NASA's Cassini catches glimpses of fresh rainfall on Saturn's biggest moon, Titan

After 14 years of making pioneering discoveries about Saturn and a handful of its 62 moons, NASA’s Cassini spacecraft has now spotted freshly-fallen rain on the surface of the planet’s largest moon, Titan. From an image captured in June 2016, the Cassini spacecraft has picked up a big, reflective spot near Saturn’s north pole, which disappeared pretty quickly, a new study reports. The researchers studying the image think that the new bright patch spotted by Cassini is different from the many lakes and seas that cover Titan’s surface. This transient patch covered a vast area of roughly 120,000 square kilometers and is likely a giant puddle of ‘methane rain’ that evaporated away quickly, the researchers explain. “It’s like looking at a sunlit, wet sidewalk,” Rajani Dhingra, lead author from the University of Idaho–Moscow, said in a statement. [caption id=“attachment_5921511” align=“alignnone” width=“1280”] New research provides evidence of rainfall on the north pole of Titan – the largest of Saturn’s moons. The rainfall would be significant to researchers, who have been waiting to spot the first signs of summer in the moon’s northern hemisphere. Image: NASA/JPL[/caption] From mapping the seasons on Saturn, researchers have recorded the periods of summer and winter in the planet’s northern and southern hemispheres. Based on this new observation, the study’s researchers think the rainfall in mid-2016 arrived later than the predictions made by earlier climate models. “Summer is happening…delayed, but it’s happening. We will have to figure out what caused the delay, though,” Dhingra said. Each season on Saturn, unlike Earth, lasts 7.5 years! This is since the planet and its moons take 29.5 Earth-years to complete one rotation around the Sun. Cassini made its first approach of Saturn way back in 2004, when the planet and its moons (importantly, Titan) were experiencing summer, clouds and rainfall in their southern hemispheres, according to Space.com. Titan is a rather special celestial body to astronomers studying habitability in our solar system, because it is the only world other than Earth that is known to have stable pools of liquid on its surface. These liquids aren’t water, but liquid hydrocarbons like methane, ethane or simple organic compounds. [caption id=“attachment_5921561” align=“alignnone” width=“1280”] In this image of Titan’s north pole captured by Cassini’s instruments, the orange box shows the “wet sidewalk” region, which suggests evidence of changing seasons and rain on Titan’s north pole. The blue box is expanded in another panel at the bottom. Dark blue arrows mark clouds, red arrows mark the mirror-like reflection from one of Titan’s lakes and pink arrows mark the “wet sidewalk” region. Image: NASA/JPL[/caption] While scientists have known that the entire cycle of clouds, rain and lakes on Titan were made of hydrocarbons like methane, this is the first real visual proof of rainfall on the distant world. And they’ve been waiting a long time for it, too, according to Dhingra. “People called it the curious case of missing clouds,” Dhingra said. “The whole Titan community has been looking forward to seeing clouds and rains on Titan’s north pole, indicating the start of the northern summer. But despite what the climate models had predicted, we weren’t even seeing any.” The rainfall-glint image was captured through the thick haze of Titan’s clouds from Saturn’s orbit by Cassini’s instruments. Cassini travelled with a lander called Huygens, which landed on Titan in 2005.   The new study was  published in Geophysical Research Letters.