Blue light observations indicate water-rich atmosphere of a super-earth

Sep 04, 2013
Figure 1: Artist's rendition of a transit of GJ 1214 b in blue light. The blue sphere represents the host star GJ 1214, and the black ball in front of it on the right is GJ 1214 b. Credit: NAOJ

(Phys.org) —A Japanese research team of astronomers and planetary scientists has used Subaru Telescope's two optical cameras, Suprime-Cam and the Faint Object Camera and Spectrograph (FOCAS), with a blue transmission filter to observe planetary transits of super-Earth GJ 1214 b (Gilese 1214 b) (Figure 1). The team investigated whether this planet has an atmosphere rich in water or hydrogen. The Subaru observations show that the sky of this planet does not show a strong Rayleigh scattering feature, which a cloudless hydrogen-dominated atmosphere would predict. When combined with the findings of previous observations in other colors, this new observational result implies that GJ 1214 b is likely to have a water-rich atmosphere.

Super-Earths are emerging as a new type of exoplanet (i.e., a planet orbiting a star outside of our Solar System) with a mass and radius larger than the Earth's but less than those of ice giants in our Solar System, such as Uranus or Neptune. Whether super-Earths are more like a "large Earth" or a "small Uranus" is unknown, since scientists have yet to determine their detailed properties. The current Japanese research team of astronomers and planetary scientists focused their efforts on investigating the atmospheric features of one super-Earth, GJ 1214 b, which is located 40 light years from Earth in the constellation Ophiuchus, northwest of the center of our Milky Way galaxy. This planet is one of the well-known super-Earths discovered by Charbonneau et. al. (2009) in the MEarth Project, which focuses on finding around nearby small stars. The current team's research examined features of light scattering of GJ 1214 b's transit around its star.

Current theory posits that a planet develops in a disk of surrounding a newly formed star (i.e., a protoplanetary disk). The element hydrogen is a major component of a , and water ice is abundant in an outer region beyond a so-called "snow line." Findings about where super-Earths have formed and how they have migrated to their current orbits point to the prediction that hydrogen or water vapor is a major atmospheric component of a super-Earth. If scientists can determine the major atmospheric component of a super-Earth, they can then infer the planet's birthplace and formation history.

Figure 2: Artist’s rendition of the relationship between the composition of the atmosphere and transmitted colors of light. Top: If the sky has a clear, upward-extended, hydrogen-dominated atmosphere, Rayleigh scattering disperses a large portion of the blue light from the atmosphere of the host while it scatters less of the red light. As a result, a transit in blue light becomes deeper than the one in red light. Middle: If the sky has a less extended, water-rich atmosphere, the effect of the Rayleigh scattering is much weaker than in a hydrogen-dominated atmosphere. In this case, transits in all colors have almost the same transit depths. Bottom: If the sky has extensive clouds, most of the light cannot be transmitted through the atmosphere, even though hydrogen dominates it. As a result, transits in all colors have almost the same transit depths. Credit: NAOJ

Planetary transits enable scientists to investigate changes in the wavelength in the brightness of the star (i.e., transit depth), which indicate the planet's atmospheric composition. Strong Rayleigh scattering in the optical wavelength is powerful evidence for a hydrogen-dominated atmosphere. Rayleigh scattering occurs when light particles scatter in a medium without a change in wavelength. Such scattering strongly depends on wavelength and enhances short wavelengths; it causes greater transit depth in the blue rather than in the red wavelength.

The current team used the two optical cameras Suprime-Cam and FOCAS on the Subaru Telescope fitted with a blue transmission filter to search for the Rayleigh scattering feature of GJ 1214 b's atmosphere. This planetary system's very faint host star in blue light poses a challenge for researchers seeking to determine whether or not the planet's atmosphere has strong Rayleigh scattering. The large, powerful light-collecting 8.2 m mirror of the Subaru Telescope allowed the team to achieve the highest-ever sensitivity in the bluest region.

The team's observations showed that GJ 1214 b's atmosphere does not display strong Rayleigh scattering. This finding implies that the planet has a water-rich or a hydrogen-dominated atmosphere with extensive clouds. (Figure 2).

