Potentially habitable exoplanet discovered

Words: Maggie Koerth-Baker - Art: Lynette Cook

There is a planet in orbit around a red dwarf star, roughly 20.5 lightyears from Earth.

It's larger than our home world. But not by much, relatively speaking. Computer models predicted that it was probably a rocky planet, or at least one covered in oceans. No gas ball floating in this patch of space. When astronomers announced the discovery, the planet became a media sensation, thanks to its location in the habitable zone—an orbit far enough from its star that water wouldn't boil away, and close enough that it wouldn't freeze. Dubbed a "Goldilocks planet", experts referred to it as the "X" marking a home for alien life on a treasure map of the Universe.

The experts turned out to be wrong (link). Within two months, new calculations showed the planet was closer to its star than everyone had thought. Goldilocks was decidedly too hot. That was in 2007. The planet: Gliese 581c.

The first half of the story was replayed last week, as a team of astronomers with the Lick-Carnegie Exoplanet Survey (link) announced the existence of Gliese 581g—a planet they now think harbors the sanctuary its neighbor 581c turned out to be too sweltering to hold. This discovery is important, don't get me wrong. Gliese 581g is no outer-space equivalent to Ida the Overhyped Monkey Fossil (link). But you can't separate coolness from context. And the context is this: The first paper is not the last word. The initial findings, for any scientific discovery, are always subject to change.

I asked Vogt about that [100% chance of life] quote. He says it's come back to bite him, but he stands by what he said. At least, as long as the proper context is understood.

A Sure Thing?

Gliese 581g, which rhymes with "Lisa," really is a big deal. We're talking about a planet that, at first glance, seems to be roughly Earth-sized—which means there's a good chance that it has a rocky, solid surface—and is located in an orbit that would give it a reasonably survivable temperature range. In fact, it's pretty much smack in the center of that habitable zone, which means that it would take large errors—much larger than those that doomed Gliese 581c—to knock it out of the running.

All of that adds up to Gliese 581g being the best place we've yet found to look for extraterrestrial life. But that's quite a bit different from saying we're likely to find life there, say astronomers outside the Lick-Carnegie team. For one thing, the whole point of astrobiology is figuring out whether Life As We Know It is the same thing as Life, said Jim Kasting, Ph.D., a geoscientist with Penn State University. (link) Based on our limited view of the Universe, it's reasonable to assume that Life goes along with rocky planets that have an atmosphere and water. But we don't know that's true. We study places like 581g to test the hypothesis.

Second, Gliese 581g is in the habitable zone, but that doesn't mean we know it's habitable. You have to remember that nobody has actually seen this planet. Any time we're talking about the discovery of distant worlds, what we're usually talking about is evidence collected using a technique called radial velocity, said Manfred Cuntz, Ph.D., associate professor of physics at the University of Texas at Arlington. (link)

"You don't see the planet. What you're seeing is the way the planet's gravity causes wobbles of the star," he said.

The indirect evidence can tell you a lot, but not whether there's water or an atmosphere. That all makes the money quote that goes with this story a little hard to swallow. You've probably heard about this. Steven Vogt, Ph.D., professor of astronomy and astrophysics at the University of California Santa Cruz (link) and lead author on the paper announcing the discovery of Gliese 581g (link), told a press conference audience, "My own personal feeling is that the chances of life on this planet are 100 percent."

I asked Vogt about that quote. He says it's come back to bite him, but he stands by what he said. At least, as long as the proper context is understood. Namely: This is just his opinion, a gut feeling. It's not what the peer-reviewed paper said. In fact, there's no way to support that statement with evidence. But when Vogt looks at the evidence he does have, he sees something exciting. The way I understood him, "100%" was just his way of expressing enthusiasm over how much more likely life on this planet was compared to what we've found before.

That said, given that the setting was a press conference and not a dinner party, it's easy to understand Kasting's assessment, "That was kind of a silly statement."

