-angle camera on the spaceshipvisible lightRange shot.The bright arc in the image is part of Saturn.From FigureThe outline of a part of the ring behind Saturn can be seen at 7. The front of Saturn is slightly illuminated by the sunlight scattered by Saturn's ring.[5]
find
American SpaceThe scientists of the Bureau's "Cassini" project found that there seems to be athe NileSimilar but much smaller river: this river is located on Saturn's moon Titan, and it leads from the "source" to a huge ocean, with a length of more than 400 kilometers.This is the first time to have such high-definitionimage displayThere is such a huge "water system" outside the earth.
Scientists infer that this line is located attitanArcticThe river is full ofLiquid hydrocarbon, because in HDradar image The whole river is dark, indicating that the surface is flat.
Shoot the Earth
The responsibility of taking photos is“Cassini”NoSaturn probeAnd MessengerMercuryDetector.NASA said in a statement on the 18th that the two probes are adjusting their status and will focus on the Earth on July 19 and 20, 2013.NASA also set up a special topic of "waving to Saturn" on its official website, calling on people to go out of their homes and welcome this rare opportunity of "interstellar photography".
The time when Cassini took pictures of the Earth wasUS Eastern TimeFrom 5:27 to 5:42 on the 19th（Beijing Time17:27 to 17:42) for 15 minutes.At that time, Saturn will block the dazzling light of the sun, providing a perfect opportunity for Cassini to take pictures of the Earth.Of course, it doesn't matter if you don't take photos at that time, because "Cassini" is 1.44 billion kilometers away from the earth when taking photos, and the earth will only be a small point in the photos eventually.[6]
Discover Saturn's rings
The Cassini Huygens Saturn probe has realized the orbit around SaturnOrbital flightAnd sent back a group oftitanThe latest and clearest picture of Titan.Scientists are both excited and puzzled.
Saturn's halo and Titan have become the two most concerned by scientistshot topicAnd they also found that it might help them findSaturn's ringsSome new clues about its emergence and future demise.The latest discovery of Saturn made scientists do more: command the Cassini Huygens probe to approach Saturn again.The second approach to Saturn may begin at the end of December 2012. At that time, the Huygens probe from Europe will take 2.5 hours to cross the atmosphere of Titan and land on the surface of Titan.
Although there is no evidence that Titan has water, the latest discovery of Cassini Huygens has opened the eyes of planetary scientists.Mark Liss, the program manager in charge of the Huygens probe landing on the surface of Titan, said: "In just one weekend,We changeThe past view was overturned from the foundationObservation stationandhubble space telescope Some data observed. "[7]
Study Titan structure
Use special equipmentFilterScientists have detected a large area of bright or dark Titan's surface covered by thick clouds.Clearly, these differences in light and shade are evidence of the rugged surface of Titan.Scientists have found at least one circular pattern in the photos sent back by Cassini, which may be a large crater left by Titan's impact by unknown visitors from space.In addition to the round outline, there are some patterns full of wide lines on the photos.[8]
Different clouds
Scientists found that, except for a particularly dazzling cloud, there was almost no trace of cloud in Titan's sky.This particularly dazzling cloud areaU.S.AOfArizonaIt's about the same size, located on the TitanantarcticIn Saturn's summer, you can get light here all day long.This rare cloud takes four or five hours to form, similar to the heaps that appear on the earth in summerCumulus。But the clouds on Titan are mainly composed ofmethaneComposition, not the main water composition.
The Cassini probe also passedspectrometerSome pictures of Titan were taken, and the wavelength of the spectrometer was visible frominfraredLight is unequal.The picture shows that Titan's surface is covered with ice andhydrocarbon。To scientists' surprise, where Titan sends out hydrocarbon signals, it can "send messages" to other places with ice at a certain wavelength.
Earlier, researchers were surprised by the beauty of the rings surrounding Saturn.AbaloneaeThe doctor said that even though he had prepared in advance, he did not expect Saturn's halo to be so beautiful and clear, which was "really shocking".