Figure 3: Observed transit depths and theoretical models for GJ 1214 b. The blue and sky-blue points are the data taken with Subaru Telescope's Suprime-Cam and FOCAS, respectively (Narita et al. 2013). The red points are taken with the IRSF 1.4 m telescope located in South Africa (Narita et al. 2013). The three solid lines (yellow, green, and purple) represent hydrogen-rich, water-rich, and extensive cloud atmosphere models based on Howe & Burrows (2012). The Subaru Telescope data indicate no strong Rayleigh scattering in the blue wavelength. Credit: NAOJ

Although the team did not completely discount the possibility of a hydrogen-dominated atmosphere, the new observational result combined with findings from previous research in other colors suggests that GJ 1214 b is likely to have a water-rich (Figure 3). The team plans to conduct follow-up observations in the near future to reinforce their conclusion.

lthough there are only a small number of super-Earths that scientists can observe in the sky now, this situation will dramatically change when the Transiting Exoplanet Survey Satellite (TESS) begins its whole sky survey of small transiting exoplanets in our solar neighborhood. When new targets become available, scientists can study the atmospheres of many super-Earths with the Subaru Telescope and next generation, large telescopes such as the Thirty Meter Telescope (TMT). Such observations will allow scientists to learn even more about the nature of various super-Earths.

Explore further: The frequency of high-energy gamma ray bursts

More information: Howe, A.R. & Burrows, A.S. 2012, Theoretical Transit Spectra for GJ 1214b and other 'Super-Earths', Astrophysical Journal, Volume 756, article id. 176. dx.doi.org/10.1088/0004-637X/756/2/176

Narita, N., Fukui, A., Ikoma, M., Hori, Y., et al. 2013, Multi-color Transit Photometry of GJ 1214b through BJHKs Bands and a Long-term Monitoring of the Stellar Variability of GJ 1214, Astrophysical Journal, Volume 773, Issue 2, article id. 144. dx.doi.org/10.1088/0004-637X/773/2/144

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Humpty
1.2 / 5 (21) Sep 04, 2013
Yes - but where are the WAYYYYYY faster than light drives, for the radiation PROOF star ships?

Yes it is incredible to find all of this - all the research and techhnology and over absolutely staggering distances, BUT in the ONE fundamental sense, unless we can dash therre and back in a day or two, we are doing nothing more than counting dust that blew past in the desert millions and billions of years ago.
Anda
1.9 / 5 (7) Sep 04, 2013
Gliese 1214b

Mass: 6.36 earth masses
Radius: 2.69 earth radii
Orbital period: 1.58 days

more like Neptune than Earth and with this orbital period it's so close to the star I don't really see the interest. Of course detection method: transit. It's an "easy" planet to observe but that's all.

Why the article doesn't mention this information? Just super-earth...

Not much interesting
Q-Star
3.9 / 5 (14) Sep 04, 2013
The interesting aspects of the thing are the technologies and methods being developed to make such incredible finds. The information gathered is good because it provides more data to use in forming theories of star system and planetary formation processes.

The referring to this type of work as searches for another "Earth" is a way of keeping the public interested. The real science in the thing is acquiring data and information upon which to further our understanding of the physical universe. It is interesting AND practical. Don't worry about "getting there" or "finding life there",,,, enjoy looking for what ya can find out about the place and how the how the relative abundances of this thing or that thing fits into the big picture.
rug
2.2 / 5 (15) Sep 04, 2013
Gliese 1214b

Mass: 6.36 earth masses
Radius: 2.69 earth radii
Orbital period: 1.58 days

more like Neptune than Earth and with this orbital period it's so close to the star I don't really see the interest. Of course detection method: transit. It's an "easy" planet to observe but that's all.

Why the article doesn't mention this information? Just super-earth...

Not much interesting


They kinda did.
Whether super-Earths are more like a "large Earth" or a "small Uranus" is unknown, since scientists have yet to determine their detailed properties.

Sure, they didn't cover the orbital period or exactly how big the planet is but overall they did dispel the idea it was exactly like earth.

