Within the Kuiper Belt—that ring of ices and volatile material beyond the orbit of Neptune—are all but one of the known dwarf planets in the solar system. Pluto is the largest of that class of planet, with Eris a close second. Next on that list is the plucky Makemake, a relatively reflective, distant, and dynamic world. From a distance of 4.26 billion miles, much about Makemake remains a mystery, though scientists are chipping away at the unknowns. Here are a few things they know—but you might not—about Makemake.
1. MAKEMAKE IS ONLY THREE TIMES AS LONG AS THE GRAND CANYON.
Makemake's orbit is a half-billion miles farther from the Sun than Pluto's. One day on the distant dwarf lasts nearly as long as ours does—22.5 hours—but the small world is in no rush to circle our star: One Makemakean year is 305 Earth years long. With a diameter of about 880 miles, the dwarf planet is about two-thirds the size of Pluto—and about three times the size of the 277-mile-long Grand Canyon—making it the 25th largest object in the solar system. That might not seem very impressive until you consider that there are hundreds of thousands of objects orbiting the Sun.
2. IT'S IMPRESSIVELY BRIGHT.
Despite being smaller than Pluto, Makemake is the second brightest object in the Kuiper Belt. Its reflective surface is a result of an abundance of methane and ethane ice present there; half-inch pellets of frozen methane may riddle its frigid surface. It's likely a reddish-brown hue, though its distance makes it hard to tell for sure.
3. IT WAS CALLED "EASTERBUNNY" …
Mike Brown of Caltech discovered Makemake a few days after Easter in 2005. (Brown also discovered the dwarf planets Eris and Haumea.) Before it received its formal name, Brown's team called it "Easterbunny." To other astronomers, its provisional name was "2005 FY9."
4. … BEFORE IT WAS OFFICIALLY NAMED AFTER AN EASTER ISLAND GOD.
In 2008, Easterbunny/2005 FY9 was designated a dwarf planet by the International Astronomical Union (IAU). When deciding what name to submit to the IAU, the proximal holiday led Brown to its namesake island (itself first visited by a European around Easter 1722), which led Brown to its people and their religious heritage. Makemake is the creator god of the Rapa Nui people of Easter Island.
5. MAKEMAKE IS PARTIALLY TO BLAME FOR PLUTO'S DEMOTION TO DWARF PLANET.
The discovery of Makemake and, just a few months before, Eris—which is larger than Pluto—forced astronomers to reconsider what, exactly, makes a planet a planet. A planet has to orbit the Sun, have enough mass that its gravity forces it into a round shape, and clear its immediate space neighborhood of other objects. Eris, Makemake, Pluto, and Haumea fail to meet all three criteria in one way or another. (Pluto's downfall: It doesn't clear its neighborhood.) After fierce debate among astronomers around the world, the IAU created the new category of "dwarf planet" for these objects—including Pluto. (Thanks, Makemake.)
6. MAKEMAKE'S SURFACE IS VOLATILE.
Makemake is no mere round rock in space. In many ways, it's a sibling of Pluto. Its surface, for example, is dominated by methane, a hyper-volatile compound that is also found on Pluto's surface. ("Volatile" means it reacts to changes in temperature.) "The processes on Pluto are driven by the movement of volatiles around the surface as temperatures change," says Alex Parker, a senior research scientist at the Southwest Research Institute in Boulder, Colorado. "If a world has a volatile-dominated surface—like Makemake does—it probably has dynamic processes on it similar to Pluto."
7. ITS MOON WAS ONLY RECENTLY DISCOVERED.
In the illustration above, Makemake has no moon. That's because it was only discovered in 2016 by Parker [PDF], who spotted it in data collected by the Hubble Space Telescope. "It was actually a very obvious satellite," he tells Mental Floss. "I didn't have to do too much digging into the data to get it to pop out; it just sort of stood out clear as day."
He continues: "As soon as I found it, I was also crestfallen, because I was sure other people who had done the preliminary analysis of the data would have almost certainly seen it—and that I would have been late to the party. My first question to the principal investigator of the program was, 'Hey, have you seen the moon in the Makemake data?' And I was sure the answer was going to be, 'Yes.' But it was, 'There's a moon in the Makemake data?' It was super exciting realizing that thing I was sure other people had spotted hadn't been and that I was the first to see it."
The moon's current official designation is S/2015 (136472), and it's nicknamed MK 2. More than 1300 times fainter than Makemake, it's estimated to be a mere 100 miles wide.
8. ASTRONOMERS ARE TRYING TO MAP MAKEMAKE WITH ITS MOON.
Makemake's moon is more than a celestial feature; it's a tool for scientists. As the 105-mile-wide object (nearly twice as long as the Panama Canal) and its planet pass in front of one another, astronomers can use the changes in brightness to map the Makemakean surface. "Just like we had preliminary maps of Pluto before we got there, we can actually use the moon as it passes in front of Makemake as a tool to map it," says Parker.
Specifically, as one object crosses the other, parts of the obscured object can be isolated. Astronomers can then derive the brightness of just the isolated part of the body (rather the whole body at once). Darker areas and lighter areas can then be mapped to the object, and models can help determine whether scientists are seeing terrain features, for example. They're not going to be naming mountains with this technique, but they can find interesting areas worth further study and modeling.
"There are many ways you can think of Makemake as a sort of Pluto prior to the New Horizons exploration. We are just starting to get glimpses of what it looks like," Parker says. "It could be this dynamic and active world, and I think that's exciting."
9. MUCH OF MAKEMAKE REMAINS MYSTERIOUS.
Scientists aren't sure how Makemake's day-night cycle influences its landforms and surface processes (which include things like geology or interactions between the atmosphere—if it has one—and the surface). The history and origin of its moon are also unknown, and raise other interesting questions for scientists. Theorists who work on planetary formation, and astronomers who study the motions of celestial objects, are revising their models to account for why moons are a defining feature for dwarf planets—including the weird ones—when half of the terrestrial planets in the solar system (Mercury and Venus) lack moons.
"Why are moons so ubiquitous among dwarf planets in the Kuiper Belt? At this point, every one of the largest objects in the Kuiper Belt [except one] has at least one moon," Parker says. "Some have two. Some have five. And so if you come up with a process for growing these planets [like accretion] ... one of the end states of that process needs to be that they all end up with at least one moon."
10. THERE ARE NO PLANS TO VISIT MAKEMAKE … YET.
No missions have yet been launched to Makemake, though the New Horizons spacecraft, having completed its reconnaissance of Pluto, has plunged deeper into the Kuiper Belt to study at least one other object there. Back on Earth, planetary scientists are considering frameworks for future Kuiper Belt missions. The development of new propulsion technologies by engineers will enable more science in single expeditions. In the longer term, orbiter missions will return to visited bodies and study them in finer detail. "Given how much variety there is in the Kuiper Belt," Parker says, "it's going to be a pretty exciting time as we shed light on these worlds."