Cassini – That Little Spacecraft That Dived Into the Lord of the Rings.

Uncategorized — By on December 17, 2017 at 10:03 am

Article by Hinna Shivkumar

Launched from the familiar landscape of Earth into the unknown vastness of space, aiming towards a planet and its companions that could be called a solar system on their own, Cassini is surely a legendary spacecraft. Why legendary, some might ask? Now, this is not some ordinary spacecraft (though, I wouldn’t say any spacecraft is ordinary). Cassini is a very special spacecraft that ended its mission this year, making its Grand Finale one of the highlights of space exploration in 2017. I would like to take you on a journey, like a time-lapse, highlighting some milestones that make Cassini-Huygens mission, a joint venture between NASA, ESA and the Italian Space Agency, special.

Journey Begins with Gravitational Assists
Cassini began its journey in 1997 as it was launched from Cape Canaveral aboard a Titan IV/Centaur. In order to pull away from the gravitational pull of the Sun and exit the inner solar system, the spacecraft required sufficient momentum. This momentum was initially provided by two gravitational-assist flybys of Venus, first in 1998 and second in 1999. A third assist was provided by the Earth in 1999, which provided Cassini with a boost in speed that carried it through space to the asteroid belt. In late 1999, Cassini became the seventh ever spacecraft to fly through the seemingly daunting asteroid belt (it is, however, not considered to pose any danger to spacecrafts since the individual asteroids are very far apart). Cassini, while flying through the asteroid belt, also had the opportunity to study this region using the Cosmic Dust Analyzer (CDA) onboard.

In late 2000, Cassini began a six-month flyby of Jupiter. During this valuable time, Cassini captured more than 26,000 images of the Jovian system. Valuable insight into the nature of the moons and rings of Jupiter was provided as Cassini and Galileo, that was already orbiting Jupiter, collectively gathered data.

Before Its Arrival
Cassini was already observing Saturn before it became a part of the Saturn system through orbit insertion. From a great distance, it had observed two small (small for the gigantic Saturn) storms into a larger one, discovered two previously unknown moons (Methone and Pallene), and had performed a flyby of Pheobe, a heavily-cratered and irregular moon of Saturn.

Part of the Saturnian System and The Huygens Probe

On July 1st, 2004, Cassini became the first spacecraft to orbit around Saturn. As it orbited the ringed planet over the next several years, Cassini had several opportunities to collect significant images and data. In October, 2004, its close encounter with Titan allowed Cassini to come within 1200 kilometers of this hazy moon’s surface. In late 2004, the Huygens probe detached itself from Cassini and began its journey towards Titan, its destination. During this time, Cassini continued exploring the diverse Saturnian system and came across incredible features such as Iapetus’ equatorial ridge. Cassini was always busy exploring some region of this part of the solar system! One of the most exciting moments of this mission came with the landing of ESA’s Huygens probe on January 13th, 2005. After a 2 hour and 27 minute descent, the probe touched down on the surface of Titan making it the first to land on a world in the outer solar system. During the descent, images captured by the probe provided incredible views of the geology of this moon. Since it was powered by batteries, the probe survived for only an additional 72 minutes on the surface.

Enceladus and Its Icy Jets
Enceladus, the icy moon of Saturn, amazed scientists to no extent. First, the magnetometer onboard Cassini discovered something strange about this moon’s interaction with Saturn’s magnetic field. Due to this, scientists decided that they would plan a return to investigate further. At its return to the south polar region of Enceladus, Cassini discovered an almost smooth surface here. However, it was the detection of huge clouds of water vapor that extended out into space that caught the attention of the scientists. In 2006, scientists detected evidence that these jets were not blown off the surface of the moon but rather were erupting from subsurface water reservoirs.

Approaching End of Primary Mission and Investigating Enceladus
Over the next months, Cassini discovered lakes on Titan, imaged new rings, located the origin of the jets from Enceladus to the now famous “tiger stripes” and collected samples from this plume and detected organic molecules in the “brew” to name a few highlights.

After the end of its Primary Mission in 2008, just four years around this ringed planet, Cassini had already gathered vast amounts of knowledge but raised even more questions about the Saturnian system and its members. It continued investigating Enceladus, discovered geologically active regions, performed the closest flyby of this moon (just 25 kilometers from the surface!) and collected more samples from the jets. The presence of salt and ammonia in these acquired samples made the evidence of the existence of liquid water even stronger. The levels of salt, for example, indicated that only the presence of liquid water could explain such high concentrations.

Mission Extended to 2017
On February 2nd, 2010, it was announced that the Cassini-Huygens mission will be extended till 2017. This would not only allow Cassini to explore the Saturnian system in more detail, but also allow Cassini to experience seasonal changes while in orbit. Cassini went on to explore the ionosphere (upper layer of atmosphere) of Titan, image moons such as Rhea (where molecules of oxygen were detected in its rather thin atmosphere) and Mimas, detect a gigantic storm 15,000 kilometers long on Saturn consume its own tail in a timespan of over a year, and image the well-known hexagonal storm around Saturn’s north pole.

The Grand Finale
After 13 years of orbiting Saturn and performing hundreds of flybys of several moons during this time, Cassini finally approached the first of its final 22 orbits through the gap between the rings and the planet on April 26th, 2017. These daring dives made Cassini explore the surprisingly dust-free gap that raised more questions for the scientists.

A month less than 20 years in space, on September 15th, 2017, Cassini made the final dive into the atmosphere of Saturn in order to protect the very moons it had explored from a distance. Titan and Enceladus became very important parts of the mission with the surprising and stunning discoveries made by this spacecraft. To keep these moons uncontaminated, scientists decided that the final plunge was necessary and was the best available option before the spacecraft ran out of fuel, used to adjust its trajectory, and potentially crash into some part of the Saturnian system.

Legacy
Cassini leaves behind numerous records but what truly makes it special is the way it painted a picture of Saturn and its moons by revealing striking images and data, potential future missions and another set of questions that will take years to answer but also advance planetary science. Above are just some highlights of the mission so we can only imagine how much data there is to process. Cassini aimed for Saturn but has paved the way for potential specific missions to moons such as Enceladus, the most promising target for a future mission in this system.

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