The dwarf planet Makemake is not as lonely as first thought. Under the constant stare of NASA’s Hubble Space Telescope, a dark moon has been spotted orbiting Makemake, which is the second-brightest object in the distant Kuiper Belt beyond Neptune.
The moon, temporarily named S/2015 (136472) 1 (nicknamed MK 2) and is only 100 miles (160 kilometers) in diameter, has evaded detection for over a decade by hiding in the glare of its parent planet. The new-found satellite is the first to be spotted around Makemake, and is 1,300 times fainter than the dwarf planet.
MK 2 is around 13,000 miles from the dwarf planet, and was spotted after scientists aimed the Hubble’s Wide Field Camera 3 at Makemake for over two hours in April 2015. During this time they discovered a faint point of light moving through the sky along with the icy world.
The Kuiper Belt is home to several dwarf planets, and has a massive amount of leftover frozen material from the construction of our solar system 4.5 billion years ago. Some of these planets are known to have satellites; however it’s the first discovery of a companion object to Makemake.
Makemake orbits the sun once every 310 Earth-years, and is one of five dwarf planets that is recognized by the International Astronomical Union. Astronomers where able to pick out the moon from Makemake’s glare by using Hubble’s sharp resolution and its exceptional ability to see faint objects near bright ones.
The team used the same technique that is used for finding the small satellites of Pluto in 2005, 2011, and 2012, even though several previous searches of Makemake had turned up empty. Alex Parker of Southwest Research Institute, Boulder, Colorado, who led the image analysis for the observations, said in a statement:
“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.”
A moon’s discovery can provide valuable information on the dwarf-planet system. By measuring the moon’s orbit, astronomers can calculate a mass for the system and gain insight into its evolution. Uncovering the moon also reinforces the idea that most dwarf planets have satellites, according to NASA. Parker added that:
“Makemake is in the class of rare Pluto-like objects, so finding a companion is important.
“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.”
MK2 orbiting around Makemake may also solve one of the most enduring mysteries about the icy dwarf planet. When Makemake was first observed scientists noted how the planet was almost entirely bright and very cold, however, some areas appear warmer than other areas.
This discrepancy suggested that there was at least one warm, dark patch that may be present on Makemake’s surface. But years of observations failed to resolve this question, as the dark patch never actually showed up in observations.
Based on the new observations, the team suggests that much of the warmer surface detected previously in infrared light may have simply been the dark surface of the companion MK 2 (Makemake is about 1,300 times brighter than MK2).
Although there are several possibilities that could explain why MK2 has a charcoal-black surface, even though it orbits a dwarf planet that’s as bright as fresh snow, one idea calls into question its size. MK 2 is small enough that it may not be able to gravitationally hold onto a bright, icy crust, this would cause it to change from a solid to gas, under sunlight.
Learn more about the discovery with NASA Goddard: