Seeker Archives

Moon-Forming Earth Impact was a Direct Hit

The Mars-sized object that hit baby Earth some 4.5 billion years ago, creating plumes of debris that eventually coalesced into the moon, was a head-on strike.

The Mars-sized object that hit baby Earth some 4.5 billion years ago, creating plumes of debris that eventually coalesced into the moon, was a head-on strike, new research shows.

PHOTOS: Spectacular Apollo Photos Inspired Moon Science

An analysis of seven moon rocks collected by Apollo astronauts, one lunar meteorite and six volcanic rocks from Earth's mantle shows that the moon and Earth have nearly identical oxygen isotopes, an indication that Earth and second body, known as Theia ("mother of the moon"), ended up quite thoroughly mixed.

The finding, reported in this week's Science, runs contrary to previous research showing less mixing of the bodies.

"We don't see any difference between the Earth's and the moon's oxygen isotopes. They're indistinguishable," geochemist Edward Young, with the University of California Los Angeles, said in a press release.

If Earth and Theia collided in a glancing side blow, as previously hypothesized, most of the moon would be comprised of Theia and it would have a different lineup of oxygen isotopes than Earth.

ANALYSIS: Earth Pulled a Heist on the Moon's Water

A head-on crash would cause more mixing, giving Earth and the moon a more similar list of building materials.

"Theia was thoroughly mixed into both the Earth and the moon and (was) evenly dispersed between them," Young said. "This explains why we don't see a different signature of Theia in the moon versus the Earth."

First photograph of Earth as a celestial body by NASA astronaut William Anders on Dec. 24, 1968, as seen by the first Apollo mission to orbit the moon.

Apollo has never looked better. More than 40 years after the astronauts explored the surface, two photo projects are showing us the moon as only a handful of people has seen before.

The Project Apollo Archive

uploaded thousands of scanned NASA images to Flickr. Also, a new crowdfunded book called "

Apollo: The Panoramas

" easily exceeded its initial goal and will begin shipping hardcover books next year. This is some of the science these photos helped NASA perform.

MORE: Moonwalkers: Stunning Photos from Apollo 11

Some rumors circulated in the late 1960s that the first Apollo astronauts to land on the moon may very well sink into the surface. That wasn't really the worry for NASA during Apollo 11; after all, the Surveyor 3 (U.S.) and Luna 9 (Soviet) spacecraft had arrived safely, among others, with little evidence of subsidence. But NASA was interested in how well the lunar module performed when astronauts arrived on the surface. In pictures, NASA surveyed information such as how far the feet penetrated into the surface, and how much of a divot the engine exhaust left behind.

MORE: Fragile Apollo Artifacts in Need of Some Love: Photos

NASA was also interested in knowing how the investigators' experiments worked on the surface. Some of the experiments were used multiple times in missions, such as the foil solar wind composition collector seen here from Apollo 12. By asking the astronauts and looking at pictures of the deployed experiments, the investigators could make improvements from mission to mission to better data collection or other aspects of the mission.

MORE: Distant Earth: A History of 'Pale Blue Dots'

Without the lunar rover, the Apollo missions would have had severely limited surface operations. The rovers could carry equipment, samples and astronauts for many miles across the surface, allowing for more intensive investigations. NASA took care to make sure the astronauts observed a "walkback limit", just in case the rover broke down and the crew had to hike back to the lunar lander.

MORE: Moon Landing: Rarely Seen Photos Inside Apollo 11

As the Apollo program matured, the astronauts received advanced training in geology so they could better make choices about their work on the surface. This allowed them to select rocks representative of the environment, and to give detailed descriptions to Mission Control about their surroundings that could be recorded for the geology team. As a part of that, Apollo 15 commander Dave Scott did a brief survey of the landscape before even setting foot, perched inside the lunar lander and sticking his torso outside to take pictures and relay information to NASA.

MORE: Return to Earth: Rarely Seen Photos Inside Apollo 11

Where were the astronauts on the surface of the moon? That was no trivial question after astronauts began using rovers to get miles away from their landing site -- this shot from Apollo 16 gives you a taste. NASA closely monitored the astronauts' discussions, looking at television cameras and trying to plot their best estimates of the crew's location on orbital maps. Later on, when the pictures were developed, NASA and others looked at them to pin down where the astronauts physically were.

MORE: When (Part of) Apollo 13 Reached the Moon

While the astronauts described their surroundings as best as possible, NASA had a special color tool available to "calibrate" the images on the moon to their true color. An identical copy of this scale was on Earth, making it possible to do comparisons from afar as to what color the moon's regolith (soil) really was. That turned out to be very important on Apollo 17, when the astronauts found what they thought was orange regolith in an otherwise greytone landscape. They were right; it was the tint of volcanic glass.

MORE: 'Lost' NASA Photos Catch Apollo Teams in Training