Shielding Earth/Moving Earth from Suns Red Giant phase.

[Johnny1A.2]

Originally Posted by Racer

Just been reading a chart of deep time that stated it would take 1 Billion Years of multiple flybys by asteroids , to move Earth far enough out to avoid being cooked . I reckon that's too long & with concentrated effort - and avoiding catastrophic interaction with Mars & Jupiter - it could be done in under 5 Million years . Humanity would've probably long left by then , but placed automated robotic 'guardians' to help preserve humanity's Cradle & any remaining natural lifeforms .

As it is , Earth will start to become uncomfortably hot by about 200 Million AD ( sooner if we keep dumping ridiculous amounts of greenhouse gases into the atmosphere ) & the Sun increasing in Luminosity .
Other predictions state as low as 50 Million years or as high as 600 Million - all depending on Continental Drift & variability in Earth's Orbit & inclination .

Sunstorm by Arthur C. Clarke and Stephen Baxter had most of the World's population pooling resources to prevent the Earth being cooked by a huge Solar Flare in 2042 A.D. & while optimistic , I reckon we'd to do something similar by around 2150 to 2200 A.D ? Semi Self Replicating Robot Probe spacecraft , using asteroid materials to create some sort of usable Shield .

What do others think ? Am I being overoptimistic ?

Seriously? This is like a bunch of paleolithic hunter-gatherers sitting around the fire, speculating about how somebody might somehow dig a cave through that mountain over there, and wondering if any stone could be hard enough to cut that much other stone. Optimism and pessimism alike are WAGs.

Within the limits of the technology and physics we know, or can project, it all comes down to just how big Sol gets in the red giant phase. If the expansion stays small enough, then the smart move isn't to try to move the Earth at all (though the orbit may change on its own as the Sun changes). Instead, you build sunshades and mirrors to cut the insolation down to whatever level is convenient.

If the Sun is going to get so big that we just must move the Earth, there's no obvious reason to go out to Jupiter or anywhere else in specific, if you've got the tech, you just widen the Earth's orbit to get far enough out to use sunshades and mirrors for the rest.

Note also that the red giant phase of a main sequence star like Sol is relatively brief (we believe). On a cosmic scale, it won't be long before Sol sheds big shells of mass and starts shrinking down to a white dwarf. At that point, you might want to close the Earth's orbit inward again to maintain insolation, at least as long as the white dwarf is still hot enough to be useful (and it'll take the white dwarf a long time to cool.

OTOH, if you've got the tech, you could leave Earth out in a big wide orbit and put an energy source in orbit at an appropriate distance to simulate the Sun.

[Daigoro]

Originally Posted by johndallman

Putting Earth at one of Jupiter's Trojan points, on the other hand, might be rather more viable. We'd have to clear it out, but that's much easier than moving Earth.

I thought you could only park objects of negligible relative mass in Trojans. Is the Earth under the limit?

[johndallman]

Originally Posted by Daigoro

I thought you could only park objects of negligible relative mass in Trojans. Is the Earth under the limit?

I think so. Jupiter is over 300 Earth masses. And if we can move Earth out there, we can presumably do occasional adjustments.

[Agemegos]

Originally Posted by Daigoro

I thought you could only park objects of negligible relative mass in Trojans. Is the Earth under the limit?

The strict limit is that the Sun has to be more than 25.19 times the mass of Jupiter, which it is, comfortably. As for the mass of the Trojan asteroid, my understanding is that the orbit is not truly stable for any non-zero mass, but that the instability only gets out of hand when the Trojan gets to be more than about 1/10 the mass of Jupiter. In any case, as John Dallman pointed out above, if you could move Earth at all, a bit of station-keeping would be comparatively easy.

Read about the Theia hypothesis for more information.

[AlexanderHowl]

I wonder if it would not just be easier to relocate everything of importance from the Earth to another system rather than moving the Earth. The Earth will not be consumed, that is an old theory from the 60s, and we have plenty of examples of stars more massive than Sol in the red giant phase that prove that stars of Sol mass only expand around 20 times or so. For example, Arcturus is a red giant of 1.08 Sol-masses and is 25 times the radius of Sol while Aldebaran is a red giant of 1.16 Sol-masses and is 45 times the radius of Sol. Gacrux is a red giant of 1.5 Sol-masses and is 84 times the radius of Sol.

Now, where GURPS Space falls flat is that it greatly underestimates L changes. Arcturus has a L of 170, which would have required it have stared as F2, which would have meant that it lost 30% of its mass. Aldebaran has a L of 518, which would have required it to start as an A2, which would have meant that it would have lost 45% of its mass. Gacrux has a L of 840, which would have required it to start as an A0, which would have meant that it would have lost 35% of its mass.

I think that a possible solution would be to increase the L throughout the lifespan of the red giant phase of a star. L would start at 25x the maximum L of the main sequence and increase by 20% for every 10% of the red giant phase that the star passed through. For example, Sol would start at L 40 but would end at L 120 as it burned through the last of its available hydrogen. During that time, mass would start at 90% and mass losses would be 1% per 10% of the red giant phase.

Of course, none of this includes red clump or asymptomatic red giant stars, which break all of the rules for standard red giant stars. Red clump stars are more massive, smaller, and brighter than red giant stars. Asymptomatic red giant stars are more massive, larger, and brighter than red giant stars.

[Bicorn]

Originally Posted by Anaraxes

The problem there is that we can't use L4. If we did, we'd be preceding Jupiter in his orbit. And so we'd be the herald of Jupiter, which would force us to rename our planet "Mercury". But that's taken, so we'd have to rename that one, too -- and then whatever one we took the ex-Mercury's new name from, and so on, et cetera ad infinitum. The complexity would get out of hand. It'd be simpler just to move to a whole new star system.

Oh, but the whole issue started with the Sun turning red giant, so we can just leave the original Mercury to be swallowed. Then the name'll be free to use.