Astronomers Find First Carbon-Rich Asteroid in Kuiper Belt: 2004 EW95
An international team of astronomers has found that a small Kuiper Belt object called 2004 EW95 is a carbonaceous (carbon-rich) asteroid — the first of its kind to be confirmed in the Kuiper Belt, a distant region of icy debris that extends far beyond the orbit of Neptune.
This artist’s impression shows 2004 EW95, the first carbon-rich asteroid confirmed to exist in the Kuiper Belt and a relic of the primordial Solar System. 2004 EW95 likely formed in the main asteroid belt and has been flung billions of miles from its origin to its current home in the Kuiper Belt. Image credit: M. Kornmesser / ESO.
Models of the Solar System’s dynamical evolution predict that after gas-giant planets formed they rampaged through the system, ejecting small rocky bodies from the inner system to far-flung orbits at great distances from the Sun.
In particular, these models suggest that the Kuiper Belt should contain a small fraction of rocky bodies from the inner Solar System, such as carbonaceous asteroids.
The peculiar nature of the carbonaceous asteroid 2004 EW95 first came to light during routine observations with the NASA/ESA Hubble Space Telescope by Queen’s University Belfast astronomer Dr. Wesley Fraser.
The asteroid’s reflectance spectrum — the specific pattern of wavelengths of light reflected from an object — was different to that of similar small Kuiper Belt objects, which typically have uninteresting, featureless spectra that reveal little information about their composition.
“The reflectance spectrum of 2004 EW95 was clearly distinct from the other observed outer Solar System objects. It looked enough of a weirdo for us to take a closer look,” said Tom Seccull, a postgraduate research student at Queen’s University Belfast.
Dr. Fraser, Seccull and their colleagues observed 2004 EW95 with the X-Shooter and FORS2 instruments on ESO’s Very Large Telescope (VLT).
The sensitivity of these spectrographs allowed the team to obtain more detailed measurements of the pattern of light reflected from the asteroid and thus infer its composition.
However, even with the impressive light-collecting power of the VLT, 2004 EW95 was still difficult to observe.
Though the object is 186 miles (300 km) across, it is currently a colossal 2.5 billion miles (4 billion km) from Earth, making gathering data from its dark, carbon-rich surface a demanding scientific challenge.
“It’s like observing a giant mountain of coal against the pitch-black canvas of the night sky,” said team member Dr. Thomas Puzia, from the Pontificia Universidad Católica de Chile.
“Not only is 2004 EW95 moving, it’s also very faint. We had to use a pretty advanced data processing technique to get as much out of the data as possible,” Seccull said.
Two features of the object’s spectra were particularly eye-catching and corresponded to the presence of ferric oxides and phyllosilicates.
The presence of these materials had never before been confirmed in a Kuiper Belt object, and they strongly suggest that 2004 EW95 formed in the inner Solar System.
“Given 2004 EW95’s present-day abode in the icy outer reaches of the Solar System, this implies that it has been flung out into its present orbit by a migratory planet in the early days of the Solar System,” Seccull said.
A paper reporting this discovery is published in the Astrophysical Journal Letters (arXiv.org preprint).
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Tom Seccull et al. 2018. 2004 EW95: A Phyllosilicate-bearing Carbonaceous Asteroid in the Kuiper Belt. ApJL 855, L26; doi: 10.3847/2041-8213/aab3dc