The fate of the Earth?
in [Physics]
|
Prev: Partially crystalline materials
Next: Speciation Process: Excrement Color Skin Proven Harmful (Poverty, Crime and Disease)
From: Sam Wormley on 10 Sep 2009 15:51 dow wrote: > > I also read somewhere that the earth might survive even if it is > briefly engufed by the sun, i.e. the surface of the photosphere > expands around it. The density of the solar material would be so low > that the planet could continue in orbit for a while. If the sun > shrinks back quickly enough, the planet might emerge. Of course, its > surface would be drastically affected. > > dow "Read somewhere" was what exactly?
From: N:dlzc D:aol T:com (dlzc) on 10 Sep 2009 20:31 Dear Yousuf Khan: "Yousuf Khan" <bbbl67(a)yahoo.com> wrote in message news:4aa8f497(a)news.bnb-lp.com... > dow wrote: >> It is now thought that the sun probably will not engulf the >> earth and moon when it becomes a red giant. The loss of >> solar mass to the solar wind will reduce the maximum >> radius of the sun and will also cause the earth's orbit to >> spiral outward. Both effects will reduce the probability of >> the earth beig engulfed. > > The solar mass loss due to the solar winds probably > won't be significant *until* the Sun goes red giant. > Current solar winds don't even represent a fraction of a > percent of total solar mass over the billions of years of > Sun's existence. Mass loss due to fusion (and then photon escape to infinity) and solar wind is currently on the order of 1 part in 10^14 per year. So probably a good guess on your part. David A. Smith
From: dow on 11 Sep 2009 00:09 On Sep 10, 8:44 am, Yousuf Khan <bbb...(a)yahoo.com> wrote: > dow wrote: > > It is now thought that the sun probably will not engulf the earth and > > moon when it becomes a red giant. The loss of solar mass to the solar > > wind will reduce the maximum radius of the sun and will also cause the > > earth's orbit to spiral outward. Both effects will reduce the > > probability of the earth beig engulfed. > > The solar mass loss due to the solar winds probably won't be significant > *until* the Sun goes red giant. Current solar winds don't even > represent a fraction of a percent of total solar mass over the billions > of years of Sun's existence. > > Yousuf Khan The process of going red giant won't be instantaneous. The sun will swell over a period of millions of years. The process will be accompanied by an increase in the rate of loss of material to the solar wind. By the time the sun is getting close to engulfing the earth, a lot of mass will have been lost, reducing the maximum radius of the sun, and also causing the earth's orbit to have spiralled outward. A simple calculation based on conservation of angular momentum shows that the radius of the orbit will be inversely proportional to the sun's remaining mass, so if 25 percent of the sun's present mass is lost, which is plausible, then the earth's orbital radius will be 4/3 of what it is now, which would probably be enough to keep the earth from being engulfed. dow
From: Sam Wormley on 11 Sep 2009 00:13 dow wrote: > > The process of going red giant won't be instantaneous. The sun will > swell over a period of millions of years. The process will be > accompanied by an increase in the rate of loss of material to the > solar wind. By the time the sun is getting close to engulfing the > earth, a lot of mass will have been lost, reducing the maximum radius > of the sun, and also causing the earth's orbit to have spiralled > outward. > > A simple calculation based on conservation of angular momentum shows > that the radius of the orbit will be inversely proportional to the > sun's remaining mass, so if 25 percent of the sun's present mass is > lost, which is plausible, then the earth's orbital radius will be 4/3 > of what it is now, which would probably be enough to keep the earth > from being engulfed. > > dow You need to show your calculation, and the assumed mass loss as a function of time and radius.
From: dlzc on 11 Sep 2009 10:16
Dear dow: On Sep 10, 9:09 pm, dow <williamsdavi...(a)gmail.com> wrote: > On Sep 10, 8:44 am, Yousuf Khan <bbb...(a)yahoo.com> wrote: > > > dow wrote: > > > It is now thought that the sun probably will not > > > engulf the earth and moon when it becomes a > > > red giant. The loss of solar mass to the solar > > > wind will reduce the maximum radius of the > > > sun and will also cause the earth's orbit to > > > spiral outward. Both effects will reduce the > > > probability of the earth beig engulfed. > > > The solar mass loss due to the solar winds > > probably won't be significant *until* the Sun goes > > red giant. Current solar winds don't even represent > > a fraction of a percent of total solar mass over the > > billions of years of Sun's existence. > > The process of going red giant won't be > instantaneous. We hope. We've not seen it happen that way elsewhere... > The sun will swell over a period of millions of years. > The process will be accompanied by an increase > in the rate of loss of material to the solar wind. With less energy driving the efflux, are you sure? Have we seen other red giants spewing contents? > By the time the sun is getting close to engulfing > the earth, a lot of mass will have been lost, > reducing the maximum radius of the sun, and > also causing the earth's orbit to have spiralled > outward. Er, no. Earth's orbit, neglecting other factors, will become more elliptical, moving both further from our current average distance, and *closer*. We have the "wrong" angular momentum for this distance and a less massive Sun, to "spiral out". > A simple calculation based on conservation of > angular momentum shows that the radius of > the orbit will be inversely proportional to the > sun's remaining mass, *average* radius. > so if 25 percent of the sun's present mass is > lost, which is plausible, then the earth's orbital > radius will be 4/3 of what it is now, which would > probably be enough to keep the earth from > being engulfed. Likely not. What is more, if "half" the sky is a heat sink at 3000K or so, we are toast anyway. David A. Smith |