A competition can incite teamwork, rivalry, and occasionally hatred. Rivalries can stimulate us to strive harder to demonstrate our abilities. The cold war involving the United States and the Soviet Union might have instigated the development of space research to become what it is today.
We tend to recall the Apollo and Voyager programs if we take a trip down our memory lane. Many people may not know that there was an ambitious mission exclusively to study Saturn, its rings, and moons. The scientists honored Giovanni Cassini and Christiaan Huygens by naming it as the Cassini-Huygens mission. Giovanni Cassini found Saturn's rings and four of its moons, whereas Christiaan Huygens discovered Titan, the largest moon of Saturn. It has set a benchmark in space exploration due to teamwork between NASA, ESA, and ASI.
The project incorporated the Cassini orbiter and the Huygens probe, assembled by NASA/ASI collaboration and ESA, respectively.
Nuclear power source
Cassini spacecraft relied on Plutonium's nuclear decay to generate electricity for its intricate tasks, as the prospect of solar energy was not feasible near Saturn. Naturally, antinuclear activists cried, "Cassini, we have come to bargain." They feared that any mishap during the launch could be potentially dangerous to the environment. But the scientists had encased the Plutonium in Aluminium, Iridium, Ceramic, and Graphite and reinforced the containers, as a precaution to any unexpected explosion.
Summary of Trajectory
On October 15, 1997, the Titan IV-B rocket launched Cassini from the Earth. As the spacecraft had quite some weight, the need for Gravitational assist was inevitable to develop significant velocity relative to the Sun. Its path to glory involved two gravitational-assist flybys of Venus (1998 and 1999), one of Earth (1999), one of the asteroid 2685 Masursky (2000), one of Jupiter (2000), and the insertion into Saturn's orbit (2004). The spacecraft had to sustain the contrasting environments of both Venus and Saturn!
Encountering Jupiter
Cassini snapped plenty of images of Jupiter - all of which contributed to a global portrait. The flyby resulted in the Great Red Spot's images with turbulence in the wake region, photos of volcanically active Jupiter's moon Io, and another vortex near the north pole rivaling the Great Red Spot. This vortex was transient, with occasional brightness in its core.
The craft witnessed prolonged storms, jet streams, and importantly, acetylene and organic methyl radicals on Jupiter. It gathered information on Jupiter's magnetosphere, by observing the sonic boom as a result of the interaction between the supersonic solar wind and this magnetic sphere. From the random light scattering, it concluded that the particles in Jupiter's rings had irregular shapes.
Phoebe
Cassini coasted for four years, engulfed by the darkness of space, to reach its final destination - the Saturn system. It flew by the moon, Phoebe - it was an object of interest as the scientists believed that it was an asteroid due to its small size and a slanting retrograde orbit around Saturn. According to Cassini's findings, Phoebe's surface contains water-ice, carbon dioxide, clay, water-bearing minerals, with a chemical composition similar to what we see in comets. The fact that the water ice ratio resembles that of Pluto or Neptune's moon Triton, reinforces its possible origin at the Kuiper belt. It could have flung out of the belt, hanging on to an orbit around Saturn. Scientists concluded that Phoebe was not an asteroid from the asteroid belt, that is between Mars and Jupiter, since there have been no records of carbon dioxide's presence in the belt. Material from Phoebe constitutes one of Saturn's rings.
Titan
One of the most exceptional achievements of the Cassini - Huygens is its observation of Titan, which is known for its dense, nitrogen-rich atmosphere. The Huygens probe detached from the spacecraft and successfully landed on the Titan surface. During its 147 minute descent, it monitored the atmospheric aerosol and confirmed the predominance of carbon and nitrogen. For about 90 minutes, Huygens analyzed Titan's hazy surface and snapped pictures of distant hills, after which it went offline. The orbiter attributed the presence of complex variants of methane and nitrogen to the smoggy environment. Some of the most remarkable discoveries are the presence of seas of liquid methane and ethane in the poles replenished by rains from the hydrocarbon clouds, the sight of hydrocarbon-rich equatorial ice dunes, and an ocean of water and ammonia underneath the surface. These characteristics make Titan one of the closest to the Earth in terms of its constitution, processes, and potential habitability.
Enceladus
Enceladus is one of the brightest and most reflective moons in this solar system because of its smooth icy surface. Cassini's magnetometer sensed a disruption in Saturn's magnetic field near Enceladus. When Cassini had a closer look near the south polar region, the truth revealed itself in the form of an icy plume. Direct sampling showed an abundance of carbon dioxide, carbon monoxide, water vapor, with a few other hydrocarbons. Cassini also found a large scale under-crust salty ocean presumably with hydrothermal vents, and geysers shooting icy jets, some of which mix with a part of Saturn's rings. The scientists understood that these jets originate from the hottest parts of the fissures/tiger stripes in the Enceladus terrain. It happens due to the high temperature and pressure caused by the consistent compression and expansion triggered by Saturn's gravity. Such a combination of water and heat, with methane as a potential candidate for food, makes Enceladus one of the most suitable places for alien microbial life.
