Astronomers have confirmed the existence of the closest planet outside the Solar System, a rocky world with an orbit potentially suitable for life. The findings put to bed concerns previous reports might have been an error.

Proxima Centauri b is as close as an exoplanet can be, orbiting the nearest star to the Sun. Consequently, its announcement in 2016 created great excitement, amplified because its mass and average temperature are probably similar to Earth's. Proxima c, a larger planet in a colder and more distant orbit, was more tentatively proposed earlier this year.

However, Proxima b was detected using the “Doppler wobble”, its gravitational tug produced in its parent star. Stellar activity can generate false positives for this method. With Proxima Centauri being a particularly flarey star, some astronomers wanted more evidence before being confident our new neighbor was not an illusion. A collaboration of 91 European scientists has now provided that, marking the European Space Agency's (ESA) new ESPRESSO instrument's first planetary confirmation.

Astronomers love coffee for long observing nights, and cheesy bacronyms for...we're not sure, but they do. So ESA apparently couldn't resist naming its new device for finding Earth-like planets Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, or ESPRESSO. 

ESPRESSO processes light collected by the European Southern Observatory's Very Large Telescope to offer unprecedented precision in measuring stars' locations, with a goal of distinguishing movements caused by a planet from stellar eruptions. Confirming Proxima b, and seeking any other planets the system might hold, was a top priority.

 The efforts have born fruit in a forthcoming paper in Astronomy and Astrophysics (preprint available on ArXiv.org), which not only establishes Proxima b's existence but fills in more detail about its characteristics.

Proxima Centauri emits one six-hundredth of the Sun's light. With an orbit lasting just over 11 Earth days, Proxima b is much closer to its source of light than Mercury is to the Sun, but its temperature should be similar to Earth's. The obstacle to life is the danger that those powerful flares have stripped away any atmosphere. 

Proxima b is at least 1.29 Earth masses, but without knowing its orbit's orientation to us we cannot rule out the possibility it is considerably heavier.

ESPRESSO's observation period was insufficient to confirm or refute the proposed outer planet Proxima c. However, the team found a potential signal that could be from a third planet with an orbit of just 5 days and a mass similar to Mars. If it exists this world would be far too hot for life, but is causing excitement of its own. There is a greater chance a planet in such a tight orbit will transit in front of Proxima Centauri, which would enormously increase our opportunities to study it.

Time to start thinking harder about a probe perhaps.