It would be no exaggeration at all to say that finding life on another planet would be one of the most momentous breakthroughs in the history of science, one that would equal, and arguably exceed, the discovery of Darwinian evolution, the nuclear physics of the atom and the origin of the universe itself.
Such a development would mean that our “pale blue dot” of a planetary home – as it was famously described by Carl Sagan when he saw the images of a distant Earth taken by the Voyager 1 spacecraft in 1990 – is not the solitary place it may sometimes appear when viewed from deep space. As it is, our mote of dust suspended in a sunbeam – another classic Saganism – is the only place that we know of where life exists. Indeed, it is the only place that we know of where life can definitely exist (although it may just be possible for it to survive in a few little nooks and crannies of the solar system).
But another entire habitable planet, or “Earth 2.0” as it is sometimes known, is quite a different matter. We have to look well beyond our own solar system for that, amid the myriad stars making up the Milky Way galaxy, one of many, many billions we can view through our telescopes.
So the announcement by Nasa that it has added an extra 715 new planets to the 1,000 or so that were already known to exist beyond the solar system is a significant step towards the goal of finding another habitable world. Four of these new planets can now be added to the five that are estimated to orbit within the “habitable zone” of their stars – neither too hot nor too cold for liquid water, which we must assume to be an essential ingredient for life.
Finding another Earth-like twin with the telltale signs of life – such as methane gas in its atmosphere or the changing hue of algal blooms in its ocean – would represent a stunning scientific and technological achievement. More than this, it would raise the deepest philosophical questions about our own place in the universe. It would mean that our pale blue dot is just one of many and that, in all likelihood, we are not alone. And that would change everything.