Saturn has more moons than Jupiter – but why are we only finding out about them now?


This Hubble Space Telescope image of Saturn and a few of its moons shows how hard it can be to spot the gas giant’s tiny orbiting companions.
NASA / ESA / Hubble

Lucyna Kedziora-Chudczer, Swinburne University of Technology

With the discovery of 20 more moons orbiting Saturn, the ringed planet has overtaken Jupiter as host to the most moons in the Solar system. Saturn now has 82 known moons, whereas Jupiter has a paltry 79.

Announced at the International Astronomical Union’s Minor Planet Centre by a team of astronomers from the Carnegie Institute for Science led by Scott S. Sheppard, the discovery is the latest advance in the 400-year history of our understanding of the satellites of our neighbouring planets.

As technology has improved, we have observed more and more of these tiny, distant worlds – and we can be reasonably confident there are still plenty waiting to be discovered.

How do we even know Saturn has moons?

Although most planets of the Solar system are visible to the naked eye and have been known to humans since antiquity, it wasn’t until Galileo Galilei turned a telescope on Jupiter in 1610 that we discovered Earth was not alone in having an orbiting companion.

Galileo saw Jupiter’s four largest moons and could make out what we now know are Saturn’s rings. Decades later, with better telescopes, Christian Huygens and Giovanni Domenico Cassini observed Saturn’s moons.




Read more:
Curious Kids: why does Saturn have rings?


It became clear that the giant planets are surrounded by multitudes of satellites, resembling smaller versions of the Solar system. By the middle of the 19th century, telescopes had improved enough that the first eight moons of Saturn – including Titan, the largest – had been viewed directly.

The introduction of photographic plates, which enabled the detection of fainter objects with long-exposure observations, helped astronomers increase their count of Saturn’s moons to 14.

Closer inspections

It was a long journey (literally) to the next big improvement in our view of Saturn’s moons. Many of the smaller moons were not discovered until the Voyager fly-by missions in the 1980s and the more recent 13-year stopover of the Cassini spacecraft in Saturn’s orbit.

Until these closer visits, we knew little about the moons aside from the fact that they existed.

One of Cassini’s goals was to explore Titan, which is the only moon in the Solar system with a thick, smoggy atmosphere. Another was to take a look at Saturn’s other mid-sized moons, including frozen Enceladus, which may hold an ocean of liquid water beneath its icy crust.




Read more:
A look back at Cassini’s incredible mission to Saturn before its final plunge into the planet


Cassini also discovered much smaller moons, so-called “shepherd moons” that interact with Saturn’s rings by carving gaps and wavy patterns as they pass through a rubble of rocks and snowballs.

Bigger telescopes, more moons

These close-up observations from space advanced our understanding of individual moons that stay near to Saturn. Recently, many more moons have been found in orbits much further from the planet.

These more distant moons could only be detected with large optical telescopes such as the Subaru telescope at Mauna Kea in Hawaii. The telescope is equipped with sensitive cameras that can detect some of the faint objects separated by millions of kilometres from Saturn.

The new moons were discovered by comparing photos like this pair taken about an hour apart. While the background stars stay fixed, the moon – highlighted with orange bars – moves between frames.
Scott Sheppard

To confirm that these objects are indeed associated with Saturn, astronomers have to observe them over days or even months to reconstruct the shape and size of the moon’s orbit.

Many small moons are fragments of shattered large moons

Such observations revealed a population of moons that are often described as “irregular” moons. They are split into three distinct groups: Inuit, Gallic, and Norse. They all have large, elliptical orbits at an angle to those of moons closer to the planet.

Each group is thought to have formed from a collision or fragmentation of a larger moon. The Norse group consists of some of the most distant moons of Saturn, which orbit in the opposite direction to the rotation of the planet. This suggests they could have formed elsewhere and were later captured by the gravitational force of Saturn.

Of the 20 new moons, 17 belong to the Norse group including the furthest known moon from the planet. Their estimated sizes are of the order of 5km in diameter.

Most of the newly discovered moons have retrograde orbits, going in the opposite direction to Saturn’s spin.
Carnegie Institution for Science

Have we found all the moons now?

Are we likely to find even more moons around Saturn? Absolutely.

Some of the newly discovered moons are very faint and at the limit of detection with currently available instruments. New, bigger telescopes such as Giant Magellan Telescope will allow us to observe even fainter objects.

