So Far, Yet Now So Near

Cold. Dark. Forgotten. And so out of reach. Alan Stern has spent more than two decades dreaming about Pluto, certain that this most distant of planets, the only one in the solar system never explored, would soon be glimpsed by a set of robotic eyes sent from Earth.

“We thought this is a cinch. We’ll have a Pluto mission in a few years,” he recalled. That was 14 years ago. Stern was fresh out of graduate school and the outer solar system was just beginning to enthrall planetary scientists.

Now 45 and head of the space sciences department of the Southwest Research Institute here, Stern and a growing band of Plutophiles are still dreaming -- but only for a little while longer. Finally, the mission is about to happen.

In the epic adventures and tragedies of the last half a century of space exploration -- men on the moon, the first robotic lander on Mars, devastating accidents and spacecraft fly-bys that captured the first dramatic images of the bizarre ice worlds Neptune and Uranus -- little Pluto had been all but forgotten.

Many astronomers even wished to dethrone it from planethood because of its puny size and strange, tilted orbit -- calling it instead a comet, a trans-Neptunian object or simply a big piece of icy debris.

Only a handful of scientists remained dedicated to the lonely and unrewarding crusade to explore Pluto, a world so dim it can barely be seen, even by the powerful Hubble Space Telescope.

Compared to pondering space exotica like black holes or seeking traces of past life on neighboring Mars, distant Pluto can seem truly marginal. Sure, there are scientific questions at stake: Is Pluto volcanically active? Why is it so small when computer models simulating the formation of the solar system show it should be the size of Neptune? What can the frozen organic remnants of material that surround the planet tell us about the origin of our solar system and life here on Earth?

But to Stern, Pluto’s pull stretches far beyond its scientific secrets.

Pluto is a boundary marking the uncharted reaches of the solar system -- the modern-day equivalent of the Spice Islands. We can go there, Stern said, so we should.

“This is going back to exploration, to the roots of the space program when everything was new and far away and mysterious,” Stern said. “It’s going over the next hill.”

Since the 1990s, at least seven major NASA Pluto proposals have been scuttled. Some were seen as unworkable. Some would have taken too long. Others cost too much. The most recent blow came in 2000, when NASA canceled another long-planned trip to Pluto and its environs called the Pluto-Kuiper Express after costs spiraled out of control.

Then in 2001, a replacement mission called New Horizons was won by Stern’s team in a competition that capped costs at $500 million. It too was stalled repeatedly by funding problems.

But an intrepid Pluto lobby determined to see the mission go forward seemed to rise from nowhere. It pelted Congress with pleas until the money was restored to the NASA budget -- twice. A blue ribbon panel of astronomers also weighed in, calling a mission to Pluto and the Kuiper Belt -- the ring of ancient debris and miniaturized planets orbiting the solar system -- a top science priority for the coming decade.

“It’s been alive and dead more times than I can count. And I’ve only been on the project a few years,” said Leslie Young, a mission scientist at the Southwest Research Institute.

Stern’s team had taken to calling itself the “Undead.” This spring, in a move that went little noticed amid the space shuttle Columbia tragedy, NASA gave Stern the final go-ahead for the Pluto mission. Because construction will soon be underway, there is little chance it will be canceled.

The New Horizons spacecraft will be built at the Johns Hopkins University Applied Physics Laboratory near Baltimore. The space department there is led by Stamatios “Tom” Krimigis, who, in a 40-year career, has built and sent scientific devices to seven of the nine planets, probing the violent and invisible magnetic bubbles that surround many of them and the solar wind that sweeps past them. Despite office walls covered with awards and citations, a decision he made more than 20 years ago still nags him.

A Titanic Decision

It was 1980 and Voyager 1 had just flown past Saturn. If it went in one direction, the spacecraft could reach Pluto by 1986. But Krimigis and other project leaders decided to go after Saturn’s moon, Titan, instead.

“At the time, I don’t think anyone would have thought it would take this long to get to Pluto,” Krimigis said.

The New Horizons mission is scheduled to launch in January 2006 from the Kennedy Space Center in Florida. It will swing past Jupiter to pick up speed, shaving four years off the journey. With an average speed of 37,000 mph, New Horizons would then fly by Pluto in 2015 or 2016, depending on the type of rocket used for launch. Alan Stern will be approaching 60.

“Some of us are going to retire before we get to Pluto,” said Bob Farquhar, the mission’s 70-year-old director. “And some of us are going to expire.”

The long journey should be no problem for the 935-pound probe. Space is considered the best place for a spacecraft. Pioneer, launched in 1972 for a 10-month mission, lasted 30 years. Galileo has been active for 14.

The spacecraft is being “designed like a thermos bottle” to survive the long, frigid trip, said Dave Kusnierkiewicz, the mission systems engineer at APL. “We’re making use of the heat that’s dissipated from the electronics to keep the spacecraft bus warm.” The antenna can function at nearly 400 degrees below zero -- just slightly colder than the planet’s surface.

The spacecraft will also explore Pluto’s moon Charon and several other Kuiper Belt objects that are within reach.

That’s all exciting to Stern, who spends his days worrying about the ratio of methane and nitrogen in Pluto’s atmosphere, craters on Charon and what his team might learn about the solar system’s first days from the material, literally frozen in time, in the Kuiper Belt. But what he’s anticipating more than anything else is that first clear glimpse of Pluto.

“I’ve been looking at that maddening point of light forever,” he said.

Even with the best telescopes, the most powerful computers, Pluto is a tiny, distant blur. Its moon, discovered in 1978, was initially thought to be a bump, or just noise in a grainy photograph. The scientific paper describing the discovery carried the tentative title: “Charon: Defect or Moon?” So far away, and reflecting only a feeble light from the sun, Pluto and Charon are simply hard to see. Even at its closest, Pluto is nearly 2.7 billion miles from Earth.

“You don’t cook many hot dogs with the light coming off Pluto. It’s just a few photons,” said Eliot Young, who also studies Pluto at the Southwest Research Institute.

The light was so faint, it was impossible to distinguish Pluto from Charon until the powerful Hubble Space Telescope came along. “That was the triumph of Hubble, to distinguish the two,” said Hal Weaver, a project scientist at APL.

When Pluto was discovered in 1930, some estimated it was as big as Earth because it was relatively bright for something so small -- a product of its icy, reflective surface. As telescopes improved, size estimates of the planet shrank, leading some to joke that Pluto would soon disappear completely. Its diameter is now established at roughly 1,500 miles, according to Stern, about two-thirds the size of Earth’s moon.

Now astronomers are left with an equally basic question: What does it look like? The only information so far comes from pictures taken with telescopes.

No Longer a Dot

The best photo, taken by the Hubble Space Telescope in 1996, shows a surface marked by dark and bright “provinces” and ragged-edged polar caps. The unexpected texture on the planet excited scientists at the time. “Pluto, it’s not just a dot anymore,” Stern said when the pictures were unveiled.

But as intriguing as they are to scientists, the photos are not much to look at. “Imagine needing strong glasses and being drunk and looking at the moon. That’s better than our pictures of Pluto,” said Eliot Young, a Pluto expert at the Southwest Research Institute.

The planet is so cold -- between 378 and 396 degrees below zero -- that water acts like a rock and most gases freeze to the surface as frost. The surface is covered with methane and nitrogen ice. The planet’s salmon color is thought to be caused by methane frost discolored by ultraviolet radiation from the sun. The bright patches may be fresh frost that condensed out of the cooling atmosphere as Pluto moved away from the sun. Stern calls this a “laundering” of Pluto’s surface.

“You only need one-eighth to one-quarter of an inch of frost to make it a winter wonderland,” said Leslie Young of the Southwest Research Institute.

Studies have shown the atmosphere, though thin, is large, and might cause a haze to form near the surface. “I call it the L.A. of the solar system,” said Eliot Young. Scientists know it may be dim on the planet, but not dark. Pluto is bathed in dusky light, the equivalent of several dozen full moons. “You could read a book by it,” Young added.

Scientists have been able to glean what they know about Pluto’s size, atmosphere and composition only through indirect measurements and, sometimes, age-old techniques. They estimated its size by watching the light from Pluto shift as it danced with Charon over a five-year period when the two bodies repeatedly eclipsed each other.

They’ve learned about the temperature, thickness and pressure of the atmosphere by watching how the light from a star gradually fuzzed out when Pluto passed in front of it. With no atmosphere, the light would have suddenly blinked off when Pluto’s mass passed before it.

Such opportunities to learn from Pluto, called “stellar occultations,” have occurred only four times in the last 50 years, each setting off a scramble of astronomers to be on the right part of the planet for the observation.

“Basically, we’re pulling out every single trick in the book,” said Marc Buie, an astronomer at the Lowell Observatory in Flagstaff, Ariz., where Pluto was discovered.

But none of the work could replace sending a spacecraft to visit, as planet watchers learned when they examined Neptune’s neighborhood for the first time in 1989.

