What If Earth Were Twice as Big?

A planet with twice Earth's diameter would be a super-Earth with stronger gravity, a heavier atmosphere and very different conditions for life — and for anyone trying to launch a rocket.

Super-Earths — rocky planets larger than ours — turn out to be among the most common planets in the galaxy, even though our solar system has none. So what would happen if Earth were twice as wide?

Much more mass

Doubling the diameter multiplies the volume by eight. Because the extra weight would squeeze the interior and make it denser, the mass would be even more than eight times today's. Surface gravity depends on both mass and size, and would end up at a bit more than twice what we feel now.

Life with double gravity

You would feel about twice as heavy. Use the weight calculator to compare with real planets.
Animals would likely evolve thicker bones and shorter, sturdier bodies. Very tall trees would be harder to grow.
Mountains would be lower, because rock can only support so much weight before it flows or crumbles.

A thicker atmosphere

Stronger gravity holds on to gas more easily. A bigger Earth would probably keep a denser atmosphere, and perhaps lighter gases too. That could mean a warmer climate and thicker air — or, if too much gas is retained, a planet more like a mini-Neptune than a rocky world. Where exactly that transition happens is an active area of research.

A hotter, longer-lasting interior

A larger planet holds its internal heat longer. Volcanoes and a magnetic field could last longer. Whether plate tectonics would be easier or harder on a super-Earth is still debated among scientists.

Hard to leave

Escape velocity would roughly double, to around 22 km/s. Because of the way rocket fuel requirements grow, that would make reaching orbit vastly harder — chemical rockets like ours might struggle to get anything useful into space at all.

Real examples

Thousands of super-Earths have been found by missions such as Kepler and TESS. Some, like Kepler-452b, orbit in their star's habitable zone, though we do not yet know whether they are rocky or what their atmospheres are like.

How to build it

Add more material in step 3 — and watch carefully that your planet doesn't collect so much gas that it stops being rocky.