Cassini has been one of the most successful of our space programs, supplying huge amount of raw and new data about our solar system, and Saturn in particular. As the orbiter runs out of fuel, space nerds all over the world seem to feel emotional after this almost 20 years long journey. Cassini is planned to plunge to its death on September this year, and as we bid our farewell to it, here is a short life history of the Cassini-Huygens Program.
Cassini orbiter, along with the Huygens lander, collectively called Cassini-Huygens mission was a part of NASA’s Flagship program, which is the most costly (over $1 billion each) of its three programs including New Frontiers and Discovery. The Flagship program concentrates on planetary habitability of not only the Solar System but all the planetary systems and also includes the Viking mission, the Voyager mission, Galileo spacecrafts, and the Chandra X-Ray Telescope. The Cassini-Huygens was a joint effort by NASA, ESA, and ASI (Italian Space Agency), and costs around $3.26 billion. While the Cassini was designed by NASA, Huygens was created by European Space Agency, and the ASI created its high gain antenna with the incorporation of a low gain antenna, which not only served as a lightweight radio, but a radar altimeter, spectrometer, a radiometer and a radio science subsystem(RSS).
Cassini-Huygens was one of the first major joint operations between NASA and ESA. When the program seemed to get no clearance in the Congress, NASA officials encouraged them to allow it on grounds that ESA had already sanctioned the program and such negative move by the US might severe political ties. Also, NASA accepted to share all data acquired from the mission equally with its partners, which includes 16 European countries. Cassini was named after Italian-French astronomer Giovanni Domenico Cassini, who discovered Saturn and its four moons, and the lander Huygens is named after Dutch astronomer, mathematician and physicist, Christaan Huygens who discovered Titan, the moon it will be landing on to conduct low atmosphere and surface studies.
The program was started in the 1980, after much collaboration, research and expertise, the orbiter and lander launched from Cape Canaveral Air Force Station’s Space Launch Complex-40, aboard the Titan IVB/Centaur Spacecraft on 15th October 1997. It is the fourth to reach Saturn and the first to settle in its orbit. It entered orbit on July 1,2004 after flybys of Venus, Earth and Jupiter. The lander Huygens separated from it on 25th December’2004 and landed on Titan on 14th January,2005 to conduct its experiments and study on the mysterious moon,and will provide a lot of useful information for years to come. The orbiter dives through the outer rings of the planet Saturn, to study about their structure, forms, origin, and also about the moons in orbit around the planet. The orbiter has also helped mapping the magnetic and the gravity field of the planets. The mission is controlled from the Jet Propulsion Laboratory, USA. In these twenty years, Cassini has provided with humongous amounts of new information and mentioning every of its achievement in detail will make my fingers hurt, so I will be giving here a point to point description of some of its major accomplishments. Don’t worry I am planning to write individually on the planets, and moons of our Solar System in the new separate ‘Space’ section one by one, where I will be writing in details the discoveries and studies associated with them, but if you are impatient, I have provided links below. So here are the major achievements of Cassini:
- Cassini provided us with the most detailed picture of Jupiter ever when it flew past it, showing in great detail the atmospheric rings of the planet, helping in studying the planet(pictured below).
- The orbiter has discovered almost SEVEN new moons of Saturn. Using it images, scientists found between the rings of the planet new moons, Methone and Polydeuces(2004), Daphnis in the Keeler gap(2005), Anthe(2007), Aegaeon in G-ring(2008), and two small unnamed moons in A and B rings respectively.
- Saturn has an unpredictable and changing rate of rotation. Due to absence of any physical structures to observe and mark the rotation, the orbiter used radio waves to measure the rotation rate of the planet, which seems to match those on Earth. It seems the rotation rate has increased by about 6 minutes, and the duration of a day in Saturn still puzzles the scientists a bit. It is between 10.6 hours to 10.8 hours, not much difference, but a property like duration of a day needs to be highly specific, and this keeps us puzzled.
- The orbiter provided some of the most clear, and detailed images of Saturn’s moons yet, including those of Phoebe, Rhea, Atlas (saucer shaped), Pan (saucer), Mimas (death star like), Helene (heart-shaped), and the ‘spongy’ Hyperion.
- In its 45 planned close flybys of Titan, Cassini showed that the moon was covered in methane, with different temperatures, and had structures upto 50 meters high. Along with information from Huygens, the extensive information on Titan makes it an important site for possible emergence of life, carbon based perhaps like ours.
