The first close-ups of Pluto reveal 11,000-foot ice mountains, a relatively thin crust of methane and nitrogen ice, and a surprising absence of craters, evidence the planet has more geological activity than scientists expected.
"This is a very young surface," said John Spencer, a co-investigator on NASA's $700 million New Horizons mission, which gave Pluto and its moon Charon a long, hard look as the spacecraft sped by on Tuesday.
The findings released Wednesday are the first taste of observations made as the spacecraft passed within 7,700 miles of Pluto. Because it was busy taking a flurry of pictures and other measurements during the encounter, the spacecraft was unable to beam data back to scientists until early Wednesday morning.
New Horizons was designed, built and managed by the Johns Hopkins Applied Physics Laboratory in Laurel, where the mission scientists have been gathered for the historic flyby 91/2 years and 3 billion miles after its launch.
Scientists expected Pluto might be pockmarked and static, given its thin atmosphere and old age. But what they are finding from data the spacecraft collected during its close encounter with the dwarf planet suggests that it remains dynamic, with some sort of internal processes possibly renewing its surface repeatedly.
"We've settled the fact that these very small planets can be active after a long time," said Alan Stern, the mission's principal investigator and a scientist at the Southwest Research Institute in Colorado.
Anticipation for the first detailed images of Pluto's surface began building from the moment New Horizons passed the dwarf planet about 7:50 a.m. Tuesday. It relayed a quick signal to Earth that it flew past Pluto unscathed hours later, a message the scientists cheered when they received it just before 9 p.m. Tuesday.
"Here it comes," said Jim Green, NASA's chief of planetary science, as mission leaders prepared to unveil their findings to a packed auditorium on the Hopkins campus.
The audience gasped when the auditorium's screen zoomed in on an image of Pluto released days earlier to show a new surface picture of towering mountains and mysterious mounds, as well as smooth plains.
"Wow," whispered Stamatios Krimigis, emeritus head of the Hopkins lab's space department.
The region was located near the base of what has been commonly known as Pluto's "heart," a large, bright area shaped roughly like a heart on its surface. Officials said they plan to officially name the area "Tombaugh Regio," after astronomer Clyde Tombaugh, who discovered Pluto in 1930.
Scientists had wondered whether Pluto lost any internal heat captured when it formed about 4.5 billion years ago, suspecting that radioactive materials in its core would have long ago decayed. But the activity apparent in its terrain suggests otherwise, they said.
"We've tended to think of these medium-sized worlds as candy-coated clumps of ice," Spencer said.
Mission scientists also released their first high-resolution image of Charon, Pluto's largest moon.
Charon likewise displayed unexpected diversity of terrain, with a reddish polar cap the scientists are calling "Mordor," after the sinister region of J.R.R. Tolkien's "Lord of the Rings" fiction, as well as long ridges, smooth areas and canyons as much as 6 miles deep.
"Charon just blew our socks off when we had our new image today," said Cathy Olkin, deputy project scientist.
The scientists did not make any significant revelations about Pluto's atmosphere or chemical composition, two other key objectives of the New Horizons mission. That is because the cache of data the spacecraft collected will be downloaded over a period of 16 months.
"Frankly, we're just skimming the top of it," Stern said.
Mission officials plan to release a new batch of images and other findings Friday.