July 15, 2014
It’s the planet that wasn’t there.
Four years after its discovery, Gliese 581g -- which had been hyped as the first potentially habitable exoplanet ever found -- has been more or less proven to not actually exist.
When planets orbit stars, their gravitational pull, while pretty small in comparison, still causes the star to wobble around a little bit in space. By analyzing the light from the star, astronomers can measure that wobbling and determine if the star has planets and if so, how big they are and how far away they orbit.
That’s the way the former Gliese 581g was originally “discovered”, though there were some other astronomers who expressed their doubts about its validity.
Now, a new study has thrown seriously cold water on the supposed existence of this formerly promising planet.
Gilese 581g orbits a red dwarf star, smaller and cooler than our Sun. Many of these stars are also considerably more rambunctious than our own, with massive stellar flares and many more starspots (aka sunspots) that change the amount of light that comes from the star.
All this interference makes it hard to find planets, especially small, potentially habitable ones, which would have to orbit super-close to their cool stars in order to be warm enough.
New evidence shows it’s very likely that the signals that seemed to come from a new exoplanet actually were caused by the star. Gliese 581g (and another planet, Gliese 581d) are a mirage produced by a hyperactive star.
So how did this happen? Are all exoplanet discoveries suspect? Do scientists really know for sure what’s going on?
The retraction of Gliese 581g offers up a couple really important lessons about science.
First of all, there’s no question that exoplanet hunting is incredibly hard to do, given the fact that they are unfathomably far away -- many times smaller and millions of times dimmer than the stars that they orbit.
And exoplanet science is a relatively new field, just less than 20 years old. The methods and technology used are cutting-edge and not quite perfect, though they grow more and more effective each passing year.
Second, it shows that hype and hyperbole can be a problem, especially when it comes to exoplanets. It’s easy and tempting for people to get excited and assume that a new discovery is more of a sure thing than it actually is.
The reality is that we don’t have nearly the ability, at this point, to definitively determine if a planet is habitable, though that will probably change in just a few years. These discoveries are still incredibly exciting, but we need to be careful that we’re not saying more about a new planet than the data do.
It’s also a testament to how science works, and why it’s so effective. The initial finding of Gliese 581g wasn’t just taken at face value. Other scientists made their own measurements and analysis of the data. And when they came to a different conclusion, they told the world.
Science works because it polices itself -- because nothing is accepted as fact until it’s rigorously tested by multiple researchers. Every idea, new and old, is subject to continuous scrutiny and refinement. Astronomers correct and challenge each other, holding their peers to high standards and keeping them honest.
The loss of Gliese 581g is a bummer, but it’s a great sign that the scientific process is alive and effective, giving us more confidence in the discoveries that do manage to survive a second, third, and fourth look. And it teaches astronomers more about stars and how to look more carefully in the future.
The future of finding an Earth-like planet is still bright. In 2010, Gliese 581g was the first and only rocky planet thought to be found in its habitable zone. Today, we know of several other worlds, ones that astronomers are a lot more sure of.
An Earth-like planet could be just around the corner. Get excited!
-By Joshua Rodriguez