If We Had No Moon
By Astrobio - Oct 29, 2007
SMART-1 principal scientist Bernard Foing.
Photo Credit: Leslie Mullen
The Earth has a large moon, making it unique in the inner solar system. Mercury and Venus have no moons, and Mars has only two small asteroid-sized objects orbiting it. In this essay, the father of the SMART-1 lunar mission, Bernard Foing of the European Space Agency, looks at the effect the Moon has had on the Earth, and explores how different our world would be if we had no planetary companion. Would life have evolved differently, or even appeared on Earth without the Moon?
If We Had No Moon
An essay by Bernard Foing
If the time of Earth’s existence was condensed into a 24-hour clock, the moon formation event occurred just 10 minutes after the Earth was born. The Earth formed 4.56 billion years ago, and the Moon formed about 30 million years later. At that time, the Earth was a magma ocean. An impactor about the size of Mars struck the Earth at an oblique angle, and removed some of the magmatic mantle. This mantle was put in orbit around the Earth, together with some of the debris from the impactor itself, and this material eventually formed the Moon.
Artist’s representation of the moon formation event. Copyright Fahad Sulehria, 2005, www.novacelestia.com
When the Moon first formed, it was very close to the Earth. It was possibly only 20 to 30 thousands of kilometers away, and it would have looked extremely large in the sky, at least 20 to 10 times bigger. But there were no living creatures on the Earth at that time to witness this beautiful scene.
The tidal effect of a body increases as a cube of the distance, so the effect of the Moon’s tidal forcing on the Earth was extremely high at this time, to the point that the early magma ocean was affected. This provided some additional energy to the heating from radioactive elements present, but after the radiogenic heating decayed, the Moon still was a source of...