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Atmosphere of Pluto - How Cold is Pluto?

Here’s a tale of Pluto… the secrete uncovered! Yes, right when the researchers are working hard to trace the evidences of life on Mars, a group of scientists concluded some interesting fact about Pluto – the last member of the solar family of planets. Pluto – a planet that still remains an enigma, is the tenth largest known orbiting family the Sun and the second largest dwarf planet discovered till date. Although not much is known about the Pluto and its atmosphere, yet researchers say that it is around 58,736,000 kilometers away from the Sun, which is an incredibly long distance. According to the researchers, it is certain that Pluto quite cold. Now the question is, how freezing is Pluto? How cold Pluto is, is still a matter of conjecture! In a research paper published in ‘Science’, volume – 261, pp 1713-1716, in 1993, a group of scientists led by S Alan Stern, at Space Science Department, South West Research Institute, San Antonio, Texas, United States, talked about something really astonishing about the atmosphere of Pluto. They researched to conclude that Pluto may be as cold as 25 to 40 Kelvins at the surface, which is some tens of degree below the temperature of the liquid Nitrogen.

The researchers studied Pluto and the atmosphere there, using the highly sophisticated device that could track even the millimetrewave thermal emission (low heat radiation) that came from Pluto. The conclusion changed many other believes about Pluto. It used to be believed that Pluto’s atmosphere had methane gas as one of the major constituents, but now the belief has changed. Such a colder surface cannot have methane in the atmosphere. The thin dark line seen in the spectra of Pluto, which was believed to be due to the presence of methane, may be caused by the gas frozen on the surface of Pluto. Stern’s team contended that the atmosphere of Pluto constitutes chiefly nitrogen and carbon monoxide, with just a little trace of methane, instead of mostly methane.

Now again another question arises. Does the temperature on Pluto remain same all through? Not obviously! Temperature on Pluto varies hugely due to its highly elliptical orbit that ranges something between 4.4 billion km and 7.4 billion km away from the Sun. Another source suggested that the temperature of Pluto comes down to as low a 33 K, which is -240 degree Celsius when it is furthest from the Sun. Different sources have been laying their own unique view points, which s why Pluto is still a wondrous enigma.

Here are some view points regarding the atmosphere of Pluto, as laid down by various sources:

Lodders, Katharina & Bruce Fegley, (Jr. The Planetary Scientists Companion. New York: Oxford University Press, 1998: 237-240), said: "… the surface temperature of 40 K implies a surface pressure of approximately 58 millibar".

Rosanna L. Hamilton has more advanced view about Pluto. Hamilton says: "Due to its great distance from the sun, Pluto's surface is believed to reach temperatures as low as -240 degrees C (-400 degrees F)".

According to "Pluto." (The World Book Encyclopedia. Vol. 15, Chicago: World Book, 1999: 580-589), "Astronomers believe the temperature on Pluto may be about -390 to -370 degrees F (-230 to -220 degrees C)"

As per "The Heavens", Chicago: World Book, 1989: 120-121, "Its estimated temperature: -369 degrees F (-223 degrees C) also makes the presence of a gaseous atmosphere unlikely".

Here are some facts about Pluto:
  • Composition of atmosphere: Methane and Nitrogen
  • Discovered by: Clyde W. Tombaugh
  • Date of discovery February: 18, 1930
  • Equatorial radius (km): 1,137
  • Equatorial radius (Earth = 1): 0.1783
  • Equatorial surface gravity (m/sec^2): 0.4
  • Equatorial escape velocity (km/sec): 1.22
  • Magnitude (Vo): 15.12
  • Mass (kg): 1.27e+22
  • Mass (Earth = 1): 2.125e-03
  • Mean density (gm/cm^3): 2.05
  • Mean distance from the Sun (km): 5,913,520,000
  • Mean distance from the Sun (Earth = 1): 39.5294
  • Mean orbital velocity (km/sec): 4.74
  • Orbital period (years): 248.54
  • Orbital eccentricity: 0.2482
  • Orbital inclination (degrees): 17.148
  • Rotational period (days): -6.3872
  • Tilt of axis (degrees): 122.52
  • Visual geometric albedo: 0.3