NASA‘s Cassini-Huygens spacecraft celebrated its 15th birthday yesterday and it’s still sending back results from Saturn.

The Cassini spacecraft was launched on October 15, 1997 and has logged more than 3.8 billion miles of space travel in the time since. The craft has flown by Venus twice and visited Jupiter on the way to Saturn, where it has been for the last eight years. During its time in orbit around Saturn, Cassini has woven a complicated path to visit many of Saturn’s 60-plus moons.

“As Cassini conducts the most in-depth survey of a giant planet to date, the spacecraft has been flying the most complex gravity-assisted trajectory ever attempted,” said Robert Mitchell, Cassini program manager at NASA’s Jet Propulsion Laboratory. “Each flyby of Titan, for example, is like threading the eye of the needle. And we’ve done it 87 times so far, with accuracies generally within about one mile [1.6 kilometers], and all controlled from Earth about one billion miles [1.5 billion kilometers] away.”

According to NASA, Cassini has sent back around 444 GB of data, including over 300,000 images. More than 2,500 reports based on Cassini data have been published in scientific journals. Water ice and organic particles have been found on Saturn’s moon Enceladus, and hydrocarbon-filled lakes have been spotted on Titan, Saturn’s largest moon.

Speaking of Titan, even now Cassini is providing a wealth of scientific data. Today at the 44th annual meeting of the Division for Planetary Sciences of the American Astronomical Society, scientists announced that radar images from the spacecraft (seen above) have revealed an “hot cross bun” feature on the surface of Titan. The circular feature, which resembles a similar feature on Venus, is compared to the way the surface of a bun will lift and crack when baked. Researchers believe a similar process involving heat, and possibly rising magma, has caused the feature on Titan.

“The ‘hot cross bun’ is a type of feature we have not seen before on Titan, showing that Titan keeps surprising us even after eight years of observations from Cassini,” said Rosaly Lopes, a Cassini radar team scientist based at NASA’s Jet Propulsion Laboratory. “The ‘bun’ may be the result of what is known on Earth as a laccolith, an intrusion formed by magma pushing up from below. The Henry Mountains of Utah are well-known examples of this geologic phenomenon.”

(Image courtesy NASA/JPL-Caltech/ASI)