The origins of a dwarf planet that lurks on the outskirts of the solar system and has become one of its strangest objects have perhaps been revealed by NASA scientists.
Dirty is about the size of another dwarf planet Pluto and is located in the Kuiper is calling, a collection of icy debris and cometary bodies beyond Neptune’s orbit – the solar systemthe most distant planet.
Haumea is notable for spinning 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 led Haumea to develop a shape that resembles a deflated soccer ball rather than a sphere. However, its shape isn’t the only unusual thing about this dwarf planet.
A strange mystery of ice
Haumea also has a surface that is mostly made of a kind of water ice unlike most other Kuiper Belt bodies.
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 led scientists to conclude that Haumea and these icy bodies share the same origin and are the only “family” of related objects found in the Kuiper Belt – the “Haumean family”.
Using computer simulations, NASA scientists including Goddard Space Flight Center in Greenbelt, Maryland, post-doctoral student Jessica Noviello investigated the question “How did something as strange as Haumea and her family happen?”
Computer simulations are needed to achieve this because the dwarf planet is too distant to be accurately measured using a terrestrial telescope, and Haumea has yet to be visited by a space mission.
These simulations allowed the team to “take apart” Haumea and then rebuild it from scratch. The goal was to understand the chemical and physical processes that shaped the dwarf planet.
“Explaining what happened to Haumea forces us to put time limits on all of these things that happened when the solar system formed, so it starts to connect everything through the solar system,” member of the team and Arizona State University at Tempe professor of astrophysics, Steve Desch said in a statement. “There are a lot of weird and ‘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 entering only three data elements on Haumea; its estimated size, estimated mass, and short “day” of four hours.
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, Noviello was able to determine how the mass of the dwarf planet is distributed and how this distribution influenced its rotation. From there, the researcher set about simulating billions of years of evolution for Haumea in search of the right set of features that would result in the dwarf planet astronomers observe today.
“We wanted to fundamentally understand Haumea before going back in time,” Noviello said.
Haumea Family Values
The team speculated that baby Haumea was about 3% larger than its current height, with this difference explaining the creation of its Kuiper Belt siblings.
Scientists also assumed that the young dwarf planet rotated at a different speed and had a larger volume than today.
Altering Haumea’s features in the models they developed allowed the team to run dozens of simulations showing how small changes like the dwarf planet’s size increasing or decreasing changed its evolution.
Arriving at a model that provided a simulated Haumea, just as astronomers observe today, told the team that they had found the correct early features and current evolutionary path of the Kuiper Belt dwarf planet.
Modeling by Noviello and his colleagues revealed that in its early years and at a time in the solar system marked by chaotic conditions, Haumea collided with another body in a powerful impact.
This resulted in pieces breaking away from young Haumea, but these fragments did not become the Haumean family’s heirlooms. Indeed, such a large impact would have thrown the pieces into much more dispersed orbits than those possessed by the bodies of the Haumean family.
Desch said the objects that make up the Haumean family would likely have formed later in the dwarf planet’s existence as its structure developed. In this last period of its evolution, dense rocky material flowed towards the center of the dwarf planet while ice of lighter density rose to its surface.
“When you focus all the mass towards the axis, it decreases the moment of inertia, so Haumea ended up spinning even faster than it does today,” Desch said. This would result in rotational speeds fast enough to throw off the surface ice that became the Haumean family.
This moment of inertia would have increased further, decreasing the rotational speed of the dwarf planet due to the radioactivity of Haumea’s melting surface ice rocks. This water soaking in the center of the dwarf planet caused the rocky material to swell into a large but less dense clay core.
The team’s research has been published in the Planetary Science Journal on September 29.
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