Hi All

That was a good book, but I am not so sure about how well pushing Uranus would work. It'd be a BIG shove to shift a planet.

Mind you we might have to do it or dismantle one of the Jovians to make the Sun-stirring super-magnet I mentioned.

However Laughlin and Adams have come up with a much more gradual way to shift the Earth...

http://au.arxiv.org/abs/astro-ph/0102126

Astronomical engineering: a strategy for modifying planetary orbits
Authors: D. G. Korycansky, Gregory Laughlin, Fred C. Adams
Comments: 21 pgs, 7 figs. Paper to appear in Astrophysics and Space Science
Journal-ref: Astrophys.Space Sci. 275 (2001) 349-366

The Sun's gradual brightening will seriously compromise the Earth's biosphere within ~ 1E9 years. If Earth's orbit migrates outward, however, the biosphere could remain intact over the entire main-sequence lifetime of the Sun. In this paper, we explore the feasibility of engineering such a migration over a long time period. The basic mechanism uses gravitational assists to (in effect) transfer orbital energy from Jupiter to the Earth, and thereby enlarges the orbital radius of Earth. This transfer is accomplished by a suitable intermediate body, either a Kuiper Belt object or a main belt asteroid. The object first encounters Earth during an inward pass on its initial highly elliptical orbit of large (~ 300 AU) semimajor axis. The encounter transfers energy from the object to the Earth in standard gravity-assist fashion by passing close to the leading limb of the planet. The resulting outbound trajectory of the object must cross the orbit of Jupiter; with proper timing, the outbound object encounters Jupiter and picks up the energy it lost to Earth. With small corrections to the trajectory, or additional planetary encounters (e.g., with Saturn), the object can repeat this process over many encounters. To maintain its present flux of solar energy, the Earth must experience roughly one encounter every 6000 years (for an object mass of 1E22 g). We develop the details of this scheme and discuss its ramifications.

[ADAM: this assumes that the present insolation must be maintained, but climate modelling suggests that the oceans might control temperature efficiently and be able to maintain near current temperatures up to ~ 4.4 gigayears from now, at an insolation of ~ 1.5 times current. However we might need to import water in the next ~ 0.5 gigayears if the oceans are leaking away into the mantle as some have suggested.]

[Big solettas might be cheaper, but eventually we will need to leave near the Sun.]

Adam