Some of the most amazing discoveries being made around our solar system these days have to do with just how much dang water is out there. I mean, just a few decades ago, a lot of people thought that what made Earth unique, and made it uniquely habitable, was its abundance of water. But, as this week's news reminds us, we're finding lots of water out there, in all kinds of forms and in all sorts of places.

First of all, you remember Titan, Saturn's biggest moon? Nice place to visit, but you wouldn't want to live there. Just last week, Caitlin told you about Titan's oceans of liquid methane and the weird formations that seem to appear and disappear in them, probably because of seasonal changes and weather patterns.

But astronomers also think that the surface of Titan could be covered in a layer of water ice, and there are signs that it might have huge oceans of water beneath it. Now, scientists with the Jet Propulsion Laboratory (JPL) say that those subsurface oceans might be ten times as salty as oceans on Earth. Astronomers figured this out using data from the Cassini spacecraft, which has been studying Saturn and its system of rings and moons for ten years.

It was actually Cassini that gave us the first clues that Titan had oceans beneath its surface. Even though its crust is stiff and icy, it turns out the ice shifts tidally as Titan orbits Saturn, indicating that there's liquid underneath. Cassini has been using radio waves to peer beneath Titan's surface, and the latest data shows that the liquid underground is a lot denser than pure water.

To account for all that extra density, scientists think that the water is probably chock-full of salt, but not the sodium chloride that makes up most of the salt in our oceans. Instead, it is likely teeming with ions of sulfur, potassium, and other minerals, and there's probably some methane and ethane mixed in there too.

So, the findings, published in the journal Icarus, might put a damper on hopes about the habitability of Titan's underground oceans because, while microbes can live in places like the Dead Sea, which have some of the saltiest water on the planet, oceans full of sulfur and potassium salt might not be the best place to make a home.

But, hey, don't despair because last week astronomer made another wet and weird observation, with the help of another little spacecraft. The European Space Agency's Rosetta craft has been observing the comet known as 67P since this winter, and it's en route to send a lander to its surface.

But, on its way there, Rosetta has found that the comet is emitting water vapor profusely, at a rate of about 300 milliliters, or two standard glassfuls, per second. That's because 67P is getting closer and closer to the Sun, so it's basically sweating buckets, which scientists say is totally healthy and normal.

At this rate, the comet can sweat out enough water to fill an Olympic swimming pool in a hundred days. But its rate of water loss is actually increasing as it gets closer to our star. The fact that there's so much water in just one comet has exciting implications for the study of the early Solar System because comets are essentially chunks of material left over from when the planets were formed.

And some theories suggest that planets, like Earth and Mars, and sometimes moons, like Titan and our moon, first acquired their water from impacts with comets. So, the more we learn about objects like 67P, the more we learn about our celestial history. 

But, the best days of the Rosetta mission are still ahead of us. Next month, Rosetta is set to hook up with the comet, where it will use its dozens of instruments to start examining its composition and study how it changes as it gets closer to the Sun.

Then, in November, Rosetta will dispatch a cute little hundred-kilogram lander that will anchor itself to the comet's nucleus, take some selfies on the surface, and then drill samples to analyze in its onboard lab.

We've never tried anything like this before, so, needless to say, I can't wait! We'll keep you posted, but in the meantime, thanks for joining me for this update of the week's space news.

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