Probe finally nears launch on mission of pure exploration
BY JUSTIN RAY
Posted: January 8, 2006
It is astronomers' insatiable quest to examine the conditions billions of years ago when the planet of our solar system were forming that pushes NASA's first robotic mission to Pluto. But political bickering has stonewalled the program for years, postponing an attempt to reconnoiter the frigid worlds never reached by humanity.
That road to the launch pad is littered with numerous mission cancellations, bad management and mishaps.
"When I started on this a long time ago I thought it was going to be easy. I thought it was a no-brainer. Space exploration is about exploration. We hadn't been to Pluto, it was good science, let's go. And it took 15 years," Stern recalls.
Dogged determination by project backers and a powerful endorsement by the National Academy of Sciences in 2002 listing a Pluto encounter as a priority in its decadal survey generated the buzz needed to push Congress to fund a spacecraft.
"When the National Academy ranked it No. 1, all the roadblocks came down," says Stern. "Despite the fact it took all those years, as a scientist it's very refreshing to see that the political system responds to scientific advice."
The $675 million creation was the New Horizons mission -- finally awaiting liftoff next week -- to visit Pluto and the unexplored Kuiper Belt region beyond Neptune, which is populated by unblemished remnant bits from the era of planetary birth.
"The scientific questions are the motivation. Science always drives missions. It's really cool to send something to Pluto but it's really the science questions that are the reasons for going there," said Bonnie Buratti, a New Horizons science team co-investigator. "Probably the most fundamental question is what does Pluto tell us about the origin of the solar system? And can it tell us anything about the origin of life?"
Pluto orbits more than 30 times farther away from Earth than the sun. It receives just 0.06 percent of sunlight as Earth, and has a surface temperature only 40 degrees above absolute zero.
Since its discovery in 1930, Pluto has remained an outcast from the solar system family of four rocky inner planets and four outer gas giants. The odd, small world flies in an inclined, elliptical orbit around our star and balks at the conventional rules for planets.
But in recent years this misfit has turned out to be just the tip of a cosmic iceberg. Pluto actually is immersed in the wide sea of objects called the Kuiper Belt.
"It is a window into the ancient solar system. It is a chance to look back into the history of the formation of the planets, and see worlds formed over four billion years ago and kept in the deep freeze -- preserved as they once were -- ever since," says Stern.
Launch of New Horizons from Cape Canaveral, Florida, comes January 17 when the Lockheed Martin Atlas 5 rocket dispatches the diminutive probe on a course to sail past Jupiter in 2007, receiving a sling-shot boost from the king planet's gravity. Encountering Pluto, however, won't happen until the summer of 2015, given the vast expanse of empty space the craft must traverse.
Leaving Earth in early 2006 is the last chance this decade at using Jupiter to speed the travel. A direct route would add years to the trip, something that scientists fear because Pluto's tenuous atmosphere is predicted to soon freeze away as its orbit loops farther from the sun.
"As Pluto moves away from the sun it cools and its atmosphere literally snows, or collapses, onto the surface," Stern says. "In fact, in 20 years time we expect there will be no atmosphere left to study. So we are racing against that clock to make sure we can study Pluto's temporary atmosphere."
"The atmosphere is kind of a weird one. It is a little bit like what the Earth's atmosphere was at the time the Earth was formed. Some of the molecules are escaping out of the top of the atmosphere, escaping into space," said Hal Weaver, the New Horizons project scientist. "Some of the instruments onboard the spacecraft are supposed to capture some of these escaping molecules so that we can tell what's coming off the top and at what rate. So that will tell us something about how planetary atmospheres form and evolve."
Examining the atmosphere is just one of the items on New Horizons' scientific to-do list during its fast flyby of Pluto. The observation campaign begins three months before reaching the planet, when the craft surpasses the best clarity possible from the Hubble Space Telescope, and continues a similar period of time after the July 2015 close encounter. The most intense collection of data comes in the heart of the flyby when the probe speeds 9,600 kilometers above Pluto's surface, soaring past the planet and its large moon Charon at 14 kilometers per second.
