Life Beyond Earth, Part 1: Linda Spilker

Linda: Ten years ago today, the Cassini spacecraft flawlessly executed a nail-biting 96 minute burn to become the first man-made object to go into orbit around Saturn. And Cassini carried with it ESA's Huygens Probe, which we later sent down to the surface of Titan. And so we celebrate today Cassini's ten-year anniversary, and I'll share with you just a few of the amazing findings that we've made with Cassini.

What we have here is one of my favorite pictures of Saturn and the rings. It's a view that you won't see from the Earth. Cassini is high above Saturn's north pole looking down and the rings form a giant bulls-eye around the planet. And you can actually see Saturn's shadow going out across the rings. Up on the north pole, you see a greenish six-sided area. We call this the hexagon. Very interesting and intriguing kind of storm.

Saturn is the second-largest planet in our solar system. It only has pretty much a hydrogen atmosphere, no solid surface underneath it. And if you could build a bathtub big enough to hold Saturn, Saturn would float. So how big is Saturn really?

Well if we put the Earth and the moon to scale, next to Saturn, along with the distance between them, we can see that Saturn is indeed huge. In fact, it would take 764 Earths to fill up the volume of Saturn, a giant planet, indeed.

Well let's look a little bit more closely at that north polar hexagon. If you look at the image on your left, you can see this greenish area surrounded by a six-sided jet stream. Voyager, 30 years ago, saw this jet stream with these six sides, and it's still there today. It's a very interesting puzzle. Greenish in color, that's its winter hemisphere. As the sun continues to shine in the north, we'll see that greenish color become more of the golden color we're used to for Saturn's atmosphere. Tiny white clouds circle inside the hexagon. And Cassini discovered at the very center of the hexagon a giant hurricane. That hurricane would span half the continental United States. It would go from Washington, D.C. to Tulsa, Oklahoma: a giant storm. The sun is shining from the right, and you can actually see shadows from the eyewall of that giant hurricane. We study the hexagon and the hurricane at Saturn to get a better understanding of the weather here on the Earth.

Let's move on to Saturn's rings. I actually started working on rings in the Voyager days. And so they hold a special place in my heart. There's a lot of intricate detailed structure inside of the rings. The rings are made up of billions upon billions of icy particles orbiting Saturn in an intricate cosmic dance. And every once in a while these particles jostle and run into one another. The rings have very simple names. As you go outward, you can have, you can see you have the A ring on your far right. Then there's a gap, the very bright B ring, most of the particles are there. The particles range in size from tiny marbles to giant mountain-sized particles. That grayish ring is the C ring, and then finally the innermost ring, the D ring.

And at the end of the mission, Cassini is gonna dive in between Saturn's D ring and the top of the atmosphere for some remarkable brand new science. You'll notice that there's a black gap in between the A ring and the B ring. That's the Cassini division, named after the astronomer Cassini, who first discovered it, and our mission is named in honor of that astronomer.

Well, Cassini had a rare opportunity in 2009. We were actually able to observe the rings when the Sun was edge on to them. And anything that would cast a shadow would be visible and seen. So let's look at the outer edge of the B ring and see what Cassini saw in 2009. Here's the outer edge of the B ring, that bright ring with all of those structures, the Cassini division on top. The Sun is shining from the top down, and you can see all sorts of shadows. Here are particles that are one or two miles in size casting these long shadows at the edge of the ring. And the ring itself is only about 30 feet thick. A good analogy for how we see these shadows. Imagine yourself riding along on the space station. You look down on Egypt, and you want to find the pyramids. But if you look at noon, you won't see any shadows, and it'll be very hard to pick them out. Now imagine that you look for these same pyramids at sunset. And they'll be casting these long shadows. And they'll be very easy to see on the desert in Egypt. And in the same way, Cassini for the first time could see that there were big particles in the rings at the outer edge of the B ring. These objects are probably made of agglomerations of ring particles. And the way these come together and coalesce, give us information about how the planets in our solar system actually came together and formed as well.

This is a view of the largest moon in the Saturn system. This is giant Titan. It's 3,000 miles across, about the size of the planet Mercury. A Titan has a liquid water ocean underneath its icy crust, and this is one possible place that might harbor life. Titan has a thick nitrogen atmosphere. It's about four times as dense as the atmosphere in this room. And the surface is a chilly minus 290 degrees Fahrenheit. There's also methane in the atmosphere of Titan, and that methane at the top is broken apart by sunlight, forms these long smoggy hydrocarbons and gives Titan that sort of golden-colored haze. And we can't really see through the haze. And it took ESA's Huygens Probe to parachute down through to the surface of Titan to give us our first view of an amazing world. It turns out that methane plays the same role on Titan that water plays here on the Earth, with the same kind of weather. Only now you have methane clouds. Methane rain. Methane flowing through the river channels, and methane filling the lakes and seas.

In fact, if you look at this image behind me, that topmost black smudge, that's Ligeia Mare, the second-largest sea on Titan. And if we look up close at that particular sea, here's the radar view with the long wavelengths. You can penetrate down through the haze. You can see the river channels of methane flowing into this particular lake, and even tiny islands in this particular sea. This, this sea Ligeia Mare is about 50 percent bigger than Lake Superior here on the Earth. And it's about 500 feet deep. That's something we found out with Cassini. And if you take the seas and you add up all the hydrocarbons that are present in the seas, it turns out there's about a hundred times more hydrocarbons on Titan than all of the reservoirs here on the Earth. It's just too bad Titan's so far away, or our hydrocarbon problems would be solved. And the seas themselves are very interesting, because you wonder, with liquid methane, could a form of life exist that would use liquid methane, rather than water, to form and move about. So very intriguing to think about that for Titan.

