Well this is big news. In recent years there has been much excitement every time a new ‘Earth-like’ exoplanet has been discovered by astronomers (exoplanets are planets orbiting other stars). However, with many of those discoveries being very distant, making exact measurements difficult, there has been much speculation as to how Earth-like, and how habitable, those planets really are.
But today (after a few embargo breaks last week), astronomers have announced the discovery of perhaps the ideal ‘Earth-like’ exoplanet candidate, orbiting the star Proxima Centauri (one of the three stars that make up the ‘left pointer’ of the ‘Southern Cross’ constellation):
There’s a new standard in town, and its name is Proxima b. This planet has just about everything we’d want in Earth 2.0: It’s just a speck bigger, with only about 30 percent more mass than Earth (or slightly higher, depending on its orbital geometry); it’s almost certainly a genuine rocky planet; and it orbits smack in its star’s habitable zone.
The best part, though, is that Proxima, the planet’s star, is right next door, just 4.3 light-years away (130 times closer than Kepler 186f), the single closest star to our sun. Astronomers across the globe are drooling. We’ll be able to take actual pictures of it, to search for clues of life, within a decade.
Let’s be clear about why astronomers are so excited, by ticking the relevant boxes:
- Very close to Earth size.
- Orbiting in its star’s ‘habitable’ zone (the ‘Goldilocks’ zone…not too hot, not too cold)
- Orbiting the star closest to Earth
The ‘actual pictures’ the article above is describing would be from an Earth-based telescope – the European Extremely Large Telescope, currently under construction in Chile. But given the third point above – Proxima b is ‘just’ 4 light years away – and the fact that the Starshot project financed by Russian billlionaire Yuri Milner (as part of his ‘Breakthrough Initiatives’) was already aiming to send a space probe to Alpha Centauri in coming decades, there is the possibility we could have an actual robot visiting the planet within some readers’ lifetimes. For continued updates on this idea, I recommend keeping an eye on the excellent Centauri Dreams website.
On a skeptical note, however, we should also remember that – for all our excitement about Earth-like planets beyond our Solar System – we actually have two very Earth-like planets right beside us. One, Mars, appears to be devoid of life, and would require significant engineering for humans to live there. The other, Venus – as this Discovery article notes – “would surely be hailed as the most Earthlike exoplanet known” if we found it orbiting another star:
It is just 5% smaller in radius and 15% smaller in mass. It is almost the exact same age as our planet, and gets its warmth from an identical star. The only thing that’s a bit off is that it orbits a bit closer to its star than Earth does, so it receives nearly twice as much radiation. On the other, it also reflects away a lot of that radiation. Its theoretical (equilibrium) temperature is just below freezing, so with a little natural greenhouse warming it would be quite an inviting place.
Instead, Venus is “a profound enigma”. While all the variables tell us it should be a hospitable place for life (and at one time, scientists have found, it may well have been), in the present day it is “more like hell on almost-Earth”.
Understanding why that is–why our planet went right while Venus went terribly wrong–is crucial for finding out whether habitable planets are common or rare throughout the universe.
So, while we should be genuinely excited about this new discovery, we should also be wary when reading headlines like this (otherwise excellent) piece at The Atlantic: “An Epochal Discovery: A Habitable Planet Orbits Our Neighboring Star“. Proxima b is in the ‘habitable zone’…but it remains to be seen whether it is actually habitable.
Links:
- “Our Nearest Star Has a Planet, and These Are the Ways It Could Be Habitable“, at Nautilus
- “An Epochal Discovery: A Habitable Planet Orbits Our Neighboring Star“, at The Atlantic
- “Proxima Centauri Planet“, at Centauri Dreams
