Icy world reveals its secrets
Cool world Astronomers have for the first time confirmed that the distant frozen dwarf planet Makemake doesn't have an atmosphere.
The new observations came thanks to a rare stellar occultation as the tiny world passed in front of a faint star, allowing scientists to look for an atmosphere and determine its size.
Astronomers, led by Jose Luis Ortiz from the Instituto de Astrofisica de Andalucia, in Spain pointed an array of telescopes at the dwarf planet during the occultation, looking for a drop in light from the distant star.
Previous observations indicated Makemake was about two-thirds the size of Pluto and may have a tenuous seasonal atmosphere that collapses to the surface as it moves away from the Sun. If it did, light from a distant star would slowly fade and brighten as it passed through the dwarf planet's atmosphere.
But as Makemake passed in front of NOMAD 1181-0235723 on 23 April 2011, the light disappeared and reappeared abruptly.
"This means the little dwarf planet has no significant atmosphere," says Ortiz.
Up in the air
However, astronomer Dr Michael Ireland of Macquarie University in Sydney says debate on Makemake's atmosphere is not over yet.
"It's on a highly elliptical 300-year orbit and so its temperature goes up and down depending on its distance from the Sun," says Ireland.
"When it's closer to the Sun, in 150 years' time, some of these surface ices could sublimate into a tenuous atmosphere."
Makemake's orbit takes it between 38 and 53 times further away from the Sun than Earth.
The new observations reported in the journal Nature, also allowed Ortiz and colleagues to determine its size and density more accurately, indicating it looks like a sphere flattened slightly at both poles with axes of 1430 by 1502 kilometres.
They were also able to measure how much of the Sun's light Makemake's surface reflects, a quantity called albedo, which provides clues about the planet's likely surface composition.
Makemake's albedo is about 0.77 which is comparable to that of dirty snow, making it higher than Pluto, but lower than Eris, the largest dwarf planet in the solar system.
Makemake is one of five bodies including Pluto which have been classified as dwarf planets by the International Astronomical Union.
It's named after the creator of humanity and god of fertility in the culture of the native people of Easter Island.