Ingredients for Life on Gliese 581g?

Credit: Lynette Cook

Just in case you haven’t heard, astronomers have released news about an “Earth-like” exoplanet orbiting within the “Goldilocks zone” of a star some 20 light-years away. This is awesome, but does it mean Gliese 581g is habitable? Does it mean life is already slithering across its surface?

Judging by an exuberant claim by Steven Vogt, professor of astronomy and astrophysics at University of California Santa Cruz, one would think we now know there’s life on this strangely familiar world.

“Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say that the chances for life on this planet are 100 percent. I have almost no doubt about it,” Vogt told Discovery News when the announcement broke on Wednesday.

100%?

Why did he say that his personal view was that the chances for life on Gliese 581g are 100%? At first glance, it is easy to see where he’s coming from.

Goldilocks Zone

Firstly, the exoplanet orbits close to a small red dwarf star (called Gliese 581), with a fast-paced orbit of 37 days. This is important as the energy output of a red dwarf is tiny when compared to our Sun (which is a yellow dwarf star, in case you were wondering) — to receive an equivalent amount of heating as the Earth, Gliese 581g needs to be much closer to its star.

Also, it isn’t orbiting too close. It is within the habitable zone (or the “Goldilocks zone,” i.e., a zone that’s not too hot or too cold) of the system. Therefore there’s a high probability that if water is present on its surface, it’s likely to be in liquid form. The presence of liquid water would be exciting as Earth Brand™ life likes liquid water.

Secondly, Gliese 581g is small for an exoplanet discovered thus far. Weighing in at a minimum mass of 3x that of the Earth, it could certainly have some Earth-like qualities. This has another implication; the world has enough gravitational oomph to hold onto an atmosphere — another ingredient that life seems to like (assuming it’s not of the bone-crushing, lead-boiling, Venus-type atmosphere).

It’s Complicated

But there’s a few complications. To be within the habitable zone of its parent star, Gliese 581g will be “tidally locked.” This means that one side of the exoplanet will always be facing the star. On the far side (or, indeed, the “dark side”) it will be cold whilst the near side will always be hot. Having one perpetual day doesn’t sound very Earth-like to me. But there is an upside to this strange orbit.

“This planet doesn’t have days and nights. Wherever you are on this planet, the sun is in the same position all the time. You have very stable zones where the ecosystem stays the same temperature… basically forever,” Vogt said. “If life can evolve, it’s going to have billions and billions of years to adapt to the surface.”

So a tidally-locked planet could have a stable atmosphere and perhaps life could evolve as a result. What could be considered to be a negative has just become a positive.

With all this good news, why wouldn’t life be thriving on this world?

Unknowns and Assumptions

There’s still a lot of unknowns and assumptions being made. For a start, the presence of Gliese 581g was detected by measuring the “wobble” of the star as the exoplanet orbits (its gravity tugs on the star as it circles). Therefore its mass and orbital radius can be derived. But we have no information about its atmosphere; the world doesn’t pass in front (or “transit”) the star from our perspective, so we can’t get a peek into its atmosphere.

Therefore we have zero clue as to whether it even has an atmosphere. It might not have an atmosphere, but then again it could have a very thick atmosphere — two extremes that would would put a stop to any Earth Brand™ life evolving. Also, we have zero clue if there’s any water there, it’s just guesswork that suggests there might be. There’s also the huge unknown as to whether life is ubiquitous in the cosmos or not.

Bread in the Oven

It’s a bit like baking a loaf of bread when you have all the necessary ingredients to make bread, but you have no clue about what quantities to use. Gliese 581g appears to have most of the ingredients for life (and with a few assumptions, it has all the ingredients for life), but we only have a general idea as to what quantities these ingredients come in.

If you threw flour, water and yeast straight into the breadmaker in random quantities, would you get a loaf of bread? What if you forgot to add the yeast?

Gliese 581g is that breadmaker. Unfortunately we have no clue if it can make bread.

For more on this incredible discovery, read Irene Klotz’s Discovery News article: “Earth-Like Planet Can Sustain Life

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Earth is no Longer ‘One of a Kind’

For this special little planet, today has been a very big day.

Although we’ve speculated that planets the size of Earth must exist elsewhere in the cosmos, it wasn’t until one of the co-investigators working with the Kepler Space Telescope said he had statistical evidence that worlds of the approximate size of Earth appear to dominate our Milky Way.

We now know Earth isn’t unique.

Alas, this historic news didn’t come without controversy. It was unofficially broken at a TED conference in Oxford earlier this month and only after a recording of a presentation given by Dimitar Sasselov was posted online did the news get out. What’s more, the announcement only became clear when Sasselov referred to a presentation slide depicting a bar chart with the different sizes of exoplanets discovered by Kepler:

A slide from Dimitar Sasselov's TED presentation.

This slide shows the number of exoplanets discovered up until this month, binned by size. We have Jupiter-like exoplanets, Saturn-like exoplanets and Neptune-like exoplanets, all compared with Earth’s radius.

The heart-stopping moment comes when looking at the bar that represents Earth-like exoplanets (i.e. worlds with a radius of below 2 Earth radii, or “<2 Re"). According to Sasselov, Kepler has detected a lot of Earth-like worlds, so many in fact that they dominate the picture. From what we have here, it would appear that around 140 exoplanets are considered to be like Earth.

