Seeker Archives

Fog Detected on Surface of Saturn Moon Titan

More evidence has emerged, so to speak, of fog over a very special place: Titan.

More evidence has emerged, so to speak, of fog over a very special place: Titan. Titan is one of the largest moons in the solar system and is full of hydrocarbons, making it an interesting Saturn moon that looks like a precursor to what Earth was billions of years ago.

PHOTOS: 10 Years Later: When Huygens Landed on Titan

After multiple pictures of fog from Mars were released, the research team behind this new work wanted to know if it was possible to find fog using Huygens. Huygens was the European Space Agency's lander, attached to NASA's Cassini probe, that briefly survived on the surface of Titan in 2005.

"Ground fog on Titan has been seen before from orbit (Brown et al. 2009) so it's not unexpected to find fog on the surface," wrote York University postdoctoral researcher Christina Smith, the lead author of the study, in an email to Discovery News. "But it hadn't been detected from the surface before, which is what we did in our research and why it's exciting."

Titan has very active weather, as shown by this infrared image of clouds near the south pole. Image taken by the Cassini spacecraft. | NASA/JPL/University of Arizona/University of Nantes

PHOTOS: Where in the Solar System is it Possible for Alien Life?

The work came from analyzing Huygens' "side-looking imager" data after the craft had landed. They noticed that some of the image frames had linear features, compared with the average data found in most frames.

"We evaluated possible origins. Clouds were considered, but no consistent movement across the frame was detected, so this is unlikely," Smith wrote. "A superior mirage was considered, but there was no temperature inversion detected on descent so again, this is considered unlikely. We considered a background rise, but due to several considerations our most likely explanation (in our opinions) is that this feature is due to a fog bank rising and falling."

NEWS: Winter Is Coming: Giant Ice Cloud Appears On Titan

Fog was first recorded on this moon in 2009. At the time, California Institute of Technology co-discoverer Mike Brown said fog must have happened because of high humidity; in other words, it had rained. Cold air is uncommon on Titan - although it likely can cool somewhat above a pool of evaporating methane - and there are no mountains high enough on the surface for fog.

Mars is also known to have fog. This image of haze over Valles Marineris was taken by ESA Mars Express. | ESA / G. Neukum (Freie Universitaet, Berlin, Germany) / Bill Dunford

"Evaporating methane means it must have rained," Brown wrote on his blog at the time. "Rain means streams and pools and erosion and geology. Fog means that Titan has a currently active methane hydrological cycle doing who knows what on Titan."

NEWS: Titan Appears Earth-Like in New Image

But this fog forms differently from Earth, both Brown and Smith point out. The Titan fog is methane and happens when liquid methane on the surface evaporates. On Earth, fog occurs when air cools to the dew point.

The new research was published in the journal Icarus.

A 2009 paper first described fog at the south pole of Titan. This image shows where the fog was located based on data from the Cassini spacecraft.

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.

Top 10 Space Stories of the Decade

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.

Top 10 Places To Find Alien Life

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.