Iapetus
Another object of interest is Iapetus. For over a century, the contrasting hemispherical colors of Iapetus caused a lot of confusion among the astronomers. On one side, it is as white as ice, while on the opposite side, it is very dark. One of the primary operations of Cassini was to find out why. The reason is pretty humorous. Cassini's discovery shows that Iapetus has tidally locked itself to Saturn because of its closeness. One of its sides always has to face the orbital direction. The catch is, Iapetus's orbit is through Phoebe's debris which constitutes one of Saturn's rings. The unlucky hemisphere of Iapetus has to remain a junkyard for Phoebe. Over time, Phoebe's material has blackened this side to the extent that it appears like charcoal.
From a different snapshot, we can view the heavily cratered surface with a bulge - the equatorial ridge - extending in the middle. Scientists speculate that the collapse of an ancient ring of material onto Iapetus's surface could have resulted in this ridge.
Other notable natural satellites
Cassini took breathtaking pictures of moons, including Daphnis, which revolves around Saturn in a path between its rings, commonly called the Keeler gap. We can see the wave-like pattern that Daphnis's gravity causes in the ring. The spacecraft presented substantial evidence of an under-crust ocean in Mimas, yet another moon of Saturn. Star Wars fandom may notice Mimas's resemblance to the Death star, due to the massive Herschel crater in the middle. It is also strikingly similar to Enceladus, except that it doesn't seem to have water jets. When Cassini flew across Hyperion - a sponge-like natural satellite of the ringed planet - it passed through an electron beam. Thus, we realized that Hyperion develops a static charge, similar to Earth's moon. Cassini detected a feeble atmosphere in Dione and Rhea as well. It also observed Tethys and discovered the moons like Methone, Polydeuces, Anthe, Aegaeon.
The Great White Spot and the Saturnian lightning
Every thirty Earth years, a mega-storm - The Great White Spot - occurs in Saturn. Sometimes, it is more massive than the Great Red Spot of Jupiter itself. Cassini hit the jackpot when nature decided to kick off the storm about ten years earlier (2010) than its estimated schedule. This mega-storm typically pushes the water vapor above the clouds. Then, the water vapor freezes and offers an icy appearance. Scientists noticed a considerable spike in ethylene gas levels during the storm, far more than they expected. Cassini was also lucky to capture the beautiful images of Saturnian lightning during its daytime - something the scientists didn't expect it to pull off.
Saturn's hexagon and rings
Cassini had the privilege to witness the colossal north polar hexagonal vortex with unbelievable symmetry. On Earth, such jet streams are usually interrupted by the mountains. When Saturn's northern pole experiences winter, the vortex is in the shadows and can be sensed in the infrared region. But as spring blossoms, it can be viewed in the visible spectrum. Cassini accomplished both the feats. Between 2012 and 2016, Cassini noticed a gradual change in the hexagonal cloud color from blue to a golden tinge. Scientists considered the prospect of seasonal changes as a possible explanation.
Cassini observed Saturn's rings during its equinox, because the Sun directly illuminates the rings' edges during this period. Cassini took countless photos of the rings, moons, and Saturn itself.
General relativity test
Cassini employed the concept of the Shapiro time delay effect to verify Einstein's theory of general relativity. There was a change in the frequency of the spacecraft's radio waves that reached the Sun's vicinity, and they had to traverse a comparatively longer distance as massive bodies bend space-time in their surroundings. Thus, Cassini firmly reasserted the validity of Einstein's general theory of relativity.
The day the Earth smiled - July 19, 2013
Wherever we go and whatever we do, all of us share an eternal bond with our birthplace. In 2013, Cassini decided to snap a photo with Saturn, its best friend by that time, with Earth and its moon. Scientists announced this in advance and requested the people to pose and wave their hands as a token of appreciation and respect to the legacy of Cassini and Huygens. The grandeur of this snapshot rivals the iconic 'Pale Blue Dot' itself.
The Grand Finale
The most significant part of a journey is the end. As dreadful as it sounds, the day of reckoning always looms in the horizon for all of us. The same was the destiny of the legendary Cassini-Huygens. After nearly two decades of marvel, the scientists decided to plunge the spacecraft into Saturn, instead of its moons, following fuel depletion, thereby ensuring zero microbial contamination of the moons' surfaces. Scientists made up their minds to immerse Cassini's ashes in the Saturnian atmosphere.
The six-month-long final chapter in the year 2017 resembled a thrilling dogfight - only this time, there were complex out-of-the-world maneuvers to avoid any collision with the ring debris. Cassini, desperate to get to Saturn, utilized Titan's gravity in its final flyby of the moon, and modified its trajectory towards the ringed planet. After 22 breathtaking passes over a few months of thrilling adventure, all the while obtaining crucial data about the rings, the magnetic field, the internal arrangement of the ringed planet, and the ultra-close images of the rings and clouds, the Cassini spacecraft exploded with a spectacular finality.
Although Cassini physically met its end three years ago, the elegant photos and videos highlighting its magnificent voyage will always serve as its Horcruxes. As long as space lovers exist, the word Cassini-Huygens has meaning.
Sources
A special thanks to https://solarsystem.nasa.gov/missions/cassini/overview/, Wikipedia, and YouTube!
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