Farewell to Cassini: the interplanetary station burned up in the atmosphere of Saturn. The last hours of the Cassini probe (15 photos)

September 15, 2017 at 04:55 PDT (11:55 UTC) the Earth stopped hearing the signal from the Cassini radio transmitter. Having completed an almost twenty-year flight and having worked for more than 13 years in the Saturn system, the American spacecraft entered the planet’s atmosphere, transmitting unique scientific data until the last second.

Cassini was launched on October 15, 1997 and entered orbit around Saturn on July 1, 2004. Over the course of 13 years, it made 293 orbits around the planet and made 162 close flybys of its moons. The device mapped their surfaces and measured their chemical composition, tracked the evolution of seasonal processes on Saturn and Titan, and studied the planet's rings, its magnetosphere, charged particles and waves in cosmic plasma.

A brief overview of Cassini’s orbital “tour,” which lasted nine years longer than originally planned and consisted of several successive missions, was made in NK No. 7, 2017.

The "Grand Finale" of Cassini's twenty-year journey was planned seven years before it was to take place. The decision to send the device into the atmosphere of Saturn was due to fears of contamination of the planet's moons by terrestrial microorganisms - especially Enceladus with its subglacial ocean, from which polar geysers erupt. A meeting with representatives of the earth's biosphere, which could survive in a viable state on the spacecraft's structural elements, would distort the appearance of local life, if any.

Last five months

The final phase of the expedition began during the S99 phase of the Cassini flight program, which began on April 11. From May 25 to July 9, the command sequence S100 was practiced, and from July 10 to the end - S101, which included 10,657 individual commands.

On April 22, 2017, the last target flyby of Titan took place with a gravity maneuver, as a result of which the lowest point of the spacecraft’s orbit shifted under the ring system. Now the device had to make 22 orbits with an inclination from 62.4° to 61.7° with a period of 6.4–6.5 days, each time passing at the periapsis between the visible surface and the rings of Saturn and moving away approximately 1.27 million km from the planet at the apocenter.

The first “dive” took place on April 26 at the 271st orbit, when Cassini flew at an altitude of 2800 km above the cloud tops of the planet at a maximum speed of 33.957 km/s. The area under the rings turned out to be practically free of dust - the RPWS device for recording radio and plasma waves noted only a few particles 1 µm in size and below. This gave rise to hope for the success of all subsequent flybys and for the implementation of a scientific program, including mapping the gravitational and magnetic field of the planet, photographing and probing the rings and surface of Saturn from a minimum distance, and direct measurements of the composition of the upper atmosphere.

Of the 17 first flights, the lowest was on May 15 at an altitude of 2660 km, and the highest was on May 28 at an altitude of 3900 km above the clouds of Saturn. It also became the deepest penetration of the spacecraft into the inner ring D. To change the height of the periapsis between individual orbits, Titan flybys on May 23 at a distance of 118,000 km and on July 10 at a distance of 264,000 km, as well as two small corrections, were used. On May 10, the OTM-471 maneuver was carried out with a speed increment of only 21 mm/s by turning on the engines for 14 seconds. The last correction of OTM-472 was more significant - on July 15, the engines worked for 153.125 seconds and changed the spacecraft speed to 143.64 mm/s.

On August 11, Cassini passed 195,000 km from Titan, due to which the altitude of the spacecraft’s pericenter decreased by 1,200 km. Therefore, in the last five flights of the spacecraft, it “struck” along the very edge of the atmosphere at an altitude of 1710 km to 1630 km, and to maintain orientation, not flywheels were used, but low-thrust liquid propellant engines. The exact height of each span has not been published; We only know that the third of them was the record low on August 27. These five orbits served as rehearsals for Cassini's final entry into the atmosphere.

When crossing the plane of the rings at speeds from 33.6 km/s to 35.0 km/s, Cassini, as a rule, oriented its highly directional antenna forward along the velocity vector to protect the more “sensitive” parts from dust particles. When “diving” into the D ring on the 276th and 277th orbits, however, there was little dust, and on the 281st it was decided not to do this; the device passed safely through the lowest section of the ring and was not damaged. Cassini carried out most of its flights in autonomous mode with subsequent “reporting” of the results, but on orbits 273, 274, 275, 278, 280 and 284 it transmitted directly to Earth while crossing the plane of the rings.

