The attempts have not gone well. In a group led by Xavier Dumusque, then at the University of Geneva, announced the discovery of an Earth-mass planet around Alpha Centauri B to great fanfare.
But three years later, an independent analysis showed no sign of the planet, suggesting it was just a data artifact. For one thing, the separation between stars A and B is increasing, and by , it will be wide enough that powerful telescopes will be able to observe each star individually.
More importantly, vastly improved new versions of instruments called spectrographs will allow far more sensitive searches for wobbles than those that were possible with the HARPS detector used by Dumusque and his colleagues.
These spectrographs are designed to pick up wobbles as slight as 10 centimeters per second. There are no plans yet for an Alpha Centauri—centric dedicated search, but if— when —new results emerge, Zhao promises, they will be trustworthy.
Presuming that the wobble searches are successful in finding planets around Alpha Centauri, they will still leave a lot of unknowns about these alien worlds. Such studies will indicate how massive the planets are and how they orbit but will reveal little about their physical qualities.
They will reveal nothing at all about what the planets look like. The only way to obtain that kind of information is to observe these bodies directly. No instrument yet created is sensitive and precise enough to do that. But slightly larger worlds are now within reach, and looking for them can already tell us a lot.
Odd as it may sound, the first order of business is figuring out what kinds of planets are not present around Alpha Centauri. Because of the proximity between stars A and B, stable planets can exist only rather close to each star, no more than about 2. Any giant, Jupiter-size planets orbiting in those inner sanctuaries would have long ago destroyed any smaller, potentially Earthlike planets orbiting in the habitable zone—the clement region where liquid water and hence, life as we know it could exist.
As of yet, wobbles have shown no sign of giant planets around Alpha Centauri, which is encouraging. To that end, Belikov and his colleagues have made the first serious attempt to directly image planets around Alpha Centauri. A similar search he performed last year came up empty, which is good news: so far, there is no hint of pesky Neptune-size planets in the Alpha Centauri system, either. NEAR is the result of an unusual collaboration between the European Southern Observatory, which runs the VLT, and the private Breakthrough Initiatives, which provided funding for critical equipment upgrades.
It is the first device built and operated specifically to find planets around Alpha Centauri. Skip to Content. Deep Dive. By Tatyana Woodall archive page.
By Jonathan O'Callaghan archive page. By Neel V. In , scientists discovered a roughly Earth-size world circling Proxima Centauri, part of the three-star Alpha Centauri system , which lies about 4. The planet, known as Proxima b, orbits in the "habitable zone," the range of distances from a star at which liquid water could exist on a world's surface. A second planet, Proxima c , was later discovered circling the star as well, but it orbits farther away, beyond the habitable zone's outer limits.
There's considerable debate about the true habitability of Proxima b , however, given that its parent star is a red dwarf. These stars, the most common in the Milky Way, are small and dim, so their habitable zones lie very close in — so close, in fact, that planets residing there tend to be tidally locked, always showing the same face to their host stars, just as the moon always shows Earth its near side.
However, if there is indeed a super-Earth in the habitable zone of Alpha Centauri, the implications are tantalizing. A planet of this type and size in a Mars-like orbit roughly one and a half Sun-Earth distances out could be even more hospitable to life than Earth.
Today Mars is only borderline habitable—too small, and with too little internal energy to have sustained its original magnetosphere and atmosphere.
If Mars had been the size of Earth, or preferably larger, it most likely would have held on to its early oceans and thick atmosphere, making it much more suitable for life. All we need is a factor of two improvement in resolution, or a four-fold improvement in detecting dim objects. I would bet we achieve that very soon.
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