Questions on the Sun

[Kitsune]

I have been having some debates with someone who claims to neither be a creationist or evolutionist. I have never actually debated one before and did not think they exist.

Some discussion about the Sun came up and want to know if someone can help me:

First, has the sun become warmer or cooler since it first formed? My understanding is that it has gotten warmer. Related, how much Warmer (or cooler) has the Sun become since the Earth has formed?

Second, how much matter does the sun turn into energy? What percentage of material has the Sun "Lost" over the course of the existance of the Earth? As well, has the Sun become physically larger or smaller over the course of its lifetime and how much has it changed?

[GrandMasterTerwynn]

I have been having some debates with someone who claims to neither be a creationist or evolutionist. I have never actually debated one before and did not think they exist.

Some discussion about the Sun came up and want to know if someone can help me:

First, has the sun become warmer or cooler since it first formed? My understanding is that it has gotten warmer. Related, how much Warmer (or cooler) has the Sun become since the Earth has formed?

Second, how much matter does the sun turn into energy? What percentage of material has the Sun "Lost" over the course of the existance of the Earth? As well, has the Sun become physically larger or smaller over the course of its lifetime and how much has it changed?

A) Solar intensity has slowly ramped up since the birth of the Sun. This is mostly due to the gradual buildup of helium "ash" in the Sun's core, requiring slowly increasing pressures and temperatures to keep up hydrogen fusion. The relevant results are that the Sun is something like 30% brighter today than it was a few billion years ago. In a few hundred million years, it will become hot and bright enough to bring an end to land-based life. In a billion years, it will become bright enough to evaporate Earth's free water stores and transform it into another Venus, killing the remaining life.

B) Helium is 0.7% lighter than the combined mass of four hydrogen atoms. So, over the course of the Sun's ten billion year lifetime, it will convert at most 0.7% of its mass to energy. Realistically, since only the mass at the inner core of the Sun achieves high enough pressures to undergo fusion, and since the Sun will end up blowing off much of its hydrogen into a planetary nebula as it becomes a white dwarf, it will end up converting maybe a tenth of that. 1

[Dooey Jo]

B) Helium is 0.7% lighter than the combined mass of four hydrogen atoms. So, over the course of the Sun's ten billion year lifetime, it will convert at most 0.7% of its mass to energy.

Just a little nitpick but shouldn't the upper limit also take into account the helium fusion during the Red Giant phase? It, obviously, won't really matter because it'll never be able to fuse all its material but still...

[Darth Wong]

I have been having some debates with someone who claims to neither be a creationist or evolutionist.

I'll bet he's actually an ID creationist. Those guys are always saying shit like that. The first thing they want to do is reassure you that they're not fanatics, because ... of course, they are. It's like Bill O'Reilly; the first thing he does is reassure everyone that he's not an extremist, he's actually a moderate, and he doesn't use spin control or deceptive rhetoric, etc. etc., and he makes this effort because it's the exact opposite of the truth.

I have never actually debated one before and did not think they exist.

Some discussion about the Sun came up and want to know if someone can help me:

First, has the sun become warmer or cooler since it first formed? My understanding is that it has gotten warmer. Related, how much Warmer (or cooler) has the Sun become since the Earth has formed?

Second, how much matter does the sun turn into energy? What percentage of material has the Sun "Lost" over the course of the existance of the Earth? As well, has the Sun become physically larger or smaller over the course of its lifetime and how much has it changed?

Do the math. The Sun puts out 3.827E26 watts of power. H-H, or "4H -> He4 + junk" fusion produces roughly 25 MeV (4E-12 J) for every 4 Hydrogen atoms reacting (6.7E-27 kg), which works out to 6E14 J/kg full-cycle. In other words, 3.827E26 watts of power require the conversion of 6.4E11 kg of hydrogen into helium plus junk products. During this process, roughly 0.7% of the reactant mass is lost, so this means we are consuming 4.5E9 kg per second, or roughly 4.5 million metric tonnes per second.

That sounds like a lot, but you have to keep in mind that the Sun's mass is roughly 2E30 kg, or 2 billion billion billion tonnes. So even at 4.5 million metric tonnes per second, it would take 5 billion years to use up 0.035% of the mass of the Sun.

[Ariphaos]

snip math

When arguing with a Creationist or IDist about this, it's better to just use Einstein's e=mc^2 equation - ~9e16 watts per kilogram. They're more familiar with it. 4e26 / 9e16 = ~4.5e9 kg per second.

Mass of sun = 2e30 kg, as you mentioned -

142e15 kg per year. Or less than a hundredth of a trillionth of the Sun's mass per year.