Like any basic science research most people will not find it interesting. Guess I just happen to be one of the few that do.
GSwift7
2.5 / 5 (11) Sep 04, 2013
I agree with the first two comments, but let me throw out something to think about that might make you change your mind a little.

Travel to another star isn't an immediate concerne, but it will be soon (relatively speaking). Compare modern tech with 200 years ago, and imagine where we will be in another 200 years. It's safe to assume human civilization will make it that long, at least.

Also consider that our research is shaped by what we already know and our goals.

If we find out now that there aren't habitable planets in range, then why worry about hyper-velocity spacecraft? OTOH, if we know that habitable planets are common and near, then our research should be shaped to prepare us for the possibility of visiting them, or at least exploring them remotely.

In 200 years I think it is reasonable that humans might live much longer as well, which makes longer space flights make a bit more sense. The gap will get shorter at least.
Q-Star
3.4 / 5 (10) Sep 04, 2013
Also consider that our research is shaped by what we already know and our goals.


In this case the research is shaped to learn the things we don't know well. Planetary system formation, & interactions. The goal is to better understand the way the universe operates. Though to some it may seem good to prioritize the search "anthropicaly", that criteria is secondary or even tertiary.

If we find out now that there aren't habitable planets in range, then why worry about hyper-velocity spacecraft? OTOH, if we know that habitable planets are common and near, then our research should be shaped to prepare us for the possibility of visiting them, or at least exploring them remotely.


Though a noble "idea", our research is much constrained by budgetary factors. That is how we shape our research goals. Going there is fun to ponder, but we aren't able to dedicate work in that direction.

The gap will get shorter at least.


Gaps get shorter as a natural course of science.
GSwift7
3 / 5 (8) Sep 04, 2013
our research is much constrained by budgetary factors - Going there is fun to ponder, but we aren't able to dedicate work in that direction


When you bring budget decisions into it, you're really having a different discussion than what I was talking about.

You said 'going there is fun to ponder', but I was talking about learning whether there's anywhere to go or not. We know that our own solar system doesn't have any place where humans could thrive (not just survive). Whether there are any places within reach where humans could actually thrive pre-empts the budget question or whether it might be 'fun'.

Here's the big BUT: But, if we find out there's a habitable world in reasonable reach, then the question of what to do about it becomes salient. Certain knowledge would drastically change the debate from whether it would be fun, to a debate about how to do it.
Lurker2358
1 / 5 (10) Sep 04, 2013
Gliese 1214b

Mass: 6.36 earth masses
Radius: 2.69 earth radii
Orbital period: 1.58 days

more like Neptune than Earth and with this orbital period it's so close to the star I don't really see the interest. Of course detection method: transit. It's an "easy" planet to observe but that's all.

Why the article doesn't mention this information? Just super-earth...

Not much interesting


If that information is correct, then the planet actually has a surface gravity somewhat less than Earth at 0.879 Earth Gravities, and has a mean density much less than Earth, at 0.326 that of Earth, or slightly denser than dry ice.

In any case, it is either NOT a "Super Earth" by the normal definition, as a super Earth is supposed to have the same average composition as Earth. Otherwise, it has an ocean which is about as deep as half or three quarters of the entire planetary radius. While that is conceivable, either way this thing would not be habitable to macroscopic Earth life.
Q-Star
2.7 / 5 (7) Sep 04, 2013
You said 'going there is fun to ponder', but I was talking about learning whether there's anywhere to go or not.


When (at some point we WILL) find such an anywhere, it will be serendipitous. Not because a dedicated search for it was made.

Whether there are any places within reach where humans could actually thrive pre-empts the budget question or whether it might be 'fun'.


Not to the scientists who depend on the limited funding.

, then the question of what to do about it becomes salient. Certain knowledge would drastically change the debate from whether it would be fun, to a debate about how to do it.


Certain knowledge WILL change the debate. But now the process is observe as much as we can, not search for certain knowledge of an mere maybe. We're not at that point in technology. I think we should learn about all the exoplanets we can, that will tell something about the big picture. Certain knowledge is not within our grasp with exo-earths yet
VendicarE
2.3 / 5 (3) Sep 04, 2013
Not many data points there.