Now we move on to another world, another moon around Saturn. This is Enceladus. Enceladus is only about 300 miles across. So 1/10th the size of Titan. And what you see here is an icy white surface with very few craters. And the brightness and the absence of craters tell us that this is a very, very young surface. And Cassini was the first to see, at the south pole you can see these bluish fractures down here at the bottom. We nicknamed them tiger stripes. They kind of reminded us of tiger stripes, and we were really amazed to see what was coming out of these tiger stripes on this tiny moon. I was amazed as everyone else when we first took a look and saw, and this is in a backlit view, coming out of those tiger stripes were jets. Jets of water vapor and water ice with some other compounds mixed in. We saw dozens and dozens of these jets actively going off. Some of the tiniest particles escape and actually go on to form a ring within Enceladus' orbit, the E ring. So just so intriguing to see. In fact, Cassini actually flew through those jets and sampled their composition. And we found carbon dioxide, we found ammonia, we found salts. We found the kinds of ingredients that you'd need to find to have life. And it turns out there's a liquid water ocean underneath Enceladus' south pole supplying these jets and vents. And in a sense we have free samples. We just don't know if there might be life inside of these free samples. So we have two worlds: Titan and Enceladus, that might possibly have life.

And finally, another iconic backlit image. This image was taken when Cassini was in Saturn's shadow. This doesn't happen very often in the mission. When we took this mosaic, that bluish ring around the outside, that's the E ring created by tiny particles coming from Enceladus. And if you look at that white ring completely around Saturn, sunlight is refracted through the atmosphere. And that's every sunrise and sunset on Saturn seen all at the same time. And there's actually three other planets in this image. If you look at the upper left there, Mars and Venus, a little bit difficult to see. And if you just look here, right here, that tiny pale blue dot is actually the Earth, actually the Earth and the moon. And when, in the 20 minutes we were taking those pictures of the Earth and the moon, we actually asked people, Go outside. Wave at Saturn. So your photons can be captured by Cassini in these pictures of the Earth and the moon. And while you're at it, out there waving, in fact, how many people here waved at Saturn on that particular day? Well that's great. Yeah, my husband Tom and I were out there waving as well. And we asked people to take pictures of themselves, selfies, and send us those selfies. And we took all of those selfies and we recreated this Saturn backlit mosaic. Here it is. Made up of thousands of selfies. So we were really happy to see all of the interest that the public had, and we're very grateful to NASA for continuing to fund extended missions. It's been 10 years.

We hope to have another three years to our mission as well. And very recently we had a naming contest. We asked people, you know, we've got this exciting 22 orbits at the end of our mission, help us name those orbits. And then we got 2,000 different entries, sorted through those, and we came up with the winning entry. And I'm pleased to present for the very first time tonight, the winner of that naming contest. Cassini Grand Finale. So thank you so much for your contributions. And that's the name of the end of our mission.

And I'm gonna be showing you a short movie that'll show you something about the science we'll be collecting in the last three years, including a chance to see what one of those orbits look like in the Grand Finale. And with Cassini, we had a rare opportunity and we seized it. Now sit back and enjoy the movie.

Voiceover: Cassini is there in the Saturn system now. It has been making discoveries for the last several years, and there's more to come.

Voiceover: By studying the satellites in this Saturnian system, we begin to understand something also about the origin of the solar system.

Voiceover: There is strong evidence now that most of the surface of Titan is in fact covered with organic material of some kind.

Voiceover: We're gonna be looking at lakes on the surface of this moon in detail. We're gonna be looking at the atmosphere to see how the climate changes over time.

Voiceover: We have some global circulation models that tell us if the winds pick up. We think there could be waves on the lakes of liquid methane.

Voiceover: Can you imagine anybody thinking that we would discover active cryovolcanism on one of these moons? Geysers?

Voiceover: One of the things that we'll do in the next couple of years is make the first ever flyby through the plume when the plume output is at its maximum.

Voiceover: And then of course there's the planet Saturn itself. As we go through our series of orbits and as the seasons change, it's like having a brand new mission.

Voiceover: One Saturn year is nearly 30 Earth years. To be there for nearly half of a Saturn year, is a once-in-a-lifetime opportunity.

Voiceover: The sun now is coming up on the north pole. So we're getting to see territory that was darkness when we first arrived in 2004. Pretty soon we'll have the whole hexagon and the hurricane inside of it illuminated by the sun. And then of course the mission's end itself is completely unique.

Voiceover: Starting in 2016, ending in 2017, these orbits will take us up and over the north and south poles of the planet.

Voiceover: We're actually going to dive in between the innermost edge of the D ring and the upper atmosphere of the planet itself.

Voiceover: From that we're gonna learn how is Saturn constructed from inside out.

Voiceover: We'll also get the magnetic field of the planet, the mass of the rings for the very first time, and get to sample a place that no spacecraft has ever flown before.

Voiceover: This is a mission that cannot be duplicated. So we really want to take advantage of this opportunity to observe seasonal variation in the system.