Star Power

One thing is increasingly clear: Gliese 581 will be remembered as a special little star. Besides 581c and 581g—outside our mythology-rich solar system, the naming of interstellar bodies takes a turn for the well-organized and prosaic(link)—astronomers have found four other planets in its orbit, and one of those, Gliese 581d, is also a potential candidate for habitability. 581g, though, is a much stronger candidate.

It's not necessarily an issue of other stars lacking potentially habitable planets. Frankly, we haven't studied enough other stars to really know. But Gliese 581 has a couple of special features going for it. First off, it's created a nice neighborhood for us to poke around in. Most stars of Gliese 581's type are prone to sunspots and solar flares, Kasting said. That activity not only makes it difficult for astronomers to get clear measurements and find planets, it also makes it more likely that any planets close enough to the star to have water will have had their equally important atmospheres fatally disrupted by solar shenanigans. Gliese 581, in contrast, is quiet and calm. So it's relatively easy for scientists to pick the planets out of the chatter, and more likely that any atmospheres that formed are still there.

Second, Gliese 581 seems to have a larger percentage of low-mass planets than other stars we've studied, Vogt said. That's important, because the big boys—usually balls of gas, like Jupiter, or ice, like Neptune—don't fit with what we know about the conditions necessary for life.

Gliese 581 is important because it combines good conditions for planet-hunting with a family of planets that are more likely to be Earth-like.

Research Paper as Soapbox

Besides the new planet and its star, the paper itself was also on the unique side. Normally, scientific journal articles are rather dispassionate, all facts and figures. But this paper was chock full of editorializing—both on the importance of collaboration between research teams, and on the need for funding for a dedicated, land-based, planet-finder telescope. Neither is really a bad goal, but the effect was weird. As Manfred Cuntz pointed out, the peer review process usually catches, and deletes, that kind of thing.

Turns out, this was Steven Vogt, being all self-expressiony again.

"I wrote the paper, and I take all responsibility for that," he told me. "I have this 15 minutes of soapbox, so I said it. And the [peer-review] referee had no problem with it. Hopefully somebody will listen."

Anytime you discover a new planet, let alone one like Gliese 581g, you know the resulting research paper will be read by a lot of people. Vogt decided to take the opportunity to make a couple of statements.

First, he said, the world of planet finding has been a particularly contentious one, driven by competition between the Lick-Carnegie team, and one based in Geneva, Switzerland. It's a quiet sort of conflict these days, but it got out of hand for many years, Vogt says, and the wounds are still there on both sides. He wanted the world to know how important Swiss data was to his team's discovery of Gliese 581g. Sort of a spoon full of sugar to make the medicine go down.

"I'm putting the Swiss on notice that this is hard work and we have to get past the stage of, 'Our data is perfect and yours isn't and nah-nah-nah,'" Vogt said. "In the paper, I said we have to work together on this. That helping each other is the best way to find the truth."

The other big issue was money. The other researchers I spoke with agreed that funding was a problem for their research, especially, Kasting said, funding to build a dedicated telescope. Right now, a research team like Vogt's gets only 15 days a year to collect data at a sort of time-share telescope that's used by a lot of different researchers to study a lot of different things. That means it takes a long time to gather up enough data points to successfully ID a planet like Gliese 581g—11 years, in this case.

"Everybody has their own agenda about getting money for next step," Vogt said. "There's all this attention on new techniques as if what we have today isn't good enough. You don't need sexy new technique. You need a big telescope that just does this, every night. Nothing else. Then you'll get these things [planets] pouring out of the sky."

