The last chord of “Cassini”

In April of this year, the Cassini probe, which has been working in space for nearly 20 years, will officially enter the last stage of its life, named “The Final of the Opera.” Let’s remember how this veteran of space changed our ideas about the shape of Saturn and revealed the secrets of its amazing moons.

Flagship of NASA

The Cassini probe is one of NASA’s most expensive and, at the same time, the longest-running and successful projects created in the past, more money-laden years for the space agency under the so-called “flagship” mission program. In addition to the “Cassini”, it includes the probes Voyager, Viking, the automatic station Galileo, which studied Jupiter, and the Chandra telescope and the Curiosity rover.

“Cassini” was one of the first projects of NASA, in which scientists and engineers took part not only from the USA, but also specialists from the European Space Agency and the Italian space agency ASI. International cooperation allowed NASA to implement this project without delay and to launch it at the originally scheduled time, in October 1997, despite the opposition of the US Congress and activists of environmental movements, which frightened the radioisotope power supply of the probe.


“Cassini” flies through the band of rings in the artist’s view

This source, 33 kilograms of radioactive plutonium-238, allowed Cassini to work out in space and in Saturn’s orbit 2.5 times longer than the planned mission time, and make a lot of discoveries that simply can not be done by observing Saturn and its satellites from Earth.

According to NASA experts, Cassini could work on Saturn’s orbit for a few more years with the gradual disconnection of the devices, but the mission’s leaders decided to complete it in a more exciting way – by making multiple flights through the rings of Saturn and colliding with the giant planet in September of this year . This “last chord” of the mission, named “The Final of the Opera,” will begin in April, when “Cassini” will get close to Titan for the last time and will step onto the trajectory of rapprochement with Saturn.

During these flights through the rings that Cassini began to make in November of last year, the probe managed to get a lot of pictures of these structures from a record-breaking distance, and also considered many new details on the surface of Titan and a number of other satellites of Saturn. These images and scientific data, as the scientists expect, will significantly change our understanding of the structure of Saturn’s bowels and the life of its rings, but the past discoveries of Cassini forced scientists to radically reconsider their ideas about their nature.

Saturn Transfigured

One of the main merits of Cassini is, of course, that this probe and the descent module Huygens, built by the Italian ASI forces, made planetologists look absolutely differently at the moons and other small planets.

When Cassini arrived in the Saturn system and received the first photos of Titan, the unseen big moon of the giant planet, covered with the eternal haze of yellow fog, the scientists were surprised that they saw a kind of twin of the Earth, almost indistinguishable in black and white tones from desert Regions of our planet.

On Titan, as the Cassini images and Huygens data showed, there are seasons, clouds, rains, rivers, mountains, lakes and even whole seas, and the behavior of airflows in its atmosphere, as further observations have shown over more than 13 Years, as a whole is described by the same formulas and laws as on the Earth. Today, many chemists seriously talk about the possibility of life in the cold hydrocarbonic seas of Titan, based on a fundamentally different chemistry than the carbon life on Earth.

Of course, Titan is not only similar to Earth, but also has its own unique and bizarre features. In his atmosphere, as the “Cassini” discovered, strange structures like giant white arrows periodically appear, and in the hydrocarbon seas of Titan there can appear peculiar “islands” from giant bubbles of nitrogen arising in the thickness of their “waters” in themselves with the growth of temperatures .

More surprisingly, in the depths of Titan, as scientists discovered five years ago, relying on the data from the Cassini radar, a gigantic subglacial ocean hides. It is located at a depth of about 100 kilometers from the surface of the moon of Saturn, and its waters resemble the properties and composition of the Dead Sea on Earth. His discovery pointed to a small, but possible existence of familiar forms of life on Titan.

Boiling extraterrestrial life

A much higher chance of finding life on another satellite of the “Lord of the Rings” – on the small ice planet Enceladus. When the “Cassini” only arrived in the Saturn system, scientists noticed that one of its rings consists almost entirely of ice particles, and that a large number of unique cosmic “rivers” of water molecules encircle the planet itself. Ice and water molecules are gradually destroyed in space under the influence of sunlight, which led NASA to look for their source.

It was Enceladus – at its south pole there is a whole “battery” of geysers, periodically throwing out a huge amount of water into space and replenishing its reserves in the ring E, where it was originally found by “Cassini”. In some cases, the force of these eruptions was so high that 100 km of water columns thrown into space by the bowels of Enceladus were successfully photographed by the Hubble Telescope from a distance of about 1.5 billion kilometers in September of last year.

