Cassini completes second pass inside Saturn’s rings

May 9, 2017


NASA’s Cassini probe survived its second pass between Saturn and its innermost rings earlier this week, giving scientists increasing confidence the region between the rings and the cloud tops is clear of large particles that might represent a threat to the spacecraft.

Virtually out of propellant, Cassini is wrapping up its extended 13-year mission at Saturn by making 22 dives between the gas giant and its vast ring system, collecting priceless science data before crashing into the planet in September in a long-planned kamikaze-like maneuver to close out a remarkably successful flight.

On April 26, Cassini made the first of 22 planned ring-plane crossings, using its large dish antenna as a shield in case scientists had underestimated the amount of ring material that might be present. Crossing the plane at more than 76,000 mph, even relatively small particles could cause serious damage.

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6 comments on “Cassini completes second pass inside Saturn’s rings


    After almost 20 years in space, NASA’s Cassini spacecraft begins the final chapter of its remarkable story of exploration: its Grand Finale.

    Between April and September 2017, Cassini will undertake a daring set of orbits that is, in many ways, like a whole new mission.
    Following a final close flyby of Saturn’s moon Titan, Cassini will leap over the planet’s icy rings and begin a series of 22 weekly dives between the planet and the rings.

    The spacecraft will make detailed maps of Saturn’s gravity and magnetic fields, revealing how the planet is arranged internally, and possibly helping to solve the irksome mystery of just how fast Saturn is rotating.

    The final dives will vastly improve our knowledge of how much material is in the rings, bringing us closer to understanding their origins.

    Cassini’s particle detectors will sample icy ring particles being funneled into the atmosphere by Saturn’s magnetic field.

    Its cameras will take amazing, ultra-close images of Saturn’s rings and clouds.

    Cassini’s final images will have been sent to Earth several hours before its final plunge, but even as the spacecraft makes its fateful dive into the planet’s atmosphere, it will be sending home new data in real time.
    Key measurements will come from its mass spectrometer, which will sample Saturn’s atmosphere, telling us about its composition until contact is lost.

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  • While Cassini is providing amazing new data on Saturn, Juno is visiting the Solar System’s other gas-giant planet.
    Many of the best images are being processed by citizen scientists

    Scientists working on the American space agency’s new Juno mission say its initial observations at Jupiter have taken their breath away.

    In particular, they have been amazed by the storms seen at the planet’s poles.

    “Think of a bunch of hurricanes, every one the size of the Earth, all packed so close together that each hurricane touches the other,” said Mike Janssen.

    “Even in rooms of hardened researchers, these images of swirling clouds have drawn gasps,” the Nasa man added.

    The Juno probe arrived at the fifth planet from the Sun on 4 July last year. Since then, it has been making a close pass over the gas giant every 53 days.

    The first data to come out of these observations are now being reported in two papers (here and here) in the journal Science, and in more than 40 others in a special collection for Geophysical Research Letters.

    The mission team says that in nearly all instances, previously cherished theories about how Jupiter works are being challenged.

    “We’re getting the first really close up and personal look at Jupiter and we’re seeing that a lot of our ideas were incorrect and maybe naive,” said Juno principal investigator Scott Bolton from the Southwest Research Institute in San Antonio, Texas.

    Those big cyclones that cover the highest latitudes of the planet are only now being seen in detail because previous missions to the planet never really got to look from above and below like Juno – certainly not at such a high resolution. Features down to 50km across can be discerned.

    The structures are very different from those seen at Saturn’s poles, for example, and the team will have to explain why. It is also not clear at this stage how long-lived they are. Will they dissipate much faster than the storms at lower latitudes, which in some cases – as with the famous Great Red Spot on Jupiter – have persisted for centuries?

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  • The Cassini mission is now approaching its end phase!

    The spectacular rings of Saturn may be relatively young, perhaps just 100 million years or so old.

    This is the early interpretation of data gathered by the Cassini spacecraft on its final orbits of the giant world.

    If confirmed, it means we are looking at Saturn at a very special time in the age of the Solar System.

    Cassini is scheduled to make only two more close-in passes before driving itself to destruction in Saturn’s atmosphere on 15 September.

    The probe is being disposed of in this way because it will soon run out of fuel. That would render it uncontrollable, and mission managers at the US space agency Nasa do not want it crashing into – and contaminating – moons that could conceivably host microbial lifeforms.

