INDEPTH: SPACE
Destination Pluto: Mission to a new frontier
CBC News Online | January 19, 2006
As you read this, an unmanned spacecraft the size of a piano is hurtling towards the outer reaches of the solar system – a nine-year space odyssey that will take it to Pluto and our first up-close encounter with the frozen planet.
The New Horizons mission is a $700-million NASA effort to explore the “ice dwarf” that revolves around a sun so distant, it would look much like any other star in the perpetually dark sky. Eight of the nine planets have already hosted visits from various Earth probes. Now, it’s Pluto’s turn.
MISSION TIMELINE
- Launch: Jan. 19, 2006
- Jupiter flypast: February 2007
- Pluto flypast: July 2015
Why Pluto?
The last planet to be discovered is an enigma; it’s unlike any of its siblings. For one thing, scientists know it’s icy. That makes it distinct from the rocky planets closer to the sun (like Mercury, Venus, Earth and Mars) or the gaseous giants further away (like Jupiter and Saturn). “An icy stranger in a strange orbit,” as NASA puts it.
Pluto is also part of the solar system’s only known binary planet. Pluto has a big moon, Charon (discovered in 1978), that is half as big as Pluto itself. Because they are so close in size, Pluto and Charon interact with each other in an other-worldly gravitational dance that keeps them less than 20,000 kilometres apart. Despite their proximity, Pluto is very different from Charon . Where Pluto has an atmosphere, Charon appears not to have one. The hope is that a close look at Pluto-Charon can shed light on how the Earth-moon system formed.
But it’s what lies around and beyond Pluto that has planetary scientists really excited. In 1992, astronomers discovered what they eventually called the Kuiper Belt. This is a
collection of perhaps 100,000 small worlds that range from 100 kilometres to 2,000 kilometres across – a distant cousin of the asteroid belt that straddles the orbits between Mars and Jupiter. Scientists say the Kuiper Belt contains the ancient flotsam left over from the time the planets were born billions of years ago. A look at these KBOs (Kuiper Belt Objects) will be like a trip back in time as astronomers indulge in some remote space archeology. This is something the Hubble space telescope can’t do – it’s just too far away.
Overview of the mission
New Horizons was launched by the most powerful rocket in NASA’s inventory, the Atlas V-551. Once it shakes off its boosters, it will be the fastest spacecraft ever launched from Earth. By the time it reaches the lunar orbit distance of 384,000 kilometres, it will be zipping along at 16 kilometres a second – 58,000 kilometres an hour.
PLUTO FACTS
- Discovered: 1930
- Orbits sun: Every 248 years
- Rotates: Every 6.4 days
- Average distance from sun: 5.9 billion kilometres
- Diameter: 2,360 kilometres
- Diameter of moon Charon: 1,200 kilometres
Then, not much happens for the next year or so. There will be a few systems checks, some mid-course trajectory adjustments and rehearsals for its encounter with Jupiter in February 2007. What’s Jupiter got to do with it, you ask? Size matters in the universe of planetary science. NASA is planning to use Jupiter’s heft to boost New Horizons’ speed to
75,000 kilometres an hour. That will allow it to get to Pluto as early as mid-2015 – five years earlier.
The journey from Jupiter to Pluto is expected to be so uneventful that scientists are planning to put New Horizons to sleep. The spacecraft will be in unpowered “hibernation” for much of that time – woken up every year or so for checkups. Five billion kilometres later, New Horizons will close in on its primary targets – Pluto and Charon.
The busiest part of the mission will take place within a 24-hour period in July 2015. That’s when New Horizons makes its closest approach to the ice planet – about 10,000 kilometres away. A series of seven onboard scientific instruments swings into action – mapping the surface, studying the atmosphere and its geology, and taking temperatures and plenty of pictures that will show features as small as 25 metres across. The signals beamed back from New Horizons will travel at the speed of light but will still take four hours and 25 minutes to reach Earth.
The next part of the mission depends on NASA getting new funding. If it gets the green light for an extended mission, New Horizons will search for one or two Kuiper Belt Objects with diameters of 50 kilometres or more, snapping and testing all the way.
From there, it’s on to interstellar space, where it will join the Voyager and Pioneer spacecraft as one of Earth’s lonely deep space emissaries.
Why did the New Horizons launch cause some controversy?
Some people looked at New Horizons and saw only a bold venture into the “final frontier.” Others noticed the plutonium. The New Horizons spacecraft is powered by 11 kilograms of highly radioactive plutonium-238 – enough to power the onboard instruments, keep the spacecraft warm and send data back for more than a decade. Some anti-nuclear activists protested the launch.
This isn’t the first space mission to use plutonium as a power source. The Mars Rovers used it, the two Voyager spacecraft used it, and dozens of other American and Soviet missions have used plutonium as far back as 1961. With outer planet missions, it is the only possible source of power – NASA says solar panels are useless that far from the sun.
NASA put the chance of a launch accident that could involve the release of plutonium at 1 in 350. But even in this scenario, the space agency said the risk to area residents was low to non-existent, saying the most likely kind of accident would result in the release of small amounts of plutonium dioxide that would lead to no or very little radiation exposure, posing no health danger.
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