Scientists also found that the“Cassini division ”Filled with dust, this is the outermost ring of Saturn found so far.This ring can cause 680 collisions between Saturn's materials every second, that is, it can leave about 100000 pieces of Saturn's size every secondSoil pit。
Saturn's huge oxygen flow
When Cassini approached Saturn this time, scientists found that Saturn's halo suddenly ejected a huge flow of oxygen.Where does this oxygen flow come from and where is its fate? Scientists think this is a new mystery and need to find the answer gradually in the future.Donald Shemanski, a member of the scientific team responsible for collecting the data sent back by the Cassini probe, said regretfully, "If this was a big event (on Saturn), we would have missed it."
Shemanski speculated that this huge oxygen flow may also be generated after the collision of two objects three or four miles long in Saturn's ring.
Another question: How old is Saturn's ring?All parties will certainly have different views on this issue.According to rough calculation, if the mass of Saturn's rings gradually disappears in a certain proportion, and there is no other material to supplement it, Saturn's rings like E ring will disappear completely in the next 100 million years.[8]
future
U.S.AColoradoKarolin Bocco, a researcher of the Boulder Space Science Association and the head of the Cassini spacecraft image team, believes that the lines and patterns on Titan's photos may be the initial data for studying the basic structure and characteristics of Titan.Baoke pointed out that other pictures of the larger moon in the solar system also have linear patterns, but Titan has a very unique linear pattern.
The researchers warn that it is impossible to observe the Titan from more than 200000 milesTopographical featuresThe distinction is very clear.What kind of terrain the Titan's surface is still waiting for closer observation by human probes.However, the United StatesUniversity of ArizonaCassini detectorOptical imagingElizabeth Tutor, a planetary scientist of the team, believes that since there are no large number of circular marks found on Titan, this indicates that Titan's geological activities are very active.
Since November 2016“Cassini”The number will start a seriesTrack changeManeuver closer to Saturn.These maneuvers will start outside the F ring (the outermost Saturn main ring).In April 2017, the last close contact with "Titan" will put the "Cassini" spacecraft into the orbit of flying over Saturn in the innermost ring of Saturn.After 22 close flyovers, the gravitational perturbation of the last contact with the distant Titan will make Cassini closer to Saturn.
End Mission
In September 2017, "Cassini" will run out of fuel. Scientists are worried that Cassini may lose control and crash into a satellite around Saturn that may have life, affecting it, so they control "Cassini" to approach Saturn and burn it into the atmosphere of Saturn.Cassini entered Saturn's atmosphere andEchoData on Saturn's atmosphere.
final,Pacific TimeAt 4:55 a.m. on September 15, 2017 (19:55 a.m. on September 15, Beijing time), the signal of "Cassini" disappeared, which means that this probe evaporated under high pressure and high temperature 83 minutes ago and was completely embraced by Saturn.[9]This also marks the end of Cassini's Saturn exploration mission.NASAThe on-site personnel monitored the signal quietly until the last moment. After the on-site person in charge announced that the signal disappeared, all stood up and applauded.The analysis of these final signals may last for several years, and the final signals of this detector may still bring new discoveries.[10]
Scientific research achievements
In June 2023,A team led by scientists from the Southwest Research Institute of the United States, using the data provided by NASA's Cassini probe, detected phosphorus, the key element of life, in the oceans of Enceladus, which exists in the form of phosphate.[12]
world record
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From January 14 to December 13, 2009, Cassini observed a thunderstorm that lasted 333 days on Saturnrecord）。[13]
Overall evaluation
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"Cassini" was precisely positioned during this long 7-year flight, and the orbit of Saturn entered was very close to the original planned orbit.Such a complex acceleration and flight route determines that at the moment of launch, the direction and force of launch should be calculated accurately, and the time and position of borrowing from Venus, Earth and Jupiter should be calculated at one time. The precise calculation of scientists is really impressive!Here, thanks to the luck of mankind, because any small stone in space that happens by accident canCassiniIt was smashed into pieces.
