An Audacious Plan to Study a 'Pristine' Comet Is Taking Shape

Called the Comet Interceptor, the European probe will travel 930,000 miles from Earth and assume a holding position until astronomers find a suitable target.

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An artist’s rendition depicting how Comet Interceptor will sit behind Earth, ready to intercept any asteroids that could pose a threat to the planet.
An artist’s rendition depicting how Comet Interceptor will sit behind Earth, ready to intercept any asteroids that could pose a threat to the planet.
Illustration: ESA

The European Space Agency announced yesterday that it had signed a contract with private space company OHB to build the Comet Interceptor, a spacecraft to study a yet-to-be identified pristine comet from the Oort cloud, due for launch in 2029.

The partnership between ESA and OHB’s Italian arm will bring Comet Interceptor to life. The spacecraft will eventually work some 930,000 miles (1.5 million kilometers) from Earth at Lagrange point 2, which is behind our planet as viewed from the Sun (fun fact: the recently deployed Webb Telescope is currently working at L2). Once there it will lie in wait as astronomers search for a suitable target, at which time it will be dispatched and sent on an exploratory mission.

Probes have visited comets before, the Rosetta mission being a recent example, but Comet Interceptor is different in that its purpose is to investigate a pristine comet, that is, a comet that’s entering the solar system for the very first time. Non-pristine comets have approached the inner solar system at least once before—a journey towards the Sun that fundamentally alters a comet’s volatile surface characteristics, obscuring its original makeup.

More on this story: The European Space Agency Has a Plan to Intercept a ‘Pristine’ Comet

Comets occasionally emerge from the Oort cloud, a spherical band of icy planetesimals at the outer edge of the Solar System. It’s impossible to predict when a pristine comet will make a sudden guest appearance, which is why Comet Interceptor is being sent out in anticipation of astronomers spotting a suitable target. Parked in L2, the probe will be well positioned to intercept the comet and document what will be a fleeting celestial event.

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When an incoming pristine comet is detected, Comet Interceptor will be dispatched to meet the body in space, studying it from multiple viewpoints. Pristine comets, and the tails of gas they produce as they approach the Sun, can offer great insights to the origin of the solar system since these dirty snowballs, as they’re often called, have not yet been weathered by a trip to the Sun. If an interstellar asteroid—such as ‘Oumuamua and Borisov, the only two we’ve detected so far—presented itself, Comet Interceptor could study that too.

“Comet Interceptor is an ambitious mission that requires a unique spacecraft—three novel spacecraft in fact—and after an intensive study and planning phase we are ready to start building the European elements,” said ESA Comet Interceptor project manager Nicola Rando in an ESA press release.

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Specifics on the three spacecraft that will make up Comet Interceptor are scant, but ESA says Comet Interceptor will consist of a main spacecraft and two probes. ESA will develop the main spacecraft and one of the probes, both of which will be carrying scientific instruments developed by European industry and institutions, while Japan Aerospace Exploration Agency is providing the other probe and its instruments.

“Comet Interceptor’s ground-breaking aims include characterising the surface composition, shape and structure of a pristine comet for the first time ever and sampling the composition of its gas and dust coma,” said Michael Kueppers, ESA’s Comet Interceptor study scientist, in ESA’s release. “Having access to this material is vital for understanding our origins, in terms of how our Solar System formed and evolved over time.”

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Comet Interceptor was approved as a project in 2019 and is scheduled for launch in 2029. Now that the agreement between ESA and OHB has been signed, design and construction of the Comet Intercept can officially begin.

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