Goldilocks Stars Pose Problems for Their Habitable Planets

[Mercury]

by Ken Croswell

Far-ultraviolet radiation from orange dwarfs could endanger planetary atmospheres.

Link: Science News

[Ann]

by Ken Croswell

Far-ultraviolet radiation from orange dwarfs could endanger planetary atmospheres.

Link: Science News

I can't understand why stars of spectral class K are considered Goldilocks stars.

I mean, we have an example of one of an abundantly habitable planet. This planet, our own Earth, is orbiting a star of (early) class G.

What's wrong with G-class stars? Why aren't they considered Goldilocks stars?

Ann

[Mercury]

As main-sequence stars convert hydrogen into helium, they slowly brighten. The Sun will be about 10% more luminous in a billion years than it is now, with catastrophic consequences for the Earth.

K dwarfs have less mass than the Sun and thus brighten more slowly. So they give a terrestrial planet a more stable climate, as stated in the Science News story.

M dwarfs have even less mass than K dwarfs and thus brighten even more slowly. But many of these stars spew out flares, possibly endangering habitable planets.

In this sense, then, some astronomers have referred to K dwarfs as "Goldilocks stars": providing more stable climates than G stars but without the nasty flares of M dwarfs.

[Ann]

As main-sequence stars convert hydrogen into helium, they slowly brighten. The Sun will be about 10% more luminous in a billion years than it is now, with catastrophic consequences for the Earth.

K dwarfs have less mass than the Sun and thus brighten more slowly. So they give a terrestrial planet a more stable climate, as stated in the Science News story.

M dwarfs have even less mass than K dwarfs and thus brighten even more slowly. But many of these stars spew out flares, possibly endangering habitable planets.

In this sense, then, some astronomers have referred to K dwarfs as "Goldilocks stars": providing more stable climates than G stars but without the nasty flares of M dwarfs.

Indeed. But I still ask myself why G stars aren't considered the best ones for life, at least up there with the K dwarfs.

Ann

[Chris Peterson]

As main-sequence stars convert hydrogen into helium, they slowly brighten. The Sun will be about 10% more luminous in a billion years than it is now, with catastrophic consequences for the Earth.

K dwarfs have less mass than the Sun and thus brighten more slowly. So they give a terrestrial planet a more stable climate, as stated in the Science News story.

M dwarfs have even less mass than K dwarfs and thus brighten even more slowly. But many of these stars spew out flares, possibly endangering habitable planets.

In this sense, then, some astronomers have referred to K dwarfs as "Goldilocks stars": providing more stable climates than G stars but without the nasty flares of M dwarfs.

Indeed. But I still ask myself why G stars aren't considered the best ones for life, at least up there with the K dwarfs.

For the reason stated? That the more stable a star, the better it ought to be at supporting life, and K dwarfs are more stable than G stars?

[Ann]

As main-sequence stars convert hydrogen into helium, they slowly brighten. The Sun will be about 10% more luminous in a billion years than it is now, with catastrophic consequences for the Earth.

K dwarfs have less mass than the Sun and thus brighten more slowly. So they give a terrestrial planet a more stable climate, as stated in the Science News story.

M dwarfs have even less mass than K dwarfs and thus brighten even more slowly. But many of these stars spew out flares, possibly endangering habitable planets.

In this sense, then, some astronomers have referred to K dwarfs as "Goldilocks stars": providing more stable climates than G stars but without the nasty flares of M dwarfs.

Indeed. But I still ask myself why G stars aren't considered the best ones for life, at least up there with the K dwarfs.

For the reason stated? That the more stable a star, the better it ought to be at supporting life, and K dwarfs are more stable than G stars?

I guess it is like a lottery. Out of millions of lottery tickets, there is one that represents the Sun and and its eminently habitable planet the Earth, and three that represent Goldilocks K dwarf stars with presumably equally habitable planets.

We got the Earth and the Sun, so we got unbelievably lucky.

