Last summer we celebrated the 50th anniversary of mankind’s first steps on the Moon. The Apollo missions marked the culmination of a space race between the Americans and the Soviets. But those missions also left a rich technological and scientific legacy that goes beyond political divisions.
A total of twelve astronauts landed on the Moon and brought back close to 2,200 lunar rock samples weighing 382 kg. Researchers across the globe are still studying some of those samples today.
Lunar rock analyses led to two major discoveries. Scientists were first able to pinpoint the age of the rocks gathered during the Apollo missions. They then correlated that age with crater counts on the Moon. This technique—of measuring the number and size of craters—is now used to estimate the age of the visible surfaces of the other planets in the solar system or of the moons orbiting the giant planets.
But, without a doubt, the greatest scientific legacy of the Apollo missions is our understanding of the origin of the Moon. Before the missions, there was no consensus among scientists as to how our natural satellite was formed.
Samples brought back to Earth revealed that lunar rocks essentially have the same composition as terrestrial rocks, supporting the idea that both celestial bodies have a common origin. The seismometers placed on the Moon’s surface during the Apollo missions have also shown that our satellite has a small iron core, which measures only about 500 km in diameter and represents just 4% of the Moon’s mass. In comparison, the Earth’s core is about 3,500 km wide and makes up 33% of our planet’s mass.
These findings advanced the theory that the Moon originated from a giant impact with the young Earth. Here’s a quick rundown of what scientists think happened.
The solar system was formed 4.56 billion years ago. About 150 million years later, Theia—an object the size of Mars with only 15% of our planet’s mass—struck the young Earth a glancing blow. The resulting impact pulverized Theia and blasted away the outer layers of our planet’s crust, which were rich in lightweight materials such as silicon, magnesium and aluminum. A considerable amount of debris, most of which was Theia’s iron core, immediately rained back down on our planet. The remaining iron-depleted material was ejected into orbit around the Earth and quickly coalesced to form the Moon with its small core. In less than a year, most of the debris from this collision accreted to form the newborn Moon. Then, in just a few hundred years, our satellite swept up virtually all the debris within its orbit. This fascinating history was unveiled thanks to the work of the Apollo astronauts!
The planets in October
The October evening sky is dominated by the giant planets Jupiter and Saturn. The brighter Jupiter will be the first to appear at twilight: You can observe it above the south-southwestern horizon about 30 minutes after sunset. The slightly fainter Saturn will be 25 degrees to the left and slightly higher than Jupiter; the ringed planet makes its appearance as the sky grows darker.
On the evening of October 3, the crescent Moon will shine only 1½ degrees to the upper left of Jupiter. The following evening, the Moon will sit midway between the two giant planets. And on the evening of October 5, the first quarter Moon will hang less than 2 degrees to the lower left of Saturn.
By late October, you’ll also catch glimpses of Venus as it gradually pulls away from the Sun and slowly emerges at dusk: Look for the Evening Star very low on the southwest horizon, about 20 minutes after sunset. On October 29, the thin lunar crescent will appear above the brilliant planet. On October 30, the Moon will shine between Venus and Jupiter, and then move to the left of the Jovian planet the following day.
And finally, you’ll be able to spot Mars at the crack of dawn, low on the east- southeastern horizon, about one hour before sunrise. In the early morning hours of October 26, the crescent Moon will hang 5 degrees above the Red Planet.