DYO: Gliese 581 — the Most Misleading Craigslist Housing Ad in the Milky Way
published during a waning gibbous moon.
09/21/2016

Gliese 581

Look at this troll of a star (Gliese 581). Credit: Digital Sky Survey / ESO.

Delete Your Orbit is a recurring column on NOW.SPACE that provides well-informed, but alarmingly petty analyses of various objects in our universe. 

If ever there were a star that could somehow embody the traits of a slumlord, it would be the red dwarf Gliese 581. For the past decade, this star has been advertising the planets in its domain in the same way that a sleazy property manager might use Craigslist to fraudulently get people to see a place they would, in a more honest world, never give a rat’s ass about. In this case, the bait was neither promises of off-street parking nor great views; instead, it was an exoplanet that, this star seemed to suggest, might not kill us if we decided to colonize it—Gliese 581 c.

If Gliese 581 were advertising its “c” unit as a trendy place for humanity’s second home, it might have posted something like this: “Newly discovered ‘super-Earth’ in trendy WaHabZo. Ready for immediate colonization.” WaHabZo, in this case, would be the newly coined term for “warm end of the habitable zone”—a concept noted for its failure to actually exist. A more accurate description of this area would be the less desirable (but up-and-coming?) neighborhood of “not the habitable zone.”

The habitable zone, as a reminder, is the region around a star where liquid water, a key ingredient for life as we know it, can exist. The ad for this newly discovered interstellar property was essentially listed back in April 2007, when scientists discovered evidence of a smallish planet around this tiny, cool star only 20.5 light years away. Hailed by those scientists as “the known exoplanet that most resembles our own Earth,” the place gained notoriety almost immediately.

Trusting as we humans can be when anything suggests the possibility of life somewhere else, we bought into the hype 100%. In a 2007 press release, lead author of 581 c’s discovery paper Stéphane Udry raved, “This planet will most probably be a very important target of the future space missions dedicated to the search for extraterrestrial life.”

Udry and co.’s optimism was based on what was admittedly limited data. The team detected the planet using a method called “radial velocity,” where extremely subtle variations in the wavelength of a star’s light can hint at the barely perceptible push and pull of planets orbiting around it. Using this method, scientists estimated that the planet was at least 5.5 times more massive than Earth. They also discerned that the planet is much closer to its (much cooler) sun than Earth is to ours, making a year on that planet a mere 13 days.

Gliese 581

The locations of various planets and figments of imagination in relationship to Gliese 581’s habitable zone. Credit: ESO/ (derivative work by Henrykus).

The idea that this would be a swell investment property for humans was rooted primarily in the size estimate and its distance from its sun. Still much larger than our own planet, the place was termed a “super-Earth,” and according to models, it seemed likely that the place was either rocky or covered entirely in oceans. “On the treasure map of the Universe, one would be tempted to mark this planet with an X,” Udry said at the time.

When we decided to take a closer look, however, it became clear that this was a masterful bait-and-switch operation rivaling the best of anything you might find on Craigslist’s darkest corners. The first unsettling discovery was the fact that the place, upon closer inspection, did not lie in the habitable zone at all, but instead probably offered not much more than a scorching lifeless hellscape incapable of sustaining even the most basic of photosynthesizing organisms. “I would not recommend mankind to move to that planet right now,” astronomer and exoplanet deflator Werner von Bloh told the New York Times. So much for trendy WaHabZo.

Here’s where things got real suspicious, though. Once a whole bunch of us were doing our due diligence investigating Gliese 581’s “c” unit, that star, perhaps in a panicked realization that people would discover the fraud, executed a near flawless bait and switch. Yes, the solar system argued, “c” isn’t great, but you should really check out this new place that just opened up—the storied “d” unit! This champ—581 d—was a bit further away from its star than the “c” unit. The same scientists who pointed out that 581 c wasn’t capable of sustaining life also argued that “despite the adverse conditions on [581 d], at least some primitive forms of life may be able to exist on its surface.” Rave reviews, I know.

Later studies continued to leave the door open for the possibility that life could be sustained on this planet. A 2010 study concluded that the mean surface temperature might be high enough to maintain liquid water. According to these authors, their results “show that Gl 581d could be the first discovered habitable exoplanet.” THIS one is so seriously Earth-like, you guys. For real this time. Forget all about that “c” unit!

But it gets oh so much better. It turns out 581 d—the slightly less sexy planet humans were baited into considering when lured with the false promises of 581 c—might NOT EVEN EXIST! Yes, that’s right! A closer analysis of the data revealed that what they were recording as fluctuations in wavelength caused by planets were actually just fluctuations from the star itself. Though still not a settled issue, it is just as possible that Gliese 581 d is a figment of our scientific imaginations as it is a real place. This Gliese 581 star has been pulling off some next level trolling. (There was also a “g” unit in the running that was hailed yet again as ‘the most Earth-like’ for a bit, but that one probably doesn’t exist either).

To recap: 581 c—not in habitable zone, not even slightly tolerable. 581 d—great place to barely survive, but also higher than average risk of not existing. The obvious question, you might think, is why this star would be doing all this false advertising. That answer is simple—it’s acting out to mask its own inadequacies as a red dwarf (read: practically not even a star).

The more obvious question is this: why do we continue to listen?

TL;DR: Gliese 581 c is an insufferably hot hell-hole unwittingly used by its shady property manager (the notably unimportant star it orbits) as a way to focus human’s attention on an otherwise lifeless, desolate and unimportant part of the galaxy.