A NASA scientist has visited a four-year-old island that satellites watched rise out of the waters — a rare opportunity to see in person a new island that lasts more than a few months.

Near the end of December 2014, scientists realized satellites were spotting a volcanic plume from territory within the nation of Tonga in the Pacific Ocean. By the end of January 2015, the eruption was over — and new land stretched between two older, small islands called Hunga Tonga and Hunga Ha'apai. (This third small island is referred to unofficially as Hunga Tonga-Hunga Ha'apai.)

Dan Slayback, a scientist at NASA who focuses on using remote sensing data, watched the eruption unfurl and started plotting a way to see the new land in person. And in October, he and a team of scientists arrived. [Photos: Mars Volcano Views Revealed by Spacecraft]

"We were all like giddy schoolchildren," Slayback told NASA's blog devoted to Earth expeditions. "It really surprised me how valuable it was to be there in person for some of this."

Plants have begun to grow in the flat plain surrounding the volcano of a new island in the South Pacific island nation of Tonga. The island Hunga Tonga-Hunga Ha’apai formed in 2015. (Image credit: Dan Slayback/NASA GSFC)

The island is an unusual survivor; most newborn islands disappear in just a couple months, as this one was predicted to do. But a 2017 analysis by NASA revised the island's life expectancy to between six and 30 years. It's one of only three volcanic islands to live longer than a few months in the past 150 years and the first to do so since a fleet of satellites began watching Earth's surface.

But when scientists stepped foot on the new island, it didn't quite match what they had expected based on their satellite views. The elevation changes were more dramatic than researchers had predicted, for example. The data that the team gathered on the ground should help scientists hone the model that they use to convert satellite images to ground heights, according to NASA.

The cliffs of a crater lake on the new island of Hunga Tonga-Hunga Ha’apai look otherworldly in this image by NASA scientist Dan Slayback during a visit to the nascent island with Woods Hole’s Sea Education Association (SEA) Semester’s South Pacific cruise in 2018. (Image credit: Dan Slayback/NASA GSFC)

NASA scientists have been particularly interested in the little island because it might be the closest we can get to ancient Mars as that planet would have looked before its oceans evaporated away and its volcanoes fell dormant.

A drone operated by the Woods Hole Sea Education Association (SEA) Semester’s South Pacific cruise visits a new volcanic island in the South Pacific island nation of Tonga. The new island was born in 2015. (Image credit: Woods Hole)

That's a particularly intriguing comparison because of a mystery Slayback discovered when he arrived on the island. Pale-colored streaks of material coming out of the volcano's cone, visible on satellite images, turned out, in person, to be sticky mud, not volcanic ash, which is pulverized rock. "I'm still a little baffled of where it's coming from," Slayback told NASA.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us @Spacedotcom and Facebook. Original article on Space.com.