This article just covers some context about Gliese 581g that I haven't seen talked about much elsewhere. There's a lot of cool details about the planet that I've left out—like, say, the fact that it's probably tidally locked, with one side always facing Gliese 581, and the other side always facing space. To read more about the planet, I recommend combing through these links:

The Astrophysical Journal—Original research paper written by Steven Vogt • [pdf] link.
NASA press release on Gliese 581g • link.
LiveScience.com/Christian Science Monitor article on Gliese 581g discovery • link.
Space.com Q&A on Gliese 581g • link.
A Message From Earth: Project that sent radio signals to Gliese 581c in 2008 • link.
Images showing position of Gliese 581 in the constellation Libra • link.
Extrasolar Planets Encyclopedia: Technical Details on Gliese 581 • link.
Seed Magazine: G is for Goldilocks link.

38 Responses to “Gliese 581g: Coolness in Context”

  1. Nash Rambler says:

    It’s a big deal in that it gives us a new place to aim for. At the very least, a new target to shoot probes at.

    • Anonymous says:

      Back of the envelope calculations show that if we launched a voyager-type probe, it would get there in ~372 million years. So we’ll get right on that.

  2. joe blough says:

    Hey, I think you mean “radial” velocity, not “radio” velocity. Otherwise this is a very nice article, thanks.

  3. sapere_aude says:

    I just want to preemptively mention this: There’s a persistent rumor going around the internet that, a few years ago, a SETI researcher from Australia detected a bright flashing light from the Gliese 581 system which might have been produced by a powerful laser used for interstellar communications. This rumor (like most internet rumors) is false.

    Yes, there is a SETI researcher in Australia who has been scanning the sky with optical sensors looking for bright flashes of light that might be signals from alien civilizations. (He reasons that an advanced alien civilization is more likely to try to signal us using a very powerful optical laser than using radio waves.) And, yes, he did detect a bright flashing light from space a few years ago that looked as if it might have been produced by a powerful laser. But, no, it did not come from the direction of Gliese 581, but from a completely different part of the sky.

    The confusion came because the news article that reported the SETI researcher’s discovery also happened to mention the discovery of a planet in the Gliese 581 system, which occurred just a month or so previously. Though the article never said that the flash of light came from Gliese 581, it left that impression. The researcher has issued a communiqué clarifying the fact that the flashing light he detected did NOT come from Gliese 581; but the rumor persists nonetheless. (BTW, the flash of light he detected was never repeated; so there’s still no definitive answer as to what it was.)

    • cinemajay says:

      That’s what they WANT you to think. Actually, I hadn’t hear this. But I’m pre-emptively tearing tin foil sheets into nice, circular hats-shapes.

  4. Sceadugenga says:

    Reading the full text of the paper, I have come to one clear conclusion:
    Astronomers really get a kick out of tweaking LaTeX to pack their papers with lots of cool symbols.

    But seriously, thank you very much for the link to the original PDF paper. I wish all science journalism did that.

  5. kateling says:

    An excellent article, thank you!

    But yes, it’s radial velocity, not radio, because it’s the measurement of the Doppler shift of the light from the star as the orbiting planet makes it wobble back and forth. We can only measure the part of the velocity that’s directly toward or away from us, i.e. radial. Nothing to do with radio waves.

  6. DeWynken says:

    Maybe I’ll be an astronaut… yeah. I’d be the first motherf*cker to see a new galaxy, find a new alien lifeform… and f*ck it. Then people will be like, “There he goes. Homeboy f*cked a Martian once.”
    — Jay, Clerks II

  7. Anonymous says:

    I’m an astronomy grad student who worked with someone in this group for awhile (and had to stop when my advisor switched schools). I did a lot of research about the habitable zones around M dwarf stars for a report for one of my classes, and I think it’s important to point out the fact that this planet (and the habitable zone) are really close to the star compared to the habitable zone around our sun.

    This means that these planets are much more susceptible to the effects of stellar wind- particles flying off the star from normal processes like flares and ejections. The only way a planet can be protected is if it has a very strong magnetic field (like the earth). These energetic particles from the star very quickly strip off any atmosphere the planet has developed. Oxygen is particularly susceptible to this stripping. These processes have been studied in detail on Venus and Mars- which both have little to no magnetic field.

