Why this rare asteroid was ‘exiled’ from our solar system

On the edge of our solar system is a cold, dark region containing asteroids, comets and icy objects, called the Kuiper Belt. It’s also the home of oddities called Kuiper Belt Objects.

These KBOs present many challenges for astronomers because they’re usually harder to study, existing in a particularly dark part of the solar system that the sun doesn’t touch.

When KBO 2004 EW95 was first observed by the Hubble Space Telescope, astronomers thought it was unusual. The data from spectroscopic observations were puzzling, because they didn’t match up with other known icy KBOs. And no matter what method they used to study it, 2004 EW95 ended up being an “outlier.”

Researchers at Queen’s University in Belfast decided it was enough of a “weirdo” to study further using new methods. A study published Wednesday in the Astrophysical Journal Letters details their intriguing findings about 2004 EW95’s origin.

The researchers painstakingly used multiple instruments at the European Southern Observatory’s Very Large Telescope in Chile to measure the object’s composition. Because the KBO was moving and incredibly faint, they compared it to looking at a giant mountain of coal against a pitch-black canvas.
The object is 186 miles across, but it’s also 2,485,484,768 miles from Earth.

The first of its kind

What researchers discovered is that 2004 EW95 is exactly what they thought: an outlier. It is the first carbon-rich asteroid to be found in the Kuiper Belt and was confirmed by multiple datasets. This means, in contrast with KBOs that are icy, 2004 EW95 is a rocky object.

This finding is important because it supports a theory about our solar system in its earliest days, called the Grand Tack hypothesis. The theory suggests that the gas giant planets Jupiter, Saturn, Uranus and Neptune formed close together in our solar system. When they began to move apart, their powerful orbits flung other leftovers and relics from planet formation to the edge of the solar system.

2004 EW95 is one of these relics originally from the asteroid belt between Mars and Jupiter. Though the asteroid is currently minus 391 degrees Fahrenheit, it wasn’t always this cold and distant from the sun. Instead, it landed in the Kuiper Belt after being exiled from its home and flung billions of miles away.

“This is key evidence in favour of predictions made by dynamical theory on the formation and evolution of the Solar System, specifically that the planets have migrated since they formed and have disturbed the orbits of smaller bodies like 2004 EW95,” lead study author Tom Seccull, a postgraduate research student at Queen’s University Belfast in Northern Ireland, wrote in an email. “It appears that in many cases these small objects were pushed into the asteroid belt, while a few like 2004 EW95 were thrown out into the outer Solar System.”

One of the more intriguing findings about 2004 EW95 is the presence of ferric oxides and minerals called phyllosilicates.

“Neither of these materials have ever been confirmed to exist on an object in the outer Solar System before,” Seccull said. “They are commonly observed on objects that orbit the Sun between Mars and Jupiter, not objects that orbit the Sun beyond Neptune more than 10 times further away.”

The astronomers were interested in the phyllosilicates because they indicate that the rocks on 2004 EW95 have been altered by the presence of liquid water, Seccull said. Its current temperature is definitely too cold for liquid water to exist on its surface. So it must have been hotter at some point, possibly because it was much closer to the Sun than it is today, Seccull said.

But what does the discovery of one carbonaceous asteroid tell us?

“The confirmation of a fundamental aspect of the Grand Tack model is a crucial step towards our understanding of how the Solar System was assembled,” study co-author Thomas Puzia, a professor at the Pontificia Universidad Catolica’s Institute of Astrophysics, wrote in an email. “It also shines light on the early formation epochs and possible mechanisms responsible for making and distributing all the objects in the Solar System we observe today, like the main planets, dwarf planets and asteroids.”

Why now?

When NASA’s New Horizon’s probe flew past the Pluto system in 2015, it didn’t detect any rocky material. Wesley Fraser, who used the Hubble Space Telescope to observe 2004 EW95 in the past, was quoted as blurting out “crap” in front of a laughing audience at a meeting when the New Horizons results were being announced, he said.

“It was surprising, and disappointing to find out that even New Horizons didn’t detect the signatures of rocky materials on the surface of Pluto,” Fraser, study co-author and lecturer at Queen’s University Belfast, wrote in an email. “So the discovery of silicates on EW95 will be very valuable in informing us about the non-icy materials present on and inside Kuiper Belt Objects. Even ones that seem to have originated in the Kuiper Belt.”

he researchers’ work discovered something that the probe could not, proving that different methods of discovery are crucial.

“I expect (and am sure hoping) that this discovery will open the flood gates,” Fraser said. “We’ve demonstrated that the discovery of new materials requires spectral data of an exquisite quality, not commonly acquired by the community. Now that we and others realize this though, we anticipate the discovery of other materials, such as organics and other silicates on other bodies. It just requires really good data, and really careful extractions!”

The researchers hope to answer new questions raised by 2004 EW95, like how many rocky bodies are in the Kuiper Belt and where they came from.

Puzia compares their method of discovering what’s in the Kuiper Belt to “dipping a finger in soup and tasting if it has the right amount of ingredients — only this time we have the soup, and we are trying to match the right recipe.”
As Secull noted, “The discovery of a new and interesting KBO like 2004 EW95 shows that there is still much we don’t know about the Kuiper Belt and there are likely other interesting new secrets to uncover about this distant part of the Solar System.”

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