Newfound planet is Earth-mass but gassy

Jan 06, 2014
KOI-314c, shown in this artist's conception, is the lightest planet to have both its mass and physical size measured. Surprisingly, although the planet weighs the same as Earth, it is 60 percent larger in diameter, meaning that it must have a very thick, gaseous atmosphere. It orbits a dim, red dwarf star (shown at left) about 200 light-years from Earth. KOI-314c interacts gravitationally with another planet, KOI-314b (shown in the background), causing transit timing variations that allow astronomers to measure the masses of both worlds. This serendipitous discovery resulted from analysis as part of the Hunt for Exomoons with Kepler (HEK) project. Credit: C. Pulliam & D. Aguilar (CfA)

An international team of astronomers has discovered the first Earth-mass planet that transits, or crosses in front of, its host star. KOI-314c is the lightest planet to have both its mass and physical size measured. Surprisingly, although the planet weighs the same as Earth, it is 60 percent larger in diameter, meaning that it must have a very thick, gaseous atmosphere.

"This planet might have the same mass as Earth, but it is certainly not Earth-like," says David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA), lead author of the discovery. "It proves that there is no clear dividing line between rocky worlds like Earth and fluffier planets like water worlds or gas giants."

Kipping presented this discovery today in a press conference at the 223rd meeting of the American Astronomical Society.

The team gleaned the planet's characteristics using data from NASA's Kepler spacecraft. KOI-314c orbits a dim, located approximately 200 light-years away. It circles its star every 23 days. The team estimates its temperature to be 220 degrees Fahrenheit, too hot for life as we know it.

KOI-314c is only 30 percent denser than water. This suggests that the planet is enveloped by a significant atmosphere of hydrogen and helium hundreds of miles thick. It might have begun life as a mini-Neptune and lost some of its atmospheric gases over time, boiled off by the intense radiation of its star.

Weighing such a small planet was a challenge. Conventionally, astronomers measure the mass of an exoplanet by measuring the tiny wobbles of the parent star induced by the planet's gravity. This radial velocity method is extremely difficult for a planet with Earth's mass. The previous record holder for a planet with a measured mass (Kepler-78b) weighed 70 percent more than Earth.

To weigh KOI-314c, the team relied on a different technique known as transit timing variations (TTV). This method can only be used when more than one planet orbits a star. The two planets tug on each other, slightly changing the times that they transit their star.

"Rather than looking for a wobbling star, we essentially look for a wobbling planet," explains second author David Nesvorny of the Southwest Research Institute (SwRI). "Kepler saw two planets transiting in front of the same star over and over again. By measuring the times at which these transits occurred very carefully, we were able to discover that the two planets are locked in an intricate dance of tiny wobbles giving away their masses."

The second planet in the system, KOI-314b, is about the same size as KOI-314c but significantly denser, weighing about 4 times as much as Earth. It orbits the star every 13 days, meaning it is in a 5-to-3 resonance with the outer planet.

TTV is a very young method of finding and studying exoplanets, first used successfully in 2010. This new measurement shows the potential power of TTV, particularly when it comes to low-mass difficult to study using traditional techniques.

"We are bringing transit timing variations to maturity," adds Kipping.

The planet was discovered by chance by the team as they scoured the Kepler data not for exoplanets, but for exomoons. The Hunt for Exomoons with Kepler (HEK) project, led by Kipping, scans through Kepler's planet haul looking for TTV, which can also be a signature of an exomoon.

"When we noticed this planet showed transit timing variations, the signature was clearly due to the other planet in the system and not a moon. At first we were disappointed it wasn't a moon but then we soon realized it was an extraordinary measurement," says Kipping.

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Returners
1 / 5 (4) Jan 06, 2014
The team estimates its temperature to be 220 degrees Fahrenheit, too hot for life as we know it.
KOI-314c is only 30 percent denser than water. This suggests that the planet is enveloped by a significant atmosphere of hydrogen and helium hundreds of miles thick.


So close, so close.

Looks like they found the "Hybrid" after all, but it's a tad to warm, as usual.

Played around with some concepts, but this is definitely not like anything in our solar system. Closest match is Saturn in terms of density, but for this combination of temperature, density, and mass there really is no match at all.

The oceans or atmosphere on this planet could be thousands of kilometers deep.

We don't have any "warm" gas planets in our solar system to compare it to, and Venus is nowhere near a close match in terms of density or temperature.

This is the Hybrid though, the only way it could get any closer to the ideal "Hybrid" is if it had Earth-like temperatures.

