Astronomers Have Discovered a Moon Hiding Deep in Our Solar System

April 27, 2016 | Joanne Kennell

Artist's impression of Makemake's dark moon
Photo credit: NASA/Goddard/Katrina Jackson

This moon has been obscured for more than 10 years.

There is a dwarf planet, named Makemake (pronounced MAH-keh MAH-keh), located about 4.6 billion miles (6.85 billion kilometers) from the sun — way out past Pluto in the Kuiper Belt — that has been keeping a secret from us for more than a decade.

It turns out Makemake, which orbits the sun once every 310 Earth-years, has a dark little moon that is just 100 miles (161 kilometers) across.

So how did the moon avoid detection for so long?

SEE ALSO: Pluto Has Gorgeous Blue Skies and Flowing Water Ice

The newly discovered moon, temporarily nicknamed "S/2015 (136472) 1," or "MK 2" for short, was able to remain hidden for so long because it is incredibly dark — more than 1,300 times fainter than its host planet. The moon reflects just a teeny-tiny amount of light so it was difficult to spot next to the glare of Makemake, which is the second brightest icy dwarf planet (Pluto is the brightest).

However, when scientists aimed the Hubble Space Telescope at Makemake for more than two hours in April of last year, they discovered a faint point of light moving through the sky along with the icy planet. In fact, Makemake was previously thought to be the only officially recognized distant dwarf planet without a moon — a distinction it has now lost.

Astronomer Alex Parker, from the Southwest Research Institute in Texas, was rummaging through the data when he spotted a faint point of light moving around Makemake about 13,000 miles (20,900 kilometers) away. However, he wasn’t sure if what he had spotted was new.

"I was sure someone had seen it already," Parker told National Geographic. He asked fellow researcher Marc Buie about it, who responded, "There's a moon in the Makemake data?"

"It was at that point that everything got exciting and kicked into high gear," said Parker. In the Hubble image below, you can see a little dot of light — that’s the moon.

Hubble imagery of Makemake's dark moon

Photo credit: NASA/ESA/A. Parker and M. Buie

The Kuiper belt, which is located beyond Pluto and contains a massive amount of frozen material left over from the formation of our solar system, is where Makemake and its moon are located. However, scientists do not understand much about these icy worlds so researchers want to use Hubble to study and determine the orbit of MK2 in order to find out more about the composition and density of Makemake.

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

One of the biggest mysteries regarding Makemake is why it appears to have different patches of dark and bright material reflective across it. And since the planet spins once every 7.7 hours, the planet’s brightness should change, but it doesn’t. However, that could be because previous infrared data was picking up MK2, not just Makemake.

Although New Horizons team members have officially submitted an extended-mission proposal for the probe, named the “Kuiper Belt Extended Mission,” which involves arriving in late September 2018 to MU69  — a Kuiper belt object that orbits beyond Neptune — Parker is hoping NASA will allow New Horizons to swing by Makemake on its way out of the solar system to take a gander.

I wonder what else is hiding in our solar system.

The research has been submitted for peer review, and is now published on the website arXiv.org.

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