Pluto and Charon Pluto and Charon
On February 18, 1930, Pluto, the last planet and the 9th in our solar system, was discovered. Normally Pluto is farther from the Sun then any other planet; however, due to the eccentricity of its orbit, 20 years out of its 249 orbital years it is closer than Neptune. Pluto's orbit is also highly inclined -- tilted 17 degrees to the orbital plane of the other planets. Ground-based observations indicate that Pluto's surface is covered with methane ice and that there is a thin atmosphere that may freeze and fall to the surface as the planet moves away from the Sun. Observations also show that Pluto's spin axis is tipped by 122 degrees.
Pluto has one satellite named Charon [SHAR-on], after the boatman in Greek mythology who operated the ferry across the River Styx to Pluto's realm in the underworld. Charon was discovered in 1978. Its surface composition seems to be different from Pluto's. The moon appears to be covered with water-ice rather than methane ice. Its orbit is gravitationally locked with Pluto, so both bodies always keep the same hemisphere facing each other. Pluto's and Charon's rotational period and Charon's orbital period are all 6.3872 Earth days.
Discovered by ............................. Clyde W. Tombaugh
Date of discovery ......................... February 18, 1930
Mass (kg) .......................................... 1.29e+22
Mass (Earth = 1) ................................. 2.1586e-03
Equatorial radius (km) ................................ 1,160
Equatorial radius (Earth = 1) .................... 1.8188e-01
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
Rotational period (days) ............................ -6.3872
Orbital period (years) ............................... 248.54
Mean orbital velocity (km/sec) ......................... 4.74
Orbital eccentricity ................................. 0.2482
Tilt of axis ......................................... 122.52°
Orbital inclination .................................. 17.148°
Equatorial surface gravity (m/sec^2) .................... 0.4
Equatorial escape velocity (km/sec) .................... 1.22
Visual geometric albedo ................................. 0.3
Magnitude (Vo) ........................................ 15.12
Atmospheric composition
Methane .............................................
Nitrogen ............................................
Discovered by .................................... J. Christy Date of discovery ...................................... 1978 Mass (kg) .......................................... 1.77e+21 Mass (Earth = 1) ................................. 2.9618e-04 Equatorial radius (km) .................................. 635 Equatorial radius (Earth = 1) .................... 9.9561e-02 Mean density (gm/cm^3) ................................. 1.83 Mean distance from Pluto (km) ........................ 19,640 Rotational period (days) ............................ 6.38725 Orbital period (days) ............................... 6.38725 Mean orbital velocity (km/sec) ......................... 0.23 Orbital eccentricity ................................... 0.00 Orbital inclination ................................... 98.80° Escape velocity (km/sec) .............................. 0.610 Visual geometric albedo ................................. 0.5 Magnitude (Vo) ......................................... 16.8
Pluto & Charon
(GIF, 124K)
This image of Pluto and Charon was taken by the Hubble Space Telescope.
Pluto is the larger object in the image.
Ground vs. Hubble Comparison
(GIF, 144K)
This image shows a comparison between a ground
based view (left) and a Hubble Space Telescope view (right)
of pluto and Charon.
Nordic Optical Telescope
(GIF, 35K)
This image of Pluto was taken with the 2.6 m
Nordic Optical
Telescope, located at La Palma, Canary Islands. It is a good
example of the best imagery that can be obtained from earth based
telescopes.
(c) Nordic Optical Telescope Scientific Association (NOTSA).
New Hubble Telescope Image
(GIF, 19K;
caption)
This is the clearest view yet of the distant planet
Pluto and its moon, Charon, as revealed by the Hubble
Space Telescope (HST). The image was taken on
February 21, 1994, when the planet was 4,400 million
kilometers from the Earth.
The HST corrected optics show the two objects as clearly separate and sharp disks. This now allows astronomers to measure directly (to within about 1 percent) Pluto's diameter of 2320 kilometers and Charon's diameter of 1270 kilometers.
The HST observations show that Charon is bluer than Pluto. This means that the worlds have different surface composition and structure. A bright highlight on Pluto indicates that it may have a smoothly reflecting surface layer. A detailed analysis of the HST image also suggests that there is a bright area parallel to the equator of Pluto. However, subsequent observations are needed to confirm is this feature is real. The new HST image was taken when Charon was near its maximum elongation from Pluto (0.9 arcseconds). The two worlds are 19,640 kilometers apart. (Courtesy NASA/ESA/ESO).
Pluto Express
(GIF, 238K)
This is a painting by Pat Rawlings of the Pluto Express mission
scheduled for launch in 2001 to arrive at Pluto around 2006-2008.
The mission will consist of a pair of
small, fast, relatively cheap spacecraft weighing less than 100 kg each.
The spacecraft will pass within 15,000 km of Pluto and Charon.
(Courtesy Pat Rawlings/NASA/JPL).
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