    I mentioned that a strong magnetic field can protect from erosion, but it is much harder for a planet to produce one if it is located very close to a star, and especially if it is tidally locked (which this planet is).

    The article does mention that this star is much less active than the average M dwarf star, but it should be noted that M dwarf stars are on average much more active than the sun.

    Anyways, I just wanted to get that out there. The discovery of this planet is exciting, but in my opinion, the chances of life (as we know it with an atmosphere and liquid water) existing on it have been a bit sensationalized. Let me know if you’re interested in reading the articles I referenced in my report and I can pass them along!


  8. xy9ine says:

    Manfred Cuntz. Teehee.

  9. TimDrew says:

    A question regarding the possibility of life thing (posed to anyone out there who may have an informed answer / conjecture): doesn’t the likelihood of the planet being tidally locked also reduce the likelihood of it having a megnetosphere? (ie. no spinning core of iron, no induced magnetic field). If such is the case, wouldn’t it have minimal protection form the radiation emitted by the stellar wind, occasional flare,e tc. emitted from its host star?

    Anyhow, this is very cool news- anticipate hearing more as the research continues!

  10. Anonymous says:

    Looks like TimDrew beat me to the punch! That’s what I get for commenting anonymously (mine is waiting to be approved as I type this). I really need to register for boingboing commenting.

    Anyways, I went back to look at my report about atmosphere stripping on planets around red dwarf stars to confirm the speed of erosion. On a planet with no or a very small magnetic field, this speed is of about 100x Earth’s atmosphere every billion years. For reference the Earth is about 4.5 billion years old, so if this planet was as old as the Earth, that would be 450 times Earth’s atmosphere eroded away in it’s lifetime.

    I didn’t specifically research the effect of atmosphere erosion on the liquid water on a planet, but I would guess that if the Oxygen was being stripped off, it would be harder for water vapor (and liquid water) to form (H2O). It would also effect the amount of Carbon Dioxide in an atmosphere- a molecule important to the greenhouse effect which would warm a planet and stabilize its temperature.


    • TimDrew says:

      Thanks for the insights! I’m still trying to find a potential gotcha explanation that might allow for feasable atmospheric retention under tidally-locked conditions.

      I’m reading the paper right now, and there is one interesting reference that seems relavent to this(page 31): points to a series of atmospheric simulations done in 1997 (Joshi et al) with synchronously rotating planets around M dwarfs; specifically mentioning that “over a wide range of conditions, and despite constraints involving stellar activity” habitable conditions may still occur. Curious to check that out…

  11. pignoli says:

    Re: False internet rumour – That doesn’t mean we shouldn’t use it as inspiration! Can we please build a massive laser and start firing prime/Fibonacci sequences in this direction then? Allowing 10 years to research and build it, we could have an answer in less than 60 years.

  12. bjacques says:

    I’d be happy if anything out there keeps on thinking the fridge is empty, so to speak.

  13. Danny O'Brien says:

    This was a great science article — a great backgrounder, a good sceptical but engaged tone, and links to the actual papers!

  14. Flying_Monkey says:

    Isn’t the whole ‘Goldilocks’ thing based on a rather anthropocentric (or terracentric) notion that ‘life’ elsewhere in the universe has to be like life on earth – or at least be based on similar conditions or foundations?

    But I haven’t seen any convincing explanation as to why this should be (most of the reasoning seems to be founded on variations of the anthropic principle, which is nothing more than circular logic) and this puzzles me because there are some pretty intelligent people who seem to espouse this view.

    Even on earth, we are now finding living things in places and conditions that were thought to be impossible just a few years ago (in extremely cold and extremely hot places). That alone should give the Goldilocks people pause for thought but, beyond that, the universe is so inconceivably vast that there is almost certainly life out there in all kinds of forms, and most likely, life that is far stranger than we can imagine. Particularly given the unlikely chain of events that had to happen to produce the range of life seen on earth, I can’t see any reason why life is more likely to be found on planets that are more like ours.

