Turns out there is something new under the Sun, at least to us; on Tuesday, April 26 scientists announced the discovery of a new moon in the Solar System—but it’s not around Earth, or Jupiter, or Saturn, or any of the planets that you’ve long been familiar with. This new moon is orbiting a distant world even farther away and smaller than Pluto: the dwarf planet Makemake (pronounced mah-kay mah-kay), located deep in the Kuiper Belt and currently over 52 times farther away from the Sun than we are.
Makemake itself was only discovered a little over a decade ago in observations from the Palomar Observatory on March 31, 2005 and announced to the public along with larger dwarf planet Eris on July 29 of the same year. It’s a relatively bright 870-mile-wide world coated, like its larger cousin Pluto, in methane and nitrogen ices. The reason it’s taken this long to identify the first satellite around it is that the moon — currently designated S/2015 (136472) 1 and nicknamed MK 2 — is 1,300 times dimmer than Makemake and only about 100 miles (160 km) across, and isn’t always in a convenient location to be spotted.
“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 Alex Parker of the Southwest Research Institute in Boulder, Colorado, who led the image analysis for the observations.
The telling images for the discovery of MK 2 were obtained with Hubble’s Wide Field Camera 3 in April 2015.
According to Alex on Twitter this discovery means all of the known Kuiper Belt dwarf planets — Pluto, Eris, Haumea, and now Makemake — have moons.
More follow-up observations with Hubble will be needed to determine the orbital characteristics of MK 2. At its distance from Makemake — about 13,000 miles, or 21,000 kilometers — if its orbit is circular it likely completes a single one at least every 12 days.
Learning the shape of MK 2’s orbit will also tell us how it was acquired; if its orbit is circular it’s likely the result of a collision, if highly elliptical or eccentric it’s probably a captured KBO.
By my count this discovery brings the total number of known natural satellites in the Solar System up to 464, including asteroids and trojans with moons (but not ring systems.) There’s 58 times more moons in the Solar System than there are official planets!
Watch a brief video about the discovery from NASA’s Goddard Space Flight Center below: