May 8, 2021

Is there an earthlike world right in our backyard?

Painting of Proxima Centauri

These days, it seems as if a week doesn’t go by without the discovery of even more exoplanets scattered around our galaxy. And that’s before the launch of the James Webb telescope which should take planet-hunting to an entirely new level. The most recent entry in the hunt for Earth 2.0 is an interesting one, however, because it’s located in the star system closest to our own.

Space.com reports that a study published this week in the journal Nature Communications reveals the potential existence of two new planets in the Alpha Centauri system. We’re not talking about Proxima b here. Discovered in 2016, that earth-sized world circles the red dwarf star Proxima Centauri and it doesn’t seem to very very promising. The new discovery deals with two possible planets circling Alpha Centauri A, a yellow star quite similar to our sun. And one of them would be in the star’s “Goldilocks zone.”

There may be a planet in the habitable zone of Alpha Centauri A.

We need to specify the word “possible” because more data will be required to confirm the discovery. But if it holds up, there may be a planet in the star’s habitable zone. Before you get too excited, however, the estimates of the world’s size could easily rule it out as a new home for humanity. The planetary candidate, dubbed Alpha Centauri A, is estimated to be roughly the size of Neptune.

Picture of Neptune
Neptune is large enough to contain 57 earth-sized planets (Photo from NASA.gov)

If that’s the case, there are two possibilities as to the physical makeup of the world. The more likely reality is that Alpha Centauri A will wind up being a gas giant just like Neptune. (Well, Neptune is technically an ice giant, but you get the point.) That would make it interesting, but not a suitable environment for human life unless it turned out to have an earthlike moon orbiting it.

Unfortunately, Alpha Centauri A will (probably) wind up being a gas giant, if it even exists.

It is possible, however, that the planet could be a rocky world like ours. There have already been discoveries of staggeringly large rocky planets in that size range, such as TOI-849b. That still doesn’t mean that we can just move in and start setting up houses. Neptune is big enough to fit 57 earths inside of it. The gravity on a planet of that mass would be literally crushing and if it’s retained an atmosphere it’s probably extremely dense.

Another interesting question is what sort of an orbit Alpha Centauri A would have. Can one star in a binary (or in this case, triple) system provide a stable orbit for a planet? It turns out that it’s actually quite common. Unless the other star or stars in the system are just destructively close, the gravitational pull from the other stars on the planet is minimal as compared to the host star.

What were the odds that there would be a rocky world orbiting in the habitable zone of the sun-like star that’s the closest to our own?

Even if Alpha Centauri A doesn’t turn out to be anything close to a suitable home for humans, this news is still remarkable, if only in terms of probabilities and statistics. What are the odds that there would be a rocky world orbiting in the habitable zone of the sun-like star that’s literally the closest to our own?

Up until now, I’d have thought the chances to be rather slim. But if both the sun and Alpha Centauri A are sporting rocky planets in the Goldilocks zone, then such worlds may be as common as three-leaf clovers. Considering how many billions of stars there are just in our Milky Way galaxy, the odds may have just increased tremendously that there’s an Earth 2.0 floating around out there and it might not be very far away at all. And if so, there could be a different set of scientists on it peering toward the sun right now and wondering if there’s any intelligent life here. Unless, of course, they’ve already arrived to look us over first. (Cue the UAP Task Force report, please.)

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