The total mass of the asteroid belt is approximately 4% of our Moon, or 7% of Pluto, which is enough to make some believe that the asteroid belt is the remnants of a mythical exploded planet named Phaeton.

Valles Marineris and the asteroid belt

Others have suggested that the asteroid belt is the remnants of the scar on the surface of Mars known as Valles Marineris. Surface material tossed into space by a cataclysmic event ended up in orbit between Mars and Jupiter.

However, the total mass excavated from Valles Marineris is not enough to make this believable. There is also the dwarf planet Ceres, which definitely did not come from Mars.

The matter excavated from Valles Marineris may in total have been about 4% of our Moon, but there is no way all of this found its way out to the asteroid belt. Much of it rained down on Earth in meteorite showers. The Sun and Jupiter must have gobbled up much of it too, and a lot was no doubt lost to space.

Phaton may have been the size of Mercury

If the asteroid belt is the remnants of a cataclysmic event, the original object must have been far larger than the total material found in the asteroid belt. An object the size of Mercury sounds more like it.

Mercury has a volume about three times that of our Moon, which means that the asteroid belt has a total volume corresponding to about 1.5% of Mercury.

However, this assumes that planets are solid to the core. If planets are hollow, which we have good reasons to believe, the numbers may be off by upwards of 100%. The asteroid belt may be a full 4% of Mercury. This would be especially true if the exploded planet had a particularly thin shell, making it all the more likely to have exploded.

Rogue planet blowing up a smaller planet