    • Scrotch says:

      I think that this has more to do with the fact that we are far more likely to recognize carbon- (and DNA-) based, hydrophilic, oxygen/CO2-respirating organisms as living than we would life based on some sort of exotic chemistry (such as methane-respirating or silicon-based organisms). And this is simply because all the life we have seen so far lives on exactly one planet.

      For all I know, there could be floating hyperintelligent gas colonies that live in the atmosphere of Jupiter, but they would be a form of life so alien (har-har) to our own that it might take us a while to recognize it.

      I’m reminded of the old video game Starflight where, if I remember right (and, if there is such a thing as spoilers to a 20 year old game, spoilers ahoy), the fuel that you used to make your interstellar spaceship go was revealed to be sentient rocks that moved so slow we didn’t even know they were alive.

    • Camp Freddie says:

      There’s some anthropic principle involved but probably not that much. The goldilocks zone is generally just shorthand for liquid water and stable carbon-chemistry. It might be possible for some life form to exist without that, but it would involve a whole lot of new chemistry. Non-carbon-based life seems unlikely, since we just can’t make large complicated chemicals without a carbon backbone (but never-say-never and all that).

      While we have extremophiles, like the volcanic vent organisms, they need a planet that is generally cool enough to keep the hot water from evaporating into space.

      The thing the goldilocks zone DOESN’T account for is the possibility of life on planets that get liquid water in some ‘exotic’ way. There could be planets or moons that get enough heat for liquid water from their core (e.g. radioactive rock decay) or from gravitational effects (like a gas giant’s moon). I reckon that there is a very high chance of life existing on a ‘non-goldilocks’ planet somewhere in the universe. It just makes sence to look at Earth-like planets first.

    • igpajo says:

      I always think of this when I hear of people getting excited about this kind of stuff. Yeah it’s great, but who’s to say there aren’t forms of life out there we can’t even conceive of.

      Reminds me of the Terry Bisson short story named “Meat”.

      • igpajo says:

        OOps…the story is actually titled “They’re Made Out of Meat.” Just wanted to head off any inevitable corrections on that.

    • Anonymous says:

      planet of teh tube wormz.

  15. Anonymous says:

    These articles tend to be little too hard for 581c and 581d; the writers should understand that a)the people behind the new find want to put down the competition a bit and b)there will be a an avalanche of critical papers for 581g with many claiming that the chances for life isn’t that high. And that criticism, when it comes, should be taken with a pinch of salt too. At this point all c, d and g are all possible places where liquid water could exist and be stable on the surface. G is the most likeliest, sure, but it will take a few decades probably to find out whether any of them could be habitable. And even if they are currently uninhabitable, Venus-like planets, they could be terraformed.

  16. Anonymous says:

    Since in all probability these planet are tidally locked, how much of the surface actually would be at a temperature for liquid water?

  17. Anonymous says:

    1: We won’t be sending probes any time soon. By the time we can, we’ll be colonizing the solar system. Our propulsion systems are nowhere near ready for the task of crossing that chasm any time soon.

    2: If there is life, even intelligent life, that planet is a prison. At 3 or more Earth masses, the only launch system that could even put anything into orbit would have to be nuclear powered. No chemical rockets like we get away with here on Earth.

    2a: So what would an emerging industrial society look like on such a heavy planet? They COULD follow our path of electrification, machine tools, and radio. So their electronics progress could mirror ours, or ours mirror theirs. Astronomy would be another matter. At several gravities large telescopes become very expensive as the mount become prohibitive to support all the extra weight of the same mass on Earth. Flight, forget it. No Wright Flyer for them, their first aircraft would have to have the strength and power of something like the F-15. That’s just for basic flight.

