This is a difficult question to answer, because the number keep growing.
Almost every year astronomers find new moons, using better telescopes on Earth and spacecraft flying through the solar systen. Some moons are so small that that their width is smaller than most cities on Earth.
Volcanoes on Earth have rivers of red hot lava pouring down the sides or massive explosions of gas, rock and dust rising into the sky. But in space volcanoes are quite different.
Mars has four large volcanoes – the biggest is Olympus Mons. It is 27 kilometres high (three times the height of Mount Everest) and 500 kilometres wide (bigger than Tasmania). The volcanoes on Mars haven’t erupted for more than two million years.
The planet Venus always has ancient volcanoes on its surface. The biggest is Maat Mons – eight kilometres high. From above, some of the volcanoes look like pancakes and others have strange patterns that make them look like ticks. Continue reading