Very interesting.
Modernmystic
3 / 5 (2) Jan 06, 2014
Not even close, but interesting. I'd say it's "closeish" to "Venus like"...
Returners
1 / 5 (3) Jan 06, 2014
Not even close, but interesting. I'd say it's "closeish" to "Venus like"...


The temperature is closer to Earth than it is to Venus, but yeah, it is above boiling water we know that.
Sinister1812
1 / 5 (1) Jan 06, 2014
It might be that another planet like Earth is rare in the universe. Who'd have thought?
vlaaing peerd
3.5 / 5 (2) Jan 07, 2014
Or it might be just difficult to spot a planet like earth, quite small, too far from it's star to easily find, especially considering the exoplanet spotting hobby is newer than hipsters.

At first they mostly discovered large, near it's parent star planets, but the amount and share of discovered earth sized planets is steadily increasing over time.

I see no reason to assume planets like ours would be rare even though the temperature zone in which liquid water is possible is very narrow.
JRi
5 / 5 (3) Jan 07, 2014
The temperature is closer to Earth than it is to Venus, but yeah, it is above boiling water we know that.


Well, not really. At 104 degC, the pressure needs to be about 1.2 bar instead of 1 bar of earth that water stays at liquid state. Confortable for some microbes found deep in the ocean volcanoes.
Sinister1812
1 / 5 (1) Jan 07, 2014
I see no reason to assume planets like ours would be rare even though the temperature zone in which liquid water is possible is very narrow.


I do, considering the temperature, pressure, environment, ecosystems, continents, moon, stable axis etc that have developed over time.
vlaaing peerd
4 / 5 (2) Jan 07, 2014
@Sinister I could agree considering "earth like" is far from well defined and you have added a few extra factors such as ecosystems and the inexplicable need for a moon. As far as planet spotting is concerned, so far "earthlike" is defined by 2 factors: the possibility for liquid water and a size, mass and gravity close to ours.

Environment/ecosystems could follow from the availability of water. Continents are not required (we are looking for earth like, not humans or land animals). I don't see the specific need for a stable axis and a moon and these seem to be common anyway.

On current data the Kepler astronomers estimate there are up to 40 billion earth sized planets in our galaxy alone, if size and liquid water are the main requirements, they could be there in the billions, if you add the others you mention it would still be in the hundreds of millions.

Multiply it by the amount of galaxies we know of and likely there are more earth like planets than grains of sand on ours.
Returners
1 / 5 (1) Jan 07, 2014
Well, not really. At 104 degC, the pressure needs to be about 1.2 bar instead of 1 bar of earth that water stays at liquid state. Confortable for some microbes found deep in the ocean volcanoes.


I'm aware of that, but this planet is almost certainly not as simple as a rock covered by water, hydrogen, and helium.

We know exotic ice at extreme depths in the ocean is a barrier to nutrient uptake needed by life, particularly an ocean that must be as deep as this one must be, based on the initial density and mass measurements.

I calculated that the rocky/metallic core is probably around 2200km radius, but it could be a few hundred km larger or smaller than that. The rest of it is made of stuff we'd know as liquids, ices or "plastic" in the geology sense (eventually due to pressures at some depth, somewhere,) and gases.

Even "Spongy" rocks and molecules, like Pumice, would be smashed under their own weight back into a dense state, though they could float on top of the water-ocea
Returners
1 / 5 (1) Jan 07, 2014
Which leads to another issue. Our concept of "Ocean" may not work for this planet the same way as Earth, since we don't know everything it's made of. It could be hydrocarbons under the Hydrogen and Helium layers.

Oceans and atmosphere might be layered by density, with some materials floating on top of others in layers ranging from miles to thousands of miles thick, which is a concept quite unfamiliar to Earth, but believed to occur in the gas giants.

I think even extremophile microbes would have a hard time dealing with this issue, if it happens, though perhaps meteor impacts or super-duper-hurricanes would contribute to stirring up and mixing the oceans and atmosphere.
Returners
1 / 5 (1) Jan 07, 2014
If anybody has any ideas for molecules that could explain the observed density, I'm all ears.

Here are some of the best options I can think of.

Methane
Water
Ammonia
Hydrogen and Helium (maybe what you see is what you get).
Other hydrocarbons known or unknown

Carbon-rich or Oxygen-rich molecules would seem to be too dense to be a majority share of the atmosphere or oceans (as compared to the approximate depth of 8000km for atmosphere plus oceans).

However, we know of artificial polymers made from Carbon and Halogens which are actually less dense than that. I doubt you'd find them in high concentrations on a planet like this, even if they formed in nature, but I'm not ruling out the possibility that some times, some way, such molecules could form in nature during planet formation.

