Pluto (planet)

[Muhammad Adnan]

Pluto (planet)

1) INTRODUCTION

Pluto (planet), ninth planet from the Sun and outermost known planet of the solar system. Pluto revolves about the Sun once in 247.7 Earth years at an average distance of 5.91 billion km (3.67 billion mi). The planet’s orbit is so eccentric that at certain points along its path Pluto is slightly closer to the Sun than is Neptune. Pluto is about 2,360 km (1,475 mi) in diameter, about two-thirds the size of Earth's moon. Discovered in 1930, Pluto is the most recent planet in the solar system to be detected.

2) OBSERVATION FROM EARTH

Pluto is far away from Earth, and no spacecraft has yet been sent to the planet. All the information astronomers have on Pluto comes from observation through large telescopes. Pluto was discovered as the result of a telescopic search inaugurated in 1905 by American astronomer Percival Lowell, who postulated the existence of a distant planet beyond Neptune as the cause of slight irregularities in the orbits of Uranus and Neptune. Continued after Lowell’s death by members of the Lowell Observatory staff, the search ended successfully in 1930, when American astronomer Clyde William Tombaugh found Pluto.
For many years very little was known about the planet, but in 1978 astronomers discovered a relatively large moon orbiting Pluto at a distance of only about 19,000 km (about 12,000 mi) and named it Charon. The orbits of Pluto and Charon caused them to pass repeatedly in front of one another as seen from Earth between 1985 and 1990, enabling astronomers to determine their sizes accurately. Charon is about 1,200 km (750 mi) in diameter, making Pluto and Charon the planet-satellite pair closest in size to one another in the solar system. Scientists often call Pluto and Charon a double planet.
Every 248 years Pluto’s elliptical orbit brings it within the orbit of Neptune. Pluto last traded places with Neptune as the most distant planet in 1979 and crossed back outside Neptune’s orbit in 1999. No possibility of collision exists, however, because Pluto's orbit is inclined more than 17.2° to the plane of the ecliptic (the plane in which Earth and most of the other planets orbit the Sun) and is oriented such that it never actually crosses Neptune's path.
Pluto has a pinkish color. In 1988, astronomers discovered that Pluto has a thin atmosphere consisting of nitrogen with traces of carbon monoxide and methane. Atmospheric pressure on the planet's surface is about 100,000 times less than Earth's atmospheric pressure at sea level. Pluto’s atmosphere is believed to freeze out as a snow on the planet’s surface for most of each Plutonian orbit. During the decades when Pluto is closest to the Sun, however, the snows sublimate (evaporate) and create the atmosphere that has been observed. In 1994 the Hubble Space Telescope imaged 85 percent of Pluto's surface, revealing polar caps and bright and dark areas of startling contrast. Astronomers believe that the bright areas are likely to be shifting fields of clean ice and that the dark areas are fields of dirty ice colored by interaction with sunlight. These images show that extensive ice caps form on Pluto's poles, especially when the planet is farthest from the Sun.

3) ORIGIN OF PLUTO

With a density about twice that of water, Pluto is apparently made of a much greater proportion of rockier material than are the giant planets of the outer solar system. This may be the result of the kind of chemical reactions that took place during the formation of the planet under cold temperatures and low pressure. Many astronomers think Pluto was growing rapidly to be a larger planet when Neptune’s gravitational influence disturbed the region where Pluto orbits (the Kuiper Belt), stopping the process of planetary growth there. The Kuiper Belt is a ring of material orbiting the Sun beyond the planet Neptune that contains millions of rocky, icy objects like Pluto and Charon. Charon could be an accumulation of the lighter materials resulting from a collision between Pluto and another large Kuiper Belt Object (KBO) in the ancient past.

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