After a remarkable journey of 20 years, NASA's lone mission to Staurn, the Cassini spacecraft, ended its journey on September 15 by disintegrating in the skies above the planet. Launched from Cape Canaveral, Florida, on October 15, 1997, Cassini arrived at Saturn in 2004, and since then it has been sending myriad of information on the second-largest planet of the solar system.
Here are 20 things that Cassini made us discover in 20 years.
1. Water, icy plumes on Enceladus
Cassini discovered that Enceladus, Saturn’s sixth largest moon, has water underneath its icy surface. According to NASA, Cassini “revealed this ocean world to be one of the solar system’s most scientifically interesting destinations”.
In addition, we learned that Enceladus also has “geyser-like” jets that would spray water vapor and ice particles, pointing to hydrothermal vents underground. Scientists also found that the water contains a lot of salts and ammonia, making it a prime candidate for research about extraterrestrial life.
2. What Titan's surface looks like
Cassini, in its journey to map Saturn’s world, also had a passenger — an entry probe called Huygens which managed to land on the planet’s biggest moon, Titan. Before the expedition, we only knew that Titan is somewhat larger than Mercury and is covered with a thick atmosphere. The Cassini-Huygens mission showed us what Titan actually looks like underneath all of it.
3. Titan’s "earth-like" world
NASA scientists have described Titan as an "early-earth in deep-freeze". The Cassini mission showed that the moon not only had an internal ocean of water, but also a nitrogen-rich atmosphere. In the process, Titan became the “the only known world with a dense nitrogen atmosphere besides Earth”.
This composite image shows an infrared view of Saturn's moon Titan from NASA's Cassini spacecraft, acquired during the mission's "T-114" flyby on Nov. 13, 2015.
4. Methane in Titan's seas
When Huygens landed on Titan, not only did it reveal that Titan was about to get on the list of potentially habitable worlds, but that it also had entire seas of methane. Scientists are still figuring out how this much methane came to be, but are of the opinion that Titan’s seas may host living organisms
5. New Saturnian moons
Cassini discovered three new moons — Methone, Pallene and Aegaeon — bringing Saturn’s moon count to a total of 62. Aegaeon is Saturn’s smallest known moon, measuring less than 1.5 km across.
6. Hydrocarbons on Hyperion
Hyperion has been called Saturn’s “most bizarre moon” due to its elongated shape and what looks like a spongy surface. Scientists found hydrocarbons — various combinations of hydrogen and carbon — on Hyperion’s surface, further confirming that “the basic chemistry needed for life is widespread in the universe”.
7. The 300-year-old mystery of Iapetus
Iapetus, one of Saturn’s major moons, is tidally locked — meaning one side always faces the sun while the other faces away. Interestingly, the side that faces the sun is covered in a light, reflective substance, while the side facing away is covered with a dark substance. Cassini finally solved that mystery.
The dark side of the moon, pun unintended, was due to another one of Saturn’s moons, Phoebe. Reddish dust from Phoebe was being swept into Iapetus’ path, resulting in the dark patches across its surface.
8. Oxygen molecules on Dione
Cassini proved that oxygen was present not just on Earth. Scientists discovered that Dione, another one of Saturn’s moons, had oxygen molecules around the icy moo, confirming that Dione had a very thin, tenuous atmosphere.
A view of tectonic faults and craters on Dione, Saturn’s moon, taken by Cassini on Dec. 24, 2005, from a distance of approximately 151,000 kilometres.
9. Moonlets in Saturn’s rings
Saturn’s rings, which are entirely made up of water ice particles, also contain small moonlets, Cassini found back in 2006. “The moonlets' existence could help answer the question of whether Saturn's rings were formed through the break-up of a larger body or are the remnants of the disk of material from which Saturn and its moons formed,” NASA wrote after the discovery.
10. Cassini uncovers new ring around Saturn
The gift that was Cassini kept on giving. The probe also uncovered a new ring around Saturn, present outside the other visible rings. The new ring is quite faint, visible only at certain angles when the sun is behind the planet.
A new diffuse ring, coincident with the orbits of Saturn's moon's Janus and Epimetheus, has been revealed in ultra-high phase angle views from Cassini.
11. Possible source of Saturn's mysterious G ring
Saturn’s G ring, a faint ring that was discovered in 1979, had scientists puzzled over how it came to be. Cassini answered that question by discovering evidence that the G ring was, in fact remnants of a moon that had broken up a long time ago.
12. The connection between Saturn's rings and the formation of planets
Cassini helped scientists understand the process behind the formation of planets by observing the behaviour of Saturn’s rings.The probe documented the formation of a small moon in between the rings, formed by the very particles that the rings are made of.
13. The shaking of Saturn's rings
Saturn’s rings are more groovy than smooth, according to Cassini’s data. The rings contain waves that are seemingly caused by the planet’s gravitational disturbances. Scientists likened these waves to a seismograph, which might help them understand just how gas giants like Saturn and Jupiter behave.
This Cassini image features a density wave in Saturn's A ring (at left) that lies around 134,500 km from Saturn.
14. New views of Saturn's auroras
Just like the lights at earth’s north pole, Saturn too has auroras that were captured in new and better angles by Cassini. The new views from the probe gave new information on how the auroras move and what influenced them — outbursts from the sun and, in some cases, influence by Mimas and Enceladus as well.
15. Saturn’s giant hurricanes
Forget Hurricanes Harvey and Irma. Saturn’s got it much worse. Cassini was able to fly close enough to Saturn to get new images of the giant hurricane that is swirling around in the planet’s north and south poles. The one located at the north pole is about 2,000 km wide, 20 times larger than the average hurricane eye on Earth. The one at the south pole is even larger - measuring about 8,000 km.
16. Decoding the Hexagon
This giant six-sided structure has puzzled scientists for a very long time. This feature encircles the planet’s entire north pole and for the first time, scientists were able to see the structure in its entirety, thanks to Cassini’s high-resolution images of it.
The spinning vortex of Saturn's north polar storm resembles a deep red rose of giant proportions surrounded by green foliage in this false-color image from NASA's Cassini spacecraft.
17. Saturn's seasonal patterns
Cassini also found evidence of seasonal patterns emerging at the planet’s poles. The north pole warmed by about 36 degrees F during spring, while the south pole cooled by 63 degrees F during fall.
18. How does Saturn rotate?
Scientists knew one Saturnian revolution took about 29-and-a-half earth years, but determining the days and nights on the gas giant eluded them. The reason? Saturn’s dense, gas-filled atmosphere. Cassini took readings of the planet’s radio waves, helping scientists better understand how the planet’s rotational schedule works.
19.How earth looks like, from Saturn
If the Pale Blue Dot was the Voyager mission’s contribution, Cassini too chipped in with its own version of it. The probe captured an image of the earth, the moon in the far corner with Saturn’s rings in the foreground. At this point, Cassini was about 1.5 billion km away from the earth.
Earth is captured here in a natural colour portrait made possible by the passing of Saturn directly in front of the sun from Cassini’s point of view.
20. How Jupiter actually looks in true colour
Cassini, while making a beeline to its destination around Saturn, took some spectacular true colour images of our solar system’s other gas giant, complete with detailed imaging of Jupiter’s giant red spot.
A true colour mosaic of Jupiter taken by the Cassini spacecraft in 2000.
