The United States is preparing to launch the first spacecraft to the distant planet Pluto. The liftoff is set for mid-January, but do not expect to hear about results within a year, as we have with Mars probes. Pluto is so far away that the journey will take at least nine years or longer. But, astronomers say the results will be worth the wait for what Pluto and its moon Charon can tell us about the origins of the solar system.
Pluto is the last major planet in our solar system to be discovered and the last to be visited in four decades of space exploration. The reason for the lag is not simply because it is more than 6.5 billion kilometers away, 50 times farther from the Sun than Earth.
The director of solar system research at the U.S. space agency NASA, Andrew Dantzler, says only in the past decade have scientists realized that this icy dwarf, smaller than the moon, might harbor important secrets about our solar system.
"Pluto is a treasure trove of scientific discoveries just waiting to be uncovered," he said. "It is different from the inner rocky planets. It is different from the outer gaseous planets. As such, it holds many clues as to how the solar system was formed."
We once thought Pluto orbited in distant solitude. But as recently as this year, astronomers have increased their count of its moons to three. The planet is also part of a wide swath of perhaps half a million small icy worlds circling the sun beyond Neptune called the Kuiper Belt, the first of which was detected in 1992.
The principal investigator for the mission to fly past Pluto, Alan Stern of the Southwest Research Institute in Colorado, says this belt is the largest structure in the solar system and has opened astronomers' eyes to the diversity of planets.
"Pluto looked like a misfit because it was the only one we saw, and just as a chihuahua is still a dog, these ice dwarfs are still planetary bodies," he said. "So the Pluto-like objects are more typical in our solar system than the nearby planets we first knew, and the opportunity is to go now and have a chance to study this most common type of planetary body in the solar system."
Because of Pluto's extreme distance, NASA is employing a lot of power to reduce travel time. It will use its biggest rocket, the Atlas Five, to get the spacecraft to a speed approaching 50,000 kilometers per hour within a few minutes, allowing it to pass the moon in only nine hours.
If the launch is not delayed, Jupiter will be in the right position for the probe to swing by for a gravity assist to increase its speed by 50 percent. If the launch occurs later in January, Alan Stern says the journey could take up to five years longer because Jupiter will be in the wrong place.
"We are going farther to reach our target and we are traveling faster than any spacecraft ever has," he said. "This is a little bit about rewriting the textbooks about the outer planets."
The spacecraft itself, called New Horizons, is a small probe, the size of a piano, jammed with seven instruments to study Pluto's atmosphere and geology and transmit the data back. After it passes Pluto, it is to continue into the Kuiper Belt to investigate one or two other bodies.
Its fuel is plutonium pellets, used mostly for aiming and course corrections. Its electronic components use less power than two 100 watt light bulbs. For most of its long journey, it will be hibernating, sending back only an occasional beacon to relay data on its status.
The man in charge of the payload is William Gibson, also of the Southwest Research Institute.
"The New Horizons payload, in summary, is the most compact, low power, high performance payload yet to fly on a U.S. planetary mission for a first reconnaissance fly-by," he said.
In the years before the spacecraft's arrival at Pluto, the mission team will study the planet with the Hubble Space Telescope to determine if it has more moons and possible dust rings they must navigate around. If they are lucky to liftoff early in the 35-day launch window to permit a fly by of Jupiter, they will test its navigation and scientific instruments to conduct further inspection of that gas giant planet.