Looking At The Weather On Saturn's Moon Titan
IRA FLATOW, host:
You're listening to SCIENCE FRIDAY. I'm Ira Flatow.
Springtime is upon us, well, not just here on Earth but also on the largest moon of Saturn - Titan. But the April showers on Titan are nothing like those you'll find here on Earth.
On Titan it rains liquid methane. How do we know about the weather on Titan? Well, the Cassini spacecraft launched in 1997 arrived at Saturn in 2004 and it has been circling the planet, its rings, its moons, ever since. And it's been measuring things like temperature, what the atmospheres are made of, what conditions are like out there in that planetary system.
My next guest has been studying Saturn and its system of moons and has just published a study in the journal Science. Elizabeth Turtle is a research scientist at Johns Hopkins University Applied Physics Lab in Laurel, Maryland. She joins us by phone. Welcome to SCIENCE FRIDAY.
Ms. ELIZABETH TURTLE (Johns Hopkins University): Hi, thank you.
FLATOW: Why go out there to look at Titan?
Ms. TURTLE: Titan is a particularly fascinating moon in the outer solar system because it's the only moon that has a dense atmosphere. Most moons don't have much of an atmosphere, and Titan's unique in this.
And its atmosphere - actually the density near the surface - is about one and a half times that on Earth, which has led to some fascinating processes and very familiar processes on the surface.
FLATOW: Such as?
Ms. TURTLE: Such as kinds of erosion that we're very familiar with here on Earth, erosion by wind and rain and deposition of large fields of dunes, for example.
FLATOW: So it has some surface to it? There's a bedrock someplace?
Ms. TURTLE: Yes, yes. The surface is - the bedrock on Titan, because it's so cold, is composed of water ice. And so the substances are very different from the substances we're used to here on Earth, but - or in different phases than we're used to here on Earth, but the processes are very similar in some cases.
FLATOW: So it's springtime, and it's raining there, but not liquid water rain.
Ms. TURTLE: Right, exactly. So it's cold enough that methane is a liquid in the - on Titan, and Titan actually has a cycle in its atmosphere similar to the cycle we have here on Earth with water.
Water is a liquid on the surface, running in rivers into the ocean. Water evaporates into the atmosphere, condenses into clouds, and rains back out onto the surface, and you get a cycle.
On Titan we have a very similar cycle, actually, but with methane playing the role of water. So we see methane in the - in lakes and seas, actually, and those are all concentrated near Titan's poles, and that methane can evaporate out into the - up into the atmosphere and condense and form bright methane clouds, which we've been observing and tracking for several years, and apparently rain out onto the surface as well.
FLATOW: Amazing. 1-800-989-8255 is our number. We're talking with Elizabeth Turtle about Titan. And does it look - does the surface look like Mars, with gulleys and, you know, rivers and things like that? Or does it look more like - how does it look?
Ms. TURTLE: In some areas the surface is very familiar, similar to Earth or Mars. We see areas that are channeled, predominately dry channels right now, although in one particular area they may still be wet. But we do see channels all over the surface.
In other ways it's very different. The equatorial regions are dominated by huge sand seas, seas of - not sand like we're familiar with on Earth, but hydrocarbon or maybe water ice particles forming these giant fields of longitudinal dunes. So the equator is very arid.
Another difference between Titan and Mars is that Titan, because it has such a thick atmosphere and such high erosional rates, there are not many impact craters on it. So it's actually more similar to Earth in that respect. A lot of the impact craters on Earth have been eroded by similar processes.
FLATOW: So how long does the spring last on Titan? Is it a couple of months, like three months like around here, or go on a little different(ph)?
Ms. TURTLE: Well, Titan months, yes.
(Soundbite of laughter)
Ms. TURTLE: But Titan's year is about 29 and a half Earth years. So a season is seven years or so. So when we - when Cassini arrived at Saturn, it was late southern summer. And now we're just going into early northern spring. The spring equinox on Titan was in August, 2009. So we're just a few Titan weeks into spring.
FLATOW: Wow, that's quite fascinating. I want to thank you for taking time to be with us and talk about it.
Ms. TURTLE: Oh, it was my pleasure.
FLATOW: Elizabeth Turtle, who was talking about Titan, and she is a research scientist at Johns Hopkins University Applied Physics Lab in Laurel, Maryland.
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