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Tuesday, July 20, 1999 Published at 15:49 GMT 16:49 UK


Natural gas found on Pluto

These images of Charon and Pluto reveal ethane

By BBC News Online Science Editor Dr David Whitehouse

Astronomers have detected "natural gas" on the surface of Pluto, in the form of frozen ice.

Using the recently commissioned Japanese Subaru telescope on Hawaii, scientists report the detection of ethane ice on Pluto, the most distant planet in our solar system.

Ethane is a simple hydrocarbon, a molecule made of two carbon and six hydrogen atoms. On Earth it is a major resource as it forms part of natural gas. On Pluto it is an indicator of how the planet and its large companion Charon, may have formed.

[ image: The telescope allows the chemistry of Pluto's surface to be revealed]
The telescope allows the chemistry of Pluto's surface to be revealed
It is a significant discovery because it may be left over from the original cloud of gas, ice and dust that formed our Sun and planets. It may have been preserved on Pluto's cold surface for four and a half billion years.

In June, when Pluto and Charon were 5.8 billion km (3.6 billion miles) from Earth, the Subaru Telescope turned its gaze towards them. Using an advanced spectrograph, it analysed the light coming from them.

The light reflected from Pluto and Charon has some wavelengths depleted because they have been absorbed by nitrogen, methane and carbon monoxide, all existing in the form of ice on the surface of Pluto. And for the first time a narrow absorption feature has been seen in Pluto's spectrum that is the fingerprint of solid ethane.

Close, but not the same

Surprisingly a detailed analysis of the light from Pluto and Charon reveals that they are not alike.

Pluto is covered in frozen nitrogen, methane, carbon monoxide and ethane "ice" (all at a temperature colder than -346 Fahrenheit or -210 degrees Centigrade).

Charon appears to be mostly covered in the more familiar water ice at a similarly low temperature.

Small bang

Astronomers are a little puzzled abut the differences but some suggest that it lends support to the theory that the Pluto-Charon system formed out of the shattered remains of a single body following a planetary collision back when the solar system was young.

Pluto was discovered in 1930 and is the furthest known planet in our solar system, taking 249 years orbit the Sun. It has a diameter of 2,274 km (1,413 miles).

Charon, discovered in 1978, has a diameter of 1,172 km (728 miles). It is unusually large, relatively speaking, for a satellite. It may therefore be more appropriate to regard the system as a double planet rather than as a planet/satellite pair.

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