September 15, 2017 – the death date of NASA’s Cassini spacecraft finally arrived. The spacecraft crashed into Saturn’s atmosphere in a dramatic event that marked the end of the 20-year long journey.
Planetary scientist Carolyn Porco, head of imaging science for the Cassini spacecraft, said in an interview that "Major Cassini mission achievements are legion".
"Technologically, it's the most daring and elaborate orbital tour of a planetary system yet executed, with vastly more flybys of planetary bodies, and the closest ever conducted, than any other mission we've ever flown. In fact, it may very well be that Cassini has conducted more close flyby manoeuvres — over 100 — than have ever been conducted in the entire planetary program."
However, Cassini, which was running low on fuel, will technically continue to probe Saturn for many years. In order to prevent Cassini from colliding with one of the two moons of Saturn, NASA decided to kill the USD 4 billion spacecraft.
"It’s inspiring, adventurous and romantic — a fitting end to this thrilling story of discovery," NASA writes. So thrilling, in fact, they created this animated video that "tells the story of Cassini's final, daring assignment and looks back at what the mission has accomplished."
As we say goodbye to NASA’s Cassini, here are some incredible discoveries made by the spacecraft during its mission Saturn.
1. Landing of Huygens probe on Saturn moon Titan
A four-foot wide atmospheric entry probe Huygens separated from Cassini on December 25, 2004 to start its 22-day journey on the surface of Titan. Saturn has 62 moons and Titan is the largest among them and it happens to be the only celestial body in space beside Earth to feature stable bodies of surface liquid.
Huygens landed on Titan on January 14, 2005 and discovered the world quite similar to what Earth witnessed before the evolution of life. Lakes, dunes, rainstorms, drainage channels appear to constantly shape and impact the surface of Titan. However, the major difference is that much of the liquid found on Titan is composed of methane and ethane, with a frigid surface temperature recorded by Huygens of -290.83 °F.
Apart from the surface liquid, Cassini later found the presence of a subsurface ocean likely as salty as the Earth’s own Dead Sea.
"This is an extremely salty ocean by Earth standards," Giuseppe Mitri of the University of Nantes in France told NASA. "Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past."
2. Most detailed close-up of Jupiter ever
Cassini, apart from probing Saturn, also got an opportunity to make flybys of Earth, Venus, and Jupiter. The spacecraft produced the most detailed true colour pictures of Jupiter ever recorded.
"Everything visible on the planet is a cloud," NASA explained in a blog post. "The parallel reddish-brown and white bands, the white ovals, and the large Great Red Spot persist over many years despite the intense turbulence visible in the atmosphere. These clouds grow and disappear over a few days and generate lightning. Streaks form as clouds are sheared apart by Jupiter's intense jet streams that run parallel to the colored bands."
3. Discovering hidden moons of Saturn
Cassini picked out seven moons that were previously unknown and were present in the orbit within Saturn’s rings. The seven moons include Methone, Pallene, Polydeuces, Daphnis, Anthe, and Aegaeon. The seventh moon was discovered in 2009 and is named S/2009 S 1. It is only 984 feet in diameter.
Daphnis has in particular caught NASA’s attention. The image clicked on January 16 offers the clearest view of the tiny moon yet. Daphnis is also called the wave breaker moon as it creates waves in the rings around it. Having a couple of narrow ridges, Daphnis also consists of a relatively smooth mantle of surface material. NASA says it is the result of fine particles gathered from the rings.
Also Read: RIP: NASA’s Cassini spacecraft embraces death, makes plunge into Saturn’s atmosphere
4. The subterranean habitable zone of Saturn’s icy moon Enceladus
There may be a subterranean ocean filled with extraterrestrial life hidden in Enceladus, the icy moon of Saturn.
Saturn's icy moon of Enceladus may be hiding a subterranean ocean filled with extraterrestrial life. Frequent Cassini flybys of the moon, which measures roughly 310 miles in diameter, have found conditions favorable for microbes.
"It has liquid water, organic carbon, nitrogen [in the form of ammonia], and an energy source," Chris McKay, an astrobiologist at NASA's Ames Research Center in Moffett Field, California, told Daily Galaxy. "Besides Earth, there is no other environment in the solar system where we can make all those claims."
Before Cassini reached to Enceladus, scientists baffled over why the moon possessed the brightest world in the solar system. On closer look, they were astonished to see massive geysers, related to ice volcanoes, emitting liquid water to create a smooth, frozen white surface. Enceladus, it seems, is an active moon which has a global ocean of warm liquid salty water underneath its crust.
“As we continue to learn more about Enceladus, and compare data from different instruments, we are finding more and more evidence for a habitable ocean world,” Linda Spilker, Cassini Project Scientist, told NASA. “If life is eventually discovered in Enceladus’ ocean by a mission after Cassini, then our Enceladus discoveries will have been among the top discoveries for all planetary missions.”
5. Saturn's giant hurricane
Cassini also discovered a massive hurricane churning away at its north pole. Notably, it was outside the Earth and it is the first time that the weather phenomenon had been observed on another planet.
You will be astonished to know this is not an ordinary hurricane. It is 50 times the size of an average hurricane on Earth (its eye alone is 1,250 miles wide) with winds four times as fast, but it is also same time completely stationary. It is also interesting to note that without access to large quantities of water vapor it formed.
"We did a double take when we saw this vortex because it looks so much like a hurricane on Earth," said Andrew Ingersoll, a Cassini imaging team member at the California Institute of Technology in Pasadena, said in a release. "But there it is at Saturn, on a much larger scale, and it is somehow getting by on the small amounts of water vapor in Saturn's hydrogen atmosphere."
Also Read: NASA Cassini Saturn probe Grand Finale: Some spectacular images captured by the spacecraft
6. 'The Day the Earth Smiled'
Cassini positioned itself in the shadow of Saturn and turned its camera back towards its host on July 19, 2013. The spacecraft has also managed to spy own blue dot in the bottom left. The picture named as "The Day the Earth Smiled" and it was unique because it marked the first time that humanity was given an advanced notice that a picture of Earth would be taken from deep space.
Planetary scientist Carolyn Porco helped to organize the event, telling people to go outside "look up, think about our cosmic place, think about our planet, how unusual it is, how lush and life-giving it is, think about your own existence, think about the magnitude of the accomplishment that this picture-taking session entails. We have a spacecraft at Saturn. We are truly interplanetary explorers. Think about all that, and smile."
7. View from the top of Cassini
In the November end, Cassini started the first of 20 orbital maneuvers designed to position the spacecraft for its final death plunge on September 17, 2017. NASA also got pictures from the spacecraft, which showed the unbeleivable detail of the hurricane that continues to spin and rage at the north pole.
"This is it, the beginning of the end of our historic exploration of Saturn. Let these images — and those to come — remind you that we’ve lived a bold and daring adventure around the solar system’s most magnificent planet," said Carolyn Porco.
As Cassini closer to the subject, NASA will receive back unprecedented details of the planet. During final plunge, Cassini will record valuable information about Saturn's hydrogen atmosphere until it lost its signal.
8. Between Saturn and its rings
Scientists were expecting to find or rather hear the sounds of dust particles when Cassini made its first dive between the planet and its rings. But all they ended up hearing was celestial white noise.
"The region between the rings and Saturn is 'the big empty,' apparently," said Cassini Project Manager Earl Maize of NASA's Jet Propulsion Laboratory in Pasadena, California, in a statement. "Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected."
The silence was unexpected because when Cassini swooped around the fringes of Saturn's main rings back in December 2016, the Radio and Plasma Wave Science (RPWS) instrument picked up on a number of particles, represented in the audio below as pops and crackles.