A newly discovered moon is seen orbiting the dwarf planet Makemake. (Hubblesite.org)
A newly discovered moon is seen orbiting the dwarf planet Makemake. (Hubblesite.org)

Astronomers have discovered a moon orbiting the dwarf planet Makemake. Makemake is the second brightest dwarf planet in the Kuiper Belt after Pluto.

Called S/2015 (136472) 1 and nicknamed MK 2, the moon was spotted in April of 2015 using the Hubble Space Telescope. Astronomers say the moon is about 21,000 kilometers from Makemake and is about 161 kilometers across.

The Kuiper Belt is believed to be made up of leftover material from the creation of the solar system about 4.5 billion years ago.

"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 study.

Makemake was discovered in 2005 and is named after a deity of the Rapa Nui people of Easter Island. It measures roughly 1,400 kilometers across. It is one of the five dwarf planets officially acknowledged by the International Astronomical Union.

"Makemake is in the class of rare Pluto-like objects, so finding a companion is important," Parker said. "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."

There is still much to learn about the moon. For example, whether its orbit is circular or elliptical.

Astronomers believe the moon orbits Makemake in a circle, making a “circuit’ every 12 days for more. If true, the moon was probably created by a collision of Makemake and another object. An elliptical orbit would point toward the moon being “captured” by Makemake’s gravity.

The moon could also help in understanding Makemake, for example why some parts of the dwarf planet appear warmer in some areas and colder in others. It may be caused by the dark surface on the moon.

Why the moon has a dark surface is also a mystery. One reason may be that it lacks enough gravity to allow ice to cling to the surface.