The origin of a dwarf planet lurking at the outer edge of the solar system that has become one of its strangest objects may have been revealed by NASA scientists.
Haumea is about the same size as another dwarf planet Pluto and lies in Kuiper belt, a collection of icy debris and comet bodies out past Neptune’s orbit – the Solar systemoutermost planet.
Haumea is notable because it spins faster than any other solar system object of similar size, completing one rotation around its axis – or a “day” – in just four hours.
This rapid spin has resulted in Haumea developing a shape that resembles a deflated football rather than a sphere. However, its shape is not the only unusual thing about this dwarf planet.
A strange ice mystery
Haumea also has a surface ie mostly made of some kind of water ice unlike most other bodies in the Kuiper Belt.
This water-ice surface is shared by some of Haumea’s siblings who also seem to share the same orbit as the dwarf planet. This has led scientists to conclude that Haumea and these icy bodies have the same origin and that they form the only “family” of related objects found in the Kuiper Belt – the “Haumean family”.
Using computer simulations, NASA scientists included Goddard Space Flight Center in Greenbelt, Maryland, postdoctoral researcher Jessica Noviello investigated the question “How did something as strange as Haumea and its family come to be?”
Computer simulations are necessary to achieve this because the dwarf planet is too far away to be accurately measured by an Earth-based telescope, and Haumea has not yet been visited by a space mission.
These simulations allowed the team to “take apart” Haumea and then rebuild it from scratch. The purpose of this was to understand the chemical and physical processes that formed the dwarf planet.
“Explaining what happened to Haumea forces us to put time limits on all these things that happened when the solar system formed, so it starts to connect everything across the solar system,” team member and Arizona State University in Tempe professor of astrophysics Steve Desch said in a statement. “There are a lot of quirky, ‘gee whiz’ parts to Haumea, and trying to explain them all at once has been a challenge.”
The model developed by the team started with the input of just three pieces of data about Haumea; its estimated size, its estimated mass, and its short four-hour “day.”
This provided a revised prediction of the size and mass of the dwarf planet and its density. It also provided a prediction of Haumea’s core size and density.
Using this information, Noviello was able to determine how the dwarf planet’s mass is distributed and how that distribution has affected its spin. From here, the scientist began simulating billions of years of evolution for Haumea, looking for the right set of features that would result in the dwarf planet astronomers observe today.
“We wanted to understand Haumea fundamentally before going back in time,” Noviello said.
Haumea family values
The team hypothesized that the infant Haumea was about 3% larger than its current size, with this difference explaining the creation of its Kuiper Belt sibling.
The researchers also assumed that the young dwarf planet rotated at a different speed and that its volume was larger than it is today.
By changing the properties of Haumea in the models they developed, the team was able to run dozens of simulations and see how small changes like increasing or decreasing the size of the dwarf planet changed its evolution.
When we arrived at a model that delivered a simulated Haumea just as astronomers observe today, they told the team that they had hit on the right early characteristics and the current evolutionary path of the Kuiper Belt dwarf planet.
Noviello and her colleagues’ modeling revealed that Haumea, in its early years and during an epoch of the solar system characterized by chaotic conditions, collided with another body in a powerful impact.
This resulted in pieces breaking off from young Haumea, but these fragments did not go on to become Haumean family objects. This is because such a large impact would have knocked the pieces out into much more scattered trajectories than the Haumei family bodies possessed.
Desch said the objects that make up the Haumeian family would likely have formed later in the dwarf planet’s existence as its structure evolved. During this later period of its evolution, dense, rocky material sank to the dwarf planet’s center while lighter-density ice rose to its surface.
“When you concentrate all the mass towards the axis, it reduces the moment of inertia, so Haumea ended up spinning even faster than it does today,” Desch said. This would result in rotation rates fast enough to shed surface ice that went on to become the Haumeian family.
This moment of inertia would have further increased and decreased the dwarf planet’s spin rate as a result of radioactivity from the rocks of Haumea’s melting surface ice. This water that soaked into the center of the dwarf planet caused rocky material there to swell into a large but less dense clay core.
The team’s research was published in the Planetary Science Journal on September 29.
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