Farewell to Cassini

Today, after 13 years orbiting Saturn, Cassini will burn up in the planet's atmosphere. This is being done to prevent Cassini from crashing into one of Saturn's moons, most notably Titan or Enceladus, to prevent any alien organisms from being exposed to any foreign objects from Earth, living or otherwise.

Credit: NASA/JPL

It's no secret that Cassini has had an incredibly rich and successful mission. It's done more than even the people behind it would have thought possible when they started. And with its demise, there's not a whole lot of representation in the outer solar system. There's Juno orbiting Jupiter, New Horizons somewhere out beyond Pluto, and that's it. And there are no immediate plans to send anything beyond Jupiter either. But there is certainly plenty of reason to go back to Saturn. Cassini has discovered so much. And so, to memorialize Cassini, let's take a look back at just what Cassini has added to the halls of science.

Discovered 7 new moons: Methone, Pallene, Polydeuces, Daphnis, Anthe, Aegaeon, S/2009 S 1 (Hey, it takes a while to name these things)

Landed the Huygens probe on the surface of Titan. This remains the only time we have landed anything in the outer solar system.

The confirmation of methane lakes on the surface of Titan. We were pretty sure they were there, it made sense, but now, thanks to Cassini, we know for sure. They're not quite big wide oceans like what we have on Earth, and Titan's lakes are confined to the polar regions, but they're there, and the biggest, Kraken Mare, is even bigger than the Caspian Sea on Earth.

The discovery of a subsurface ocean on Enceladus. Of all the things Cassini has done, and it's a lot, I haven't mentioned quite a bit, this is the biggest. I don't think anyone saw this coming. When the Voyagers passed by, they saw an icy little moon, surprisingly smooth and very bright (Enceladus is the most reflective body in the Solar System), but otherwise it was assumed that this was just another dead ball of ice, like most of Saturn's moons. Understandably, it was Titan that captured the imagination.

But when Cassini arrived, things began to change. First, Cassini found the "tiger stripes", a series of fractures in the southern polar region that could be less than a thousand years old. The entire region seemed to be less than a million years old. Then, geysers were discovered erupting from the same place. These geysers are actually the source of material for Saturn's E Ring. This is a dead giveaway, there was definitely a liquid water ocean underneath the surface, and while it was initially believed to be limited to the southern polar region, it's now accepted that the ocean covers the entire moon, and is likely a couple dozen kilometers deep. It's a miniature Europa, and without Cassini, we never would have known about it. It might even be easier to explore Enceladus than Europa, despite being twice as far away, because unlike Europa, Enceladus isn't bathed in lethal amounts of radiation.

Like I said, Cassini has done far more than what I've mentioned, but I think those are the big highlights. It's hard to argue with the accomplishments of Voyager, Hubble, or Spirit and Opportunity, but Cassini certainly isn't far behind in the annals of NASA's most successful missions. It's lived a good life, and a spectacular death dive into Saturn's atmosphere is a pretty good way to go out.

Cassini Has Been Good for Astrobiologists

As you may (or may not) be aware, Cassini's mission around Saturn will be coming to an end this year. For 13 years, Cassini has orbited Saturn, and has discovered a lot. I think that I'll make a more comprehensive post about Cassini closer to October, when Cassini performs its death dive into Saturn, but for now, I want to highlight this. It is interesting how a planet a billion miles away from the sun possesses two moons with the potential of hosting life. Enceladus especially has been a huge surprise. I don't think anyone was expecting Enceladus to be anything more than a ball of ice. But here we are today, with photo evidence of massive geysers spewing organic material out into space. Cassini doesn't have the capability to detect life, but the ingredients are there.

Then, of course, there's Titan. Titan is a fascinating place. A thick atmosphere, a methane cycle that mirrors Earth's water cycle, large methane seas hundreds of feet deep, even rivers of methane, Titan really does resemble an Earth in deep freeze. No one knows if life can use methane instead of water, there are pros and there are cons. But it would be very interesting to find out. Life on Enceladus would be, well, different to life on Earth, but not that different. It would be recognizable to us, and would probably resemble deep-sea life on Earth. But life on Titan? It would be a truly alien biochemistry.

Basically, we need to go back to Saturn. And soon. Enceladus and Titan are just too inviting as targets to resist. Mars is closer, and Europa is basically just a bigger Enceladus, but for my money, if there's life in the solar system, it'll be around Saturn.