Already in its first flyby, the ISS camera captured images of Saturn with a resolution 10 times better than in the previous 13 years. Photographing the planet, rings and satellites and probing them with VIMS, CIRS and UVIS spectrometers in various combinations was carried out on all subsequent orbits. In the rings, of particular interest were various edge effects, disturbances and small instabilities, known under the code name “propellers”. They were named after the great pilots of the 20th century - Bleriot, Santos-Dumont, Earhart.

Of the satellites, Titan and Enceladus were most often observed, especially its southern polar region with geysers, but there was time to photograph Dione at the 280th orbit and for very small satellites. The tiny Bebhionn - a double object with a diameter of only 6 km, extending at the apocenter 25 million km from Saturn - was captured on orbits 272, 273, 276, 280 and 282. The twice larger 14-kilometer Kiviuk, which is also suspected of a binary nature, photographed on July 28, August 9 and 16, and Trümr on August 23 and September 3–4. In addition, on June 6, spectrometry of the star ε Orionis was carried out during an eclipse by its satellite Tethys (Tethys).

On August 10 and 16, the ISS camera observed Neptune in the sky near Kiviuk. This meant that Cassini was able to image eight of the nine planets (including Pluto, but excluding Mercury).

The radio complex was used to determine the characteristics of Saturn’s gravitational field and to illuminate the rings, and the CDA cosmic dust analyzer tried to “catch” their matter. The RADAR device scanned them with a resolution from 4 km to 100 m on the 276th and 277th orbits, and also studied the atmosphere of Saturn: on the 288th orbit in passive mode, and on the 290th and 292nd in active mode . Scientists were interested in ammonia concentrations in the atmosphere below the ammonia cloud layer as evidence of Saturn's weather.

The 292nd orbit, also the 22nd in the Grand Finale series, began with the passage of the apocenter September 5 at 18:47 UTC onboard time. 9th of September at 00:09–00:14 the device sequentially passed the plane of the rings and the pericenter of the orbit and 13 hours later began transmitting the received information to Earth. 11 September, towards the end of its orbit, Cassini experienced the pull of Titan. The flight was one of the distant ones - at 19:04 UTC the device passed 119,049 km above the surface of the satellite - but the gravitational influence of Titan reduced the speed of the spacecraft by 29 m/s, as a result of which the pericenter of the orbit plunged into the atmosphere of Saturn.

The 293rd orbit has begun 12-th of September at 05:27 UTC onboard time. Over the past two days, the spacecraft has imaged Titan and Enceladus, which is setting beyond Saturn's northern horizon, the planet and individual features of its rings, including a compaction with the code name Peggy on the outer edge of the A ring, which may represent a forming small satellite. Finally, the VIMS spectrometer and other optical instruments observed the area of ​​the upcoming Cassini fall. The last photo was taken September 14 at 19:58 UTC.

At 21:45 UTC, according to the time the signal arrived on Earth, which corresponded to 20:22 onboard time, the last 14.5-hour communication session began. Cassini transmitted information at a frequency of 8.43 GHz at a speed of 66,360 bps, freeing its solid-state storage device from recorded data within 11 hours. The spacecraft signal reached the Long-Distance Network station in Goldstone with a power level of -128.06 dB, that is, 1.56.10-19 W. The latest photographs were accepted and promptly posted in raw form on the Cassini project website.

Once you have finished resetting your data, September 15th at 07:14 onboard time, the spacecraft began a five-minute turn to such a position that the mass spectrometer of ions and neutral atoms INMS was located at the front of the spacecraft in the direction of flight and could directly measure the composition of the upper atmosphere of Saturn and its changes in altitude. On Earth, the 70-meter DSS-43 antenna near Canberra, capable of supporting reception at a speed of 124,426 bps, took over the baton. Cassini, however, immediately reconfigured the board so that in the last three and a half hours, scientific information was sent to Earth at a speed of 27,650 bps in near real time - just a few seconds after it was received on board. The transmission was carried out in the X- and S-band with reception on the 70-meter and, by way of reservation, on one of the 34-meter antennas in Australia. In addition, Doppler observations were carried out by the New Norcia station of the European Space Agency.

