Earth-sized planet found in habitable zone of red dwarf

[-Velocity-]

http://www.space.com/25530-earthsize-exoplanet-kepler-186f-habitable-discovery.html

Kepler has finally delivered on an Earth-sized world in the habitable zone of a star.

It's about 1.1 Earth radii, and orbits in the outer area of the habitable zone, about 50 million kilometers from its host star. It's far enough away from its host star that I have to wonder if it's actually tidally-locked or not. Mercury is not tidally locked to the Sun, orbits just a bit further out from the Sun than this planet does from its host star, and this planet's host star is a red dwarf and so it's significantly less massive. If this planet is not tidally locked, I think that could significantly improve its habitability. I'm still not 100% on board with the idea of habitable, tidally-locked planets.

Anyway, if anyone could find any more info on the host star, I'd appreciate it. All the article states is that it's a red dwarf 490 light-years away.

[KASASpace]

http://www.space.com/25530-earthsize-exoplanet-kepler-186f-habitable-discovery.html

Kepler has finally delivered on an Earth-sized world in the habitable zone of a star.

It's about 1.1 Earth radii, and orbits in the outer area of the habitable zone, about 50 million kilometers from its host star. It's far enough away from its host star that I have to wonder if it's actually tidally-locked or not. Mercury is not tidally locked to the Sun, orbits just a bit further out from the Sun than this planet does from its host star, and this planet's host star is a red dwarf and so it's significantly less massive. If this planet is not tidally locked, I think that could significantly improve its habitability. I'm still not 100% on board with the idea of habitable, tidally-locked planets.

Anyway, if anyone could find any more info on the host star, I'd appreciate it. All the article states is that it's a red dwarf 490 light-years away.

What happened to Kepler-62?

It had two planets in the habitable zone, and one was quite close, but it was a super Earth........

Red Dwarf you say?

The Star's designation is Kepler-186 according to that article, so just look up that star.....

Okay, I will.

Try here

[Tommygun]

I wonder how much radiation it picks up from the red dwarf at that distance.

It receives one-third the heat energy, but what about the rest of the radiation spectrum.

[The Jedi Master]

I'm imaging a cold world that looks like northern Canada. I'm assuming that is what you would get at that distance from an already-cold star. Habitable, but cold.

On a totally unrelated note, are they drawing up generation ship plans or anything?

[Klingon Admiral]

I'm imaging a cold world that looks like northern Canada. I'm assuming that is what you would get at that distance from an already-cold star. Habitable, but cold.

On a totally unrelated note, are they drawing up generation ship plans or anything?

There is no such thing as a single biome planet.

And no, we aren't.

[Rakaydos]

I'm imaging a cold world that looks like northern Canada. I'm assuming that is what you would get at that distance from an already-cold star. Habitable, but cold.

On a totally unrelated note, are they drawing up generation ship plans or anything?

Why not take a 50 year trip with a warp drive?

[The Jedi Master]

There is no such thing as a single biome planet.

Mars is a desert. Venus is a volcano world. And so forth.

[Duxwing]

Mars is a desert. Venus is a volcano world. And so forth.

It has two principal biomes: cold polar desert, and hot middle desert.

-Duxwing

[Mr. Entropy]

I wonder how much radiation it picks up from the red dwarf at that distance.

It receives one-third the heat energy, but what about the rest of the radiation spectrum.

Looking at the blackbody curve (assuming a temperature of 3500K) for the star shows a peak wavelength at around 800nm, that's infrared. There's very little UV emission, and almost no x-rays or gamma rays. Most of the output is radio, microwave, and IR, with visible output mostly red-orange.

Here is a tool that plots a blackbody curve for a given temperature

[Klingon Admiral]

It has two principal biomes: cold polar desert, and hot middle desert.

-Duxwing

A exogeologist could now probably tell you while the flat desert on the one side of mars is a completely different biome from the slightly hilly desert on the other side. Or why 30 kilometres ice above a subglacial ocean are completely different from 45 kilometres of ice above solid ground. And as it is within the habitable zone, liquid water and thus a hydrosphere is possible, which would greatly complicate the surface features of the planet. Heck, it could even be completely submerged in water. Or it could be a barren rock floating through the void.

[Syphus]

There's so much talk about this and the "habitable zone" and it being "earth sized". But people seem to forget that two of the three earth-sized planets in the habitable zone in this solar system are not exactly friendly places.

