If the earth were the size of Jupiter, what would its 'moon' be in both relative size and distance? I did some quick figuring and think I roughly figured out that if placed at the position of the sun, Jupiter's moon would be Neptune in both relative size and current distance from the sun. That seems very distant and I'm questioning my calculations. The moon is 27% as large as the earth and is ~27,700 times the earth's diameter distant. Jupiter is ~87,000 miles in diameter. That would make it's moon ~23,500 miles in diameter and ~2.41 billion miles distant. Neptune comes relatively close to those results. It would be slightly larger than our moon (30,600 miles in diameter vs. 23,500) and slightly farther away (2.8 billion miles away vs 2.41) but still close for comparison purposes. That puts the moon relatively MUCH more distant from the earth than what I would have thought off the top of my head.


1 Answer 1


The basic numbers are:

  • Radius of Earth 6370km
  • Radius of Moon 1740km
  • Earth-moon distance 384000km and
  • Radius of Jupiter 71500km

So the scale factor is 71500/6370 = 11.22

The radius of the moon scaled is 1740×11.22 = 19500 km, and its distance becomes 384000×11.22 = 4310000 km

For comparison, Neptune has a radius of 24600 km and a distance from Jupiter of that is always more than 3700000000 km

The size of the "moon" is comparable to Neptune, but the distance from Jupiter to Neptune is nearly 1000 times greater than the distance to the "moon".


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