With the completion of New Horizons' primary mission of Pluto fly-by, should we now set our sights even much higher, ambitiously taking aim at other star systems? If so, Alpha Centauri would be probably 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 solar system, located "only" about 4.3 light years from us. The problem is, getting there in our lifetime is still a mission impossible, or maybe 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 - and may be gravitationally bound to the duo.

However, what still baffles astronomers is the existence of exoplanets in this system. In 2012, the discovery of a planet orbiting Alpha Centauri B was announced, but three years later a new research debunked this theory calling the previous finding a "ghost in the time series". Moreover, in 2015, another study proposed the existence of other 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. But before any mission concepts are prepared, a deeper look into the system could be very helpful. Now the trick is that we currently don't even have 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.

4.3 light-years equals 25 trillion miles, so knowing at least some basic information about this destination is quite essential before embarking on such a demanding trip. With current technology, a robotic probe send from Earth would require some 40,000 years to reach Alpha Centauri, making the mission totally useless for us.

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 was 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 propulsion system would be developed, every concept of mission to other stars could be doomed to fail.

"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 were projects that included sending unmanned interstellar spacecraft with a velocity of 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 spacecraft capable of reaching up to 7.1 percent the speed of light, thus the whole journey would take only 50 years.

Similar study, the "Project Longshot" was developed by the U.S. Naval Academy and NASA, from 1987 to 1988. The project would use a spacecraft powered by nuclear pulse propulsion 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 really 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 a very original 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 per cent 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 fly-by performed by an unmanned probe.

When will we be able to develop such a propulsion allowing us to travel at least at a speed of 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 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.