[Tommygun]

Looking at the blackbody curve (assuming a temperature of 3500K) for the star shows a peak wavelength at around 800nm, that's infrared. There's very little UV emission, and almost no x-rays or gamma rays. Most of the output is radio, microwave, and IR, with visible output mostly red-orange.

Here is a tool that plots a blackbody curve for a given temperature

OK thanks, well I guess you'll get frostbite long before you get skin cancer then.

[Rakaydos]

Looking at the blackbody curve (assuming a temperature of 3500K) for the star shows a peak wavelength at around 800nm, that's infrared. There's very little UV emission, and almost no x-rays or gamma rays. Most of the output is radio, microwave, and IR, with visible output mostly red-orange.

Here is a tool that plots a blackbody curve for a given temperature

Would the planet need a magnetic field to ward off radiation, or would the weaker star put out more survivable levels even without?

[Mr. Entropy]

Would the planet need a magnetic field to ward off radiation, or would the weaker star put out more survivable levels even without?

Use the tool I linked to make a side-by-side comparison of the Sun (5800K) and the M1 dwarf (3500K). As you decrease the temperature of a blackbody (such as a star), the intensity of emitted radiation decreases. Dramatically.

The yellow line is the blackbody curve for the Sun. The red line is for the red dwarf. Because there is little to no UV or x-ray emission, a magnetosphere/ionosphere is not necessary for Earth-like life. On Earth, the atmosphere absorbs much of the infrared radiation from the Sun, while the upper atmosphere and magnetosphere protect against higher-energy radiation.

Edited April 18, 2014 by Mr. Entropy

[Rakaydos]

Are you compensating for the inverse square law from the body being in about the orbital radius of mercury?

[Tommygun]

When they say it receives one-third the heat energy, are they referring to solar irradiance?

I know Mars receives a bit less than half the solar irradiance that Earth does.

If that's the case, it is going to be awfully cold unless the atmosphere is very different or much much thicker.

[Mr. Entropy]

Are you compensating for the inverse square law from the body being in about the orbital radius of mercury?

If that was directed at me, then the answer is no, because it's unnecessary. A blackbody spectrum is a measure of the intensity of wavelengths emitted by a blackbody (stars act as blackbodies) at a given temperature. It is not a measure of the intensity of radiation received from a source, so distance is not considered.

[Rakaydos]

Given that my original question was about how much radiation the planet would receive, I dont see how your answer is relevant, then.

[-Velocity-]

Looking at the blackbody curve (assuming a temperature of 3500K) for the star shows a peak wavelength at around 800nm, that's infrared. There's very little UV emission, and almost no x-rays or gamma rays. Most of the output is radio, microwave, and IR, with visible output mostly red-orange.

Here is a tool that plots a blackbody curve for a given temperature

I'm reasonably certain that the problem with red dwarfs and UV is not in any way related to their blackbody spectrum; it's the fact that for some reason, red dwarfs tend to be much more magnetically active than Sun-like stars. Big solar flares (coronal mass ejections, CMEs) tend to be very bright in ultraviolet.

So, I would expect the UV on red dwarf planet to not be relatively minor much of the time, and suddenly spike when a large stellar flare is going on. If there was no ozone or the ozone simply wasn't thick enough, it would not be unreasonable to suppose that life on a red dwarf planet might evolve UV receptors that would signal them to take shelter in some way when a CME was occuring.

This is a small solar flare on our Sun in ultraviolet:

[-Velocity-]

Use the tool I linked to make a side-by-side comparison of the Sun (5800K) and the M1 dwarf (3500K). As you decrease the temperature of a blackbody (such as a star), the intensity of emitted radiation decreases. Dramatically.

The yellow line is the blackbody curve for the Sun. The red line is for the red dwarf. Because there is little to no UV or x-ray emission, a magnetosphere/ionosphere is not necessary for Earth-like life. On Earth, the atmosphere absorbs much of the infrared radiation from the Sun, while the upper atmosphere and magnetosphere protect against higher-energy radiation.

Incorrect. The blackbody spectrum has nothing to do with the actual level of magnetic activity on the star. Everything I've ever read about red dwarfs says that they are actually more active stars than Sun-like stars. Much more active, in fact. Thus, UV levels on a red dwarf planet could actually spike to very high levels frequently, when there are large stellar flares.

Secondly, the large number of stellar flares and coronal mass ejections coming off of a red dwarf star might make a magnetosphere even MORE necessary than on a planet around a Sun-like star.

