Just under 20 years ago, the magnificent result of 17 countries’ expertise, collaboration and tireless effort took to the skies from Cape Canaveral, USA, in one of the most ambitious endeavours of space exploration. After approximately seven years of travel, the target was in sight – the Cassini spacecraft had made it into orbit around the sixth planet from the sun in the desolate, outer reaches of our solar system. Saturn, the crown jewel of our cosmic neighbourhood, was in our reach of study and exploration like never before.

Cassini’s mission was intended to last for around 13 years after its arrival in July 2004, during which it would orbit the planet Saturn and its numerous moons, gathering information via its several onboard instruments. Additionally, the spacecraft carried the Huygens probe on board, which it released into the hazy depths of the atmosphere of Saturn’s largest moon, Titan, in January 2005.

Shrouded in an opaque layer of organic particles, astronomers already knew that Titan was dissimilar to any other known moon in our solar system in that it contains a thick atmosphere – denser even than Earth’s. The probe landed safely on Titan’s surface, from where it continued to relay data back to Earth, making it the first and only (to date) landing in the outer solar system.

Huygens allowed us a glimpse of Titan’s surface as it descended on its frigid landscape, and relayed back information on a world that is surprisingly similar to a frozen relic of what we expect Earth to have looked like, some three billion years ago.

Since then, Cassini has been orbiting the ringed planet as planned, acquiring an in-depth view of Saturn itself. Saturn is a gas giant, just like Jupiter, Uranus and Neptune, meaning that it is mostly made out of gas, and thus only the upper regions of its atmosphere can be seen through telescopes. The spacecraft witnessed the aftermath of Saturn’s Great White Spot, a large, recurring storm occurring in Saturn’s atmosphere once every 30 years.

The storm was of such magnitude that it was the largest ever recorded in our solar system, larger even than Jupiter’s Great Red Spot, which itself measures at least twice the size of Earth.

Additionally, Cassini also ob­served a change in Saturn’s colour, particularly in its polar hexagonal feature, probably due to a change in the planet’s seasons bringing about a shift in solar- induced reactions in its upper atmosphere.

In April, Cassini made its final flyby of Titan before entering the grand finale of its mission. At present, Cassini is completing a set of perilous manoeuvres that will see it dive between Saturn’s famous rings several times over the course of the next few months.

Being made mostly out of small pieces of rock and ice, Saturn’s rings highly reflect sunlight, making them easily visible from Earth even though they are just 10km thick. They are thought, by one hypothesis, to be the remains of one of Saturn’s moons that edged too close to the planet, resulting in it breaking apart due to gravitational forces and forming the rings we see today. One day, these rings will probably disappear as their orbit inches closer to Saturn, until they are engulfed by the planet’s atmosphere.

Cassini will end its series of complicated manoeuvres with a final, planned plunge into Saturn’s atmosphere on September 15 this year. Cassini will disintegrate as it hits Saturn’s atmosphere, marking the end of its 20-year-long venture. Its final tra­jectory and ending has been planned as such to avoid possible contamination of any of Saturn’s moons, two of which (Titan and Enceladus) have been earmarked as potential candidates for life.

Josef Borg is a PhD student at the Institute of Space Sciences and Astronomy, University of Malta, and vice-president of the Astronomical Society of Malta.

Did you know?

• Jupiter’s Ganymede and Saturn’s Titan are both larger than Mercury. The two largest moons in the solar system, Ganymede and Titan are intermediary in size between Mercury and Mars. At diameters of approximately 5,260km and 5,150km respectively, the two moons are significantly larger than the closest planet to the sun. Mercury, the smallest pla­net in our solar system, measures just 4,880km across.

• Saturn is the farthest planet easi­ly seen with the naked eye from Earth. The five planets closest to Earth – Mercury, Venus, Mars, Jupiter and Saturn – have been known since ancient times as they are brightly visible in the sky as star-like points of light. The planets Uranus and Neptune were discovered much later, after the start of telescope use, as they are much fainter and not visible to the unaided eye.

• The Juno spacecraft is currently in orbit around the largest of the gas giant planets, Jupiter. In a bid to understand more about the largest planet in our solar system, Juno was launched in August 2011 and reached the giant planet in July 2016. In simi­lar fashion to the Cassini spacecraft (see main article), it will be de-orbited deliberately into Jupiter’s atmosphere once its mission is over, particularly to avoid contamination of Jupiter’s moon Europa, another candidate world for life.

• The International Space Station (ISS) completes one orbit of the Earth in just over 90 minutes. If you thought airplanes are fast, think again. At an orbital speed of 27,600km/h, or 7.67km/s, the ISS completes a total of over 15 full orbits of the Earth in a day. When the space station passes overhead close to sunrise or sunset, the sky is dark enough for us to see it as it reflects sunlight while travelling at around 22 times the speed of sound.

For more trivia see: www.um.edu.mt/think

Sound bites

• Possible NASA mission to Europa named ‘Clipper’. Europa Clipper is a proposed NASA mission that would investigate the habitability of one of Jupiter’s moons, Europa. Underneath the moon’s icy surface, an extensive ocean is thought to exist. The mission was officially renamed ‘Clipper’ in 2017, after that title was used as a nickname for years. Clipper refers to “the clipper ships that sailed across the oceans of Earth in the 19th century, three-masted sailing vessels renowned for their grace and swiftness,” according to a NASA statement.

https://www.space.com/37282-europa-clipper.html

• Solar eclipse just two months away. On August 21, people across the United States will see the sun disappear behind the moon, turning daylight into twilight, causing the temperature to drop rapidly and revealing massive streamers of light streaking through the sky around the silhouette of the moon. On that day, the US will fall under the path of a total solar eclipse. Unfortunately, the event will not be visible from the Maltese islands as the sun would have already set for us here.

https://www.space.com/33797-total-solar-eclipse-2017-guide.html

To find out some more interesting science news, listen in on Radio Mocha every Monday and Friday at 1pm and on Radju Malta 2.

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