We train our telescopes on the farthest reaches of the universe looking for mysteries. Yet, we still have a few in our own solar system. And astronomers just revealed one of them.

Far beyond Neptune lies the Kuiper Belt. This is where Pluto, the former ninth planet, calls home. Today, Pluto is classified as a dwarf planet along with three others – Eris, Haumea and Makemake. We all know Pluto has a series of moons. Eris has one moon. Haumea has two moons. But astronomers couldn’t find a moon around Makemake. Until now.

A team of astronomers harnessed the power of the Hubble Space Telescope to spot the small moon. Hubble’s Wide Field Camera 3 is great at teasing details of faint objects near bright ones. Because Makemake’s surface is frozen, it reflects most of the sunlight hitting it. It’s the second brightest dwarf planet (Pluto is first) in the Kuiper Belt.

Makemake and MK 2

Why wasn’t this moon found earlier? Alex Parker from the Southwest Research Institute explains. “Our preliminary estimates show that the moon’s orbit seems to be edge-on, and that means that often when you look at the system you are going to miss the moon because it gets lost in the bright glare of Makemake,” said Parker.

Finding the moon, designated S/2015 (136472) 1 and nicknamed MK 2, will open up the study of Makemake. Once astronomers have a better grip on the moon’s orbit, they can figure out the mass of the system and how it may have evolved. Additional Hubble observations will determine if MK 2 is in a circular or elliptical orbit. And the answer will drastically change the perception of how Makemake and its moon came to be.

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If MK 2’s orbit is circular, then the moon likely came from a collision between the dwarf planet and another Kuiper Belt Object. A more elliptical orbit suggests MK 2 was a Kuiper Belt object captured by Makemake. If it is a circular orbit, preliminary estimates say it takes 12 days (or longer) to complete one orbit around the dwarf planet.

The discovery of MK 2 may also answer a head scratcher for astronomers about Makemake’s surface. Infrared studies of the dwarf planet in the past showed what appeared to be dark, warmer areas on the surface. But one thing always puzzled researchers. The dwarf planet’s brightness didn’t vary as it rotated on its axis. Dark patches would have rotated out of view causing the brightness to change.

It turns out the infrared data was probably showing MK 2. It just didn’t have the resolution to separate the two.

Why would MK 2 be so much darker than Makemake? One theory is the moon is small enough that it can’t gravitationally retain a bright, icy crust.

With one question answered, much of the Kuiper Belt remains a mystery. The New Horizons team (Pluto probe) submitted their mission extension to NASA earlier this month. If approved, the spacecraft will venture deeper into this area and observe as many as 20 objects.

Unfortunately, New Horizons won’t be anywhere near Makemake.

New Horizons path to Kuiper Belt

Image via NASA/JHUAPL/SwRI

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