Short history behind ‘The Grand Finale’ of Cassini

Ever since the Russians (then U.S.S.R) sent Sputnik, which resulted in the ‘space race’ between the U.S and Russia, many space exploration probes were sent into space, of which only half were successful. The most famous ones among them would be the Voyager Space probes, as one of them have reached interstellar space with another one about to.

But Cassini is altogether in a different side of the spectrum of space exploration. The Cassini mission was done under the ‘Flagship’ program of NASA, whose primary aim is to explore the Solar System. And its findings have given us the hope of extraterrestrial life in our Solar System.

The mission was officially named  ‘Cassini-Huygens’,  a joint endeavor by NASA, ESA (European Space Agency) and ASI (Italian Space Agency – Agenzia Spaziale Italiana). The name Cassini was given to honor the Italian astronomer, Giovanni Cassini and Huygens to honor Christiaan Huygens, the Dutch physicist cum astronomer. Huygens studied the rings of Saturn and discovered one of its moons – Titan, while Cassini also discovered some of the moons of Saturn.

The entire setup was an unmanned robotic spacecraft. The Cassini orbiter was designed and made by NASA in the Jet Propulsion Laboratory (JPL), while the Huygens probe was made by the ESA. The ASI provided the telecommunications equipments.

When all was set, Cassini – Huygens probe blasted off into space in the ‘Titan IV’ rocket in 1997. The space probe used Venus (twice) and Earth for gravity assistance, to accelerate itself to reach Saturn. By mid 2000, it started to cross the Asteroid belt (the chain of asteroids between Mars and Jupiter). By the end of 2000, Cassini made a flyby of Jupiter, and clicked some pictures and performed some scientific experiments. On July 1, 2004, after travelling for about seven years, Cassini had successfully established a stable orbit around Saturn.

By the end of 2004, the Huygens probe detached itself from Cassini and approached Saturn’s moon Titan after 3 weeks. After descending through Titan’s atmosphere for about two and a half hours, the Huygens probe made ground contact in January, 2005. Huygens was the first probe to land on a body in the outer Solar System and the farthest from Earth. Even the scientists who made the lander were not sure of its survival. The probe performed various experiments and clicked pictures and sent them back to Cassini, which relayed them to the Earth. It found that the hazy atmosphere had amino acids, the basic building block of life, in gaseous and solid form. Also, scientists predicted that liquids (probably methane) could have been on the surface due to the erosion patterns on the rocks and surface.

Cassini’s primary mission lasted from 2004 till 2008. During this phase, it discovered new rings of Saturn, new moons and provided very good pictures of the Saturn family. But the analysis of the moon Enceladus tops everything. It’s because the findings indicated the presence of water in Enceladus. There were ice water geysers in the south pole of the moon. Also the presence of carbon dioxide and monoxide in the atmosphere was confirmed in its experiments. Scientists described the water eruptions as being “like carbonated water with an essence of natural gas”.

In 2008, having completed its primary objective, Cassini’s mission period was extended up to 2010. It was named  ‘Cassini Equinox Mission’ as it matched up with the equinox phase of Saturn. During this phase it discovered another new moon – Aegaeon, and made detailed study of Enceladus and giving new insights of the water activities in it, making scientists believe “…Enceladus has almost all of the ingredients that you need to support life as we know it on Earth”.

The mission was extended again in September, 2010, up to 2017, for the last time. Both the mission extensions helped Cassini study the climate and seasonal patterns of Saturn (Yes, despite being a Gas Giant, Saturn does have varied seasons and climates). During the course of the mission it explored the various moons of Saturn and found a saltwater reservoir beneath Enceladus’ icy surface. It also found a large sea in Titan, mostly containing liquid methane.

After spending about two decades in space, exploring the Saturn system, Cassini was nearing its end. It was running out of its power source which helped it to conduct experiments and correct its orbit. Scientists came up with different strategies to end its mission which included – collision into Saturn or one of its moons; escape to other giant planets; to set in a heliocentric orbit. They finally decided to plunge Cassini into Saturn’s atmosphere after estimating the success probability and consequences of various plans, one of the primary reasons being non contamination of the moons of Saturn as they have ‘prebiotic’ conditions that can sustain life.

The descent took place over a course of seven months, starting from April. During this time Cassini dived into the gap between Saturn and its inner most ring in an elliptical path, completing 22 orbits, each orbit reducing the distance between Saturn and Cassini. On 11, September, Cassini used Titan to change its trajectory towards Saturn. Over the next few days Cassini accelerated towards Saturn.

On September 15, the last day of Cassini’s daring adventures in space, it directed its transmitting antenna towards Earth, so that it can directly send the precious data back. The downloading of these data was done first by the NASA’s DSN (Deep Space Network) antenna station in California and then by Tidbinbilla tracking station located in Australia. (This is because the Earth’s rotation changes the side of Earth facing Saturn)

Cassini began to enter Saturn’s atmosphere by 4 pm (IST).It was Cassini’s last chance and the data obtained were precious, for they gave very good information about Saturn’s atmosphere. The friction between Cassini’s body and the atmosphere heated it up, still it managed to transmit data. At 4:02 pm Cassini began to lose control and lost contact with the Earth, thus ending its mission. Yet, it worked for 30 seconds longer than predicted. It transmitted data back to Earth in its final moments, and the data took about one and a half hours to reach us.

The accomplishments of the Cassini – Huygens mission as listed by NASA are:

• Completion of the first detailed reconnaissance of Saturn and its family of moons and rings
• Delivery of Huygens probe to Titan for the first landing on another planet’s moon
• Discovery of erupting geysers and a global subsurface ocean on Enceladus
• Finding of clear evidences of present-day hydrothermal activity on Enceladus – the first detection of hydrothermal activity beyond Earth
• Revelation of Titan as a world with rain, rivers, lakes and seas
• Revelation of Saturn’s rings as active and dynamic – a laboratory for how planets form

The ending of the mission was a bittersweet moment for the scientists and engineers who worked in it. The success of this mission beyond expectations will help NASA in its next exploration mission, in this case Jupiter’s moon Europa, which is also a prime target for sustenance of life and habitability.

After all, why live in a single planet when we have numerous others in our own backyard!

Extra reading for interested readers:
Chronological depiction of the Cassini mission
Details about the Grand Finale
Cassini mission page, NASA
Details about the probe