Opinion: Should Alpha Centauri be the first target for interstellar probes?

Tomasz Nowakowski

Artist’s concept of the Project Daedalus. Image Credit: Robert van der Veeke

With the completion of New Horizons’ primary mission of a flyby of the dwarf planet Pluto, should we now set our sights even much higher, ambitiously taking aim at other star systems? If so, Alpha Centauri would probably be considered as the best target for an interstellar spacecraft due to its ‘proximity’ to Earth.

This system, consisting of three stars and possible planetary companions, is the nearest to the Solar System, located ‘only’ about 4.3 light years from us. The problem is, getting there in our lifetime is considered a “mission impossible” – or perhaps not.

The neighboring system hosts a pair of stars named Alpha Centauri A and Alpha Centauri B. Alpha Centauri C, also known as Proxima Centauri, is a small and faint “red dwarf” – a small and relatively cool star which might be gravitationally bound to the duo.

However, astronomers are uncertain as to whether exoplanets exist in this system. In 2012, the discovery of a planet orbiting Alpha Centauri B was announced, but three years later a new report debunked this theory calling the previous finding a “ghost in the time series”. Moreover, in 2015, another study proposed the existence of another alien world accompanying the “B” star.

What is interesting, the two hypothetical exoplanets would be Earth-like if they really exist. This could be another motivator to send our spacecraft there. However, before any mission concepts are prepared, a deeper look into the system could be very helpful. At present, there isn’t a telescope that could directly image a planet in this system.

“This would have to be done from space – even then, it would be hard. We don’t have a space telescope that can do this right now, especially for small planets. There are no gas giant planets there; if there were any, we would have detected them,” Debra Fischer, astronomer and exoplanet hunter at the Yale University, told Astrowatch.net.

The distance of 4.3 light-years equals 25 trillion miles, so knowing at least some basic information about this destination is essential before embarking on such a demanding trip. With current technology, a robotic probe sent from Earth would require some 40,000 years to reach Alpha Centauri.

NASA’s New Horizons spacecraft, which is the fastest-moving spacecraft ever launched from Earth, currently travels at about 36,400 mph. If the probe were to be aimed at the Alpha Centauri system, it would reach it 78,000 years after launch.

A huge technology advancement is required to make interstellar journeys feasible. Unless new means of propulsion are developed, the sheer distance to other potential worlds – makes true exploration of these systems impossible.

“Once we have the ability to accelerate a probe to 10 percent the speed of light, that is the first place we’ll go! It’s the closest star system and, therefore, a great target,” Fischer said.

In the past, there have been projects that included sending unmanned interstellar spacecraft with a velocity of approximately 4.5 or even 7.1 percent the speed of light. Between 1973 and 1978, a study was conducted by the British Interplanetary Society to send a probe using a fusion rocket that would reach Barnard’s Star located 5.9 light years away.

The study, named “Project Daedalus”, aimed to develop a two-stage spacecraft capable of reaching up to 7.1 percent of the speed of light with the first stage over a period of two years; then the second stage would take over and propel the spacecraft to about 12 percent of the speed of light over a period of 1.8 years, before being shut down for a 46-year cruise period.

A similar study, “Project Longshot”, was developed by the U.S. Naval Academy and NASA, from 1987 to 1988. The project would have used a spacecraft powered by nuclear pulse propulsion system to reach an average velocity of approximately 30 million mph (4.5 percent the speed of light). That would allow the mission to arrive at Alpha Centauri some 100 years after launch.

There is a long list of concepts and projects tasked with designing a propulsion system of the future that would allow interstellar travel. In contrary to the ideas based on conventional propulsion, many concepts include using antimatter rockets, warp drive, or wormholes.

A laser-powered interstellar sail ship is one concept that seems feasible in the near future. It was presented by Geoffrey A. Landis of NASA’s Glenn Research Center in 2002. Landis described a starship with a diamond sail, a few nanometers thick, powered by solar energy, which could achieve 10 percent of the speed of light. Using this type of propulsion, it would take 43 years to reach Alpha Centauri, if it passed through the system. However, slowing down to stop at our neighboring system could increase the trip up to 100 years. Thus, it would be more appropriate for a flyby performed by an unmanned probe.

When will humanity be able to develop a propulsion system that will allow spacecraft to travel at a speed of at least 10 percent the speed of light? That remains disputable.

“We have to have the probe travel faster than 10 percent the speed of light and we need [a] high-gain antenna in the outer Solar System to pick up the signal that the probe sends back. This is a technology horizon that currently seems far away. 50 years? 100 years? Hard to say!” Fischer concluded.