- In 2006, a hurricane was observed in the south pole of Saturn, which had an eyewall just like those on Earth, though it was stationary unlike those of Earth. A study of these hurricanes will help us understand our atmospheric conditions much better.
- The Great White Spot, a storm that happens every 30 years on Saturn, showed temperature spikes in the stratosphere when viewed in infrared, and also 100 times higher levels of ethylene, a colourless gas. Ethylene is very unlikely to be found on Saturn, and is one of the major puzzles.
- The hexagon pole of Saturn changed colour from Blue to Golden, which is currently thought to be because of haze created by sunlight when it passes through the atmosphere during different season. The hexagonal shape of the pole in itself is a big mystery.
- Along with Huygens, Cassini has provided many new information on the ocean worlds, Titan and Enceladus, thereby supporting the view that they might be supporting of will support a prebiotic life form, the origin of life. Encleadus has been found to be covered in a global ocean of liquid water with salts and organic chemicals (essential for carbon based life), with warm temperatures that were thought to be impossible, sending a wave of shock in the scientific community. Titan is covered with structures similar to Earth’s with dunes, mountains and volcanos, cloud cover similar to Los Angeles, and similar climate patterns like Earth’s when life is said to have originated here. Titan serves as a perfect candidate for studying early climate and behaviour of Earth.
- The study of rings has shown us that the ring system of Saturn greatly resembles our Early solar system, with breaking and clustering of objects, and a propeller process with creation of moons in between rings, similar to as planets are thought to have formed here. It’s almost as time travel!
- We learnt a lot about Saturn’s moons. Apart from Titan and Enceladus, we found Phoebe might be from out of the Solar System, captured by the planet’s gravity. Phoebe might also answer the two tones of the moon Lapetus, the dust from Phoebe must be evaporating the ice from one part to the other of the moon Lapetus, thus the two tones. Hyperion is found to be very less dense, hence colliding objects instead of blasting it out, compress in and are responsible for its spongy structure. Enceladus’ icy blasts are found responsible for the formation of the E-ring and the shine of the surfaces of other moons. Cassini also discovered canyons on Dephinis and plumes on Prometheus. Rhea is the first to have an atmosphere of Oxygen (although a thin one), apart from Earth.
- Scientists also had not expected to find Saturn’s magnetosphere — the region around the planet strongly influenced by Saturn’s magnetic field — to be filled with an electrically excited gas, or plasma, of oxygen. It turned out this was another surprise from Enceladus, as the water vapor from its plume is broken apart by sunlight and the liberated oxygen spreads out through Saturn’s magnetic bubble. Cassini detected this oxygen on approach to Saturn, but its origin was perplexing at first.
- Cassini also helped explain Saturn’s “spokes,” first spotted during the Voyager flybys of the early 1980s. Cassini scientists figured out that they are made of tiny ice particles that are lifted above the surface of the rings by an electrostatic charge, the way a statically-charged balloon held over a person’s head will lift hairs. Their charge appears to be related to the angle of sunlight striking the rings — a seasonal effect. Along with this we learn about the hidden moons formed in between the rings, and more about the origins of the rings themselves. The changing angle of the sun also showed scientists an array of vertical structures in the rings, including fluffy peaks of material as high as the Rocky Mountains at the outer edges of the A and B rings. The vertical structures and the shadows they cast also revealed wavy patterns in the parts of the rings that resemble a miniature Milky Way, giving scientists insight into the way galaxies form.
Cassini truly played a landmark role in the understanding of our neighbour, and its contributions shall be remembered forever. As the plutonium powered engine of the orbiter runs out of fuel, to avoid loss of control and possible impacts and pollution of the worlds in the future, the Cassini is to dive into the planet Saturn. This brave and daring move, despite its chances, is a risk worth taking. It will provide us with the closest images of the rings, and the first data from the inner atmosphere of Saturn. We will also know more about the icy dusts of the rings, explaining more about the origins, all these data will be sent hours before the orbiter finally dies. After its 120 planned dives through the ring system (once every two weeks), it will make its final dive through the A and B-rings on 15th September, 2017. After 13 years in orbit, the Cassini will rest forever, ending two decades of journey, creating a legacy for the future missions. Goodbye Cassini, and Thank You. Happy Reading!
-The Cosmogasmic Person.
Source for Images: https://www.nasa.gov