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Cassini takes Titan's temperature

Morgan Rehnberg, Correspondent
Jul 10, 2015, 21:58 UTC

Sen—NASA’s Cassini spacecraft might be circling gaseous Saturn—our Solar System’s second largest planet—but it’s actually better situated to study Earth-like planets than almost anything else we have. This week it put that position to work by studying how seasonal variations can affect a terrestrial planet’s atmosphere.

Its key is Titan, the Solar System’s second largest moon and perhaps the body that best resembles our own planet in the cosmic neighborhood. Cassini anchors its orbit about Saturn on Titan; these frequent passes make it ideally suited for studying this complex world.

What makes Titan so interesting? Like Earth, it has a thick atmosphere and liquid at its surface—a combination repeated nowhere else around the Sun. Also as in our own atmosphere, the gas nitrogen dominates. The rest is nearly all methane, the likely source of the liquid on Titan’s surface.

Although Titan has no tilt relative to Saturn’s equator, the planet’s own obliquity ensures that, also like Earth, Titan experiences seasons. Right now it’s winter in the north and summer in the south, but unlike on Earth, it takes years—not months—for the seasons to change.

One of Cassini’s focuses this week was on these seasonal changes within the atmosphere. How does the temperature change? Does this lead to compositional differences? The 113th close encounter between spacecraft and moon made now an ideal time to address this question; on July 7, Cassini passed the northernmost point on Titan that it will see for the remainder of the mission.

Using temperature data captured from the spacecraft’s Composite Infrared Spectrometer, Cassini scientists will be able to better understand how light from the Sun—feeble at Saturn—heats the atmosphere.

And perhaps most exciting of all? Because Titan seems to resemble what we expect many planets around other stars to look like, the insights gained at Saturn could have applications across the galaxy.

The Cassini-Huygens mission is a collaborative effort between NASA, ESA, and the Italian Space Agency. Launched in 1997, it reached Saturn in 2004 and has since been studying the planet, its moons, and its rings. In 2005, the Huygens probe made the first landing on Titan, Saturn’s largest moon. After completing its second mission extension in 2017, Cassini will make a series of close passes to the planet and then end its time at Saturn by plunging into the planet’s atmosphere.