Little Pluto is a little bigger than anyone imagined.
On the eve of NASA’s historic flyby of Pluto, scientists on Monday announced that the New Horizons spacecraft has nailed the size of the faraway icy world.
Measurements by the spacecraft set to sweep past Pluto early yesterday indicated the diameter of the dwarf planet is 2,370km, plus or minus 19km — about 80km bigger than previous estimates in the low range.
New Horizons principal investigator Alan Stern said this means Pluto has a lower density than thought, which could mean an icier and less rocky interior.
New Horizons’ 4.8 billion kilometer, nine-and-a-half-year journey from Cape Canaveral, Florida, was set to culminate yesterday morning when the spacecraft was expected to zoom within 12,500km of Pluto at 49,900kph.
Mission managers said there was only one chance in 10,000 that something could go wrong — like a debilitating debris strike — this late in the game.
However, Stern said: “We are flying into the unknown. This is the risk we take with all kinds of exploration.”
Pluto was a full-fledged planet when New Horizons launched in 2006, only to become demoted to dwarf-planet status later that year.
New Horizons has already beamed back the best-ever images of Pluto and its big moon, Charon, on the far fringes of the solar system. Pluto has four other satellites.
“The Pluto system is enchanting in its strangeness, its alien beauty,” Southwest Research Institute planetary scientist Stern said.
With the encounter finally at hand, it all seems surreal for the New Horizons team gathered at Johns Hopkins University’s Applied Physics Laboratory. The energy there was described as electric.
Project manager Glen Fountain said New Horizons, at long last, is like a freight train barreling down the track, “and you are seeing this light coming at you and you know it is not going to stop, you cannot slow it down.”
“Of course, the light is Pluto, and we are all excited,” Fountain said.
Three new discoveries were revealed on Monday, a tantalizing sneak preview as the countdown to closest approach reached the 21-hour mark.
Besides the revised size of Pluto — still a solar system runt, not even one-fifth the size of Earth — scientists have confirmed that Pluto’s north pole is indeed icy as had been suspected. It is packed with methane and nitrogen ice, scientists said.
Also, traces of Pluto’s nitrogen-rich atmosphere have been found farther from its surface than anticipated. New Horizons detected lost nitrogen nearly a week ago.
The New Horizons spacecraft is the size of a baby grand piano with a salad bowl — the dish antenna — on top. It was to come closest to Pluto at 7:49am Florida time yesterday. Thirteen hours later, at about 9pm, flight controllers were to learn whether everything went well.
The spacecraft will have sent the confirmation signal four-and-a-half hours earlier; that is the one-way, speed-of-light, data transmission time between New Horizons and Earth.
Stern expects “a little bit of drama” during closest approach, when the spacecraft is out of touch with ground controllers.
New Horizons cannot make observations and send back data at the same time, so scientists opted for maximum science during those most critical hours.
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