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Cassini is about to take its final dive into the rings of Saturn, and scientists are still debating the status of water on our moon.

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The Cassini mission to Saturn has revealed lots of new data and all kinds of mysteries.

And, as the spacecraft approaches its final days, the surprises just keep coming. Take Saturn’s rings, for example.

Scientists thought the rings were as old as the planet. But, according to some of Cassini’s recent measurements, it’s starting to look like we might have been wrong. The Cassini spacecraft is our fourth probe to visit Saturn.

It was launched 20 years ago and arrived in 2004. Cassini’s long list of achievements include hundreds of flybys, checking general relativity, discovering new moons, and detailed studies of storms on Saturn. And, in the past few months, it’s been helping us figure out how old Saturn’s rings are, by getting up close and personal.

One of the goals of these dangerous dives between Saturn and its rings is to figure out the mass of the rings, using two pieces of data: the exact path of Cassini, and the frequency of the radio signals coming from the probe. Both of these things are affected by the gravitational pull of different parts of Saturn, and more massive objects have stronger gravitational pulls. Force depends on how much mass something has, along with its acceleration.

So scientists can use these data from Cassini to calculate how much of Saturn's mass is in the planet, and how much is in the rings. Figuring out the mass of the rings can also tell us their age, when we consider what they’re made of too. We think Saturn’s rings were originally made of pure water ice, but they’re constantly hit by other space debris.

Right now, around 5 or 10% of the rings are made of other dusty junk. More massive rings would take longer to get polluted and could survive a lot of bombardment over time. Some scientists thought that the rings might have been formed at the same time as Saturn, nearly 4.6 billion years ago.

This is when rocks were smashing into each other a ton, gradually coalescing into the solar system we know today. But, in an online news conference last week, a scientist working on the Cassini mission said that these recent data are pointing more towards less massive, younger rings. In fact, the rings could be just 100 million years old, maybe formed from an icy object that broke apart after getting too close to Saturn and its gravity.

At least, that’s how it looks from early calculations. But there’s still lots of data to analyze. Cassini’s final hurrah will involve snapping a few final pics of Saturn’s moons, a weird hexagonal jet stream at the planet’s north pole, and Peggy, not the Schuyler sister, but an icy mini-moon inside the rings.

Then, a week from today, Cassini will dive into the planet’s atmosphere, melt, and be torn apart. During this dramatic end to its mission, the probe will be measuring the composition of the atmosphere, the magnetic field strength, and the length of a day on Saturn, all in greater detail than ever before. So thanks, Cassini, for everything you’ve taught us.

Moving closer to home, we’re still trying to figure out whether there’s water in our moon. We’ve talked a little about this before on SciShow Space, the Moon might’ve formed in a huge collision with the Earth, which could’ve emitted a lot of heat and made all the water evaporate. But underground water on the Moon is looking more likely, which throws a little wrench in that idea.

It suggests that, somehow, water stuck around or got deposited later. So scientists don’t agree about what happened in our Moon’s past, and two very recent studies even have conflicting evidence. In one paper from July, researchers at Brown University were searching for water in volcanic deposits on the surface of the Moon.

Scientists have been interested in these deposits since 2008, when they analyzed volcanic glass that was brought back from the Apollo missions and found trace amounts of water. Because they think the eruptions that made these deposits come from deep underground, studying them could tell us whether there’s water in the Moon’s mantle. The researchers analyzed these deposits using spectrometers in satellites, which split the light coming from an object into different frequencies.

Water molecules absorb and reflect specific frequencies, which we can look for. And the paper published in Nature Geoscience suggests that there’s water in these deposits across a lot of the lunar surface, including where the Apollo samples were collected. So they take this as evidence that the whole mantle could have water in it.

It’s not just a weird find in few small areas. But another study, published in August in the journal PNAS, isn’t so sure about water beneath the Moon’s surface. A group of researchers were analyzing a famous Moon rock from the Apollo era nicknamed the“rusty rock,” because it has a patch of rust, also known as iron oxide.

And you can’t make rust without water in the reaction, so some scientists thought this was evidence of water inside the Moon. But the rusty part of the rock also contained some light forms of zinc. And researchers think this zinc actually evaporated and then condensed onto the rock, like water droplets on a saucepan lid, in a super hot environment.

Like one we’d expect during the big collision that could’ve formed the Moon. So the composition of this rock suggests that the Moon’s interior was once hot enough that it would’ve lost most of the light elements because of vaporization, leaving heavier ones behind. And any trace amounts of easily-evaporated stuff, like water, are just leftovers from this period in the Moon's history.

So, despite the rust, these researchers argue that this rock is evidence that the Moon’s interior isn’t watery. The next step for scientists will be explaining these conflicting findings, maybe showing how water could’ve survived on the Moon, or exactly how those volcanic deposits formed. And we’ll keep updating you here as they figure out these contradictions.

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