Surprising data from NASA's Stardust programme has revealed that comets have heat-formed components.

Scientists analysing samples from the seven-year mission to collect material from the tail of comet Wild 2 found glassy particles that must have been formed at high temperatures. Stardust curator Michael Zolensky said: "It seems that comets are a mixture of materials formed at all temperatures, at places very near the early sun and at places very remote from it."

The revelation means comets may not be as simple as the clouds of ice, dust and gases they were thought to be. The researchers compare the high temperature material to Hawaiian beach sand, with iron, magnesium, calcium, aluminum and titanium components.

Stardust principal investigator Donald Brownlee spelt out the paradox of the finding: "The interesting thing is we are finding these high-temperature minerals in materials from the coldest place in the solar system."

Stardust returned to Earth in the Utah desert back in January. Next for the international community of 150 scientists working on the samples is to examine the interstellar dust material the probe returned. ®