In the meantime, the 20 new moons need names. Carnegie Science has invited everyone to help.The Conversation

Lucyna Kedziora-Chudczer, Program Manager / Adjunct Research Fellow, Swinburne University of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mission over: the final countdown to Cassini’s fatal plunge into Saturn



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An illustration of Cassini as it plunges into Saturn’s atmosphere.
NASA/JPL-Caltech

Ed Kruzins, CSIRO and Richard Stephenson, CSIRO

When the Cassini space probe makes its final descent into Saturn later today, data from the final nine hours of the mission will be sent back to NASA’s tracking station in Canberra, Australia.

As the probe descends, it will capture images and data from Saturn and its atmosphere, revealing more of the planet’s secrets. Under the spacecraft’s normal operations, its instruments first store and later forward images and data to Earth.

But in Cassini’s final hours, it will be transmitting home in real time, with the signals picked up by the CSIRO-managed Canberra Deep Space Communication Complex (CDSCC).


Read more: The secrets of Titan: Cassini searched for the building blocks of life on Saturn’s largest moon


The CDSCC is part of NASA’s Deep Space Network, one of three tracking stations around the world that provide vital two-way radio contact with Cassini and 30 other spacecraft including Voyagers 1 and 2.

Cassni’s final journey in local AEST times.
NASA/JPL-Caltech/CSIRO

Cassini’s final bonanza of data, transmitted as weak radio signals, will take 83 minutes to travel 1.5 billion km at the speed of light to reach the giant dish antennas in Canberra.

At an estimated 9:54pm AEST tonight (September 15), CSIRO’s team at CDSCC will capture the final signals as Cassini, travelling at more than 111,000km per hour, plunges into Saturn’s atmosphere.

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How to destroy the probe

NASA decided to safely dispose of Cassini into Saturn, ending its mission as a shooting star. With the spacecraft nearly out of fuel and possible loss of control, this plan will prevent accidental collisions with any of Saturn’s moons and potential biological contamination by microbial stowaways from Earth.

Viewed from Saturn, the last moments of Cassini would look similar to a meteor entering Earth’s atmosphere.

An illustration of Cassini breaking apart after entering Saturn’s atmosphere.
NASA/JPL-Caltech

From Earth, the world will await the bittersweet moment when NASA’s Jet Propulsion Laboratory mission control announces loss of signal. Cassini’s final call home will have been made.

It will mark the end of a 20-year mission, a joint venture between NASA, the European Space Agency and the Italian Space Agency.

Mission objectives

Inspired by the earlier flypast by the twin Voyager spacecraft, the two-part mission was actually known as the Cassini-Huygens mission.

The main craft was designed to study Saturn and its environs, while the piggybacking Huygens probe was to land on Titan, the planet’s largest moon.

Throughout its odyssey, every step of Cassini’s journey has been followed by the dishes at CDSCC in Canberra. It was the first tracking station to make contact with Cassini after its launch from Cape Canaveral in October 1997.

The Cassini spacecraft and Huygens probe begin their seven-year journey to Saturn after a successful launch on October 15, 1997.
NASA

It then tracked Cassini throughout its seven-year journey to Saturn, handling the vital communications as it arrived and was placed into orbit around the planet in July 2004.

As the first spacecraft to orbit Saturn, it has studied the planet, its rings and its 62 moons, seven of which were discovered by Cassini.

In 2005 the Huygens probe transmitted data as it landed safely on the surface of Titan. This was the first landing on a world in the outer Solar System.

The Huygens probe’s descent to Titan.

Saturn’s wonders revealed

Cassini has now witnessed almost half a Saturn year, which is 29 Earth years long.

While Voyagers 1 and 2 had spectacular encounters with the outer planets interspersed by years of travel, Cassini has delivered science on a daily basis.

Like a Swiss Army Knife of spacecraft, Cassini has a plethora of scientific instruments on board.

Eight of Cassini’s science instruments are planned to be turned on during the final plunge, including the Ion and neutral Mass Spectrometer (INMS).
NASA/JPL-Caltech

While the most inspiring data is the images, for staff at CDSCC the excitement has centred around performing dozens of unique radio science experiments with the Cassini team.

Using a process called bistatic radar, which is the deep space version of sonar, the data received made it possible to measure the size and distribution of particles in Saturn’s rings.

Saturn reigns supreme, encircled by its retinue of rings. You can also see Saturn’s famous north polar vortex and hexagon.
NASA/JPL-Caltech/Space Science Institute

It was also used to map the terrain and depths of ethane and methane lakes on the surface of Titan. For Cassini’s final bistatic observations of Titan earlier this year, key members of Cassini’s science team travelled to Canberra to witness the data coming into CDSCC first-hand.

