Australian Scientists Bid Cassini A Final Farewell, Before It Plunges Into The Atmosphere Of Saturn

Australian Scientists Bid Cassini A Final Farewell, Before It Plunges Into The Atmosphere Of Saturn
Image: NASA/JPL-Caltech/Space Science Institute

On Friday night, NASA’s Cassini spacecraft will end its 20 year mission exploring Saturn by entering the giant planet’s atmosphere – beaming back as much science as possible to the CSIRO team at the Canberra Deep Space Communication Complex – before it meets its firey doom.

Gizmodo will be there on the ground with the CSIRO/NASA teams in Canberra to bid our final farewell, and in the days leading up to the event space nerds from around the country have penned statements in honour of the spacecraft’s service to humanity.

Here’s what those who know Cassini best have to say.

Cassini has spent the last 147 days spiralling between Saturn’s rings and the planet, with 22 dives into this uncharted territory over the last few months.

While NASA had extended the mission in the past, the operating scientists worried that, with propellant running low, the probe might otherwise have accidentally crashed into one of Saturn’s nearby moons, contaminating it with Earthling bacteria stuck to the spacecraft.

So we have to say goodbye.

Professor Peter Tuthill is an ARC Future Fellow at the School of Physics, University of Sydney

Cassini’s final spectacular dive into Saturn is a grand finale to mark the end of one of the most exciting eras of discovery in planetary science. This was a major flagship-class mission, bristling with cameras and scientific experiments, that has managed to entrance the scientific community and the public alike with exquisite images and data from the spectacular system of rings, moons and storms raging in the banded atmosphere of Saturn itself.

The outstanding science resulted in two mission extensions, and its final swansong is now almost 20 years since launch.

Working with Cassini has been the adventure of a lifetime. It has done so much, including the only landing of a probe on the surface of a moon beyond Earth’s, and precipitating an entire new field of gravitational physics with its spectacular images of the rings and inner moons.

Our work with Cassini at Sydney was unique – we employed Saturn’s rings as a giant telescope floating in the outer solar system and used them enhance the resolving power of the on-board cameras so that we could study distant dying stars.

This work by my student Dr Paul Stewart was recognized this year with the Astronomical Society of Australia award of the Charlene Heisler prize for the best Astronomy Dissertation.

Dr Paul Stewart is from the University of Sydney’s School of Physics

It was a great honour to be working directly on the mission – flying this fantastic spacecraft around Saturn will always be a highlight of my career.

My work involved using Cassini to turn the Saturn’s rings into a kind of giant telescope in order to study distant stars.

This research was not foreseen when Cassini was designed, like many of the discoveries it has made, and is now no longer possible without a spacecraft in the Saturn’s orbit.

The Cassini mission has been a once-in-a-generation opportunity to explore Saturn, its fascinating rings and icy moons.

Mission highlights include finding liquid water on the moon Enceladus, the discovery of lakes, rivers, and weather systems on the moon Titan, and a new understanding of Saturn and its ring system.

On the Earth, everywhere there is liquid water we find life. The decision to end the Cassini mission so dramatically, by crashing into Saturn, was therefore taken to avoid the possibility of contaminating any of the planet’s moons which may have water.

Glen Nagle is the Outreach and Administration Lead at NASA’s Operations Support Officer, Canberra Deep Space Communication Complex, NASA’s Deep Space Network, CSIRO Astronomy and Space Science

Our CSIRO-NASA tracking station been with Cassini since it launched and opened it eyes on the universe, and we’ll be there with this incredible spacecraft until its very last breath of data.

Our giant antenna dishes will receive the spacecraft’s final treasure trove of data before it plunges into Saturn’s atmosphere, ending its mission as a shooting star.

It’s fitting that CDSCC is there for Cassini’s grand finale. We confirmed its safe arrival at Saturn in July 2004, and we captured the data and images as its piggybacking Huygens probe landed on Saturn’s largest moon, Titan, to reveal a shoreline strewn with icy rocks.