Premature
Torbjorn_Larsson_OM
4.3 / 5 (3) Sep 04, 2013
I think this is at least the 2nd time that people have been able to check for clouds in exoatmospheres. So far zip, IIRC.

@Humpty:

We are doing science on planetary formation and astrobiology, with a lot larger ROI than your idea of going there for exploration. It is too expensive and won't ever happen.

[And if we colonize, which is a possible economy, we won't get results either. The travel times are so large that the population will diverge socially and biologically, and it is unlikely that there will be communication of results.]

@Lurker2358: The general definition of superEarth is that it is of higher mass than Earth but small enough to not be an ice giant. We do know of water-world superEarths, see the composition fig here: http://en.wikiped...er-Earth
typicalguy
5 / 5 (3) Sep 04, 2013
I'm not sure why people here are complaining about this research. They've got some planets that are easy to observe and they're gathering a lot of data on them and since they know the planets are there, they can use that knowledge to try out and perfect new detection techniques that can be useful for future planets. Planet detection and analyzing their features is a science in it's infancy. This research is good even if it's highly unlikely to detect life there.
GSwift7
3.5 / 5 (6) Sep 05, 2013
they can use that knowledge to try out and perfect new detection techniques that can be useful for future planets. Planet detection and analyzing their features is a science in it's infancy


Agree 100%.

This is so new that we are still learning how to do it, and figuring out what is possible with our present level of telescopes.

This will inform us on how to build the next generation of telescopes to be most effective (there's a lot of different instruments you can place on any given telescope, and that changes how you build them). We might even save money by avoiding building something we don't need, or an underpowered instrument.

As for whether this kind of research is worth it or not; I personally think figuring out whether we are alone or not, and how unique earth-like planets are, will be one of the most important discoveries of all time. I strugle to think of many things more important, in terms of big picture stuff.
obama_socks
1.3 / 5 (13) Sep 05, 2013
Detection and investigation from afar of Earth-like planets in other star systems with the best tech means are certainly worth the money. But there doesn't seem to be much urgency to build the ships to take our specie to such planets since we haven't as yet found one that will, without a doubt, support life as we know it. We may have to make do with the one we're on and improve it, inasmuch as we are able.
Once we find a suitable watery planet in the Goldilocks zone that could support plant and animal life, as well as necessary microbes, it would be best to first send AI to investigate it thoroughly, much like what we are doing on Mars.
Once that and several other things are accomplished, then and only then should our kind begin to plan for the next stage of discovery...sending volunteers.

However, there is no rush as it is not imperative that we leave Earth in the near future. Gathering and understanding the data is most important right now.
On secondthoughtthinkagain
1.6 / 5 (13) Sep 05, 2013
I have issue with the term super-Earth, and wonder why this dumber than dumb term is used by otherwise bright people. The only relationship this planet has to Earth is that they are both smaller than Neptune - Frankly this is hardly enough justification for that term.

Much better to stick to the original terminology and call it a rocky/icy body as verses a gaseous body. Or if required come up with a different definition. So what do we call Venus and Mars now?

mini-Earths?
Q-Star
2 / 5 (4) Sep 05, 2013
Much better to stick to the original terminology and call it a rocky/icy body as verses a gaseous body. Or if required come up with a different definition. So what do we call Venus and Mars now?


The super-Earth, Earth-like & such are unfortunate terms that eased into the idiom of exoplanet studies. Here we call Mercury, Venus, Earth & Mars the terrestrial (terra-earth) planets as opposed to Jupiter, Saturn, Uranus & Neptune, the Jovian (Jupiter-like) planets (gas giants).

Dealing with exoplanets, keep in mind that only the most rudimentary of information is available to us. It may be many decades before the technology and methodology is available which would allow us to say even "close-to-being-like-earth". They wrongly give a false impression of what we are able to determine. Grossly false impression.

When ya see "Earth" in the description think "terrestrial or rocky", "gas or gas giant or super Jupiter" think gas giant.
rug
1.9 / 5 (14) Sep 05, 2013
I have issue with the term super-Earth, and wonder why this dumber than dumb term is used by otherwise bright people. The only relationship this planet has to Earth is that they are both smaller than Neptune - Frankly this is hardly enough justification for that term.


