A "dwarf planet" discovered seven years ago near the edge of the Solar System is a dead, frozen world with no atmosphere, scientists have learned.
Makemake, named after an Easter Island god, is one of five distant objects orbiting the Sun that are recognised as dwarf planets.
It is about two-thirds the size of Pluto, the most distant of the nine traditionally recognised planets, and further away from the Sun.
But it is not as far out as Eris, the most massive known dwarf planet.
A chance passing in front of a star allowed astronomers to check whether Makemake had an atmosphere, as had been suspected.
They discovered that it had virtually none.
Scientists were also able to measure the amount of reflectivity of the dwarf planet's surface.
It was found to be similar to that of dirty snow - higher than that of Pluto but lower than that of Eris.
Dr Jose Luis Ortiz, from the Astrophysical Institute of Andalucia in Spain, who led the astronomers, said: "As Makemake passed in front of the star and blocked it out, the star disappeared and reappeared very abruptly, rather than fading and brightening gradually.
"This means that the little dwarf planet has no significant atmosphere.
"It was thought that Makemake had a good chance of having developed an atmosphere.
"That it has no sign of one at all shows just how much we have yet to learn about these mysterious bodies.
"Finding out about Makemake's properties for the first time is a big step forward in our study of the select club of icy dwarf planets."
Dwarf planets were officially recognised by the International Astronomical Union (IAU) in 2006 after a debate about the correct definition of a planet.
The IAU decided to demote Pluto to the status of dwarf planet, meaning that officially the Solar System now has eight "regular" planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Details of the Makemake research appeared in the latest issue of the journal Nature.
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