The dwarf planet Makemake (pronounced MAHkayMAHkay) is about 2/3 the diameter of Pluto, and farther from the Sun. That makes it hard to observe. Astronomers using a set of telescopes in South America tracked it during an occultation: a brief interval when it passed in front of a faint star. By measuring the light curve—the variation in light as Makemake eclipsed the star—the researchers determined that the dwarf planet has no substantial atmosphere, and probably no sizable moon.

Makemake potentially occults three stars in a typical year, though not all of these are useful, due to the faintness of the background star. The current study involved an occultation visible from South America on April 23, 2011. Just as eclipses may be partial or total, the “shadow” of Makemake passed over a swath of the continent, allowing telescopes in various locations to measure the passage of the star behind different parts of the dwarf planet. The researchers tried to obtain data from 16 telescopes, but only 7 of those returned successful measurements.

Each telescope saw a clear, sharp drop in the background star’s light, a strong indicator that Makemake has no substantial atmosphere. [Read more….]