Because we are different.

Dwarf planet lacks atmosphere

22 November 2012

LONDON, 22 NOV: Astronomers have discovered that a distant dwarf planet, about two-thirds the size of Pluto, lacks atmosphere.

The planet 'Makemake' travels around the Sun in a distant path that lies beyond that of Pluto but closer to the Sun than Eris, the most massive known dwarf planet in the Solar System.

Previous observations of chilly Makemake have shown it to be similar to its fellow dwarf planets, leading some astronomers to expect its atmosphere, if present, to be similar to that of Pluto.

But astronomers led by Jose Luis Ortiz (Instituto de Astrofisica de Andalucia, CSIC, Spain) in a new study have found that like Eris, Makemake is not surrounded by a significant atmosphere. “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,” said Jose Luis Ortiz.

The team's new observations add much more detail to the view of Makemake ~ determining its size more accurately, putting constraints on a possible atmosphere and estimating the dwarf planet's density for the first time.

They have also allowed the astronomers to measure how much of the Sun's light Makemake's surface reflects ~ its albedo.

Makemake's albedo, at about 0.77, is comparable to that of dirty snow, higher than that of Pluto, but lower than that of Eris. It was only possible to observe Makemake in such detail because it passed in front of a star ~ an event known as a stellar occultation.

Occultations are particularly uncommon in the case of Makemake, because it moves in an area of the sky with relatively few stars. Accurately predicting and detecting these rare events is extremely difficult.

Makemake is one of five dwarf planets so far recognised by the International Astronomical Union. The others are Ceres, Pluto, Haumea and Eris.