[-Velocity-]

There's so much talk about this and the "habitable zone" and it being "earth sized". But people seem to forget that two of the three earth-sized planets in the habitable zone in this solar system are not exactly friendly places.

Incorrect for both planets-

1) Mars is not Earth-sized, it is much smaller than Earth.

2) Venus IS effectively Earth-sized, but it is not inside the habitable zone- it is too close to the Sun. Earth is, in fact, near the the inner edge of the habitable zone, or so they say. Our planet's remaining habitable years are supposedly numbered at 500 million to 1 billion.

Venus may have been inside the habitable zone in the distant past, but went runaway greenhouse as the Sun brightened and the habitable zone slowly moved further out. Its seems possible that there were three "habitable" planets 4 billion years ago, but only the Earth remains so today. Venus is too close and Mars is too small.

Personally though, I wonder if Venus might always have had too thick of an atmosphere. I have a hard time imagining how so much carbon dioxide could build up AFTER planetary formation was already complete.

Edited April 18, 2014 by |Velocity|

[The_Rebel_Flagship]

If that's the case, it is going to be awfully cold unless the atmosphere is very different or much much thicker.

Well considering the fact that this planet is said to be 10% more massive than Earth, I'd say the atmosphere is plenty thick!

[Mr. Entropy]

Incorrect. The blackbody spectrum has nothing to do with the actual level of magnetic activity on the star. Everything I've ever read about red dwarfs says that they are actually more active stars than Sun-like stars. Much more active, in fact. Thus, UV levels on a red dwarf planet could actually spike to very high levels frequently, when there are large stellar flares.

Secondly, the large number of stellar flares and coronal mass ejections coming off of a red dwarf star might make a magnetosphere even MORE necessary than on a planet around a Sun-like star.

Ok, I'll be honest here, I derped and didn't even consider the magnetic activity. But after a bit of reading on the subject (and finding a few potential doctoral dissertation topics in the process) I'm able to sort of prove my point, albeit in a different manner than intended. I'll admit, its a stretch, but not theoretically impossible. Turns out we're both right, sort of.

It is believed that the variable phase of a red dwarf only lasts for a comparatively short period of the star's evolution, roughly 1.2 billion years out of a potential multi-trillion year life span, after which it's rotation slows and its magnetic activity weakens. For example, Barnard's star, an M-class red dwarf about 6 light years away, has little to no flare activity, the last notable flare event occurred in 1998 (although it's only been observed since 1916, so we can't say for certain how active it is. The Kepler-186 system is believed to be of similar age to the solar system, about 4.5 billion years, so it might be stable. Need to do more research.

If the planet were to have formed further away from the star, and later migrate into the habitable zone after the star stabilizes, then it could in theory support Earth-like life without a magnetosphere. But that assumes that life would evolve in the same way as on Earth, which is very unlikely in this environment. In either case, a magnetosphere would be very helpful, but not necessarily required, as life could in theory evolve through natural selection to resist flares. Assuming the atmosphere wasn't eroded during the variable phase of the star's life, anyway. Even the most powerful magnetic field possible for a terrestrial planet wouldn't be enough to adequately protect the atmosphere during this time.

What I'm saying is that it's not outside the realm of possibility for this planet to support some kind of life without a magnetosphere, even though a weak rotation-induced magnetic field likely exists around the planet, making the argument moot. That said, it is rather unlikely, but not impossible. Even on Earth we find things living in the most inhospitable environments imaginable.

[-Velocity-]

Ok, I'll be honest here, I derped and didn't even consider the magnetic activity. But after a bit of reading on the subject (and finding a few potential doctoral dissertation topics in the process) I'm able to sort of prove my point, albeit in a different manner than intended. I'll admit, its a stretch, but not theoretically impossible. Turns out we're both right, sort of.

It is believed that the variable phase of a red dwarf only lasts for a comparatively short period of the star's evolution, roughly 1.2 billion years out of a potential multi-trillion year life span, after which it's rotation slows and its magnetic activity weakens. For example, Barnard's star, an M-class red dwarf about 6 light years away, has little to no flare activity, the last notable flare event occurred in 1998 (although it's only been observed since 1916, so we can't say for certain how active it is. The Kepler-186 system is believed to be of similar age to the solar system, about 4.5 billion years, so it might be stable. Need to do more research.