These geysers, which scientists began to call “tiger stripes,” allowed NASA to make one of the most important discoveries concerning Saturn and Enceladus. Analysis of the chemical composition of their emissions, through which Cassini flew several times last year, allowed scientists to make an astonishing conclusion – the Enceladus Ocean, unlike Titan, is warm and has an almost “terrestrial” chemical composition.

As planets today assume, the bowels of Enceladus remain constantly hot due to the fact that they are constantly “squeezed” and “stretched” by the attraction of Jupiter, which warms its ocean, and, as NASA specialists discovered in 2011, launches chemical reactions between the rocks of the stone core of Enceladus And water in the ocean. All this, in the opinion of mission participants and many other scientists, makes Enceladus the most likely candidate for the role of refuge of extraterrestrial life.


“Final of the Opera”, the last stage of the life of the probe “Cassini”

In addition to Enceladus and Titan, another subglacial ocean may be hiding in the depths of Dione, the smallest companion of Jupiter from among his large satellites. Almost all of its properties, in addition to the supposed thickness of 65 kilometers, remain a mystery to scientists, since the oscillations in the motion of Dione in orbit, which gives rise to the water layer in its interior, are too small for them to be accurately recorded by Cassini.

Illusions of the “Lord of the Rings”

In addition to the secrets of Saturn’s moons, Cassini devoted a large amount of time to studying the giant planet itself, its rings and its immediate surroundings. Even before the approach to Saturn, the probe opened four previously unknown saturnites of Saturn, and then found three more other moons, and also specified the orbits of many of them.

Not all features of Saturn, which seemed simple and understandable when viewed from the Earth, were the same in its orbit – for example, several years ago, Cassini discovered that the thick and dense rings of Saturn are a kind of optical illusion, and that the material in them roughly Three times less than planetologists thought before.

The same observations made scientists doubt that the rings of Saturn exist since the formation of the solar system – they now suggest that they could have originated several hundred million years ago as a result of the destruction of one of the satellites of the gas giant, getting too close to the “lord of the rings”.

Another, no less important discovery was that the Cassini helped astronomers very accurately measure the rotation speed of Saturn and determine the duration of its day – 10 hours 32 minutes and 45 seconds. Such measurements are very difficult to perform for giant planets that do not have a solid surface and permanent structures, and, as the experience of the NASA probe has shown, they can be done only from a close distance to the planet.

In addition to all this, Cassini made a lot of small but important discoveries – he got pictures of the mysterious “hexagon” on the pole of Saturn, a giant “eternal hurricane”, measured the temperature in different layers of the planet’s atmosphere, uncovered the secret of the birth of the so-called “white spots” Temporary hurricanes from water vapor, appearing on Saturn every 30 years.

Torn note

What will Cassini do after the last rendezvous with Titan, which should take place at the end of April this year? After this meeting, the probe will for the last time change its orbit and exit into the previously unexplored region of space, located between the rings of Saturn and the giant planet itself, gradually approaching it.

Here he will make 22 turns, after which the “Cassini” will cease to exist, “drowning” in the upper layers of the atmosphere of Saturn. As scientists hope, during its death the probe will have time to transmit a sufficient amount of data on the arrangement of the lower layers of the atmosphere of the planet and the properties of its magnetic field, before the pressure of the bowels of Saturn crushes it.

The first span of “Cassini” through the emptiness between the rings and Saturn, according to the current plans of NASA, will be held on April 26. What the probe will be doing at this time, NASA promised to reveal the public very soon, on Tuesday, April 4. The main task of the probe at this stage is already known today – measuring the exact mass of Saturn’s rings and determining their age, as well as chemical analysis of dust in the orbit of Saturn and its matter in the bowels.

Why did NASA decide to destroy such a valuable and still capable of much apparatus? Why the leadership of the “mission” simply does not disconnect the probe and leave it in Saturn’s orbit in memory of the descendants?

The answer to this, as explained in the agency, is very simple – scientists are afraid that on the surface of the Cassini skin and inside its instruments bacteria spores may be hidden. If Cassini collides with Enceladus or Titan, these bacteria can get into their subglacial oceans or the hydrocarbonic seas of Titan and begin multiplying in them. Therefore, NASA made a difficult decision to destroy the probe before it exhausted its resources, and use the “last chords” of his life for unique research.

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