Science / Medicine : Pluto’s Status as a Planet Confirmed by Researchers Using Telescopic Data
Recent analysis of telescopic data has shown that nearly six decades after its discovery, far-flung Pluto is indeed a planet and not an asteroid or satellite, researchers said.
William McKinnon, associate professor of earth and planetary science at Washington University in St. Louis, said he has demonstrated that the composition of Pluto is just what is expected of a solid planet in the outer solar system.
McKinnon said his research should put to rest the long-held notion that Pluto is a fugitive satellite that escaped Neptune’s gravitational influence.
“Pluto has been denied a certain amount of respect since its discovery in 1930,” McKinnon said in a statement. “But it also has been a constant source of controversy and fascination. It’s the runt of the planet world and the most eccentric planet, too.
“Our work shows, though, it was formed independently in the outer solar system. It has every right to be considered a planet--not an escapee from Neptune. As a planet, it is peerless.”
McKinnon was aided in his research by Steven Mueller of Southern Methodist University. The two used recent analysis of telescopic data made available because of Pluto’s unique orbit, which has allowed earthbound scientists their best chance for the next century to make measurements of Pluto and its moon, Charon.
The two men developed a computer model based on analyses of meteorites, photometric measurements and Newtonian physics and demonstrated that Pluto’s interior is made up of roughly of three parts rock to one part ice. Such an abundance of rock suggests a high density typical of the other solid planets that were all formed in the solar nebula, the hot gas and dust out of which planets evolved from tiny grains billions of years ago.
“The relative amount of ice just about matches that predicted theoretically to form in the cold outer solar system,” McKinnon said.
The abundance of rock rules out the possibility of its being a satellite of Neptune, said McKinnon, who is also a member of the university’s McDonnell Center for Space Sciences and a NASA consultant.
A close look at Pluto would show a dark, eerie, icy landscape with thin air and temperatures so cold that 350 degrees below zero Fahrenheit would seem like a balmy spring day. Pluto is, on average, 40 times farther away from the sun than is Earth; sunlight takes nearly six hours to reach the planet.
Although from Pluto the sun appears as a tiny luminous disc, Pluto’s sky would not be completely black. Sunlight would be filtered through a thin haze of methane and other gases.
Pluto, less than one-fifth the size of Earth’s moon, has a “cockeyed orbit,” said McKinnon; it takes 248 years to complete one orbit around the sun. However, for 20 of those years, it slips inside the orbit of Neptune.
In other work, scientists at the University of Arizona lunar and planetary laboratory now believe that in addition to methane, the distant planet’s atmosphere contains substantial amounts of carbon monoxide and traces of nitrogen and argon.
Writing in the British scientific journal Nature, Roger Yelle and Jonathan Luine reported Wednesday their findings are based on observations of the planet during its recent pass in front of a star.
The planetary scientists also said they calculated the average surface temperature of Pluto as minus 360 degrees Fahrenheit and the atmospheric temperature about 40 miles over the surface as minus 279 degrees Fahrenheit.
Pluto has been inside Neptune since 1979, making Neptune the farthest planet from the sun until 1999, when Pluto goes back to its outer track. Thanks to the eccentric orbit, scientists have their best window to observe and learn from Pluto and Charon, which no spacecraft has ever visited or imaged.
PLUTO AT A GLANCE Distance from the sun:
Shortest -- 2,748,000,000 miles
Greatest -- 4,571,200,000 miles
Distance from Earth:
Shortest -- 3,583,000,000 miles
Greatest -- 4,670,000,000 miles
Diameter: 1,900 miles
Length of year: About 248 Earth-years
Rotation period: About 6 Earth-days
Temperature: About -342to -369 F.
Atmosphere: Methane
Satellites: 1
Source: World Book