If the planet were to have formed further away from the star, and later migrate into the habitable zone after the star stabilizes, then it could in theory support Earth-like life without a magnetosphere. But that assumes that life would evolve in the same way as on Earth, which is very unlikely in this environment. In either case, a magnetosphere would be very helpful, but not necessarily required, as life could in theory evolve through natural selection to resist flares. Assuming the atmosphere wasn't eroded during the variable phase of the star's life, anyway. Even the most powerful magnetic field possible for a terrestrial planet wouldn't be enough to adequately protect the atmosphere during this time.

What I'm saying is that it's not outside the realm of possibility for this planet to support some kind of life without a magnetosphere, even though a weak rotation-induced magnetic field likely exists around the planet, making the argument moot. That said, it is rather unlikely, but not impossible. Even on Earth we find things living in the most inhospitable environments imaginable.

Thanks for the info, you appear to be right about strong red dwarf flaring activity being a youthful phase; I earned something new, thanks! I looked up a paper on Google scholar. In a paper titled "Habitability of planets around red dwarf stars" we have:

Climatic implications of starspots were modelled in Joshi et al. (1997). dM stars generally exhibit spots proportionately much larger than those on our Sun. These can cause decreases in stellar luminosity of some 10–40% for a few Earth months (Rodono, 1986). The extreme of a 40% decrease in luminosity lasting 4 months would result in a maximum decrease in surface temperature of 27 K in a zone running west along the 20N circle from the 0 meridian. Areas near the eastern terminator, in particular, would be liable to reductions to and below the freezing point of water. However, this would not involve temperature extremes that are excessive in terms of the tolerances of Earth tree species and it is reasonable to conjecture that native plants would evolve with the ability not to suffer fatal injury from low temperatures associated with sunspot growth activity.

Flare activity on dMe stars (chromospherically active red dwarf stars showing hydrogen-alpha in emission) is commonplace and has been studied for decades. Flares on a given star may vary greatly in intensity and duration (Kunkel, 1969; Pettersen and Coleman, 1981; Giampapa and Liebert, 1986; Rodino, 1986; Worden et al, 1984), although there are generalised relationships between mean flare energy and quiescent stellar output (Lacy et al., 1976). Flaring is most typical of young stars and seems to be related to rapid rotation. It wanes (the e-folding timescale is roughly 1.0 Gyr (Stauffer and Hartmann, 1986; Demarque et al., 1986), as rotation decays through stellar winds (but members of binary systems can be spun up, or retain rapid captured rotation; see Zahn, 1994, and references therein). Some stars flare very frequently, for example UV Ceti was seen to flare about every twenty minutes during observations reported by Mochanacki and Zirin (1980).

Flares will be associated with increases in a star’s output of X-rays, UV, visible, IR, and charged particles emitted as stellar winds (which enhance the radio flux, as well), but essentially no radiation of wavelengths less than about 2900 Å would reach the ground through an Earth-like atmosphere.

M. J. Heath, L. R. Doyle, M. M. Joshi, and R. M. Haberle, “Habitability of planets around red dwarf stars,†Origins of Life and Evolution of the Biosphere, vol. 29, no. 4, pp. 405–424, 1999.

So it looks like you are probably be correct about the flaring, at least for the majority of red dwarf stars. However, I'd bet the older red dwarfs still flare some... you probably never get rid of it. I know that Sun-like stars also go through a very active phase in their youth (much shorter than 1 Gyr though) called the "T Tauri" stage.

Anyway, the point of the magnetic field is to deflect charged particles, it has nothing to do with UV. A lot of people see "radiation" and think it's all the same; nothing could be further from the truth.

The magnetic field reduces radiation from sources like cosmic rays at the surface, and also helps prevent stellar winds from eroding the atmosphere. However, I don't think that a magnetic field is 100% necessary. At atmosphere also acts to protect the surface from ionizing radiation. Additionally, the atmosphere-protecting value of a magnetic field may be literally a little over-blown. Just look at Venus- the thickest atmosphere of all the terrestrial planets, and virtually no magnetic field to speak of.

Consider two other things-

The magnetic field would be more necessary when the star is young. Lots of planets can maintain a magnetic field in their youth, but not in old age (ex: Mars, I think the Moon too, IIRC).

The planet probably has to have a decent rotation rate to generate a magnetic field. Tidally-locked red dwarf planets would likely spin too slowly.

Edited April 18, 2014 by |Velocity|

[Rakaydos]

The planet probably has to have a decent rotation rate to generate a magnetic field. Tidally-locked red dwarf planets would likely spin too slowly.

Woult the 5th planet out from it's star have any reason to be tidaly locked? I'd expect there would be enough gravatational "noise" from the other planets to prevent it.