On August 24, 2016 – just four months after the launch of Breakthrough Starshot – the European Southern Observatory announced the discovery of Proxima b, the first known exoplanet in the Alpha Centauri system.
This planet is currently envisaged as the primary target of an eventual Breakthrough Starshot interstellar mission.
The Alpha Centauri system comprises a binary pair of Sun-like stars, Alpha Centauri A and B, accompanied by Proxima Centauri, which at 4.22 light years is the closest star to the Sun. The new planet has roughly the mass of the Earth, and may have a rocky composition. Although it lies in the “habitable zone” of its star, where the temperature might allow liquid water, it is unknown at the moment whether it has either water or an atmosphere, or whether other conditions on its surface are suitable for life. These and other properties will be objects of intense investigation in the coming years.
Even if it is not habitable, Proxima b, being by far the closest known exoplanet to Earth, is a dramatic discovery and an obvious first target. A mature Starshot mission would attempt to aim its nanocrafts within 1 Astronomical Unit (93 million miles) of the planet. From this distance, its four cameras could potentially capture an image of high enough quality to resolve surface features such as continents and oceans, if they exist. To achieve comparable resolution with a space telescope in Earth’s orbit, the telescope would have to be 300km in diameter.
For more information on Proxima b, see here.
Other targets in the Alpha Centauri system
It is currently unknown whether there are more exoplanets orbiting Proxima Centauri or the other stars in the Alpha Centauri system. Further targets in this system would be good news, since even at 20% of light speed it would take over 50 years to reach the next closest Sun-like star.
As a binary system of Sun-like stars, the chance of Alpha Centauri A or B hosting an Earth-like planet is thought to be considerable. Furthermore, we know that these stars lack Jupiter-like planets in close orbits, which would have reduced the likelihood of an Earth-like one. The star system may be up to 3 million years older than the Sun – giving more time for life to emerge on any potential habitable planet. In the next two decades, ground and space telescopes will enable astronomers to find out if Alpha Centauri has other planets – and if so, their size, mass, atmospheric composition and possible signs of life.
Along the path to an ultimate Alpha Centauri mission, the light beamer and nanocrafts may enable other important astronomical applications, including:
Contribution to solar system exploration
The Breakthrough Starshot concept could enable rapid solar system missions. At 20% of light speed, a nanocraft could reach Mars in an hour (it currently takes around 9 months), Pluto in a day (the New Horizons probe took 9 years) and interstellar space in about a week. Even at 2% of light speed, journey times would be significantly reduced.
Using the light beamer as a telescope
The light beamer would constitute a kilometer-scale telescope in its own right. No such instrument exists today for optical astronomical observations.
The light beamer could potentially be used to detect Earth-crossing asteroids at large distances.