The Cassini spacecraft is a collaboration between the National Aeronautics and Space Administration (Nasa), the European Space Agency (ESA) and the Italian Space Agency. The spacecraft was launched in 1997 on board a Titan IV, and took seven years to reach Saturn, its intended destination. During the journey, Cassini paid a visit to Venus, the Moon and Jupiter.

Cassini's portrait of Jupiter. Image: Nasa.
Cassini’s portrait of Jupiter. Image: Nasa.

As the spacecraft would have spent most of its time in orbit around Saturn, it was too distant from the Sun to be powered by solar panels, and thus uses plutonium as a power source. Cassini has discovered 7 previously unknown moons of Saturn during the course of its mission, including the “waverider” moon, Daphnis, which causes ripples in the rings of Saturn that are kilometres long.

Daphnis, a moon of Saturn that Cassini discovered. Image: NASA
Daphnis, a moon of Saturn that Cassini discovered. Image: NASA

One of the most memorable images captured by Cassini is a spectacular view of the rings of Saturn in full colour. Additionally, many objects from the solar system are visible in the same frame, including the Earth. The rings of Saturn and many of its moons can also be seen. Nasa scientists had informed the people of the Earth in advance that Cassini was going to take this photograph, and had asked everyone to look skyward and wave.  The photograph is called “The Day the Earth Smiled.”

The_Day_the_Earth_smiled
The Day the Earth Smiled. Image: Nasa.

Cassini had captured videos of moving methane clouds on Saturn and had found deep canyons on Saturn’s biggest moon, Titan. On 7 December 2016, Cassini used the gravity of Titan, to slingshot around the moon and begin a series of ring grazing orbits. Nasa scientists expected a number of new observations and photographs from the ring grazing orbits, bringing Cassini closer than ever to the tiny moons near the ring system around the gas giant. Cassini did not fail to deliver, one of the first images from the ring grazing orbits was an image of the hexagonal jet stream around the north pole of Saturn.

The hexagonal jet streams around the north pole of Saturn. Image: Nasa/JPL-Caltech/Space Science Institute.
The hexagonal jet streams around the north pole of Saturn. Image: Nasa/JPL-Caltech/Space Science Institute.

Cassini went on to take an image of Mimas appearing to crash into the rings of Saturn, and various images of Daphnis causing waves in the rings. During the ring grazing orbits, Nasa made one of the most dramatic announcements ever. Cassini had discovered plumes of water erupting from Enceladus. When Cassini was designed, scientists did not suspect that these geysers existed on Enceladus. Nasa made Cassini pass over Enceladus, and used the instruments meant to study the outer atmosphere of Titan, to study the geysers erupting from Enceladus. The resulting observations determined that microbes had plenty of food to feed off on Enceladus, and it was an environment hospitable to life.

Cassini observing the plumes of water erupting from Enceladus. Image: Nasa.
Cassini observing the plumes of water erupting from Enceladus. Image: Nasa.

Today’s Google Doodle has commemorated the start of the final few orbits of Saturn. During these orbits, Cassini will dive between Saturn and its innermost rings. There are 22 such orbits scheduled, the first of which will take place on 26 April 2017. The size and density of the particles in the region between Saturn and the innermost rings will be studied during the first dive, to prepare the spacecraft for subsequent orbits. Cassini will be using its dish shaped antenna as a shield during the first dive, in case there are particles that are larger than expected. Nasa scientists do not expect any matter larger than smoke particles, but is being cautious.

The final orbits of Cassini. Image: Nasa.
The final orbits of Cassini. Image: Nasa.

As the antenna will be used as a shield in the first dive, Cassini will not be able to maintain contact with the Earth during the initial maneuver. Cassini has already bid farewell to the “Deathstar” moon Mimas, as well as Titan with a hazy atmosphere. During the dive, Cassini will flyby four moons of Saturn, Janus, Atlas, Epimetheus and Daphnis. Cassini will also observe the Earth and the Sun during the first deep dive orbit. There are distant flybys of Pan, Pandora, Prometheus, Epimetheus and Aegaeon coming up. There are also several distant flybys of Titan. The slingshot maneuver around Titan on 22 April, just before initiating the final set of deep dive orbits, was the last close flyby of a moon of Saturn by Cassini.

Cassini Grand Finale by the numbers. Image: Nasa JPL
Cassini Grand Finale by the numbers. Image: Nasa JPL

On 15 September, Cassini will execute its final maneuver. There is not sufficient fuel on the spacecraft to extend the mission further, and that means that Nasa will no longer be able to control the spacecraft. Nasa is being careful, and does not want to contaminate the moons of Saturn, in case they harbour life, with Enceladus being one of the most promising candidates. In a science abundant maneuver, Cassini will fly past Janus, Pan, Pandora, Epimetheus and finally enter the outer atmosphere of the gas giant. Cassini will be transmitting information during the course of its final dive, till the very moment when the friction from the atmosphere burns up the dependable spacecraft and turns it into a shooting star.

After a 20 year mission, Cassini ultimately become a part of the gas giant.

Publish date: April 26, 2017 12:35 pm| Modified date: April 26, 2017 1:01 pm

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