We’ve done unique radio science experiments, bouncing powerful radio signals off that moon’s surface to probe its terrain and methane filled lakes.

We’ve helped examine Saturn’s rings and determine the size of its particles which range from dust grains to the size of mountains. These deep space observations were only possible because of the technology we operate and the expertise of our CSIRO team.

Cassini has been a daily part of our lives for nearly 20 years, and when we receive the final call home and its signal disappears from our screens, that will be a bittersweet moment.

Matthew Agnew is a PhD student in the Centre for Astrophysics and Supercomputing at the Swinburne University of Technology

The Cassini spacecraft has been a scientific workhorse for us for over a decade, providing fascinating insights into the Saturnian system since arriving in orbit in 2004. Over the years, Cassini has provided us with unprecedented information about the structure and dynamics of Saturn’s atmosphere, its moons and its rings.

We’ve learnt about the atmosphere and surface of Titan and its lakes of methane, and about the subsurface liquid ocean of Enceladus and its jets that erupt from its surface, containing evidence that there may be thermal vents deep within its ocean similar to those found here on Earth.

Now, with Cassini running low on fuel, it has transitioned to its last scientific mission: The Grand Finale.

As explorers of the Solar system, we have a duty of care to keep places with the possibility of life untouched for future exploration, and so Cassini has undergone a series of spectacular orbits between Saturn and its rings to avoid collision with Titan or Enceladus. In doing so, Cassini will provide us with the closest scientific observations of Saturn and its rings ever achieved, before commencing its dive into Saturn, ultimately sending back its final stream of scientific data until it burns up in the thick atmosphere.

Professor Iver Cairns is from the school of physics at The University of Sydney

Cassini has exposed many of the major mysteries of the Saturnian system and answered many questions left by the Voyager and Pioneer spacecraft. The new images of the moons and rings, including the plumes from Enceladus and the associated new evidence for a liquid conducting ocean there, plus those of Saturn itself, are really exciting as well as beautiful.

The results from ESA’s Huygens lander on Titan are eye-opening. Moreover, the fields and particle measurements show the richness of the space weather environment in the Saturnian system.

Dr Rebecca Allen is an astrophysicist from the Swinburne centre for Astrophysics and Supercomputing

After 20 years in space, and over a decade of continuous observations, the Cassini spacecraft will complete its last mission by diving into the atmosphere of Saturn. Even in its final hours, Cassini may help resolve one of the greatest mysteries of Saturn, what lies beneath its shrouded vail.

However, this mission is a consolation prize, as the main purpose of sending Cassini crashing into Saturn is to preserve any primordial life that may be present on Saturn’s Moons, Titan and Enceladus.

In fact, it is because of Cassini that we know Titan has a sophisticated hydraulic cycle composed of Methane and Ethane, instead of water. There are giant lakes on Titan’s surface that span hundreds of kilometres and could host life unlike anything on Earth.

Enceladus was once thought a giant ice ball, but observations of its poles have revealed geysers spewing water far out into space leading scientists to believe that a liquid water ocean may be present beneath the surface and possibly hosting life similar to what primordial life could have looked like deep in the oceans of a young Earth. And there are weirdos too. Hyperion has a very low density and resembles a giant sponge, as debris impacts penetrate deep into its surface. Besides its strange appearance, Hyperion has a statically charged surface, they only other one ever observed besides our own moon.

Cassini has helped astronomers not only characterise Saturn’s many moons, but also to understand the complicated relationship they have with each other, their host planet, and it’s ring system.

By studying these celestial bodies, as well as observing the aurora on Saturn’s poles, we now know that Saturn has a large, powerful, and constantly evolving magnetosphere.

This majestic gas giant has always fascinated us since its discovery; however, Cassini’s data will allow us to not only understand more about giant gas planets and their satellites, but also to observe a system that may not be too different from the early solar system itself.

Therefore, the Cassini mission has provided us with a wealth of information about a distant planet, but has also given us a glimpse of what an early planet system may resemble helping us understand more about the history of our solar system.

