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In the late 2020s, the ESA is slated to launch a "comet interceptor." The goal is to send the unmanned spacecraft into one of Earth's stable Lagrange points, where it will wait for a comet to fly close to the Earth. Once it spots a target, the spacecraft will deploy two mini-probes and the trio will skim the object for information. Once the mission is carried out, it'll be the first ever probe to have a target that was not specifically defined beforehand. This is necessary because comets arrive too suddenly and depart to swiftly for a mission to be planned and launched as it happens.
BlueVeins · 22-25
@GlitterBug In the 16th century (and other periods), it was hypothesized that there was a planet on the opposite side of the Sun for Earth, sharing Earth's orbit. This planet would never be visible from our position because it had the same speed, and would also be potentially habitable on account of having the same semi-major axis. We now know that this planet doesn't exist due to the gravitational influence it would have on Venus and vice versa, and also because our space probes would've spotted it. But the principle itself is still valid in that one [i]could[/i] hypothetically exist without fucking anything up in, say, another stellar system.