13 years of exploration around Saturn will come to a dramatic end on Friday as Cassini takes its final plunge into the planet it has been sent to observe.
After years of exploration, gathering a treasure trove of scientific data on one of the solar system’s most iconic planets, the Cassini spacecraft’s hours are numbered and the countdown is on to its demise.
Launched on 15 October 1997, Cassini won’t last to its 20th anniversary as it completes a collision course with Saturn’s atmosphere on Friday, 15 September.
Cassini has spent the past 13 years orbiting Saturn as part of the international Cassini-Huygens mission. A joint endeavour of NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI), a total of 27 nations contributed to this mission to learn more about the ringed planet.
Originally scheduled for a four-year tour, Cassini’s mission was extended twice and now, the craft is running on fumes. Without sufficient fuel to adjust its course, operators risk losing control of Cassini. This could result in an unplanned impact with one of Saturn’s satellites.
The key discoveries of Cassini’s mission have been the global ocean and indications of hydrothermal activity on Enceladus, as well as liquid methane seas and intriguing prebiotic chemistry on Titan, so scientists want to preserve these pristine moons for further exploration. And so, the decision was made to direct Cassini into the gas planet’s atmosphere to burn up.
The Grand Finale
In the lead-up to the craft’s end, Cassini has been making weekly dives through a 2,000km gap between Saturn and its rings. The craft has completed 22 of these ‘Grand Finale orbits’ since April, offering scientists at home closer inspection of the inner and outer edges of Saturn’s rings as well as the planet’s small inner moons and the upper reaches of its atmosphere. This dramatic swan song has delivered the closest ever images of the distant planet.
The ESA had its role to play in the Grand Finale, receiving signals from Cassini to gather crucial radio science and gravitational science data. Then, on 11 September, the beginning of the end for Cassini kicked off with a final flyby of Titan, giving the gravitational assist needed to put the craft on course for impact with Saturn.
How it will all end
All predicted times are subject to change, but the forecast for Cassini’s dying hours are as follows.
Today, 14 September, sees Cassini’s last image captured and a final transmission of all data on its recorder. With 1.4bn km of space between Earth and Saturn, radio signals from Cassini will take about 83 minutes to reach home, and it’s expected that these last images from the spacecraft will begin appearing on the Cassini raw image gallery by 3am GMT (4am IST).
This last blast of Cassini snaps should contain images of Titan, Enceladus, the tiny ‘moonlet’ dubbed Peggy, a propeller feature in Saturn’s ring, and a colour montage of Saturn and its rings, including the aurora at its north pole.
On Friday, 15 September, the spacecraft will reconfigure for real-time science transmission until the final loss of signal, currently expected around 11.54am GMT (12.54pm IST). At this point, Cassini will be roughly 1,500km above the tops of Saturn’s clouds. Though Cassini’s photography duties will have ended, the craft will continue to capture high-value science data from its spectrometers, cosmic dust analyser, magnetometer and more. In total, eight instruments will collect data during the final plunge, transmitting it back to Earth in near-real time.
Shortly after this reconfiguration, Cassini will cross the orbital distance of Saturn’s F ring (the outermost of the main rings) for the last time. After about three hours, atmospheric entry will begin and thrusters will boost to 100pc capacity in a last-gasp effort to keep its high-gain antenna pointing at Earth for as long as possible. Eventually, the signal will be lost as the craft goes down in a blaze of glory. The intrepid explorer will burn up in Saturn’s atmosphere and disintegrate.
Follow Cassini’s crescendo
NASA will host a live stream of the dramatic conclusion of Cassini’s mission on its Public Education channel. Live commentary will begin at 11am GMT (12pm IST) on Friday and a post-mission press conference is currently scheduled for 1.30pm GMT (2.30pm IST).
Live status updates are constantly being added to NASA’s Jet Propulsion Laboratory website and tweets from @CassiniSaturn are also being shared via @esascience, while @esaoperations will be sharing live updates from ESA’s mission control in Darmstadt on Friday.
Teams at ESA operations will follow Cassini’s final plunge using the agency’s deep-space ground station in Canberra, Australia.