Dr Alice Gorman is a Senior Lecturer in the College of the Arts, Humanities and Social Sciences at Flinders University and an internationally recognised leader in the emerging field of space archaeology

There’s a long history of spacecraft doing science while in their death throes.

Galileo, the only spacecraft to orbit Jupiter, was sent to its death in Jupiter’s atmosphere in 2003 to avoid contaminating the moons with bacteria. It transmitted data right up until the last minute, when the heat and pressure created by plunging into the atmosphere at 48 km/s tore it apart.

In 2012, NASA deliberately crashed the Ebb and Flow spacecraft into a mountain at the Moon’s north pole to make sure they didn’t accidentally land on lunar heritage, destroying sites like Apollo 11 where humans first set foot on the Moon. Their demise was incorporated into an experiment to calculate fuel needs for future lunar missions.

ESA’s Rosetta spacecraft was crashed into Comet 67P Churyumov-Gerasimenko in 2016, measuring gas and dust, and sending back images until it was about 20 m above the surface.

Without Cassini, we’ll have no eyes or senses close to Saturn any more. We’ve become used to seeing the close-up images of one of the solar system’s most beautiful features. Cassini might be a distant robot, but for many people, it’s like saying goodbye to an old friend after seven years of captivating interplanetary postcards.

Professor Dean Rickles is an ARC Future Fellow and co-director of the Centre for Time, at The University of Sydney

After 20 years in space, the Cassini spaceprobe is now running on fumes… On the 15th September as it plunges through Saturn’s atmosphere, eventually burning up, its final moments might reveal the most important information yet. It will transmit through each of the layers of Saturn’s rings, amongst other things, generating data about how moons form.

Cassini was the 17th-century astronomer famous for discovering four moons of Saturn and discerning the structure of Saturn’s rings. The Cassini probe inspected both the moons and the rings at a level of detail that could not have been imagined by Cassini himself. Some of the most interesting findings of the overall mission were from the Huygens lander (a craft designed by the European Space Agency) that Cassini carried, which landed on the moon Titan in 2005 – thereby becoming the most distant landing ever.

It discovered a moon peppered with Earthly river channels and lake beds and seas of liquid methane. Cassini probed other moons, finding on Enceladus even more Earth-like features, with an icy crust under which sits an ocean that might well be teeming with life.

It is imperative that another probe be sent to Enceladus in the near future to find out more. Finding life elsewhere in the Universe is obviously one of the most exciting aspects of space exploration, and without Cassini we would never have known about Enceladus’ remarkable features.

Dr Alan Duffy is a Research Fellow at Swinburne University of Technology in Melbourne

As long as I’ve been an astronomer Cassini has been orbiting Saturn sending back breathtaking images. I’ll shed a tear at the end of this spacecraft as it has been one of the greatest scientific explorers of all time. Cassini revealed Saturn to be beautiful but also full of surprises, with an Earth-sized six sided storm at the Pole still shocking to me.

The greatest surprise Cassini uncovered was in the moons rather than the planet itself. The giant Titan with thick orange smog hiding its surface from view revealed rain, rivers and seas but of liquid methane not water. The frozen moon Enceladus has salt water geysers which erupt, sending all the ingredients life needs into space from vast oceans beneath the ice-crust.

Cassini’s greatest discovery, of a world more capable of sustaining life than almost any other besides Earth, means that we have to destroy it at the end of its mission than risk it contaminating Enceladus with stowaway Earth-born bacteria. One last great effort for science at the end of a glorious mission.

Dr Brad Tucker is a Research Fellow and Outreach Manager at Mt. Stromlo Observatory at the Australian National University

Cassini has been a part of our lives for over two decades. Cassini has changed our understanding of Saturn and its moons – from the composition of the rings to the potential for life that exists on Enceladus and Titan. It is only fitting that because of what Cassini has shown, that we do not want to contaminate potential habitable system with Earth-born material. At the same time, we will be able to see as deep as possible into Saturn. We live in a time where we must carefully think of what we do, and be responsible stewards of our Solar System. It is an exciting time to understand our Solar System and Cassini has set us up for future projects in the quest for knowledge and life.