    The approaching end means scientists and engineers are now taking risks with Cassini that would never have been contemplated when the probe arrived at the planet 13 years ago.

    Chief among these risks are the dramatic flybys Cassini undertakes every six days. These see the spacecraft plunge through the gap between the top of Saturn’s atmosphere and the rings.** It is a completely unexplored region from where Cassini is returning some unique data.**

    This includes making a detailed map of the gravity field in which the contributions from the huge world and the rings can be teased apart.

    Cassini is essentially trying to weigh the rings. Their mass says something about their age.

    The more massive they are, the older they are likely to be. Some scientists think they could even have formed with Saturn itself 4.6 billion years ago. They would certainly need a large mass to withstand the forces that might erode them over time, such as collisions from tiny meteoroids. But it is looking like the opposite may actually be true – that their mass is less than previously estimated.

    If confirmed it points to the rings being the remnants of some object that has broken apart around Saturn in the recent past.

    “For younger rings, it would require a comet, or a centaur (one of a group of small, icy objects), or perhaps even a moon moving too close to Saturn. Saturn’s gravity would break apart that object and then the remaining bits would go on to form rings,” explained Linda Spilker, Nasa’s Cassini project scientist.

    “Perhaps that’s happened more than once. Maybe some of the differences we see in the rings are from different objects that were broken apart. But if the rings are less massive they won’t have had the mass to survive the micro-meteoroid bombardment that we estimate to have happened since the formation of the planet.

    “So, we’re heading in the direction of the rings being perhaps 100 million years old or so, which is quite young compared to the age of the Solar System,” she told BBC News.

    Dr Spilker did however caution that these were early days in the analysis of the new data and the uncertainties were still large.

    Other team members have been outlining plans for the remaining 18 days of the mission.

    Cassini will take its final images on Thursday 14 September – “What we’re calling the ‘Last Picture Show’; the final set of images of some of the selected targets of the Saturn system,” said Earl Maize, Nasa’s Cassini project manager.

    These include pictures of the moons Titan and Enceladus, the strange hexagon-shaped jet stream at the planet’s north pole, and the little moonlet embedded in the rings known as Peggy.

    The spacecraft will then be reconfigured for its death plunge. This means prioritising those instruments that can gather atmospheric data.

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  • So as science investigates the planets and moons of the Solar-System, each project builds on the work of earlier ones, so and provides new insights into what were previously viewed as unrelated subject areas, – giving a more joined up over-view.

    After Cassini: Pondering the Saturn Mission’s Legacy

    Jupiter’s moon Europa has been a prime target for future exploration since NASA’s Galileo mission, in the late 1990s, found strong evidence for a salty global ocean of liquid water beneath its icy crust. But the more recent revelation that a much smaller moon like Enceladus could also have not only liquid water, but also chemical energy that could potentially power biology, was staggering.

    Many lessons learned during Cassini’s mission are being applied to planning NASA’s Europa Clipper mission, planned for launch in the 2020s. Europa Clipper will fly by the icy ocean moon dozens of times to investigate its potential habitability, using an orbital tour design derived from the way Cassini has explored Saturn.
    The Europa Clipper mission will orbit the giant planet — Jupiter in this case — using gravitational assists from its large moons to maneuver the spacecraft into repeated close encounters with Europa.
    This is similar to the way Cassini’s tour designers used the gravity of Saturn’s moon Titan to continually shape their spacecraft’s course.

    In addition, many engineers and scientists from Cassini are serving on Europa Clipper and helping to develop its science investigations. For example, several members of the Cassini Ion and Neutral Mass Spectrometer and Cosmic Dust Analyzer teams are developing extremely sensitive, next-generation versions of their instruments for flight on Europa Clipper.
    What Cassini has learned about flying through the plume of material spraying from Enceladus will help inform planning for Europa Clipper, should plume activity be confirmed on Europa.

    Cassini also performed 127 close flybys of Saturn’s haze-enshrouded moon Titan, showing it to be a remarkably complex factory for organic chemicals — a natural laboratory for prebiotic chemistry.
    The mission investigated the cycling of liquid methane between clouds in its skies and great seas on its surface.
    By pulling back the veil on Titan, Cassini has ushered in a new era of extraterrestrial oceanography ­– plumbing the depths of alien seas — and delivered a fascinating example of earthlike processes occurring with chemistry and at temperatures markedly different from our home planet.

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