Comet 3I/ATLAS heads past Earth back into deep space

by · UPI

Dec. 19 (UPI) -- Comet 3I/ATLAS passed its nearest point to Earth early Friday and approaching within 168 million miles.

After its brief visit Friday the interstellar object 3I/ATLAS will head back toward the outer solar system before continuing its journey through the Milky Way, according to scientists.

3I/ATLAS was only the third known interstellar object to enter our solar system, following 'Oumuamua in 2017 and Borisov in 2019.

Its arrival gave scientists a rare chance to study the building blocks of distant comets and planets.

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NASA first detected the object in July, tracing its path back beyond our solar system.

Astronomers were unsure of 3I/ATLAS's exact size, but estimates by the European Space Agency place it between a few hundred feet and several miles wide.

Meanwhile, Hubble data suggests the comet's icy nucleus measures roughly 1,400 feet to 3.5 miles across.

Its trajectory indicated the comet supposedly originated in an ancient region of the Milky Way far older than the 4.6‑billion‑year‑old solar system.

Comet 3I/ATLAS surprised astronomers by shining brighter than expected as it neared its closest approach to the Sun at the end of October.

The theorized comet, which is rich in water, appears to come from the Milky Way's older thick disk rather than the sun's younger thin disk suggesting 3I/ATLAS may be as old as 7 billion years.

It neared the end of its journey through the solar system, its data will continue to help scientists refine our understanding of the Milky Way.

Researchers Qicheng Zhang of Lowell Observatory and Karl Battams of the U.S. Naval Research Laboratory noted in a paper that 3I's unusually rapid brightening was unexplained.

"The reason for 3I's rapid brightening, which far exceeds the brightening rate of most Oort cloud comets at similar [radial distance], remains unclear," they wrote.