The origins of a dwarf planet that lurks on the Solar System’s outer edge and has become one of its strangest objects may have been revealed by NASA scientists.
haumea is about the size of another dwarf planet Pluto and is located in the Kuiper belt, a collection of icy debris and comet bodies out past Neptune’s orbit – the solar system‘s outermost planet.
Haumea is notable because it spins faster than any other similarly sized object in the Solar System, completing one rotation around its axis — or one “day” — in just four hours.
This rapid rotation has led to Haumea developing a shape that more closely resembles a deflated soccer ball than a sphere. However, its shape is not the only unusual thing about this dwarf planet.
A strange ice secret
Haumea also has a finish that is mostly from a 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 appear to share the same orbit as the dwarf planet. This has led scientists to conclude that Haumea and these ice bodies share 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 have underneath Goddard Space Flight Center in Greenbelt, Maryland, postdoctoral researcher Jessica Novviello asked, “How did something as crazy as Haumea and his family come about?”
Computer simulations are needed to achieve this, as the dwarf planet is too far away to be accurately measured with a ground-based telescope and Haumea has yet to be visited by a space mission.
These simulations allowed the team to “disassemble” Haumea and then rebuild it from the ground up. The aim was to understand the chemical and physical processes that formed the dwarf planet.
“To explain what happened with Haumea, we have to time-limit all of these things that happened when the solar system was forming so that it starts to connect everything in the solar system together,” team member and professor of astrophysics at the Arizona State University at Tempe said Steve Desch in a expression. “Haumea has a lot of weird, ‘gee whiz’ parts, and trying to explain them all at once was a challenge.”
The model the team developed began by entering just three pieces of data about Haumea; its estimated size, mass, and short four-hour “day”.
This provided a revised prediction of the dwarf planet’s size and mass, as well as its density. It also provided a prediction of Haumea’s core size and density.
Using this information, Novviello was able to determine how the dwarf planet’s mass is distributed and how this distribution affected its spin. From here, the researcher set about simulating billions of years of evolution for Haumea, looking for the right features that would lead to the dwarf planet astronomers observe today.
“We wanted to understand Haumea fundamentally before looking back in time,” Noviello said.
Values of the Haumea family
The team estimated that the infant Haumea was about 3% taller than its current size, with this difference being responsible for the emergence of its Kuiper Belt siblings.
Scientists also assumed that the young dwarf planet rotated at a different speed and its volume was larger than today.
By changing the characteristics of Haumea in the models they developed, the team was able to run dozens of simulations to observe how small changes, such as the dwarf planet expanding or shrinking, altered its evolution.
Achieving a model that provided a simulated Haumea as astronomers observe today told the team they had hit the right early features and current evolutionary path for the Kuiper Belt dwarf planet.
Modeling by Noviello and her colleagues revealed that in its early years and during an epoch of the Solar System characterized by chaotic states, Haumea collided with another body with a violent impact.
This resulted in pieces breaking off from the young Haumea, but these fragments did not become objects of the Haumea family. This is because such a large impact would have sent the pieces into far more scattered orbits than the bodies of the Haumean family.
Desch said that the objects that make up the Haumean family likely formed later in the dwarf planet’s existence as its structure evolved. At this later stage of its evolution, dense, rocky material sank into the dwarf planet’s center while lighter ice rose to its surface.
“If you concentrate all the mass on the axis, the moment of inertia decreases, so Haumea ended up spinning even faster than it does today,” Desch said. This would result in rotation speeds fast enough to shed surface ice, which later became the Haumean family.
This moment of inertia would have increased further, reducing the dwarf planet’s rotation speed as a result of radioactivity from the rocks of Haumea’s melting surface ice. This water, seeping into the center of the dwarf planet, swelled rocky material there into a large but less dense clay core.
The team’s research was published in the Planetary Science Journal on Sept. 29.
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