The instructions to the device for the final stage of the flight were simple. Cassini approaches the planet from the northern hemisphere. The entry point into the atmosphere is on the day side, 10° north of the equator. The device must carry out measurements with eight of 12 instruments (INMS mass spectrometer, CIRS and UVIS spectrometers, magnetospheric and plasma instruments MIMI, RPWS, MAG, CDA cosmic dust sensor and a highly stable radio complex generator) and transmit data to the last. This opportunity will be provided by on-board liquid propellant rocket engines with a thrust of 0.5N, supporting the orientation of the highly directional antenna to the Earth within ±0.1° from the specified one due to the issuance of short pulses.

Ballistics experts predicted that Cassini would feel the effects of Saturn's thin upper atmosphere at an altitude of 1915 km above the cloud tops and above a pressure level of 1 atm. Like all such boundaries, it was to a certain extent conditional. When flying outside the atmosphere, it is enough for the engines to fire once every few minutes, compensating for only a slight turning moment from the planet’s gravitational field. With increasing density of the gas shell and velocity pressure, the turning torque and operating frequency should increase. The conditional entry point was taken to be the moment when the duty cycle—the proportion of time during which liquid-propellant rocket engines operate—reaches 10%.

To cope with the effect of the atmosphere on the protruding elements of the Cassini structure, most notably the 11-meter magnetometer boom, the liquid-propellant rocket engines will gradually increase the duty cycle from 10 % to 100 %. This stage will take about a minute, during which the earthly vehicle will descend along a gentle trajectory to the 1500 km mark. Here the disturbing moments from the oncoming flow will become stronger than the stabilizing impulses of continuously operating engines. The device will begin to turn, going into an uncontrolled somersault, and the Earth will move away from the axis of its antenna. In another thirty seconds, the Earth probe will begin to collapse, and a couple of minutes later the planet’s atmosphere will absorb its debris.

The latest published forecast was that Cassini would begin re-entry on September 15 at 03:31 PDT (10:31 UTC) onboard time and lose orientation a minute later. 83 minutes 27 seconds after this, at 04:55:16 PDT (11:55:16 UTC), the last signal from the spacecraft will reach the Earth, and it will no longer hear Cassini.

In general, this prediction came true: the device was able to withstand the atmosphere of Saturn for 91 seconds, and in the last 20 seconds the engines worked at 100 % of their capabilities. The useful signal in the X-band with scientific information was interrupted at 11:55:39, and in the S-band at 11:55:47. According to telemetry data, it was clear that in these last 8 seconds Cassini began to slowly turn back. Then telemetry disappeared from the signal received on Earth and only the carrier frequency remained, but after 24 seconds it also stopped arriving. Having buried itself in the atmosphere of Saturn at an altitude of 1391 km at a speed of 34.449 km/s, the earthly apparatus ceased to exist.

“This is the final chapter of an amazing mission, but it is also a new beginning,” said NASA Associate Administrator Dr. Thomas Zurbuchen. “Cassini’s discovery of ocean worlds on Titan and Enceladus changed everything and shook our understanding of amazing places to look for life beyond Earth to its core.”

“Cassini may have left us, but its scientific gifts will keep us busy for many years to come,” said JPL project scientist Dr. Linda J. Spilker. “We have only scratched the surface of what we can learn from the mountain of data he has sent us over his lifetime.”

“The Cassini management team did an absolutely stellar job of bringing the spacecraft to its fitting end,” said project manager Earl H. Maize. “From designing the trajectory seven years ago to navigating 22 heart-stopping dives between Saturn and its rings, it was this fantastic group of scientists and engineers who came up with a fitting end to a great project.”

Over 20 years of flight, Cassini covered 7.9 billion km, received and executed 2.5 million commands as part of 101 stages of the flight program, carried out 360 maneuvers and corrections*, discovered six satellites of Saturn, took and transmitted 453,048 images to Earth, and a total of 635 GB of scientific information , on the basis of which 3948 scientific articles were published by the end of the expedition.

In a few hours, one of the longest, most expensive and successful space missions in the history of space exploration will end its journey, burning up in the atmosphere of the most spectacular giant planet, Saturn. The Cassini spacecraft, which has been operational for almost 20 years, will transmit the latest unique data. the site talks about the history and key discoveries of this amazing device.

