Makemake Reveals Its Secrets

European astronomers have used ESO’s Very Large Telescope, the New Technology Telescope, and TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope, to check for the first time whether one of the largest objects known in the outer Solar System – the dwarf planet Makemake (pronounced MAH-keh MAH-keh) – is surrounded by an atmosphere.

This is an artist’s impression of the dwarf planet Makemake, one of the largest objects known in the outer Solar System. It was discovered in 2005 by a team from the California Institute of Technology led by Dr Mike Brown (IAU / M. Kornmesser / ESA / Hubble)

Makemake, formerly known as 2005 FY9, is about two thirds of the size of Pluto, and 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. The word Makemake is Polynesian in origin and is the name of the creator of humanity and the god of fertility in the mythology of the South Pacific island of Rapa Nui or the Easter Island.

The astronomers, led by Dr José Luis Ortiz of the Instituto de Astrofísica de Andalucía, Spain, have combined multiple observations using ESO’s telescopes with data from other small telescopes in South America, to look at Makemake as it passed in front of a distant star.

The results, published in a paper in the journal Nature (ESO’s version), show that this dwarf planet 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,” Dr José Luis Ortiz said.

“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 indicate that Makemake has a density of 1.7 ± 0.3 grams per cubic centimeter, which in turn allowed the team to infer the shape and appearance of an oblate spheroid – a sphere flattened slightly at both poles – with axes of 1430 and 1502 km (889 and 933 miles). The astronomers also measured how much of the Sun’s light Makemake’s surface reflects – its albedo. At about 0.77, Makemake’s albedo 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 and the successful observation by a coordinated observing team, scattered at many sites across South America, ranks as a major achievement.

“Pluto, Eris and Makemake are among the larger examples of the numerous icy bodies orbiting far away from our Sun,” Dr José Luis Ortiz concluded. “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.”

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Bibliographic information: Ortiz JL et al. 2012. Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation. Nature 491, 566–569; doi: 10.1038/nature11597