Astronomers have discovered that a dwarf planet in our solar system named Makemake has no atmosphere. The object, which orbits in the outer solar system, was expected to have an atmosphere similar to another dwarf planet, Pluto, but new observations show that is not the case.

The new discovery was made when European Southern Observatory (ESO) astronomers in observatories in Chile observed Makemake drifting in front of a distant star. Astronomers used three different telescopes, including the Very Large Telescope (VLT), at the ESO’s Lasilla and Paranal sites to observe the occultation. A study based on the findings will be published this week in the journal Nature.

“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,” said Jose Luis Ortiz, who led the ESO team. “This means that the little dwarf planet has no significant atmosphere,” says José Luis Ortiz. “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.”

The new observations allowed astronomers to more accurately determine Makemake’s size, mass, density, and albedo – the amount of the Sun’s light an object’s surface reflects. Not much is accurately known about Makemake before now because of its distance and lack of moons. It orbits in an area of the sky that has few stars, making stellar occultations like the one observed by Ortiz and his team rare and difficult to predict.

Makemake was assumed to have an atmosphere because of its similarities to other dwarf planets. The object is two thirds the size of Pluto. It orbits the sun beyond the orbit of Pluto, but closer to the sun than the most massive dwarf planet, Eris, which is about 25% more massive than Pluto.

“Pluto, Eris and Makemake are among the larger examples of the numerous icy bodies orbiting far away from our Sun,” said Ortiz. “Our new observations have greatly improved our knowledge of one of the biggest, Makemake – we will be able to use this information as we explore the intriguing objects in this region of space further.”

(Illustration courtesy ESO)