Neptune’s moon Triton had surprises for astronomers -- volcanic geysers shooting more than a mile high when Voyager 2 flew by. “I never would have predicted seeing geysers on Triton, so all bets are off for Pluto,” said Richard Binzel, a mission team member from the Massachusetts Institute of Technology. Added Stern: “Pluto could be Triton on steroids.”

It’s unclear whether the surface is young and paved with new ice or traces of volcanic activity, or ancient and densely cratered, Binzel said. Many scientists who monitor Pluto from ground-based telescopes believe it has been growing darker for several decades. They would like to know why.

“It’s changing. Despite being far from the sun and cold, it’s active,” said Andrew F. Cheng, an APL physicist in charge of a high-resolution mapping camera to detect cratering, geometric shapes created by frost patterns and other detailed surface features on Pluto and Charon.

Others, like Bonnie Buratti, a science team member from JPL, are not so sure. Pluto may look darker not because it is changing but because we are seeing a different side of it as it rambles around the sun. And images obtained so far are too poor to answer the question, she added.

“Is Pluto active or is it a dead object like the moon?” she said. “I’m just not sure.”

Mission a Must

Stern and others have argued for years a mission is the only way to find out. “No tools, no telescope, no amount of money can tell us much more,” Stern said. “We have to go.”

The mission’s far-reaching scientific plan and its relative low cost were two reasons it survived the budget ax. Another was Stern’s persistence.

The one-time shuttle astronaut candidate juggled working the science with orchestrating a full press on members of Congress to get the mission approved.

“You had a bunch of Ph.D.’s running around like lobbyists,” Stern said.

He also kept the media interested and saw editorial after editorial appear. “It can take longer for a space mission to escape from Washington, D.C., than to cross the solar system,” wrote the editors of Scientific American.

“Mars and Jupiter. Mars and Jupiter. Don’t they get enough attention?” lamented a Chicago Tribune editorial.

“I hadn’t appreciated the depth of the enthusiasm for Pluto,” said space exploration veteran Krimigis. “I’ve never seen anything like it.”

Little Pluto deserves at least some of the credit. Something about the tiny world seems to capture people.

“I didn’t choose Pluto. It chose me,” said Leslie Young, who spent the year after her college graduation working on the first stellar occultation and part of her graduate training working on the second.

Some think Pluto’s pull comes from being the only unexplored world in the solar system. Still others say the diminutive size and underdog quality of the frozen planet keep people so attached.

“It’s the little planet that could,” Stern said.

*

(BEGIN TEXT OF INFOBOX)

Getting to know Pluto

1930: Clyde Tombaugh, a 24-year-old astronomer working at Lowell Observatory in Flagstaff, Ariz., discovers Pluto on Feb. 18 when he notices a small point of light in two different positions on different nights.

1955: The length of a day on Pluto is found to be 6.4 Earth days.

1976: Pluto’s salmon color is determined to be caused by methane ice on the surface, darkened by ultraviolet radiation from the sun.

1978: Astronomer James Christy discovers bump on image of Pluto that turns out to

be a moon. He wants to name the moon Char after his wife, Charlene, but rules say the name must come from mythology. He settles on Charon, the ferryman who piloted dead souls across the river Styx.

1979: Pluto’s orbit temporarily moves inside Neptune’s orbit as part of a recurring pattern.

1983: The Infrared Astronomical Satellite finds Pluto’s temperature is 360efore degrees below zero. Later measurements find some parts even colder.

1985: In a five-year period during which Pluto and Charon eclipse each other several times, scientists discover the actual diameter of Pluto (1,500 miles) and Charon (750 miles.)

1987: Water ice is discovered on Charon.

1988: Observations of Pluto as it passes in front of a star reveals it has an atmosphere.

1992: First Kuiper Belt object discovered in Pluto’s vicinity.

1996: Hubble Space Telescope gets best images of bright spots, dark bands and ragged-edged polar caps on Pluto.

1999: Pluto moves outside Neptune’s orbit and again becomes the farthest planet

from the sun.

2000: NASA officials cancel Pluto-Kuiper Express mission at JPL after cost overruns, spurring anger and a grass-roots effort to rescue mission.

2001: Responding to orders from Congress, NASA opens bids for $500-million Pluto mission, which is awarded to the Johns Hopkins University Applied Physics Laboratory but not given final approval.

2002: Blue ribbon panel of astronomers declares Pluto and Kuiper Belt mission top priority for planetary science.

2003: NASA gives final approval for New Horizons mission to Pluto.

Source: A. Stern, J. Milton ‘Pluto & Charon: Ice Worlds on the Rugged Edge of the Solar System.’; NASA