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.
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.
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.