From ESA: “Cassini concludes pioneering mission at Saturn”

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European Space Agency

15 September 2017
Nicolas Altobelli
ESA Cassini–Huygens Project Scientist

Tel: +34 91 813 1201


Markus Bauer

ESA Science Communication Officer

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The international Cassini mission has concluded its remarkable exploration of the Saturnian system in spectacular style, by plunging into the gas planet’s atmosphere.

Confirmation of the end of mission arrived at NASA’s Jet Propulsion Laboratory at 11:55 GMT/13:55 CEST with the loss of the spacecraft’s signal having occurred 83 minutes earlier at Saturn, some 1.4 billion km from Earth.

Last Enceladus plume observation

With the rocket propellant for manoeuvering the spacecraft fully expended as planned touring Saturn and its moons for the last 13 years, the mission concluded with the intentional plunge into the gas planet. This ensures that Saturn’s icy moons, in particular ocean-bearing Enceladus, do not risk being contaminated by microbes that might have remained on board the spacecraft from Earth, and are left pristine for future exploration.

Cassini spent the last five months diving between Saturn’s rings and atmosphere in a series of 22 grand finale orbits culminating in a final farewell to Titan on Monday, which set it on course for Saturn.

The grand finale orbits were supported by ESA ground stations, which received signals from Cassini to gather crucial radio science and gravitational science data.

ESA DSA-1 New Norcia, Western Australia. Credit: ESA

NASA Deep Space Network
Canberra, AU

Madrid, Spain

Goldstone, Mojave Desert, USA


Cassini’s final image – natural colour view

Ring Crossing: In this still from the short film Cassini’s Grand Finale, the spacecraft is shown diving between Saturn and the planet’s innermost ring. Credit: NASA/JPL-Caltech

Atmospheric entry began about a minute before loss of signal, and the spacecraft sent scientific data in near real-time until its antenna could no longer point towards Earth. Its last images were sent yesterday, before the final plunge, and during its final moments it made the deepest ever measurements of the plasma density, magnetic field, temperatures and atmospheric composition in Saturn’s atmosphere.

“Cassini has been revolutionising our views of the Saturn system since the moment it arrived, and for 13 incredible years right until the very end today,” says Alvaro Giménez, ESA’s Director of Science.

“This mission has changed the way we view ocean-worlds in the Solar System, offering tantalising hints of places which could offer potentially habitable environments, with Titan giving us a planet-sized laboratory to study processes that may even be relevant to the origin of life on Earth.”

Launched on 15 October 1997 and arriving in Saturn’s orbit on 30 June 2004 (PDT), Cassini carried ESA’s Huygens probe that landed on Titan on 14 January 2005. During its two and half hour descent it revealed the surface that had been previously been hidden by the moon’s thick hazy atmosphere, showing a world with eerily Earth-like landscapes.

Cassini would continue to make exciting discoveries at Titan from orbit, with its radar finding lakes and seas filled with methane and other hydrocarbons, making it the only other known place in our Solar System with a stable liquid on its surface. In the moon’s atmosphere Cassini detected numerous complex organic molecules, some of which are considered building blocks of life on Earth.

First colour view of Titan’s surface

Saturn’s moon zoo

Saturn’s moons continued to surprise, with one of the major discoveries of the entire mission the detection of icy plumes erupting from fissures in the southern hemisphere of Enceladus. Later discoveries would indicate hydrothermal activity at the bottom of a sea floor, hinting at this world as one of the most promising places to search for life beyond Earth.

The mission also showcased the unique characteristics of Saturn’s many other moons, from Iapetus and its equatorial ridge to Hyperion, which looks like a giant sponge, and from ravioli-shaped Pan, to Mimas, which resembles the Death Star from Star Wars.

Many of Cassini’s discoveries can be attributed to the longevity of the mission, which included two mission extensions, allowing the spacecraft to cover half of Saturn’s seasonal cycle.

First, a two-year extension was granted to observe changes as Saturn reached equinox, when the Sun shone edge-on to the rings. Subsequently, an additional seven years was given to follow up on earlier discoveries at Enceladus and Titan, and watch as summer sunlight fell on to the northern hemisphere of Saturn and its moons while winter darkness moved in on the south.

This long-term monitoring allowed scientists to watch seasonal changes, including how weather patterns in Saturn’s dynamic atmosphere evolved, and revealing the long-lived north polar vortex inside a hexagon-shaped jet stream. Cassini also watched how Titan’s hydrocarbon cycle evolved with the seasons, its clouds raining methane onto the surface.

Saturn’s ring features

The extended mission time was also crucial to track the evolution of small-scale dynamical features in the rings, like the ‘propellers’, disturbances in the rings created by moonlets. Over time the ‘spokes’ in Saturn’s rings – features that rotate along with the rings like the spokes in a wheel – appeared and disappeared with the seasons. And at equinox, the exquisite detail of the vertical structures in the rings, driven by gravitational perturbations of nearby moons, was revealed.

“Cassini and Huygens represent an astonishing scientific, technological, and human achievement,” says Nicolas Altobelli, ESA’s Cassini project scientist.

“The mission has inspired us with awe-inspiring images, including those humbling views looking across more than a billion kilometres of space back to the tiny blue dot of our home planet.

Cassini’s Pale Blue Dot
Released 23/07/2013 9:16 am
Copyright NASA/JPL-Caltech/Space Science Institute
In this rare image taken on 19 July, the wide-angle camera on the international Cassini spacecraft has captured Saturn’s rings and our planet Earth and Moon in the same frame.
The dark side of Saturn, its bright limb, the main rings, the F ring, and the G and E rings are clearly seen; the limb of Saturn and the F ring are overexposed. The ‘breaks’ in the brightness of Saturn’s limb are due to the shadows of the rings on the globe of Saturn, preventing sunlight from shining through the atmosphere in those regions. The E and G rings have been brightened for better visibility.

Earth, 1.44 billion km away in this image, appears as a blue dot at centre right; the Moon can be seen as a fainter protrusion off its right side. The other bright dots nearby are stars.
This is only the third time ever that Earth has been imaged from the outer Solar System. The first image was taken by NASA’s Voyager-1 in 1990 and famously titled “Pale Blue Dot”. In 2006, Cassini imaged Earth in the stunning and unique mosaic of Saturn called “In Saturn’s Shadow – The Pale Blue Dot”.
The new images marked the first time that inhabitants of Earth knew in advance that their planet was being imaged. That opportunity allowed people around the world to join together in social events to celebrate the occasion.
This view looks towards the unilluminated side of the rings from about 20º below the ring plane.
Images taken using red, green and blue filters were combined to create this natural colour view. The images were obtained with Cassini’s wide-angle camera on 19 July at a distance of 1.212 million km from Saturn, and 1445.858 million km from Earth. The illuminated areas of both Earth and the Moon are unresolved here. Consequently, the size of each ‘dot’ is the same size that a point of light of comparable brightness would have in the wide-angle camera.

While it is certainly sad when a mission ends, it is also a time to celebrate this pioneering journey, which leaves a rich scientific and engineering legacy to pave the way for future missions.”

Mission planners already have the next generation of ocean-world explorers lined up, although this time it’s Jupiter that will get the limelight. ESA is preparing to launch the Jupiter Icy Moons Orbiter, Juice, in 2022, with a key focus on the habitability potential of the large ocean-bearing satellites Europa, Ganymede and Callisto, while NASA is planning the Europa Clipper mission for dedicated flybys of that icy moon.

ESA/Juice spacecraft

NASA/Europa Clipper

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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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