The star nearest Earth? Alpha Centauri? I can hear it now. Someone is getting “literal” on me and declaring that the star “nearest” Earth is our own sun. Okay, they’re right, but only in one sense. Our sun is literally a star, certainly. But in the vernacular, “star” usually refers to those tiny points of light in the night sky—not the daytime. So, even though the star nearest to the Earth is our sun, literally, it is not so in the everyday sense of common language.
Other purists will likely complain that Proxima Centauri is closer than “Alpha Centauri.” They would also be right, but only in a sense. Proxima is not a star that we can see in the night sky. Okay, I’m quibbling. But Proxima is also a part of the Alpha Centauri system. So, you see, in one sense Alpha Centauri really is the star nearest Earth. And it’s actually 3 stars.
The star nearest Earth now has a known planet
October 17, 2012, NASA announced the discovery of a planet orbiting Alpha Centauri B, the second brightest star in the trinary (ternary or 3-component) system. In that announcement, they congratulated the European Southern Observatory (ESO) team (Xavier Dumusque, et al) for their discovery.
That world is far too near to its sun to allow life as we know it, but the mass of that world is close to that of our own home planet. We don’t know the exact mass, because we don’t know the tilt of the planet’s orbit. But the minimum mass is approximately 1.13 ± 0.09 times the mass of Earth. If the orbit is perfectly edge-on, then this minimum mass would be the actual mass. The greater the orbital tilt, the greater the actual mass.
But the orbital period of this world is a brisk 3.24 days. That means that its year is less than half of our week. This also means that the planet is so close to its sun that it likely remains scorched on one side and frozen on the other. It is doubtful that it even has an atmosphere. The intense heat of being so close to its sun surely has stripped the world of any but the thinnest veil of gas.
And yet, if the mass is considerably more than that of Earth (high orbital tilt), then the planet might retain an atmosphere by the shear brute force of gravity. But the heat would still be unbearable. That heat would likely be transferred by winds all around the world, in a way much like that on Venus.
The prospect of finding other worlds in this nearest star to Earth
Each of the 3 stars of Alpha Centauri might have planets. What interests us most are the brighter two. Proxima is little more than a hot planet itself, with violent flares from time-to-time.
Could an Earth-like world exist in the habitable zone. Could such a world remain unperturbed by the elliptical orbits of Alpha Centauri A and B about one another? The prospect is exciting. To find a world just like Earth in the star system next door is a dream come true for those of us who have had many dreams of such things. What would that world be like? Would it have jungles like our own world? Would it be completely desert? Or would it contain only oceans and perhaps a few islands?
Traveling to the star nearest Earth has long been a passion of mine. To see the worlds of that ancient star system would be like waking up at Christmas with lots of presents. And Alpha Centauri is indeed ancient—at least a billion years older than our star system. If it developed life and civilization on a timetable similar to that in our own system, its civilization would’ve been a billion years old when ours just started.
The star nearest Earth in 3D
The image, below, is from the “Stars in the NeighborHood” software.
The Viewing Cube on the left shows Alpha Centauri selected with the green “focus” marker. Just above the Alpha Centauri system, the similar yellow dot represents our own sun. The distance between them is a mere 1.33 parsecs (4.33 light years).
On the right in the screen shot above, the Locator Cube shows the blue Viewing Cube’s location within our galactic vicinity. The yellow dot within marks the position of our sun.
To the right, this second screen shot (from “Stars in the Hood” software) shows alternately the night sky looking toward Alpha and Beta Centauri and the “Distance View” of the same portion of sky.
Here, the more distant, Beta Centauri is selected with the green “focus” marker. Alpha Centauri is just to the left. In the “Distance View,” the size of the stars is an indication of how far away they are.
As you can see, the star nearest Earth, Alpha Centauri, is very large (close) while Beta Centauri is very small (distant). This is despite the fact that they appear to have very similar brightness in our night sky.
Below, the software image shows the location of Beta Centauri. This is nowhere near our own Solar neighborhood. This brings into sharp contrast the closeness of Alpha Centauri—the star nearest Earth.
In all of our gargantuan galaxy, the relatively tiny distance to Alpha Centauri seems small indeed. It’s somewhat comforting to know that there are planets next door.
For more details, check out the Alpha Centauri Stellar Closeup.
What if we someday find a planet like our own in our next-door neighbor system? What are your thoughts on finding an Earth-like planet so close?