“The statistical result is loud and clear,” said Sasselov. “And the statistical result is that planets like our own Earth are out there. Our Milky Way galaxy is rich in these kinds of planets.”

But why the controversy? Isn’t this good news?

It would appear that the Kepler co-investigator chose not to wait until the official press release from NASA. He publicized these groundbreaking results in the U.K. at an event where you had to buy tickets to attend. This isn’t usually the stage you’d expect this kind of discovery to be announced — a move that will undoubtedly upset many.

“What is really annoying is that the Kepler folks were complaining about releasing information since they wanted more time to analyze it before making any announcements,” Keith Cowing, of NASAWatch.com, wrote in a SpaceRef article today. “And then the project’s Co-I goes off and spills the beans before an exclusive audience – offshore. We only find out about it when the video gets quietly posted weeks later.”

This sentiment is understandable. Only last month there was some frustration vented at the Kepler team for holding back data on 400 exoplanet candidates. While this might be standard practice — the discovering team should be allowed some time to publish work on any discoveries they have uncovered — telling the world’s scientists they will have to wait until February 2011 before they can get their hands on this invaluable data was a bridge too far.

In light of this, for a Kepler scientist to then jump the gun and disclose a groundbreaking discovery at an international conference without the backing of an official NASA release seems a little hypocritical.

But there is another argument to put out there: Why should anyone sit on such a profound discovery? Perhaps NASA and the Kepler team should have issued an earlier press release announcing to the world that 140 candidate Earth-like worlds have been detected and that further work will need to be done to confirm.

Ultimately, this controversy is just background noise when compared to what we have learned today. Official confirmation or not, Dimitar Sasselov’s message is clear. Although these detections need to be confirmed (hence why these worlds are referred to as “candidates”), it would appear there is an overwhelming preponderance of exoplanets measuring 2 Earth radii or less.

For me, that fact alone is astonishing — the first scientific evidence that worlds of Earth dimensions are not rare.

Earth is no longer unique.

For more, read my Discovery News article, “Kepler Scientist: ‘Galaxy is Rich in Earth-Like Planets‘”

Here’s One We Didn’t Discover Earlier

The 1998 archive Hubble image of HR 8799 after image analysis - one of the star's exoplanets have been resolved (NASA/HST)

The 1998 archive Hubble image of HR 8799 after image analysis - one of the star's exoplanets have been resolved (D. Lafrenière et al., ApJ Letters)

What’s just as exciting as directly imaging an exoplanet in a new observing campaign? To discover an exoplanet in an old observing campaign.

Like so many significant astronomical discoveries, archival images of the cosmos provide a valuable tool to astronomers. On its most basic level, astronomers can compare new images with images taken by the same (or different) observatory months, years or decades ago. This method can lead to the discovery of planets, asteroids and comets (when comparing two pictures of the night sky, a celestial object appears to move relative to the background stars). However, a new technique to analyse archived Hubble data in the search for exoplanets, has just revealed one of three known exoplanets orbiting the star HR 8699. The image in question was captured in 1998, when astronomers thought HR 8799 was an exoplanet-less star
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Introducing the Exomoon, and Detecting them via Exoplanet Wobble

Can astronomers really detect exomoons?

Can astronomers really detect exomoons?

Exomoon: The natural satellite of an exoplanet.

Before today, I hadn’t heard anything about the possibility of looking for moons orbiting planets in other star systems. Sorry, exomoons orbiting exoplanets in other star systems. But a British astronomer has calculated that it is possible to not only detect exomoons, but it is possible to deduce their distance from the parent exoplanet and their mass.

All this is done by measuring the exoplanet’s “wobble”; a practice more commonly used in the pursuit of the exoplanets themselves. By detecting the wobble of distant stars, the gravitational pull of the exoplanet becomes obvious. The same can be done with exoplanets, possibly revealing the presence of Earth-like exomoons.

Of the 300+ exoplanets discovered, 30 are within the habitable zones of their stars. If these large gas giant exoplanets (usually several times the mass of Jupiter) have an exoplanet system of their own, these exomoons also fall within the habitable zone…

Makes you think, doesn’t it?

For the full article, check out Astronomers Now Looking For Exomoons Around Exoplanets on the Universe Today…

Alien Worlds: Extrasolar Planets Imaged for First Time

The day has finally come. We now have direct, infrared and optical observations of planets orbiting other stars. Yesterday, reports from two independent sources surfaced, one from the Gemini and Keck II observatories and the second from the Hubble Space Telescope. Brace yourself for an awe-inspiring display of planets orbiting two stars…
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New Addition to the Exoplanetary Menu: The WASP-12b Sizzler

The hotspot: A very, very hot Jupiter has been discovered (ESA/C Carreau)

The hotspot: A very, very hot Jupiter has been discovered (ESA/C Carreau)

So how hot is the hottest known planet? Usually the temperature of a planet orbiting another star is of little concern to us. At the end of the day, are we really looking for an interstellar getaway? The chance that we’ll be colonizing any extra-solar planets in the near future is pretty low, but that won’t stop us from peering up the the heavens studying “Hot Jupiters” orbiting stars hundreds of light years away. However, astronomers have just discovered a planet I doubt we’ll ever want to visit. Enter WASP-12b, the hottest, and fastest gas giant ever observed…
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