    2b: The good point of all that gravity, is while they might make nuclear weapons like we do, they can’t deliver them. No nuclear warfare with only 3 min to decide what to do, and planet wide destruction of cities in a matter of an hour or two, not even strategic bomber warfare that takes on the order of a day or two to play out. Cannon? That’s about all they’d have until they reached a very advanced state of nuclear power. And that said, chemical based munitions would only give you early 20th cen range. So you could have an advanced industrial species that when they are as advanced as ourselves, cannot fly, cannot access space, and conducting even basic astronomy would be as expensive as spaceflight is for us, but with very very limited means of conducting warfare, they would not be able to destroy themselves as we can.

    • kateling says:

      The force of gravity on the surface depends on the size of the planet as well as the mass, and this one is estimated to be larger than Earth as well as more massive. So the gravity isn’t expected to be all that much stronger. The paper estimates it at ~1.1 to 1.7 times stronger than Earth.

      • Anonymous says:

        Orbital velocity and escape are dependent on mass. Assuming a Earth like density this planets radius ranges from 9300 km to 10,400 km compared to Earth’s 6400 km. It’s orbital velocity ranges from 11.3 km/s to 12.6 km/s compared to Earth’s 7.8 km/s. It’s escape velocities are on the order of 15.9 km/s to 17.8 km/s compared to Earth’s 11.2 km/s. It would take a Saturn V to launch a Voyager on a tour of their solar system as compared to our Titan IIID. But the real point is with so little return on the investment would they even embark on developing rocket propulsion when you need 3 times the thrust as on Earth, 9 times the power, and only get 1/4th the useful payload. We barely did it ourselves, and only to serve the overbearing needs of global nuclear weapons delivery. It’s unlikely they would embark on the effort (Assuming they are a plunder/theft driven species as we are.) if your first ICBM happens when you reach the Minuteman III/R-36 (1970’s) stage instead of Atlas/R-7 (1950’s). Petrol based fuels just don’t have the energy density needed on such a massive planet. Even Earth is near the upper end. If Mars had an industrial civ they could open the Solar System on coal and gasoline. The Gelieseians might use petrol for shipping and ground transport, but not much else. They’d have to wait for high efficiency nuclear power to take to the air and the Cosmos the way we have with petrol.

  18. Darren Garrison says:

    Lynette Cook needs to go back to the drawing board (both figuratively and literally) on that land-covered planet illustration. A recent post from the metlist*


    and my observation based on that


    *which is Google unsearchable, but this post hasn’t been indexed yet

  19. Laroquod says:

    Sure, there might we other ways of getting life in other conditions than in what we think of as a habitable zone. However, we have no idea what those conditions might be. On the other hand, we know exactly what the conditions are for life on this planet; therefore, given the incredibly limited resources we have (11 telescope days a year as an example from the article) and the incredibly large search space (gajillions of possible stars), not only does logic dictate that we start looking for life in classic ‘habitable zones’ — we would actually be insane to come at the problem any other way.

  20. Doctor Morbis says:

    You’re tearing me APART, Gliese!

  21. Flying_Monkey says:

    I note that Maggie’s headline says ‘habitable’ which implies potential human colonization rather than there being existing life – although the text talks about the latter. I sometimes wonder whether this whole search is really underpinned as much by an unspoken (and perhaps even subconscious) desire for new territory (yes, it is that ‘final frontier’ thing) as some more pure scientific goal. Are we really interested in finding ‘new life and new civilizations’ or is it just, to mix SF references, a desire for “a new life in the off-world colonies” that is driving this, and which also provides an additional explanation for the prevalence of the Goldilocks argument? I am not suggesting that Maggie is thinking this, but I do think it’s deep down there in a lot of us.

  22. beastface says:

    Would it be possible to create some kind of artificial moon on this planet? Would it some how get the planet to start rotating?

  23. Fred Beecher says:

    Sadly, this planet likely doesn’t exist. It has captured my imagination like nothing else, but a second group of scientists analyzing the same data with a different method has found no trace of the planet.


  24. Ugly Canuck says:

    This star is not yet done with us….not planet g, but planet d of this system is the one….


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