Far Beyond Pluto, Hubble Discovered A Little Moon Around Icy Neighbor Makemake

Deep in space, in the farthest stretches of our solar system, lies an icy dwarf planet called Makemake. Until now, scientists believed it was all alone out there in the Kuiper Belt, but the Hubble telescope has discovered a little moon around it.

As Slate’s resident astronomer Phil Plait put it, the fact that a tiny moon was discovered orbiting around a distant icy body may not seem like a big deal — but it is.

“Finding a moon like this gives precious insight into what the outskirts of our celestial neighborhood are like, a region that is terribly far away and dark, and very difficult to explore. Each discovery about it is a clue to how it came to be, how it changed over time, and why it looks the way it does now. All of this tells us more about our existence, and informs us about our own world.”

The object Hubble discovered, while still cloaked in mystery itself, could reveal some of Makemake’s enduring secrets, including about what it’s made of and its density, Space.com added.

Makemake (pronounced MAH-kay-mah-kay) is named after a Rapa Nui god that created humanity; the Rapa Nui are the folks who lived on Easter Island, CNN explained. It lives in the Kuiper Belt, which is full of comets and frozen rocks and orbits the sun beyond Neptune. It’s one of five objects that’s recognized to be a dwarf planet, defined as an object that orbits the sun and has been forced into the shape of a sphere by its own gravity but hasn’t “cleared its neighborhood” of other “orbiting material.” Its fellows are Pluto, Eris, Haumea, and Ceres.

It’s a little thing at about 870 miles in diameter, which is a tenth the size of the Earth. That size, however, makes it the biggest Kuiper Belt Object, or KBO. Only Pluto and Eris are bigger. It takes almost eight hours to rotate, seems to have a reflective surface, contains tons of frozen methane, and its orbit is elliptical. It completes a turn around the Sun in 309 Earth years.

And until now, scientists discovered nothing in its immediate neighborhood, although they observed it many times. The moon, nicknamed MK2, is so close it may have been lost in the icy planet’s glare; it’s also 1,300 times fainter. Astronomers also think that they’ve been seeing its orbit edge-on, meaning it’s too close to its planet to be discovered from Earth. It’s size also didn’t make it easy to see; it’s only 100 miles wide.

Since Hubble discovered MK2, scientists are most interested in its orbit, because that will help them piece together how it was formed. Since they didn’t observe it long enough as it went around the KBO, this is still an unsolved mystery.

If it has a tight, circular orbit it probably formed when Makemake and another KBO collided. If it’s wider and longer, it was likely sucked into the orbit around the object. Whichever version proves true, the event would’ve happened several billion years ago when our solar system was new.

“Makemake is in the class of rare Pluto-like objects, so finding a companion is important,” Alex Parker of the Southwest Research Institute (SwRI) in Boulder, Colorado, which helped make the discovery. “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 even more important for what it can tell scientists about Makemake. Observations of its space companion can help them calculate its density and determine if it and Pluto are similar. The range of the moon’s path around the sun can also reveal the planetary body’s mass and help them figure out what materials coat its surface.

[Photo by NASA/Getty Images]