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Will NASA Go Before Pluto Freezes Over?
By Andrew Bridges
Pasadena Bureau Chief
posted: 08:00 am ET
10 September 2000
ET
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pluto_mission_000910 BOULDER, Colo. Concerned by the possible delay or cancellation of a first-ever mission to Pluto, backers of the endeavor argue there is no time like the present to explore the tiniest and most distant of the solar systems nine planets. Indeed, by foregoing the launch of a probe to Pluto in 2004, as currently planned, mission proponents warn NASA could miss an opportunity to study the planets atmosphere and surface that has not presented itself since the 1740s and wont again until the 2230s. [inset] "Pluto has all these time-critical aspects," said S. Alan Stern, of the Southwest Research Institute in Boulder, Colorado and a member of the science definition teams for the proposed mission. "It really ought to be now. I cant find any reason to wait." For Pluto, in its 248.5-year orbit around the sun, roams from 30 to 50 astronomical units from our star. Each astronomical unit, or AU, is equivalent to the distance separating Earth from the sun, or 93 million miles (150 million kilometers). Pluto made its closest approach to the sun in 1989; now, as it recedes, it is steadily growing cooler. The sky Is falling As the planet draws farther into the cold reaches of space, its nitrogen and methane atmosphere an atmosphere so large and puffy, the planets lone moon, Charon, orbits within its reach literally freezes out. "The atmosphere," Stern said, "is snowing away. All that atmosphere is piling on the surface." 
| Pluto-Kuiper Express. |
The Pluto-Kuiper Express, as the proposed mission is called, would arrive at the outermost planet after a journey that could take eight to 10 years. How much of Plutos atmosphere it could catch by the time it gets there is not clear. Some scientists fear the entire atmosphere could collapse, leaving nothing to study. "That is a concern: no one really understands much about the physics of what the atmosphere will do," said Richard Terrile, chief scientist of the outer planets program and the Pluto mission project scientist at NASAs Jet Propulsion Laboratory. ~ King of the underworld, in the dark Furthermore, Plutos exaggerated 118-degree polar tilt means significant portions of the planet would be lost to the shadows as it moves into winter in its southern hemisphere. After 2015, nearly half of Pluto and Charon would be cloaked in shadows that will persist for decades, removing them from the view of any passing probe. "The longer you wait, the less of its surface you are going to see," Terrile said. The heavens cant wait Getting to Pluto is no mean feat, either. Its incredible distance from Earth requires either the use of an extremely large rocket to hurl any spacecraft on its way or the clever use of Jupiter to move it along. 
| Pluto (center) and its tiny moon Charon. |
Mission planners gravitate toward the later, cheaper choice by swinging the probe past Jupiter it would pick up, slingshot-like, a boost toward Pluto. But Jupiter isnt always at the ready, as it too orbits the sun, albeit on the 12-year track. A December 2004 launch would allow the Pluto-Kuiper Express to complete a Jupiter gravity-assist maneuver. The planet would be available in 2006, as well, but would require a larger and more expensive launch vehicle to work, Terrile said. Any delay beyond 2006 would force a decade-long wait for Jupiter to swing around again, meaning the probe would not arrive at Pluto until the mid 2020s. "There is certainly an important window right now that would allow us, quite reasonably, to finish the first reconnaissance of the solar system," Terrile said. Money woes, planetary blows However, casting aside science, NASAs looming budget crisis may deal Pluto its deathblow. In a recent conference call with reporters, Ed Weiler, NASAs associate administrator for space science, said costs have risen on anywhere from 10 to 15 different agency missions, from a few percent to as much as 40 percent. To accommodate the spike in costs, NASA must contemplate delaying or canceling missions. Pluto is among those. Jay Bergstralh, NASAs acting director for solar system exploration, said he is in the midst of putting together a two-phase look at how the agency will undertake the exploration of the outer solar system in the near future. The first phase will look at the motives for exploring the edge of the solar system, what are the questions to be asked and how NASA might go about answering those questions. The second phase, to begin next month, will examine mission specifics, including Pluto-Kuiper Express and what a delay to it might mean. "There are excellent reasons to go to Pluto as soon as possible," Bergstralh said. However, it is fast becoming clear that NASA will not be undertaking as ambitious a program of planetary exploration that it was ramping up to do as recently as last year. The outer planets, for example, could become a once-every-four-years proposition, Bergstralh said. As a result, Pluto may be passed over for the time being, losing out to missions like the Europa Orbiter, a spacecraft that will probe Jupiters icy moon. "Were going to have to make some hard choices. Were not going to be able to do missions as often as we would have liked to," Bergstralh said.
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