Meet Haumea, the strangest dwarf planet of them all

The Kuiper Belt, the donut-shaped ring of icy bodies that stretches far beyond Neptune’s orbit, is home to some of the strangest objects in our solar system. Inside this icy region, there are trillions of comets, asteroids, and heavenly remnants leftover from the earliest days of our solar system, some of which many humans may already be familiar with, like Pluto, Eris, and Makemake

Yet one of its most interesting oddities is the dwarf planet, Haumea.

Though it was discovered less than two decades ago, information about the dwarf planet is sparse as Earth-based telescopes have a hard time making precise measurements because of how distant it is. But the little we do know about Haumea suggests that it is an extremely strange and important entity. Shaped almost like a deflated football, the planet spins faster than anything else of its size, whirling on its axis in only four hours. Besides having two moons, Haumea also has a very faint ring system and is covered almost exclusively in crystalline water ice, making it an excellent candidate to investigate whether it might have once hosted life. 

“From an astrobiological perspective, there are a lot of things we don’t yet know about how life got started, even on Earth, and we live here,” says Jessica Noviello, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re still trying to figure out exactly what kinds of ingredients need to go into creating life in the first place, and we know that one of the most important is water.”

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Another reason researchers are so interested in learning more about Haumea is because it’s the largest of a dozen “sibling” water-rich objects that appear to have similar orbits to each other. To date, it’s the only such “family” system in the Kuiper Belt, but scientists like Noviello say one of the area’s biggest mysteries is how this unique system came together—including its intriguing configuration. 

To try and piece together a sharper picture of the planet’s origins and evolution, Noviello and a team of researchers used computer simulations to model billions of years of its past history to see what kind of conditions may have led a “baby Haumea” to the system’s mature modern-day incarnation.

By plugging Haumea’s estimated size, mass, and rotational rate into their model, the researchers were able to use these simulations to break the planet down and build it up from scratch to investigate many of the chemical and physical processes that helped its development. Once they had all three of these aspects, they calculated the object’s angular momentum (its ability to continue to spin) throughout history with the assumption that it stayed constant. After running dozens of simulations filled with different variables and small changes to test how each variable would affect its evolution, they came up with a few results that seemed to be on the right track. 

“One of the leading ideas is that these family members were knocked off by a big collision,” says Steven Desch, a professor of earth and space exploration at Arizona State University. If pieces of Haumea were bumped due to some clumsy meet-cute with another object, there would be considerably more fragments, and many of them would have differences in their orbits. But that isn’t the case, Desch notes. Instead, their models posit that when planets were still forming, Haumea did collide with another object, but the pieces that flew off back then are not what’s seen in today’s Haumean family, as other researchers have suggested. 

The family instead came much later, when the planet’s dense rocky structure settled in the center and became its core, while lighter density ice rose to its outer layers. “The effect of having all that water percolate through the core and react with rock and turn dense rock into a less dense clay is it swells up the core,” says Desch. In effect, some of the mass on the outside of Haumea was flung off, and those pieces created the Haumean family scientists study today. 

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Their model was also able to make predictions about the amount of ice on Haumea, as well as the planet’s volume. With the help of another code called IcyDwarf, researchers even concluded that at one point Haumea was warm enough to sustain a liquid water ocean in its interior for about 250 million years. Though that ocean has since frozen over, Noviello says it’s invaluable discovering what the origins of another planet might have looked like, if only to help humans discover more icy and ocean worlds in the future. 

“Knowing about the diversity of ocean worlds and their potential for life in the solar system helps us put everything into context and focus on the best targets for more extensive observations for detecting any kind of bio signatures in the future,” she says. “On Mars, the phrase is to follow the water and it’s no different with exoplanets.”

Correction (October 20, 2022): This story has been updated to correct the amount of time the Haumea spins on its axis. One of the references of Jessica Noviello‘s name was previously misspelled. We regret the error.

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