Name and development

It must be said right away that calling the mission simply Cassini is incorrect. The correct name of the joint brainchild of NASA, ESA and the Italian Space Agency is Cassini–Huygens. The orbital device, which was developed in the USA, was named in honor of Giovanni Domenico Cassini, who discovered the four satellites of Saturn (the so-called “Louis stars”: Iapetus, Rhea, Tethys and Dione) and the gap between the rings - the Cassini gap; The lander was named Huygens, in honor of Christiaan Huygens, who built a mathematical model of Saturn's rings and explained the phases of the planet. The Italian space agency independently developed and built the long-distance space communications antenna, with the help of which the probe communicates with the Earth.

Giovanni Domenico Cassini

Wikimedia Commons

This was one of the first experiences of cooperation between Europe and America in space and, perhaps, the most expensive. The total cost of the mission is 3.26 billion US dollars, of which NASA spent 2.6 billion, 500 million and 160 million were donated by Italy (for comparison: the cost of the first (successful) Indian mission was only 70 million). It was a very large device: the launch mass of the complex was 5712 kilograms. In the entire history of unmanned planetary exploration, only three missions were heavier, and all were Soviet. “Phobos-1”, “Phobos-2” and “Mars-96”, which never left the vicinity of the Earth.

Assembling the apparatus at NASA

The idea to create a heavy vehicle (the so-called “Flagship” class; among the devices of this level are the Jupiterian Galileo and the Martian Curiosity) arose back in the 1980s, after the Voyager spacecraft flew past Saturn. 27 countries participated in the creation of the apparatus. A new heavy probe with a descent module and a large supply of plutonium to generate electricity (there is already very little light in the Saturn region, and the devices have to be powered with electricity using an RTG - a radioisotope thermoelectric generator, in which heat from the decay of plutonium is directly converted into electrical energy) set off for Saturn October 15, 1997 with a fantastically beautiful night start.

Launch of Cassini

During flights from planet to planet, the direct route is the most unprofitable: a lot of fuel has to be wasted, so spacecraft always use so-called gravitational maneuvers, accelerating in the gravitational field of other planets. So Cassini immediately after launch went... to Venus. Yes, sometimes you have to fly in the opposite direction to save money. The device performed its first three gravity maneuvers near the second and third planets of the solar system. On April 26, 1998 and June 24, 1999, the probe flew past Venus twice, and on August 18, 1999, it visited our Earth, at the same time testing its cameras and taking a luxurious portrait of the Moon.

Photo of the Moon taken during the third Cassini gravity maneuver

Vortex at Saturn's north pole

Of course, a lot of research has been devoted to the rings of Saturn. Some of them (for example, the Ante arc or the Pallene ring) were discovered by Cassini itself.

On April 26, 2017, the Cassini spacecraft entered the last stage of its life, called the "Grand Finale" - the probe approached Saturn's largest moon Titan for the last time before ending its mission. Cassini has already sent the last photos it took to Earth, after which it came as close as possible to Titan, the most Earth-like moon of Saturn, the gravity of which allowed the device to accelerate and go on its last flight in orbit between the rings of Saturn and the upper layers of the atmosphere of the gas giant, NASA reports.

Researchers hope that during the final flight of the Cassini probe, the device will be able to collect the maximum amount of previously unknown information that will allow them to determine the length of Saturn's day, as well as the age of its rings. True, being in Saturn’s orbit will cause the probe to fall into the dense layers of the giant planet’s atmosphere, as a result of which it will simply burn up.

The Cassini probe set off on its final flight between Saturn and its rings - latest photos

The Cassini probe's final flight around Saturn will be the finale of a 12-year mission, during which it obtained many new photographs of the planet and also illuminated its hydrocarbon lakes and seas using its radars. But before complete combustion in the atmosphere of the gas giant, the device will have time to make another 22 flights between the rings of Saturn and their “lord,” collecting and transmitting data about this planet until its very end.

Let us recall that the Cassini probe first arrived at Saturn on June 30, 2004 and became the first artificial satellite of this planet. On January 14, 2005, the Huygens probe, which Cassini carried on board, first landed on Titan. On September 15, 2017, the research mission of the Cassini spacecraft will end - over the years of studying the Saturn system, the probe passed near this huge satellite 126 times, and each time it switched to a new trajectory that directed it to new research objects.

The Cassini probe is the last flight between Saturn and its rings (video):

On September 15, 2017, the Cassini spacecraft burned up in Saturn's atmosphere. This event united space lovers all over the Earth. Cassini was not just any satellite. He served as one of the main symbols of space research, and science in general. The same symbol as the Hubble telescope or the Large Hadron Collider.