What non-exotic solids or liquids have densities close to being that low?

Liquid Oxygen should have reacted...
Dry Ice, too heavy, too hot, could be liquid/supercritical CO2
GSwift7
5 / 5 (3) Jan 07, 2014
The temperature is closer to Earth than it is to Venus, but yeah, it is above boiling water we know that


JRi beat me to it. The thick atmosphere will allow liquid water at much higher temperatures, due to the high pressure.

It might be that another planet like Earth is rare in the universe. Who'd have thought?


Kepler didn't stay functional long enough to spot earth-sized planets in earth-like orbits. If it had lasted just a few more months, we probably would have found a bunch of potentially earth-like planets. It really takes at least three transits to spot them, which means a little more than two earth years of observation, at the minimum, if you catch it at just the right time. Three or four years would have been awesome. Unfortunately, we just didn't get that much good observation time out of Kepler before it failed.
GSwift7
not rated yet Jan 07, 2014
If anybody has any ideas for molecules that could explain the observed density, I'm all ears


It is almost certainly hydrogen, helium, nitrogen, carbon, oxygen, etc. Just look at the list for Saturn or Jupiter and it's likely to be somewhat like that. We really just have to guess at this point.

As for the nature of the planet, don't jump the gun on trying to reason it out. Just accept the fact that we don't know much about it yet, and wait till we learn more.

Honestly, I didn't expect to see a planet like this. Then again, this isn't a sun-like star we're talking about here. When you're talking about sun-like stars, this thing might not be possible.

I wonder what they'll call this class of planet; a gas earth maybe?
OceanDeep
not rated yet Jan 07, 2014
"is Earth-mass but gassy"

Like Rush Limbaugh!
Torbjorn_Larsson_OM
3 / 5 (2) Jan 08, 2014
"The team estimates its temperature to be 220 degrees Fahrenheit, too hot for life as we know it."

Well, I am beaten to it, but that line is just wrong. In such high pressures there is a larger range of liquid water. We now have seen extremophiles surviving 130 degC and procreating in 122 degC. The upper limit is believed to be ~ 150 degC, when RNA and other essential organics destabilizes too much.

@vlaaing peerd: Well answered, but it is perhaps counterproductive in this case since Sinister IIRC has a track record of being anti-scientist creationist. In any case he is, as is standard creationist formulae, trolling the discredited idea of Rare Earth. It was serious science around -00, but IMHO daft as it is an open-ended bayesian model. And now _every_ factor in the original formulation has been shown to be wrong as regards habitability.
Torbjorn_Larsson_OM
1 / 5 (1) Jan 08, 2014
@Returners: "exotic ice at extreme depths in the ocean is a barrier to nutrient uptake".

Sure, but impactors would deliver a lot of nutrients. They may have up to half of our volatiles. It is ice moons, where impactors will be delayed by ice convection, that is more iffy in that regard.

@GS: "Kepler didn't stay functional long enough to spot earth-sized planets in earth-like orbits."

Luckily, it stayed functional long enough for the team to make a good estimate of the frequency of such Earth analogs. 20 % of G stars with the optimistic HZ definition, or 10 % with the pessimistic. Comes out as a few % of stars.
Graeme
not rated yet Jan 11, 2014
Perhaps there are other ways to have a planet with a shadow this big. Maybe it is orbited by a ring. Or perhaps there is a fleet of solar energy harvesting satellites. Detailed shape of the change in amount of light or transmittance spectrum of the planet may show whether or not there is an atmosphere of H2. Light variations reflected from a planetary ring as it orbits the star could give a clue as to whether there is one.
Sinister1812
not rated yet Jan 17, 2014
@vlaaing peerd: Well answered, but it is perhaps counterproductive in this case since Sinister IIRC has a track record of being anti-scientist creationist. In any case he is, as is standard creationist formulae, trolling the discredited idea of Rare Earth. It was serious science around -00, but IMHO daft as it is an open-ended bayesian model. And now _every_ factor in the original formulation has been shown to be wrong as regards habitability.


LOL Really? Calling me anti-scientist creationist? When I have never mentioned God or creation here once, as I am an atheist. I support science 100%, but I am simply saying that another Earth has not yet been discovered, not that it doesn't exist out there (it might). Earth-size? Yes. Earth-like? We don't know. You misunderstood my argument, and felt the need to lash out personally and label me a "creationist troll" and "anti-science". I am neither of those things, so no, you didn't remember correctly.