Charley Lineweaver is an Associate Professor in the Research School of Earth Sciences, at the Australian National University College of Science

The single most impressive highlight of Cassini’s 20 year odyssey was the landing of the Huygens probe on the surface of Titan, 12 years ago.

It showed us a moon with an atmosphere 50 per cent thicker than Earth’s atmosphere, above a landscape sculpted by methane rain, methane rivers and methane lakes – a methanological cycle at -180°C, comparable to the hydrological cycle at +15°C of our home planet. Can life be based on liquid methane rather than water?

Arrivederci Cassini.

Your imminent death will not be in vain.

You will burn up and become part of the planet that you have taught us so much about.

Professor Trevor Ireland is from the Research School of Earth Sciences at The Australian National University

Saturn’s rings have been a source of fascination for over 400 years. Galileo first saw them but then a couple years later they had disappeared going into an edge-on configuration. Maxwell the mathematician noted that the rings could not be solid and must be an assemblage of objects orbiting Saturn. A likely source of this material is a collision between moons or disruption by Saturn itself.

Cassini has shown that the rings are incredibly thin, less than a kilometre thick, and shepherded by a number of small moons. They are a mixture of mud and ice. A key question to be established by Cassini in its final orbits is how massive are the rings, and how old are the rings?

In passing inside the rings, Cassini can determine the gravitational perturbation associated with the mass of the rings. The take on it is that the higher the mass in the rings, the older the rings are likely to be. Are they as old as Saturn itself? Highly unlikely.

The shepherding moons are pushing and pulling the material in the rings, causing friction and likely evaporation. The rings must be relatively young, but that still means they could be hundreds of millions of years old. Cassini has provided a wealth of information on the Saturnian system. From Enceladus to Titan it has been absolutely thrilling. Farewell Cassini.

Fred Watson AM is an astronomer at the Australian Astronomical Observatory

If there was ever a space project that totally exceeded the expectations of the scientific world, it has been the Cassini mission to Saturn.

Launched in 1997, Cassini reached its target after a seven-year journey, and immediately began re-writing the textbooks.

Now, 13 years later, we have a remarkable catalogue of amazing discoveries. Storms and a hexagonal jet-stream in the planet’s atmosphere, ripples and spokes in its rings, global oceans and oily seas on its moons. And they are just the start – the best may be yet to come.

With the spacecraft’s fuel running out, mission controllers have thrown caution to the winds in an audacious series of orbits that have threaded Cassini between the rings and the planet before the final plunge into Saturn’s atmosphere on 15 September.

The last photos and data sets are likely to be spectacular.

Associate Professor Lisa Harvey-Smith is a Research Group Leader from ATNF Science at CSIRO Astronomy & Space Science, and Adjunct Associate Professor at The University of New South Wales

Cassini has been a triumph, uncovering many unexpected mysteries on Saturn including vertical features in its rings and raging hurricanes at its poles. Even after Cassini dives into Saturn’s belly this week, the data this remarkable spacecraft produced will keep planetary scientists busy for many years to come.

For over a decade the Cassini spacecraft has brought us incredible insights into the planet Saturn, its moons and its fascinating system of rings. The Huygens lander, launched from Cassini, was the first spacecraft to touch down on a moon of another planet. When Huygens landed on Titan it discovered a world much like the early Earth, with lakes and rivers of methane and ethane and a soupy atmosphere with complex pre-biotic molecules. Huygens was a triumph of interplanetary exploration. It opened a new world of understanding on Saturn’s largest moon and gave new understanding to our search for life elsewhere in the solar system.

CSIRO is proud to operate an important part of NASA’s deep space tracking network that receives the faint signals from interplanetary explorers such as Cassini.

We’ll be sorry to see Cassini go, but we will remember all the good times.

We’ll be live-blogging Cassini’s farwell from Canberra, and you can follow along on social media with the #CassiniAus #GrandFinale hastags. NASA TV will be covering the event, as well.

You can watch along here.