Cassini was launched back in 1997. Just imagine - this is the year Titanic, Quake 2 and the first Fallout were released. During the work of Cassini, an entire generation grew up. Many modern astronomy lovers became interested in space thanks to Cassini. Therefore, today we remember the history of the mission and pay it the tribute it deserves.

From concept to launch pad

In 1980–1981, the pair made a historic flyby of Saturn. They took the first detailed photographs of the planet, its rings and satellites, and analyzed the atmosphere and magnetic field. The results amazed astronomers. It turned out that Saturn's rings consist of hundreds of thin rings forming a complex system. Titan, Saturn's largest satellite, was obscured by a layer of hydrocarbon haze that was opaque in the visible spectrum. The satellite Iapetus looked as if the designer of the solar system had forgotten to paint it: one of its hemispheres shone brightly, like fresh snow, the other was black, like soot.

Cassini assembly

The Voyagers were physically unable to stay near the planet and study it longer. To unravel the mysteries of Saturn and its moons, a fundamentally different mission was required. A device that could go into orbit around the planet and explore it for several years.

In 1982, scientists from NASA and ESA began the first consultations about a joint long-duration mission to the Saturn system. It would consist of an orbiter and a lander that would land on Titan and see what was happening on its surface. The mission was named after Giovanni Cassini, the famous 17th-century astronomer who discovered the four moons of Saturn and the gap in its rings.

The negotiations were not easy. At that time, relations between NASA and ESA were complicated by the cancellation of a number of joint projects. But in 1988, the partners finally agreed on the distribution of responsibilities. NASA was supposed to build the Cassini orbiter, ESA was supposed to build the Huygens descent probe for Titan. It was named after Christiaan Huygens, who discovered the rings of Saturn and Titan itself.

Model of the Huygens apparatus

Cassini's problems didn't end there. The total budget of the project exceeded three billion dollars (80% of the funds were allocated by NASA), and the American Congress has repeatedly threatened to deprive the project of funding. Even at NASA, not everyone supported the mission. But Cassini survived, thanks in no small part to the efforts of ESA lobbyists. Things even went as far as letters to US Vice President Al Gore asking him not to close the program. As a result, although with difficulty, the mission received the necessary funding.

The latest threat to Cassini is the green ones. Shortly before the launch, environmental activists began demonstrations at Cape Canaveral and filed a lawsuit demanding a ban on the launch. Cause? 32 kilograms of plutonium-238 on board the station. The fact is that the vicinity of Saturn reaches 100 times less sunlight than Earth. Therefore, to generate energy, Cassini was equipped with a radioisotope generator.

Environmental activists stated that in the event of an accident there would be radioactive contamination and demanded to “save the Earth” from Cassini. And no matter how much NASA experts explained that even in the event of an accident the plutonium would remain in a protected container, this could not convince the “greens.” Fortunately, the court did not take into account the environmental horror stories and did not cancel the launch.

Launch of the Centaur rocket with Cassini on board

Seven years in flight

Cassini launched on October 15, 1997 and headed towards... Venus. There is no mistake here. The mass of the station was almost six tons, which made it one of the largest interplanetary vehicles in history: only the Soviet Phobos weighed more. The rocket's power was not enough to send such a colossus directly to Saturn. So engineers took advantage of gravity. Cassini flew by Venus twice, then Earth, and finally Jupiter. These gravity maneuvers allowed the vehicle to achieve the required speed.

Flying past Jupiter, Cassini managed to study this gas giant. He discovered several new storms in its atmosphere and took the highest quality photographs of the planet at that time. At the same time, engineers checked the functionality of the station’s instruments.

"Portrait" of Jupiter made from several Cassini photographs

In the early summer of 2004, Cassini reached the vicinity of Saturn. On June 11, the craft passed Phoebe, one of the planet's most distant satellites, which orbits nearly 13 million kilometers from the gas giant (that's 36 times the distance between the Earth and the Moon). Cassini had only one chance to visit this unusual moon, and its trajectory was specifically designed for a close flyby.

On July 1, Cassini performed an extremely difficult maneuver, on the outcome of which the fate of the entire mission depended. It was successful. Cassini turned on its main engine for 96 minutes and slowed down so that the planet's gravity could pick it up. So it became the first artificial satellite of Saturn in history.