Well, I guess we better start looking into all the K dwarfs out there to find the three perfect ones and and their eminently habitable planets.

Ann

[Chris Peterson]

Indeed. But I still ask myself why G stars aren't considered the best ones for life, at least up there with the K dwarfs.

For the reason stated? That the more stable a star, the better it ought to be at supporting life, and K dwarfs are more stable than G stars?

I guess it is like a lottery. Out of millions of lottery tickets, there is one that represents the Sun and and its eminently habitable planet the Earth, and three that represent Goldilocks K dwarf stars with presumably equally habitable planets.

We got the Earth and the Sun, so we got unbelievably lucky.

Well, I guess we better start looking into all the K dwarfs out there to find the three perfect ones and and their eminently habitable planets.

Ann

I'm inclined to think that life is easy. That anyplace with liquid water is a likely host. That conditions don't need to be anything like here, because life is adaptable. That stability isn't very important.

But "habitable"? What does that mean. Does it just mean able to support life, or does it mean complex life? I suspect the latter is much more rare, precisely because (if we consider Earth as an example... statistically weak, but all we have) that probably does require a good deal of stability. Life formed on Earth when it had barely cooled down, but it took a few billion years to get beyond single cells.

[Ann]

For the reason stated? That the more stable a star, the better it ought to be at supporting life, and K dwarfs are more stable than G stars?

I guess it is like a lottery. Out of millions of lottery tickets, there is one that represents the Sun and and its eminently habitable planet the Earth, and three that represent Goldilocks K dwarf stars with presumably equally habitable planets.

We got the Earth and the Sun, so we got unbelievably lucky.

Well, I guess we better start looking into all the K dwarfs out there to find the three perfect ones and and their eminently habitable planets.

Ann

I'm inclined to think that life is easy. That anyplace with liquid water is a likely host. That conditions don't need to be anything like here, because life is adaptable. That stability isn't very important.

But "habitable"? What does that mean. Does it just mean able to support life, or does it mean complex life? I suspect the latter is much more rare, precisely because (if we consider Earth as an example... statistically weak, but all we have) that probably does require a good deal of stability. Life formed on Earth when it had barely cooled down, but it took a few billion years to get beyond single cells.

I didn't say "habitable". I said "eminently habitable". By that I meant, of course, "extremely full of all sorts of life forms, including many many species of highly complex life".

Ann

[Chris Peterson]

I guess it is like a lottery. Out of millions of lottery tickets, there is one that represents the Sun and and its eminently habitable planet the Earth, and three that represent Goldilocks K dwarf stars with presumably equally habitable planets.

We got the Earth and the Sun, so we got unbelievably lucky.

Well, I guess we better start looking into all the K dwarfs out there to find the three perfect ones and and their eminently habitable planets.

Ann

I'm inclined to think that life is easy. That anyplace with liquid water is a likely host. That conditions don't need to be anything like here, because life is adaptable. That stability isn't very important.

But "habitable"? What does that mean. Does it just mean able to support life, or does it mean complex life? I suspect the latter is much more rare, precisely because (if we consider Earth as an example... statistically weak, but all we have) that probably does require a good deal of stability. Life formed on Earth when it had barely cooled down, but it took a few billion years to get beyond single cells.

I didn't say "habitable". I said "eminently habitable". By that I meant, of course, "extremely full of all sorts of life forms, including many many species of highly complex life".

Ann

In which case, stability of climate seems likely to be of very high importance. And there's a lot more to that than just the stability of the parent star. For instance, Mars is (or at least, was) habitable, even eminently habitable. But its inclination varies hugely because it doesn't have a large moon to stabilize it. So it's not just the star that is important, but matters of orbital dynamics, of mass, of space environment (which can impact atmospheres), and probably other variables, as well. Many of which we don't have much of a handle on as far as exoplanets are concerned. Hopefully those are holes that will get filled in over the next years as our observational abilities grow.