Astronomers using the Japanese Subaru Telescope on Hawaii have detected frozen ethane on the surface of Pluto. Ethane, a substance prized on Earth as a component of natural gas, may have even greater significance on Pluto, where it could provide clues to the evolution of the early solar system.

Indeed, the ethane ice may be a remnant of the vast gas cloud that collapsed some 4.5 billion years ago to become the sun and planets. The substance may have been preserved since then by the extreme cold that exists at the distance of Pluto's orbit.

Alternatively, the ethane may have been created throughout the lifetime of the solar system from the reaction of methane and ultraviolet light. Further observations may determine which of these two theories is correct.

The ethane is dissolved in a bed of nitrogen ice that covers much of Pluto's surface at a temperature of -387 degrees F (-233 degrees C).

The Subaru Telescope conducted the observations in June. The telescope, owned by the National Astronomical Observatory of Japan, saw "first light" earlier this year but is still under construction. It is scheduled for routine operation in 2000. The telescope's Cooled Infrared Spectrograph/Camera observed both Pluto and its moon Charon.