In this golden age of exoplanetary science the announcement of a planet 30% more massive than the Earth, in an 11.2 day orbit around a low-mass star with a luminosity 0.15% of the Sun's would usually elicit little more than a raised eyebrow.

Except for the fact that this world orbits the nearest star to ours; Proxima Centauri.

It means that at a cosmically trifling 24 trillion miles (4.243 light years) from where you are at this instant is an alien system with a planet that could conceivably harbor life as we know it. That planet is estimated to be around 4.9 billion years old, it receives about 65% of the Earth's stellar irradiation, and its skies - whatever else is in them - are bathed in the red-hued rays of a diminutive star only 12% the mass of our Sun.

Say hello to the closest truly alien world.

Planets have been upending our preconceptions about the nature of the universe for a long time. Over the centuries, as science and western culture came to accept a heliocentric solar system governed solely by physics, we've also (mostly) accepted a larger and larger version of reality - of which we are a smaller and smaller part.

Although this expanding view of an expanding cosmos has led to speculations about who or what else might be out there in the surrounding universe, most of us have also been remarkably good at pushing these questions to the back of our minds. As a species we've had plenty of other pressing things to worry about. We're also still hominids that like lower hanging fruit - be they edible or intellectual. The fact that it wasn't until the 1990's that we finally confirmed the existence of planets around other stars is evidence for that tendency (or at least evidence that most scientists only jump onto bandwagons once they're comfortably rolling). 

Despite this slow start, exoplanetary science has been positively explosive in its revelations. Astronomical campaigns have already told us that pretty much every star in the Milky Way has a high probability of harboring planetary bodies. Prior to the Proxima Centauri detection we'd determined a roughly 1-in-5 odds for any cool star to have an Earth-scale planet orbiting them at a distance that could be compatible with a temperate surface environment. In other words, the chance of finding a candidate habitable world around the nearest star to the Sun was about the same as winning a US federal research grant.

So in retrospect, the Proxima detection is not hugely surprising. Yet it feels profoundly important.

In astronomy, distance is a big deal. The closer stuff is to us, the better the chances are that we'll be able to probe details. A planet around a star 4.243 light years away is a dandy target. Although Proxima is such a low-luminosity beast, it's so close that it still ranks as an 11th magnitude star in Earth's skies. That means that we receive 400,000 times more light from Proxima than the faintest stars that our giant telescopes can easily detect. And even though this planet hugs Proxima at an orbital separation of about 0.05 astronomical units, simple trigonometry indicates that we can hope to disentangle its planetary glow from that of its parent star, opening up the options for exploring its properties.

And it's more than pure planetary astronomy that benefits from shorter distances, so too does a search for extraterrestrial intelligence. So too does any effort to launch an interstellar probe. The cosmic proximity of Proxima is incredibly compelling at all levels, and raises many new questions: Does this system harbor life? Are we willing to go for broke to find out?

There are still potential show-stoppers. Astrobiologists will quickly point out that Proxima Centauri is a disturbed little star: it's convective, it has a powerful magnetic field, and has regular flares that may have helped erode this planet's atmosphere over the eons. We also don't really know whether a world like this - probably tidally-locked with an equal day-year period - can sustain a wet, temperate climate. 

But similar caveats exist for any terrestrial-analog exoplanet that we've detected at present (given our woefully limited data), and those worlds are all much further away. By comparison, finding Proxima Centauri b is like being introduced to your immediate neighbors for the first time and discovering that at least they're not obviously criminals, and they might ask you over for tea.

Perhaps the most important thing above all else is that our cosmic circumstances need not have been like this. The nearest interesting exoplanetary system didn't have to be the very closest one to us. We've hit it very lucky - there is an interstellar stepping stone that we might just manage to stretch over to.

So what are we going to do about it now?

Personally I think that this could (and should) mark a turning point in our cosmic outlook. Shifting our view of the universe won't happen overnight, and taking action on that new perspective may take even longer. But it's got to happen.

The worlds of Proxima Centauri may turn out to be utterly inhospitable, yet the very act of confirming that fact will have immeasurable scientific impact. And perhaps this newly discovered planet is a temperate, habitable, and inhabited place. That wouldn't just have scientific impact, it would literally open the cosmos for us.