"Most of the science will be obtained in a 36-hour period in what we call the closest approach to Pluto and Charon," said David Kusnierkiewicz, the mission systems engineer.
The nuclear-powered New Horizons is equipped with seven instruments, including cameras, spectrometers and in-situ particle measurement devices that will reveal the landscape and chemical makeup of the planet and moons, provide stereoscopic imaging for 3-D visualizations of the topography, calculate the composition and density of material coming off of Pluto's rapidly escaping atmosphere and search for rings and more moons.
"When we arrive at Pluto we'll be photographing everything in the system at high resolution. The best we can do now with the Hubble, despite all of its capabilities, is about 400 or 500 kilometers per pixel. That is like putting a state in a single pixel. We're going to change that. We'll map everything that is sunlit in the system at one kilometer resolution," says Stern.
The spacecraft's eagle-eye camera will snap imagery as good as 25-to-50 meters per pixel resolution in selected areas to reveal surface details. The spectrometer and camera data sets will be married together by scientists to depict the composition properties with features spotted in the imagery.
"We have spectrometers that are going to let us measure the composition of the atmosphere, the structure of the atmosphere and the composition of the surface, and not just the bulk compositions but every location we put a pixel we'll get a spectra. So we expect to have millions of spectra that we can locate on the surface. What do the polar caps look like vs. the dark regions? What does it look like inside the craters where we have a window into the interior? What does it look like on the side of cliffs where we might be able see strata at the highest resolution?"
"There's lots of interesting organic material over the surface," Weaver says. "Some of these ices when they sublimate they go directly from the solid phase into the vapor phase. Then it refreezes depending on whether we are in day or night and comes back on the surface in a very bright frost layer. One of the things we want to do is study the distribution of that frost over the surface to learn about the seasons and the weather on the Pluto just like we study on the other planets. This is our first attempt to really characterize Pluto in a detailed way."
The recent discovery by the Hubble Space Telescope of two small moons orbiting Pluto along with Charon adds a new dynamic to the mission. Hubble saw the two tiny specks of light during 8-minute glimpses at Pluto. The candidate moons, initially dubbed S/2005 P1 and S/2005 P2, are roughly 44,000 kilometers from Pluto and about two or three times as far from Pluto as Charon.
"We might actually be able to fly pretty close to both of those satellites -- maybe one of them before we encounter Pluto and one after," Weaver said.
A goal of New Horizons was looking for more moons. But the Hubble find has complicated the mission's packed agenda.
"We already have four things to look at now. As we start to fill up our timeline, it will give us less time for just searching around for things we don't even know about. We have a lot of things we know about we want to try and understand better," Weaver said.
After departing the Pluto neighborhood, New Horizons will cruise deeper into the Kuiper Belt with the intention of rendezvousing with one or two smaller objects in the region.
Exploring Pluto and the primitive bodies Kuiper Belt should shed new light on not only the building blocks of the planets but life itself, Buratti says. Shards of Kuiper Belt Objects that get jostled to the inner solar system, becoming short-period comets, could have delivered water and carbon-bearing material to Earth that sparked life.
"We know life arose on the Earth somehow but we don't really understand how. We do know there had to be molecules that are rich in carbon, hydrogen, nitrogen, oxygen. These complex pre-biotic organic molecules had to get to the Earth somehow because it was too hot where the Earth formed.
"We know that the interstellar medium has the clouds of gas and dust that the sun formed out of is loaded with organic molecules. We believe they formed in the outer solar system and were transported by comets from the Kuiper Belt."
Added Weaver, "That's a mechanism for bringing that primitive material from the outskirts of the solar system into the inner solar system."
New Horizons begins its noble journey into the unknown at 1:24 p.m. EST (1824 GMT) next Tuesday.
"What could be more exciting than exploring the edge of the solar system? This whole undiscovered terrority -- the Kuiper Belt -- there is nothing like it. We didn't know it existed when you and I were children. It is the frontier, and that is what the space program is about," says Stern.
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