'Doctor' Cassini Takes Titan's Temperature

When you go for your annual health checkup, you might expect the doctor to take your temperature. Well, it looks like Saturn's moons also get the same treatment, courtesy of NASA.

When you go for your annual health checkup, you might expect the doctor to take your temperature. Well, it looks like Saturn's moons also get the same treatment, courtesy of NASA.

PHOTOS: 10 Years Later: When Huygens Landed on Titan

Seen below is an animation of how Titan's global temperature has changed over the past 12 years and you may notice a trend: the south gets cooler while the north heats up.

Using Cassini's Composite Infrared Spectrometer (CIRS) instrument, mission scientists have been able to monitor the thermal infrared radiation coming from the moon's surface. Titan is the only moon in the solar system with a thick atmosphere, so gauging its surface temperature can be difficult. However, the Titan atmosphere has what's known as a "spectral window" at an infrared wavelength of 19 microns, allowing this type of thermal radiation to pass, without being absorbed by atmospheric gases, into space.

NEWS: Titan Appears Earth-Like in New Image

The atmospheric haze still makes measurements hard, however, and the global temperatures have been averaged from east-to-west, creating the banded temperature structure.

Cassini arrived in Saturn orbit in 2004 when Titan's southern hemisphere was in summer. As expected, during this time, the southern hemisphere was at its warmest. "Warm" is relative, however. Saturn orbits the sun at nearly 10 times the distance Earth orbits the sun, so sunlight is very weak by the time it reaches Titan and has a less dramatic heating effect than on our planet.

For example, the peak summer temperature on Titan has been measured at -292 degrees Fahrenheit (-179.6 degrees Celsius or 93.6 Kelvin) near the equator, but when measured at the poles during this time, the temperature was only 6 degrees Fahrenheit (3.5 degrees Celsius or Kelvin) cooler.

PHOTOS: Cassini's 10th Year: Recent Saturn Mind Blowers

Saturn orbits the sun once every 30 years, so its seasons last 7.5 years. Cassini, being a long duration mission to the ringed gas giant, has been able to watch seasonal changes in Saturn's atmosphere for 12 years, but in this case has watched 2 seasons unfold on Titan's surface.

Alas, Cassini's mission is nearing an end. Running low on the fuel it uses for propulsion, mission managers are planning a "Grand Finale" that will see the orbiter alter its trajectory around Saturn so that it flies through the planet's ring plane. Eventually, by September 2017, Cassini will drop closer to Saturn's upper atmosphere, burning up as a human-made meteor.

For more detail on how these Titan observations were made, browse the NASA news release.

This sequence of maps shows varying surface temperatures on Saturn's moon Titan at two-year intervals, from 2004 to 2016.

Ten years ago,

the European Huygens probe descended through Titan's atmosphere

and became the first ever robotic mission to touch down on a world in the outer solar system. During its daring 2 hour, 27 minute descent through the murky atmosphere of Saturn's largest moon, the probe revealed an unprecedented view of of the alien environment. On landing, Huygens survived on the hydrocarbon-rich surface for only 72 minutes before its batteries drained, but the data it transmitted via NASA's Cassini spacecraft was nothing short of revolutionary -- data that continues to be analyzed 10 years after that fateful day on Jan. 14, 2005.

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Here are just a few mind-blowing images from Huygens as it gave us our first intimate look at the solar system's only moon known to possess a thick atmosphere and vast liquid methane-ethane lakes -- a world that, like Jupiter's moon Europa, invokes exciting hypotheses of extraterrestrial biology.

After traveling with the Cassini mission for seven years during its interplanetary transit from Earth to Saturn orbit, the command was given for Huygens to detach from its mothership. For 21 days, the small disk-like probe was by itself, cruising toward Titan. As Huygens ripped through Titan's atmosphere, eventually slowing down enough for its heatshield to drop away and parachutes deploy, the probe got to work, rapidly photographing its descent and collecting atmospheric data. On Wednesday, The European Space Agency released the full series of

stunning processed descent images

, showing how the moon's dune-covered surface slowly came to view as Huygens slowly drifted to the surface below.

NEWS: Cassini Spies a Sunny Day on Titan's Seas

Looking down, Huygens also captured a slowly evolving view of its eventual landing spot. Shown here, a fish-eye view of the landscape below starts to detail some of the surface features the probe would be soon analyzing up-close. In the run-up to landing day, mission scientists were unsure whether Huygens would land on a solid surface or splash down in a methane/ethane puddle or lake. As it turned out, the probe "splatted down" in Titan's alien mud -- a mix of small grains of ice.

ANALYSIS: Titan's 'Magic Island' Appeared Mysteriously From the Depths

Photographs during descent gradually showed an alien, yet familiar, landscape. Titan is covered in dunes, valleys and lakes -- all shaped by erosion processes we'd find on Earth. The valleys are cut by liquid action and the thick atmosphere produces winds and weather systems that form dune fields of fine hydrocarbon sand. But these Titan weather systems are not driven by an Earth-like water cycle. As the atmosphere is too cold to support water in a liquid state, other chemicals, such as methane and ethane exist as a liquid, forming their own cycle. Methane rain is now known to fall onto the landscape, creating rivers that erode valleys and form deltas in vast liquid methane-ethane lakes.

NEWS: Sands of Time Move Slowly on Saturn Moon Titan

By landing a probe onto Titan's surface, the joint NASA/ESA Cassini-Huygens mission was able to get "ground proof" of flyby imaging and radar. Last year, Cassini completed its 100th Titan flyby, so in the 10 years since Huygens landed, planetary scientists have been getting a front row seat of the moon. But in 2005, Titan science was as foggy as the moon's atmosphere, so by overlaying ground-based observations with Cassini images, a better interpretation of landscape features spotted by Cassini could be made.

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Although low-resolution and grainy, the first images of the landscape surrounding Huygens after it landed at 13:34 CET (12:34 GMT) on Jan. 14, 2005, stunned the world. Rounded stones appeared to litter the grains of hydrocarbon sand and ice. The eroded rocks immediately reminded us of eroded pebbles -- rocks that have undergone liquid action for long periods of time. The landing zone resembled a dried-up lake bed and surrounding that area, evidence for rapid, transient flows of liquid could be seen.

NEWS: Cassini Spies Wind-Rippled Sea on Titan

The Huygens lander, in its short solo mission, punched well above its weight, opening our eyes to an alien world within our solar system that is littered with prebiotic chemicals, a world that resembles a young Earth, beckoning our inquiring minds to return some day.

For more on the Huygens landing and the top 10 scientific discoveries made by the probe's continuing science, browse the special ESA anniversary news release.