By Chelsea Whyte
Comets from the Oort cloud at the edge of the solar system pass by Earth every once in a while, but by the time we’ve spotted them, we don’t have much time to catch up to them – which is what happened in 2017 when an interstellar rock called ‘Oumuamua sped by Earth.
A planned mission from the European Space Agency (ESA) aims to increase our chances of getting up close and personal with a speeding comet or interstellar object before it leaves our cosmic neighbourhood.
“The idea is we’ll wait for a comet to come to us, near Earth’s orbit, and then send a spacecraft to shoot past it,” says Colin Snodgrass at the University of Edinburgh, the deputy lead for ESA’s Comet Interceptor mission.
ESA has announced that they will begin building spacecraft for this mission, set to launch in 2028. Unlike previous comet missions – like Rosetta, which visited the comet 67P – Comet Interceptor will have a chance to take images and measurements of a more pristine astronomical object that hasn’t been subject to heat from the sun.
The Rosetta mission had to spend 10 years accelerating to match the speed of 67P, but that won’t be possible for Comet Interceptor. “This comet will be going much faster because it’s coming from the Oort cloud and those really shoot through the inner solar system, so it’s really a fast flyby mission. The entire time we encounter it will be days, high resolution images will be taken in minutes to hours,” says Snodgrass.
Comet Interceptor includes a mothership and two sub-spacecraft that will be launched into space and lie in wait while astronomers on Earth track possible targets. When they identify a comet on a path near Earth, they will deploy the spacecraft to catch up with it. All three carry cameras and instruments to measure the magnetic fields, charged particles, and the composition of its gas and dust.
The three spacecraft will park at a spot in space about 1.5 million kilometres from Earth known as L2, where the Earth and sun’s gravitational pull and the centripetal force on an object perfectly balance out, allowing a spacecraft to remain there with very little effort.
“We’ll encounter the comet at tens of kilometres a second. Every dust grain you meet is a rifle bullet, so we’ll have shielding to protect them, but the idea is the main spacecraft passes further away at a safer distance where there’s less dust. And the smaller ones get closer, but having a higher risk of not surviving,” says Snodgrass.
Though the target is a comet of known origin, he says that if another interstellar object is spotted, the mission could make that the target and chase it down to get a better picture of its makeup and origins.
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