It was kind of a cultural thing at the time. McDonalds had the super size drinks and fries so it kinda seeped into the terminology. Basicly they are saying it's a super sized earth-like planet.

Much better to stick to the original terminology and call it a rocky/icy body as verses a gaseous body.

Feel free to use it. Most people will still know what you mean.

So what do we call Venus and Mars now?

mini-Earths?

Venus is so close the the earths size I think you could just stick with earth-like. Mars on the other hand...mini earth. I like it. I think I'll start using that.
GSwift7
3.7 / 5 (6) Sep 06, 2013
only the most rudimentary of information is available to us. It may be many decades before the technology and methodology is available which would allow us to say even "close-to-being-like-earth". They wrongly give a false impression of what we are able to determine. Grossly false impression


yeah, that's a polite understatement.

I would place money on more than half of the current claims turning out to be wildly wrong. We have absolutely zero evidence that the parameterizations they use are correctly scaled. Every single bit of it is based on inference. In many cases, they build up a chain of interdependent inferences, so if any of the base inferences turns out to be wrong, then all the ones supported by it come crashing down like a house of cards.
obama_socks
1 / 5 (15) Sep 06, 2013
Precisely. But the religion of science can never be wrong, don't you see? It is blasphemy; a complete heresy to admit to such things after scientists have spent decades in research and book learning to make the little progress they have come to expect of themselves. Scientists are a breed apart from everyone else and should be venerated and, when meeting one, show respect by genuflecting in their general direction.

m(^L^)m
Captain Stumpy
1.6 / 5 (13) Sep 06, 2013
IMHO Personally, I would really love to see more space travel, but I don't see it happening until it becomes a commercially viable enterprise.
until someone can make a snot-load of dough on it, we aint going nowhere fast. and that is one BIG thing that hurts our long term colonization efforts. there is no NEED!
and we haven't even figured out how to successfully keep ourselves in space for extended periods without physiological changes that would inhibit our re-entry into an environment with gravity.
aside from that and the immense amounts of time that would as surely alter/ evolve the travelers and the colonizers might be an entirely different species... SURELY an entirely different culture, and not really compatible. probably would evolve a completely separate language...
time spans are too great with current tech and knowledge...
Captain Stumpy
1.6 / 5 (13) Sep 06, 2013
but I also hold out hope... for every scientific find, there is a door closed, and a dozen opened...
who knows what tomorrow will bring...
it would be really NICE if we could get politics out of science, but that will never happen...
at least it is really cool knowing that there 'could' be somewhere to go... and as they find more, they figure out how to look better, etc....
Lurker2358
1 / 5 (10) Sep 07, 2013
Much better to stick to the original terminology and call it a rocky/icy body as verses a gaseous body. Or if required come up with a different definition. So what do we call Venus and Mars now?

mini-Earths?


The way this article's author is using the Term "Super Earth" is not the same way it is used on the Science Channel, that's for sure.

On there, they use the term "Super Earth" to imply a planet with Earth-like composition, but being more massive than the Earth. On the Science Channel, Water Worlds are usually classified as a different type of planet, as a "Super Earth" is intended to imply a planet which could conceivably support Earth-Like surface characteristics.

A planet that is covered in an ocean of only a few hundred meters to a few kilometers need not be considered a "Water World," as Earth itself could conceivably produce those conditions.

Water World is used for planets who's oceans are incredibly deep, and typically produce exotic ices at depth.
Fleetfoot
4.7 / 5 (3) Sep 08, 2013
.. it has an ocean which is about as deep as half or three quarters of the entire planetary radius. While that is conceivable, either way this thing would not be habitable to macroscopic Earth life.


Fish, dolphins, whales etc. would not have a problem. Not so good for the mice though.

This is the sort of planet that could harbour "intelligent" life yet be undetectable by any SETI search due to the lack of any technology.
Lurker2358
1 / 5 (9) Sep 08, 2013
Fish, dolphins, whales etc. would not have a problem. Not so good for the mice though.

