Astronomers announced three years ago that they had discovered an exoplanet very close to our Earth and potentially habitable. It orbits the nearest star to our planet, Proxima du Centaureand is located at 4.25 light-years, a mere 40 trillion km, or 700,000 times the distance between Earth and Mars. According to specialists, Proxima b, the name of this planet, is said to have the right conditions for life. For the time being knows still nothing. To clear our heads, we just have to go there...
Ahe search for exoplanets has been in full swing for the past few years. We discover them almost every day to such an extent that we may wonder if this focus by astronomers in the search for a new planet is not a little worrying. Has our beautiful blue planet come to the end of its days and are we already thinking of emigrating to the far reaches of space? Once this outburst of anxiety has passed, we will observe that the planet Proxima b seems to have strong similarities with Earth. If only out of curiosity, wouldn't it be interesting to take a look at it?
The problem is that this exoplanet, which revolves around the star closest to us, is still at a great distance. With today's fastest means of propulsion, such as the New Horizon probe that left for Pluto at a speed of 17 km per second, it would take 78,000 years to reach our destination. It's a long journey, on a human scale.
So, astronomers and other rocket scientists are using all the capabilities of their neurons to come up with a solution and give us a slightly faster trip. Several projects are in the running, more or less crazy. Some imagine recovering the blast from an explosion of nuclear warheads in order to reach an acceleration speed equivalent to 5 % of the speed of light, or 15,000 km/s. At this speed, the journey would still last a good century, and there is no guarantee of the condition of astronauts who would have been subjected to such nuclear explosions.
Another project consists of mastering nuclear fusion to build an engine capable of taking us to 10 % of the speed of light, i.e. 30,000 km/s. If we manage to master this technology and above all to find enough fuel to go that far, the journey would take 36 years.
Another solution intrigues the specialists a lot. It is the project Starshot which aims to reach the star Proxima du Centaure and therefore its planet Proxima b at 20 % of the speed of light. At 60,000 km / s, the journey would take only 20 years. The project is based on a seemingly crazy technology: propelling mini probes - nanocrafts - by ultra-powerful laser beams. This project could be shelved in the catalogue of infeasible ideas, but we must hesitate before proceeding with this vertical classification. Indeed, the concept has been supported from the outset by the astrophysicist Stephen Hawking, who is not strictly speaking a fantasist. It is financed by a Russian billionaire with a passion for space, Yuri Milner, who has already paid 100 million dollars to carry out a "proof of concept"; and in the project's steering committee we find a certain Mark Zuckerberg, the founder of Facebook, among other personalities ready to inject their billions. In this case, we need to take a closer look at this science-fiction-like project.
The Project Breakthrough Starshot aims to send thousands of space probes weighing about 1 gram, equipped with solar sails, to Proxima du Centaure. The low weight of these probes, combined with the power of terrestrial lasers used to propel them (up to 100 GW) would allow them to reach 20 % of the speed of light in vacuum and thus be able to return images of the exoplanets orbiting Alpha du Centaure in about 20 years.
For Mark Zuckerberg, speaking in an statement at the launch of the project, " The new idea here is that instead of using a large, fuel-intensive spacecraft like people tend to imagine traditional space travel, we will create a fleet of small spacecraft - or nanocraft - that we can accelerate to 20% of the speed of light using an array of laser beams from the surface of our planet. "
Nanocrafts are gram-sized robotic spaceships, consisting of two main modules: the Starship first of all. As Moore's Law has allowed a dramatic reduction in the size of microelectronic components, it is now possible to envisage fully functional space modules on a gram scale. These probes will be equipped on the one hand with identical equipment (communication via an integrated laser, energy storage, possibly sail control...) and on the other hand with specific equipment (depending on the probe, camera, radio detector, molecule analyser...) enabling them to carry out a mission.
The other part of the device is the LIghtSail. Advances in nanotechnology are making it possible to produce metamaterials that are increasingly thin and light. These technologies allow the manufacture of sails of a few hundred atoms, weighing less than one gram for a sail area of 4 m2 (2m x 2m).
These probes would be dropped by the thousands into high orbit by a mother ship. They would then be accelerated by the laser beam at once.
The purpose of the laser emitter is to illuminate the solar sail and accelerate the space probe by means of radiation pressure. The power of the laser will be of the order of 100 GW. The laser beam will in fact be generated by a combination of several lasers of lower power. The laser pulse will last about 10 minutes, delivering 1 TJ to the sail and allowing the spacecraft to reach its cruising speed (0.2 c).
The French astrophysicist, Francis Rocard, questioned by our confreres from Science and Future states: " It's a crazy project, but not impossible! " He adds: " What's interesting here is the idea of using very small probes. The technologies to achieve such miniaturization didn't exist 10 years ago. The advantage is that the lighter the craft, the easier it is to propel. And even if some of them get lost along the way, it increases the chances that a few will make it to their destination. "
Since the discovery of Proxima b, the scientists involved in the project have been extremely excited. Harvard physicist Avi Loeb, a member of the Starshot project board, tells the journal Business Insider : " this discovery provides an ideal target for a flyover mission. ». He continues, enthusiastic: " This will allow us to send a fleet of probes to Proxima that would review the images taken towards Earth more easily. ». It should be noted that the current telescopes cannot photograph the new planet. Avi Loeb adds "The curiosity to learn more about this planet, especially if it can support life, has given the Starshot project a sense of urgency.. "For the astrophysicist, the challenge is to perhaps offer us a substitute planet. He clarifies his thought: " The lifetime of the star Proxima is nearly a thousand times longer than the remaining lifetime of our Sun. Therefore, a habitable rocky planet around Proxima would be the most natural place where our civilization could aspire to move, before our Sun dies, in 5 billion years. "
The Starshot team hopes to achieve a launch in 2-3 years, and to reach Proxima about 20 years later. It would take at least 4.24 years - the distance in light years from here to the star - to return to Earth. So a little patience...