3 ms·

> Countering that is the immense gravitational weight of the star itself, pressing inward with all the might that 1,027 tons of hydrogen and helium can muster.

by tromp 3y ago

> Countering that is the immense gravitational weight of the star itself, pressing inward with all the might that 1,027 tons of hydrogen and helium can muster. More like 2 x 10^27 tons. The first option steals momentum from Jupiter to reach a larger orbit: > So instead, we’ll have to resort to asteroids. We can send them on long orbits that loop around Jupiter, using their gravitational interactions to speed up the asteroid in exchange for a slight slowing of the giant planet’s motion. We can then return the asteroid to Earth, looping it in the opposite direction, slowing it down and giving us a boost. > The difference from a single pass will be barely measurable, let alone noticeable. It’s not like random floating space rocks can carry that much kinetic energy with them. But we just have to set it on repeat, looping over and over for hundreds of millions of years, nudging the Earth into ever higher orbits to escape the increasing ferocity of the Sun. If our descendants can manage it, it will keep our planet in the safe band of the habitable zone.

FiatLuxDave 3y ago
One big problem with the article's proposal to steal momentum from Jupiter to move Earth to a larger orbit is that it is an energy absorbing process. In other words, there has to be an external source of energy to move momentum from Jupiter to Earth. This is because the ratio of specific energy to specific momentum is higher for lower orbits than it is for higher orbits. In other words, the closer you are to the Sun, the more energy you get for a specific amount of momentum (because the gravity is stronger there). This is assuming near circular orbits. So, you can gain energy by moving momentum from Earth to Jupiter, but you lose it the other way. Another planet, such as Saturn, would be needed as an energy donor (moving momentum from Jupiter to Saturn, then using the excess energy to move momentum from Jupiter to Earth) to make the energy equation balance.

by tromp 3y ago

FiatLuxDave 3y ago

One big problem with the article's proposal to steal momentum from Jupiter to move Earth to a larger orbit is that it is an energy absorbing process. In other words, there has to be an external source of energy to move momentum from Jupiter to Earth. This is because the ratio of specific energy to specific momentum is higher for lower orbits than it is for higher orbits. In other words, the closer you are to the Sun, the more energy you get for a specific amount of momentum (because the gravity is stronger there). This is assuming near circular orbits. So, you can gain energy by moving momentum from Earth to Jupiter, but you lose it the other way. Another planet, such as Saturn, would be needed as an energy donor (moving momentum from Jupiter to Saturn, then using the excess energy to move momentum from Jupiter to Earth) to make the energy equation balance.