Staff found it exhilarating to watch the pure excitement on the faces of Cassini’s team standing in their Canberra control room as the spacecraft’s faint signals were being received.

Bistatic scattering reveals the details on Titan.

To some of us, the data may have appeared as not much more than a slightly higher peak in a hash of radio noise, but to the mission team it meant discovering a shoreline or a lake bottom on the surface of a world more than a billion kilometres away. Being a part of these discoveries was a proud moment for CDSCC and its CSIRO team.

The rest of the probes

As we say goodbye to Cassini, CDSCC continues to track more than 30 other spacecraft, not only NASA probes but also those of other international space agencies in Europe, Japan and India.

The Canberra antennas still support both Voyager spacecraft for several hours each day, receiving data from the edge of the Solar System and beyond.

Canberra Deep Space Communication Complex will keep track of other spacecraft after Cassini’s final plunge into Saturn.
CSIRO CDSCC

NASA’s Juno has only just begun its primary mission, transmitting scientific data as it orbits Jupiter. Its highly elliptical orbit brings the spacecraft dangerously close to Jupiter (5,000km) before retreating away from the radiation-intense planet.

New Horizons, which flew past Pluto in 2015, has set a course for an encounter with a Kuiper Belt object on January 1, 2019. The spacecraft is periodically woken from hibernation to check system functions before being returned to slumber.

The next few years will see a quantum shift as the Deep Space Network moves to supporting proposed human missions to the Moon, asteroids and Mars.

Some key numbers for Cassini’s Grand Finale and final plunge into Saturn.
NASA/JPL-Caltech

For now though, CDSCC is concentrating on Cassini’s final moments, delivering its last breath of data to NASA scientists who will continue to study the information for decades to come.


Read more: A look back at Cassini’s incredible mission to Saturn before its final plunge into the planet


Using the big 70-metre antenna dish at CDSCC as the prime receiver, it will be backed up by a smaller 34m dish. To add even further redundancy into the system, the European Space Agency has a 35m dish in New Norcia, Western Australia, which will also listen to Cassini’s radio whispers.

Cassini’s final hours will be a bittersweet moment for the CDSCC team, losing a spacecraft that for 20 years had become a daily part of our lives.

We will say a fond farewell to an incredible mission, safe in the knowledge that we’ve been a part of an adventure that revealed Saturn as a real place, full of wonders, for future generations to explore.


There are a several ways to watch Cassini’s final hours, including:

You can also follow Cassini on Twitter @CassiniSaturn and Facebook at NASACassini.

The Conversation

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Ed Kruzins, Facilities Program Director Nasa Operations Canberra Deep Space Communication Complex , CSIRO and Richard Stephenson, Deep Space Network Operations Supervisor, CSIRO

This article was originally published on The Conversation. Read the original article.

The secrets of Titan: Cassini searched for the building blocks of life on Saturn’s largest moon


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Cassini captures Saturn’s largest moon, Titan.
NASA/JPL-Caltech/SSI

Courtney Ennis, La Trobe University

Lakes and seas of liquid methane, rain from hydrocarbon clouds, and evidence of poisonous hydrogen cyanide in the atmosphere of Titan were just some of the discoveries the Cassini probe made of Saturns’s largest moon.

The space probe has now made its final pass of Titan as it heads towards its grand finale plunge into the ringed planet later this week.

Dubbed Cassini’s “goodbye kiss” by NASA, Titan has been the subject of much scrutiny by the probe, with 127 flybys on its 13-year mission exploring the planetary system.


Read more: A look back at Cassini’s incredible mission to Saturn before its final plunge into the planet


One of Cassini’s greatest feats is its contribution to untangling the complicated chemistry of Titan, no doubt one of the more chemically diverse objects in our Solar System.

One last look at Titan on Cassni’s final journey.
NASA/JPL-Caltech

We have known for some time that the combination of ultraviolet rays from the Sun and particle bombardment has altered the mainly nitrogen and methane atmosphere over time.

This chemistry has sustained a thick, orange smog layer surrounding the entire body, shrouding Titan’s oceans and landscape from view prior to Cassini’s arrival.

The murky orange disk of Saturn’s moon Titan.
NASA/JPL/Space Science Institute

Probing Titan

With Cassini’s toolkit of advanced sensing instruments – combined with atmospheric sampling by the Huygens probe during its 2005 descent to the surface – the mission has developed a comprehensive picture of Titan’s chemistry.

