Hubble Discovered a New Moon Hiding in Our Solar System

Video summary of Makemake moon discovery. Video: NASA Goddard/YouTube

Astronomers have been racking up so many exoplanet discoveries recently that it can be easy to overlook how many surprises are still hidden in our own solar backyard. Case in point: a moon has just been discovered orbiting the dwarf planet Makemake, which is the third largest object in the Kuiper belt, after Pluto and Eris. This "belt" of ice, asteroids, comets, and dwarf planets encircles the solar system starting at Neptune's orbit, and it remains one of the most mysterious and under-explored regions of the solar system.

Captured by the Hubble Space Telescope and described in a newly published study led by astronomer Alex Parker of the Southwest Research Institute, the new moon on the block has an estimated diameter of 100 miles, roughly one ninth the size of Makemake. Its formal name is S/2015 (136472) 1, but it goes by MK 2 for short.

"Makemake is in the class of rare Pluto-like objects, so finding a companion is important," Parker said in a NASA statement. "The discovery of this moon has given us an opportunity to study Makemake in far greater detail than we ever would have been able to without the companion."

Because the moon orbits its host world edge-on from our perspective on Earth, it was lost in Makemake's reflective glare up until this point. But with the help of Hubble's precision instruments, Parker and his colleagues able to identify the moon and pick out some basic details, including that MK 2 orbits Makemake once every 12 days at a distance of about 13,000 miles.

Fortunately, there should be a lot more data from this farflung planetary system on the way, including firmer specs on the moon's orbital geometry, which can provide clues about the origins of both worlds. For now, here's a warm Earth welcome to this tiny moon orbiting a dwarf world at the frontier of the solar system, and a pat on Hubble's proverbial back for finally singling it out.