That’s not to say it is not an intriguing proposal. Entering orbit around Proxima b, the spacecraft could spend a year studying and imaging the planet, and possibly even collect samples of the gas in its atmosphere. Once the mission was concluded, the spacecraft would use its sail to make the journey back to Earth in the same manner it arrived, and on a similar time scale – a round trip of about 300 years.
Owing to the large distances between us and Proxima, the spacecraft would be largely autonomous, as two-way communication would take almost nine years. A small 1-watt laser on board would be used to send data back to Earth, and this same laser could be used for small course corrections as the spacecraft traveled to the star and entered orbit around the planet.
And to increase the chance of success, Heller and Hippke suggest that multiple spacecraft could be sent, anywhere between 10 and 10,000. Some of these could be sacrificed en route to ensure the mission’s success. For example, to perform a photogravitational assist, the spacecraft must tilt their sails against a star once they fly past, to prevent the photons speeding it up again. This limits their field of view, so some spacecraft could be pointed forwards to plot the trajectory.
The cost of such a proposal isn’t clear, although without the need to build a huge laser on Earth, it could be argued it would be a lot less than Starshot’s idea. The biggest hurdle would be developing the sail itself, which would need to be thin and light enough to keep the weight of the entire spacecraft to under 100 grams. For this reason, the authors proposed using some sort of graphene-inspired material, although the best composition isn’t yet known.
Yuri Milner (left) enlisted the help of experts like Stephen Hawking for his Breakthrough Starshot idea. Jemal Countess/Getty Images
There’s perhaps another incentive, too. These sails would be large, spanning several tens of meters in size with their sails. Once in orbit around Proxima b, they would likely occasionally flash with the light of the star. If there was intelligent life on the planet, it’s possible they would notice the spacecraft.
“As the sail approaches their stellar system, they would notice a new star in their skies, which would have almost precisely the same electromagnetic spectrum as their host star," the authors noted in an online Q&A.
“In principle, if these potential inhabitants of Proxima b were able to identify the sail as being artificial, they might conceive of a way to deliberately betray their presence to the cameras aboard the sail.”
Is it a bit fanciful? Sure. But the technology involved is not too far-fetched. Whether an agency or organization would commit to a mission lasting more than 100 years is another question, but there’s little doubt the scientific return for our descendants would be tremendous.