Touchdown on Titan with the Huygens probe.

Intriguingly, on top of the hundreds of molecules accounted for, chemical models developed here on Earth incorporating Cassini data predict the existence of even more complex material.

Of potential significance to biochemistry, these molecules have evaded observation over the relatively short Cassini mission, being either out of view or present at levels below the detection limits of the equipment.

Even if only formed in small quantities in the atmosphere it is plausible that these life-bearing species have built up on the surface over Titan’s history.
So what are these chemicals and how do they come to be?

This composite image shows an infrared view of Saturn’s moon Titan from Cassini’s flyby in November 2015. The near-infrared wavelengths in this image allow Cassini’s vision to penetrate the haze and reveal the moon’s surface.
NASA/JPL/University of Arizona/University of Idaho

Cyanide snow

Unlike Earth, oxygen atoms are rather scarce in Titan’s atmosphere. Water is locked as surface ice and there appear to be no abundant sources of O₂ gas.

In oxygen’s place, we see nitrogen play a more significant role in Titan’s atmospheric chemistry.

Here, common products of nitrogen reactions are the cyanide family of compounds, of which hydrogen cyanide (HCN) is the simplest and most abundant.

As the numbers of cyanide molecules build up at lower, colder altitudes they form cloud layers of large floppy polymers (tholins) and budding ice aerosols.

As the aerosols descend to the surface, shells of methane and ethane ice form further layers on the exterior. This acts to protect the inner organic material on its descent to the surface before being dispersed in hydrocarbon lakes and seas.

Cassini’s view of Titan’s high northern latitudes in May 2012, the lakes on the left are full of liquid hydrocarbons while those on the top right are only partially filled, or represent saturated ground or mudflat.
NASA/JPL-Caltech/ASI/Cornell

Surprisingly it is these cyanide compounds, chemicals closely associated with toxicity and death to Earthly lifeforms, that may actually provide avenues for life-bearing biomolecules to form in space environments.

Some simulations predict that cyanides trapped in ices and exposed to space radiation can lead to the synthesis of amino acids and DNA nucleobase structures – the building blocks of life on Earth.

Excited by these predictions and their implications toward astrobiology, chemists have rushed to explore these reactions in the laboratory.

Synchrotron experiments: Titan-in-a-can

Our contributions to astrochemistry have focused on simulating the atmosphere of Titan and its cyanide haze.

With a specialised gas cell installed at the Australian Synchrotron, we are able to replicate the cold temperatures associated with Titan’s cloud layers.

Cassini’s spectrum view of the southern polar vortex shows a signature of frozen hydrogen cyanide molecules (HCN).
NASA/JPL-Caltech/ASI/University of Arizona/SSI/Leiden Observatory and SRON

By injecting cyanides (the friendlier variety) into our cell we can determine the size, structure and density of Titan aerosols as they grow over time; probing with infrared light from the facility.

These results have provided us with a list of signatures for which we can locate cyanide aerosols using infrared astronomy.

The next step will be to seed these aerosols with organic species to determine if they can be identified in extraterrestrial atmospheres.

Perhaps these signals will act as a beacon for future explorations designed to search for complex organic material in more remote space locations – potentially even on the “giant Earth” exoplanets in distant star systems.

Life off Earth

Space provides us a unique perspective to turn back the pages of chemistry.
Among the planets, moons and stars – and the not quite emptiness between – we can study the initial reactions thought to have started chemistry here on Earth.

Using ever more sensitive telescopes and advanced spacecraft, we have uncovered chemical nurseries – pockets of gas and ice exerted to harsh space radiation – in our Solar System and beyond.

Such cold, icy objects as Titan, the moons of Jupiter, Trans-Neptunian Objects (such as Pluto and other minor bodies in the Kuiper belt and beyond), as well as microscopic interstellar dust particles, all generate higher-order organic molecules from simple chemical ingredients.


Read more: Cloudy with a chance of life: how to find alien life on distant exoplanets


As far as we know, the lack of heat and liquid water precludes life to exist at these worlds.

However, we can look for clues regarding life’s origins on a primitive Earth. Were life-bearing chemicals delivered via comet impact, or made in-house near the early ocean shores or deep sea volcanoes? Observing the chemistry of distant objects could one day provide the answers.

The ConversationThese forays into our chemical history have been enabled by the significant steps we have taken in our exploration of space including, as a glowing example, the resounding success of Cassini’s exploration of Titan.

Courtney Ennis, Research Fellow, La Trobe University

This article was originally published on The Conversation. Read the original article.