Meteoroid from Oort Cloud Was Made of Rock, Not Ice, Scientists Say

by johnsmith

This decimeter-sized (2 kg) rocky meteoroid entered the atmosphere of our planet about 100 km north of Edmonton, Alberta, Canada at 13:23:17 UTC on February 22, 2021. The object came from the Oort cloud, a reservoir of icy planetesimals and the source of long-period comets.

The February 2021 fireball captured by the Global Fireball Observatory camera at Miquelon Lake Provincial Park, Alberta, Canada. Image credit: University of Alberta.

Just at the edge of our Solar System and halfway to the nearest stars is a collection of icy objects sailing through space, known as the Oort cloud.

Passing stars sometimes nudge these icy travelers towards the Sun, and we see them as comets with long tails.

Scientists have yet to observe any objects in the Oort cloud directly, but everything detected so far coming from its direction has been made of ice.

Theoretically, the very basis of understanding our Solar System’s beginnings is built upon the foundation that only icy objects exist in these outer reaches and certainly, nothing made of rock.

This changed in February 2021 when astronomers captured images and videos of a rocky meteoroid that flew through the skies over central Alberta, Canada, as a dazzling fireball.

“This discovery supports an entirely different model of the formation of the Solar System, one which backs the idea that significant amounts of rocky material co-exist with icy objects within the Oort cloud,” said lead author Dr. Denis Vida, a meteor physicist in the Department of Physics and Astronomy at the University of Western Ontario.

“This result is not explained by the currently favored Solar System formation models. It’s a complete game changer.”

All previous rocky fireballs have arrived from much closer to Earth, making the February 2021 meteoroid — which clearly traveled vast distances — completely unexpected.

Dr. Vida and colleagues calculated it was traveling on an orbit usually reserved only for icy long-period comets from the Oort cloud.

“In 70 years of regular fireball observations, this is one of the most peculiar ever recorded,” said Dr. Hadrien Devillepoix, a researcher at Curtin University and the principal investigator of the Global Fireball Observatory.

During its flight, the meteoroid descended much deeper into the atmosphere than icy objects on similar orbits and broke apart exactly like a fireball dropping stony meteorites — the necessary evidence that it was, in fact, made of rock.

Conversely, comets are basically fluffy snowballs mixed with dust that slowly vaporize as they approach the Sun. The dust and gases within them form the distinctive tail that can stretch for millions of km.

“We want to explain how this rocky meteoroid ended up so far away because we want to understand our own origins,” Dr. Vida said.

“The better we understand the conditions in which the Solar System was formed, the better we understand what was necessary to spark life.”

“We want to paint a picture, as accurately as possible, of these early moments of the Solar System that were so critical for everything that happened after.”

The findings were published in the journal Nature Astronomy.


D. Vida et al. Direct measurement of decimetre-sized rocky material in the Oort cloud. Nat Astron, published online December 12, 2022; doi: 10.1038/s41550-022-01844-3

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