A) Solar intensity has slowly ramped up since the birth of the Sun. This is mostly due to the gradual buildup of helium "ash" in the Sun's core, requiring slowly increasing pressures and temperatures to keep up hydrogen fusion. The relevant results are that the Sun is something like 30% brighter today than it was a few billion years ago. In a few hundred million years, it will become hot and bright enough to bring an end to land-based life. In a billion years, it will become bright enough to evaporate Earth's free water stores and transform it into another Venus, killing the remaining life.

Are you sure about that? Remember, Earth is cooling off and slowing its rotation, as well as being pushed back by the Sun, so the total energy the biosphere is receiving does not ramp straight up with the Sun's output.

Granted, it still ramps up faster than the planet cools eventually. Kind of interesting, really, it also implies a limited window for sentient life to evolve in.

[Kitsune]

I'll bet he's actually an ID creationist. Those guys are always saying shit like that. The first thing they want to do is reassure you that they're not fanatics, because ... of course, they are. It's like Bill O'Reilly; the first thing he does is reassure everyone that he's not an extremist, he's actually a moderate, and he doesn't use spin control or deceptive rhetoric, etc. etc., and he makes this effort because it's the exact opposite of the truth.

Well, this persons stance is that if you have not actaully seen it than you cannot say for certain that it happened the way you describe.

[wolveraptor]

Tell him that the evolutionary theory doesn't say that "trilobites evolved in precisely this way...", but rather is a mechanism for the gradual change of species over time. We know this occurs due to several examples of excellently preserved fossil lineages, including hominids, dino-birds, horses, elephants and probably more that I can't pull off the top of my head.

The precise way in which some species, which left poor fossil records, evolved is certainly up to debate: however, the fact that evolution occurs, and the way it does, are not disputable.

[GrandMasterTerwynn]

A) Solar intensity has slowly ramped up since the birth of the Sun. This is mostly due to the gradual buildup of helium "ash" in the Sun's core, requiring slowly increasing pressures and temperatures to keep up hydrogen fusion. The relevant results are that the Sun is something like 30% brighter today than it was a few billion years ago. In a few hundred million years, it will become hot and bright enough to bring an end to land-based life. In a billion years, it will become bright enough to evaporate Earth's free water stores and transform it into another Venus, killing the remaining life.

Are you sure about that? Remember, Earth is cooling off and slowing its rotation, as well as being pushed back by the Sun, so the total energy the biosphere is receiving does not ramp straight up with the Sun's output.

The contribution of Earth's internal heat is considered to be negligible in this instance. While Earth's internal heat provides the energy for selected niches of life (i.e. those lifeforms dwelling around undersea geothermal vents and surface hot-springs) it escapes the planet along limited, narrow areas. Most life on Earth relies on insolation. Also, our thick atmosphere with it's potent greenhouse effect serves to mitigate the effects of the length of our day, so the only factor that really remains is the level of solar energy being absorbed by Earth. And Earth is too massive for photon pressure to affect a meaningful change in Earth's position or velocity with respect to the Sun, so the Sun hardly "pushes back" the Earth.

Thus, the only meaningful factor to consider here is the level of solar radiation striking Earth. Earth's atmosphere may compensate for increasing insolation somewhat (more evaporation leading to more clouds, and clouds boost the planet's albedo, or ability to reflect light.) However, insolation will eventually creep up enough further compensation becomes impossible and the planet either dries out, or goes into a runaway greenhouse effect.

Granted, it still ramps up faster than the planet cools eventually. Kind of interesting, really, it also implies a limited window for sentient life to evolve in.

Yes, a given planet falling within a range of mass sufficient to hold onto a sizeable atmosphere will only be habitable for a finite fraction of its lifespan. It will cease to become habitable when the stellar flux in its area increases enough where it becomes to hot for life to exist, or when its internal heat source peters out, and the interior of the planet cools to the point where outgassing of volatiles is no longer sufficient to replace the atmosphere lost due to stellar heating. In the former case, you wind up with Venus. In the latter case, you wind up with Mars.



There's a

[Winston Blake]

I'll bet he's actually an ID creationist. Those guys are always saying shit like that. The first thing they want to do is reassure you that they're not fanatics, because ... of course, they are. It's like Bill O'Reilly; the first thing he does is reassure everyone that he's not an extremist, he's actually a moderate, and he doesn't use spin control or deceptive rhetoric, etc. etc., and he makes this effort because it's the exact opposite of the truth.

Well, this persons stance is that if you have not actaully seen it than you cannot say for certain that it happened the way you describe.

Sounds like typical (Matrix-induced?) solipsism. I'd suggest DW's Science, the Grand Illusion, and Other Neat Stuff essay, under "What makes Science so Great?".

