Pluto is covered with surprising dunes made of methane ice, which have formed relatively recently despite the frigid dwarf planet's very thin atmosphere, international researchers said Thursday.

Pluto's atmosphere has a surface pressure 100,000 times lower than Earth's, which researchers suspected might be too little to allow tiny grains of solid methane to mobilize and become airborne.

Yet mild winds blowing across Pluto's surface at speeds of some 19-25 miles (30-40 kilometers) per hour have forged these ripples at the border of an ice plain and mountain range, said the report in the journal Science.

"The likely source of the dune grains is methane ice blown from nearby mountains," said the Science report. "Although nitrogen ice cannot be ruled out."

The dunes are scattered across a belt-like area some 45 miles (75 kilometers) across, and were spotted with NASA's New Horizons spacecraft when it flew by in 2015, said the report.