This is the sort of planet that could harbour "intelligent" life yet be undetectable by any SETI search due to the lack of any technology.


You're forgetting that an object covered entirely by water, especially a super-earth or "water world", would have trouble with nutrient transport. When exotic ices form at the bottom of the oceans (water becomes a solid under it's own weight if there is enough depth and enough gravity), it will create an impenetrable boundary between the water and the sea floor, which would only be broken by volcanism.

Dolphins would probably not be able to breathe on such a world, because the water vapor content in the atmosphere would be so high they'd drown.

Additionally, the insanely low albedo combined with no land to radiate away heat, means that the planet is cooled only by convection, and that means the water would be incredibly hot relative to it's location.
Fleetfoot
5 / 5 (1) Sep 08, 2013
You're forgetting that an object covered entirely by water, especially a super-earth or "water world", would have trouble with nutrient transport. When exotic ices form at the bottom of the oceans (water becomes a solid under it's own weight if there is enough depth and enough gravity), it will create an impenetrable boundary between the water and the sea floor, which would only be broken by volcanism.


True but that would be a stable boundary, above would essentially be a closed system as our oceans are above the floor. Decay of sediments would recycle nutrients.

Dolphins would probably not be able to breathe on such a world, because the water vapor content in the atmosphere would be so high they'd drown.


Evolution would fit their analogue to the niche. My point was that they would be unlikely to develop interstellar EM technology regardless of the level of intelligence without access to minerals and dry land.
triplehelix
1 / 5 (9) Sep 09, 2013
Compare modern tech with 200 years ago, and imagine where we will be in another 200 years. It's safe to assume human civilization will make it that long, at least.


This isn't a very logical argument as you assume technology is limitless.

This argument assumes infinite progression. I am not saying it is the case, but it is wholly possible that we are maybe getting to the maximum technology level our laws of physics allow.

I agree strongly with the first comment. It's all nice finding these Earth-like planets, but they're so far away what we're seeing now is many many millions of years old as that's how long it's taken the light to reach our telescopes. Also, until we invent much faster than light speed, even leaving our own solar system would take decades, and reaching the nearest star without light or FTL speeds would take millenia.

yyz
5 / 5 (2) Sep 09, 2013
"It's all nice finding these Earth-like planets, but they're so far away what we're seeing now is many many millions of years old as that's how long it's taken the light to reach our telescopes."

All these exoplanet finds have been around stars within our galaxy. The most distant known exoplanet is no more than 30,000 light years distant:

http://en.wikiped...iewpoint
GSwift7
2.6 / 5 (5) Sep 10, 2013
In general use, the term super-earth means the planet is significantly larger than earth, but still has similar density. Any body with similar density to Earth has the potential to be Earth-like, more or less.

Your argument over surface covering doesn't even enter into it, since we have no method to determine surface covering yet.

Also keep in mind that the oceans of Earth are such a small percentage of the Earth's total mass/volume that our surface water can be ignored when calculating the Earth's density. When seen from space, the surface of the Earth, from the highest mountain to the deepest ocean basin, is proportionally smoother than a bowling ball. Surface features are NOTHING in the case of a rocky planet.

The difference between a 1 mile deep global ocean and no oceans at all wouldn't change the density of the whole planet by enough to be measurable from another star.
GSwift7
2.6 / 5 (5) Sep 10, 2013
All these exoplanet finds have been around stars within our galaxy. The most distant known exoplanet is no more than 30,000 light years distant:


You are totally correct, so I'm not disagreeing in any way, but that does bring up a point regarding intelligent life.

Even a planet 200 light years away, looking at us right now, would probably see no signs of the technology we used 200 years ago.

A planet 30,000 years away, looking at us right now, would see an uninviting world with most of its continents covered by mile thick layers of ice, with little chance of intelligent life surviving here. The global climate would look too cold and dry to be a good place to visit.

If you look at the wide range of climates the Earth has sustained over geologic time scales, I think it starts to look silly when people theorize about the "habitable zone". We don't have a clue what the difference is between a snowball, a greenhouse or a poison gas chamber. Earth has been all three.