[Ariphaos]

The contribution of Earth's internal heat is considered to be negligible in this instance. While Earth's internal heat provides the energy for selected niches of life (i.e. those lifeforms dwelling around undersea geothermal vents and surface hot-springs) it escapes the planet along limited, narrow areas. Most life on Earth relies on insolation. Also, our thick atmosphere with it's potent greenhouse effect serves to mitigate the effects of the length of our day, so the only factor that really remains is the level of solar energy being absorbed by Earth. And Earth is too massive for photon pressure to affect a meaningful change in Earth's position or velocity with respect to the Sun, so the Sun hardly "pushes back" the Earth.

It's the solar winds that push back the Earth - as the sun's output increases, so does the number of particles it's throwing off. As I understand it it will meaningfully push back Earth's orbit over the course of the Sun's lifespan. The Sun will swallow Earth's current orbit, but not actually swallow Earth, for example.

In this case, probably just as negligable, but I was curious as it is currently believed that the reason Earth wasn't a frozen ball for the first few billion years was its cooling process. Although that should be roughly a sixteenth of its original value.

Thus, the only meaningful factor to consider here is the level of solar radiation striking Earth. Earth's atmosphere may compensate for increasing insolation somewhat (more evaporation leading to more clouds, and clouds boost the planet's albedo, or ability to reflect light.) However, insolation will eventually creep up enough further compensation becomes impossible and the planet either dries out, or goes into a runaway greenhouse effect.

This also precludes a reaction from the biosphere itself to try and maintain the status quo somehow.

Not that it could do so for long, I'm just surprised at your 'within a billion years' comment.

[GrandMasterTerwynn]

The contribution of Earth's internal heat is considered to be negligible in this instance. While Earth's internal heat provides the energy for selected niches of life (i.e. those lifeforms dwelling around undersea geothermal vents and surface hot-springs) it escapes the planet along limited, narrow areas. Most life on Earth relies on insolation. Also, our thick atmosphere with it's potent greenhouse effect serves to mitigate the effects of the length of our day, so the only factor that really remains is the level of solar energy being absorbed by Earth. And Earth is too massive for photon pressure to affect a meaningful change in Earth's position or velocity with respect to the Sun, so the Sun hardly "pushes back" the Earth.

It's the solar winds that push back the Earth - as the sun's output increases, so does the number of particles it's throwing off. As I understand it it will meaningfully push back Earth's orbit over the course of the Sun's lifespan. The Sun will swallow Earth's current orbit, but not actually swallow Earth, for example.

In this case, probably just as negligable, but I was curious as it is currently believed that the reason Earth wasn't a frozen ball for the first few billion years was its cooling process. Although that should be roughly a sixteenth of its original value.

Earth originally had a substantially thicker atmosphere with a more robust greenhouse effect. However, the composition of the planet's atmosphere changed as the greenhouse gases were locked up by various geological and biological processes.

Thus, the only meaningful factor to consider here is the level of solar radiation striking Earth. Earth's atmosphere may compensate for increasing insolation somewhat (more evaporation leading to more clouds, and clouds boost the planet's albedo, or ability to reflect light.) However, insolation will eventually creep up enough further compensation becomes impossible and the planet either dries out, or goes into a runaway greenhouse effect.

This also precludes a reaction from the biosphere itself to try and maintain the status quo somehow.

Not that it could do so for long, I'm just surprised at your 'within a billion years' comment.

The biosphere can adapt, to a point, but there's a range of temperatures and pressures at which the chemical reactions which drive biology can take place in a reliable fashion. And the billion years figure is the one commonly given for the timescale at which the Sun will become too hot to permit liquid water to exist on the surface of Earth. It will actually become exceedingly difficult for life to cope with increasing insolation some time before that. Some estimates put that threshold as low as a hundred million years from now.

[wolveraptor]

Red Dwarf stars are much more stable than larger ones like our own. Also, life bearing planets would need to be much closer to it to recieve an adequate amount of light. The powerful pull of gravity that would result from such a close proximity might keep a planet's core heated for quite some time.

If all that is true, does that mean the timespan for life to evolve in such a system is much, much longer than our own?

[GrandMasterTerwynn]

Red Dwarf stars are much more stable than larger ones like our own. Also, life bearing planets would need to be much closer to it to recieve an adequate amount of light. The powerful pull of gravity that would result from such a close proximity might keep a planet's core heated for quite some time.

If all that is true, does that mean the timespan for life to evolve in such a system is much, much longer than our own?

Yes. Red dwarves will be capable of supporting life for at least tens of billions of years, and likely over a hundred billion years. The end result being that planets orbiting red dwarves will be the last strongholds for life in the universe tens of billions of years after the last Sunlike stars die.