This is how Cassini saw Saturn

Thirteen years for Saturn

"I've seen things you humans wouldn't believe..." If Cassini could talk, it would definitely quote Blade Runner. From the very beginning of its operation, the device began to make discoveries, one more incredible than the other. For those who love statistics, let's say that during the 13 years of its stay at Saturn, the station took about 400 thousand photographs and sent over 600 gigabytes of information to Earth. Based on their results, about 4,000 scientific articles have already been written - and this number will grow, because Cassini data will be analyzed for many years to come. To describe all the achievements of the mission, a whole collection of essays would be required. We will only briefly mention the main milestones.

One of the mission's priority targets was Titan. In January 2005, the Huygens probe separated from Cassini and made a historic landing on its surface. The Huygens images showed complex terrain with areas resembling river beds and coastlines. Photographs from the surface show rounded stones with traces of liquid exposure.

Titan from both sides in the Cassini photo

Subsequently, Cassini completed over a hundred flybys of Titan. The device scanned the surface of the satellite with a radar, and shooting in the infrared range made it possible to look under its haze. It turned out that Titan has lakes, rivers, seas and even rains. But not from water, but from liquid hydrocarbons - a mixture of ethane and methane. The temperature on Titan is such that these substances can exist in three states at once (liquid, gas, solid) and perform the same role that water plays on our planet. This is the only body in the solar system besides the Earth where there is a full fluid cycle, and permanent bodies of water exist on the surface. More precisely, hydrocarbons.

Huygens landing on Titan, concept art

Recording of atmospheric wind on Titan made by Huygens during landing

Overall, conditions on Titan closely resemble early Earth in the pre-oxygen era. The satellite turned out to be a kind of time machine: it made it possible to study the processes that could lead to the emergence of life on our planet. Some scientists even make cautious assumptions that, despite the low temperatures, the simplest forms of life may already exist on Titan.

Mercator Plateau photographed by Huygens

Video of landing based on photographs from the device

But in the Saturn system there was an even more attractive target for astrobiologists - Enceladus. Before the Cassini mission, it was considered simply one of Saturn's many icy moons of little interest. But after Cassini’s first visit to Enceladus, these ideas had to be radically revised.

Enceladus, planet of giant geysers

It turned out that, despite its relatively small size (the diameter of the satellite is 520 kilometers, almost six times smaller than that of the Moon), Enceladus is one of the most geologically active bodies in the Solar System. Its south pole is densely dotted with geysers that constantly emit water into space. This water forms a separate ring around Saturn. The discovery of Enceladus geysers has become a scientific sensation. The Cassini program was urgently changed, and in subsequent years the device visited the satellite more than once. Several times Cassini flew directly through its emissions, analyzing their chemical composition.

Geysers of Enceladus

Data collected by Cassini showed that beneath Enceladus's icy surface lies a global ocean of liquid water. Its depth is estimated at 10 kilometers, the thickness of the ice above it ranges from 2 to 30 kilometers. Chemical analysis of the ejected water revealed salts, organic compounds and substances in it, indicating that active hydrothermal processes are taking place in the ocean of Enceladus. Now this satellite is considered the most suitable place for life in the solar system outside of Earth.

Cassini was able to solve the mystery of the “underpainted” Iapetus. It turned out that the differences in the color of the satellite are due to dust: meteorite impacts knock it out from the distant moons of Saturn, and it settles on the leading hemisphere of Iapetus (this is the hemisphere with which it moves “forward” in its orbit). Dust-covered areas heat up more than neighboring regions. As a result, ice evaporates from them and condenses where the surface temperature is lower: on the trailing side and in the circumpolar regions. A positive feedback is formed: dark areas become even darker, and vice versa.

Cassini also discovered another unique feature of Iapetus - the ring-shaped mountain range "Wall of Iapetus" that stretches along its equator. The unusual formation has a height of up to 13 kilometers, a width of up to 20 kilometers and a total length of about 1,300 kilometers. According to one theory, Iapetus once had a ring, and its particles fell to the surface and formed a wall.

