In how many years from now will the moon be twice as far from our planet than it is now?

Answer 1

Current projections suggest it will never get that far away.

The Moon is receding because of tidal forces. Putting it as simply as I can, the Moon's gravity causes a tidal bulge to form on the Earth. This bulge is then carried forward by the Earth's rotation (which, by the way, is why high tide doesn't correspond to when the Moon is overhead). This unequal distribution of mass then has two effects. One is that it drags the Moon forward in its orbit, effectively raising it. This is what is causing the Moon to move further away. The other is that the Moon, in turn, pulls back on this bulge, slowing the Earth's rotation.

So, at the same time the Moon is receding, the Earth is slowing. Eventually there will come a point where the Earth will be tidally locked with the Moon in the same way the Moon currently is to the Earth. That is to say, the Earth and Moon will always present the same faces to each other as the period of Earth's rotation will equal the period of the lunar orbit, which in turn will equal the period of the Moon's rotation. When this happens there will no longer be the 'dragging' effect that the current tides produce, and the Moon will stop receding and the Earth will stop slowing. Current estimates are that this will happen in a few billion years and the Moon will only be about 50% further away by then. There is some uncertainty over whether this will happen before the Sun starts to expand and cause bigger problems for the entire system, however.

Answer 2

It won't make it..! Twice the current distance between Earth and Moon would be about 880,000 km, but before that range is reached the recession will have stopped due to gravitational stabilization of the system. Instead, it's been computed that the moon will go outward to about 550,000 km. Turns out that we won't be around then because it will take about 50-billion years, and the sun will have died long before then.

Answer 3

Never. If it moves farther away, the gravitational pull will be insufficient to maintain orbit.