Black and white Iapetus in Cassini images

But, of course, Cassini studied not only the satellites of Saturn, but also the planet itself. Over the years of the mission, the device captured several changes of seasons. They manifested themselves especially clearly in the hexagon - this is the name given to the amazing hexagonal-shaped vortex located at the north pole of the planet. The width of this formation is 25 thousand kilometers, approximately two diameters of the Earth. Cassini recorded how, with the arrival of summer in the northern hemisphere of Saturn, the hexagon changed color from dark blue to golden. The intensity of ultraviolet radiation increased, this triggered photochemical reactions, and compounds (tholins) began to be synthesized at the north pole, which changed the color of the storm.

Saturn's hexagonal vortex in 2016

Cassini has photographed Saturn's ring system many times. The images demonstrated their extraordinary complexity and variability. Numerous satellites of Saturn exert their gravity on the rings of the planet, which is why vortices, waves, kinks, loops and other structures are formed in them. Some small moons orbit directly within the rings. Their gravity accelerates the particles of the rings, which is why ruptures form in them. Other satellites play the role of “shepherds”. For example, the orbits of Prometheus and Pandora pass inside and outside the F ring. The gravity of a pair of satellites holds the particles of the rings in the same orbit, preventing them from scattering in different directions.

The highest quality photo of Saturn's rings

We must not forget about Cassini’s goal of popularizing space research. It turned out to be easy. Saturn is perhaps the most beautiful planet in the solar system, and its photographs have probably inspired many people to connect their lives with space.

One of Cassini's most famous images was taken on July 19, 2013. On that day, the device performed panoramic photography of the planet and its surroundings. At the time of photography, the Sun was exactly behind Saturn, effectively highlighting its rings. One of the pictures also showed our planet. From a distance of 1.5 billion kilometers, it appears as a pale blue dot.

“The Day the Earth Smiled”: the famous photo underwent extensive color correction to make the planets more visible. The earth is a barely noticeable point on the lower right under the rings

Cassini's final adventure

Cassini is often called the ideal space mission. The device operated well beyond its nominal four-year lifespan and completed all tasks without major incident. But, alas, any technology has a factor that limits its operating time. In the case of Cassini, these were the fuel reserves necessary for course corrections. Without it, control of the device would have become impossible. An uncontrolled station could crash into one of Saturn's moons and carry terrestrial microbes there. To exclude such a scenario, NASA decided to burn Cassini in the planet’s atmosphere.

But before this, the device had to survive the final adventure - 20 orbits at the outer edge of Saturn's rings, and then another 22 orbits between the planet's atmosphere and the inner edge of its rings. No vehicle has ever dived into this gap. The maneuver was considered very dangerous, but since the mission was already close to completion, NASA decided to take the risk.

Artist's impression of Cassini's final flight

As before, Cassini brilliantly completed all its tasks. He collected data that should solve the main mystery of Saturn - the age and origin of its rings. According to one version, they formed along with the planet. According to another, the rings are much younger and appeared as a result of the recent (by cosmic standards) destruction of one of Saturn’s moons. Cassini data will be analyzed for many more months, but preliminary results so far speak in favor of the second version.

Cassini had one last task to complete. During reentry, the vehicle used thrusters to keep its antenna pointed at Earth for as long as possible. Already falling apart, Cassini still continued to transmit data on the composition of the gas envelope and the magnetic field of Saturn. Even here, the device managed to exceed the target, surviving in such extreme conditions 30 seconds longer than the simulations predicted. At 11 hours 55 minutes 46 seconds universal time, NASA's deep space communications complex in Canberra received the last signal from Cassini. By that time, the device itself had already disintegrated into fragments and turned into a flaming meteor.

NASA said goodbye to Cassini without mourning. Still, this is not a disaster, but the end of a successful mission (NASA/Joel Kowsky)

The ending of the mission evoked conflicting emotions: pride, admiration, sadness and emptiness. Cassini has been in operation for so long that it is difficult to remember a time when it was not there. You can imagine what the mission participants, who had been working on the project since the 1980s, experienced as they watched the device’s signal disappear.

It becomes even sadder when you realize that you will have to wait at least a decade for the next such expedition to the distant planets of the solar system. Unfortunately, space exploration is a slow business, and there is no mission on the horizon comparable to Cassini's ambition. One can only be consoled by the fact that many new discoveries will be made based on the data collected by the station.

Cassini's legacy will live on for a very long time. The photographs he took of Saturn and its moons will remain with us forever. Thanks to Cassini, we were able to see in all their glory these cosmic bodies that were previously just dots in the sky for us.