News / Science & Technology

'Man in the Moon' Explained

The Earth (unseen) casts a faint shadow over the southwestern part of a full moon during the penumbral lunar eclipse in Cairo October 19, 2013. A penumbral lunar eclipse occurs when the moon crosses the Earth's shadow, causing a slight dimming on the moon
The Earth (unseen) casts a faint shadow over the southwestern part of a full moon during the penumbral lunar eclipse in Cairo October 19, 2013. A penumbral lunar eclipse occurs when the moon crosses the Earth's shadow, causing a slight dimming on the moon

Related Articles

NASA Heads Back to the Moon

Unmanned rocket blasted off late Friday from Virginia's Eastern Shore with robotic explorer that will study lunar atmosphere, dust

NASA Breaks Data Transmission Speed Record With Laser Shot to Moon

NASA downloaded data at a rate of 622 megabits per second (Mbps) using a pulsed laser beam
VOA News
Scientists believe they know why the near side of the moon appears to have larger impact craters than the far side.

"Since time immemorial, humanity has looked up and wondered what made the man in the moon," said Maria Zuber, a geophyisics professor the Massachusetts Institute of Technology (MIT) and the principal investigator with NASA's Gravity Recovery and Interior Laboratory (GRAIL). "We know the dark splotches are large, lava-filled, impact basins that were created by asteroid impacts about four billion years ago. GRAIL data indicate that both the near side and the far side of the moon were bombarded by similarly large impactors, but they reacted to them much differently.”

Much of the bombardment of the moon occurred about 4 billion years ago, an era termed the Late Heavy Bombardment (LHB). During that time, a hailstorm of giant asteroids pummeled the solar system, slamming into the moon, along with young planets like Mercury, Venus, Earth, and Mars. Earth lacks most traces from this period because of erosion and plate tectonics.

Data from NASA’s twin GRAIL probes, which orbited the moon from January to December 2012. During its mission, the probes circled the moon, making measurements of its gravity. Scientists from MIT and the University of Paris used this data to generate a highly detailed map of the moon’s crust, showing areas where the crust thickens and thins. In general, the group observed that the moon’s near side has a thinner crust than its far side.

Katarina Miljkovic of the Institut de Physique du Globe de Paris, generated computer simulations of asteroid impacts on the moon by plugging in crustal thickness data from GRAIL. Milijkovic also incorporated estimates of the moon’s early internal temperatures from thermal modeling, based in part on lava deposits that flooded the large impact basins on the moon’s near side. Scientists have observed that more volcanic activity occurred on the near side, generating higher internal temperatures than on the moon’s far side.

“Impact simulations indicate that impacts into a hot, thin crust representative of the early moon’s near-side hemisphere would have produced basins with as much as twice the diameter as similar impacts into cooler crust, which is indicative of early conditions on the moon’s far-side hemisphere,” notes Miljkovic.

Together, the findings seem to indicate that the asteroids impacted the moon with less intensity than previously thought during the LHB. The asteroids also may have been smaller than previously thought.

Zuber said the near side’s thinner crust and higher temperatures may have made the surface more deformable than the thicker, cooler crust of the moon’s far side. These results suggest that the LHB may have involved less massive asteroids than scientists have thought.

“I’d certainly been a believer in the Late Heavy Bombardment from looking at those large impact basins,” Zuber said. “The idea of a Late Heavy Bombardment remains, but it will be have to be re-examined.”

Here's a short video about the study:

You May Like

800-Pound Man Determined to Slim Down

Man says he was kicked out of hospital for ordering pizza; wants to be an actor More

Australia Prepares to Resettle 12,000 Syrian Refugees

Preference will be given to refugees from persecuted minorities, and the first group is expected to arrive before late December More

S. African Miners Seek Class Action Suit Against Gold Mines

The estimated 100,000 say say they contracted the lung diseases silicosis and tuberculosis in the mines More

This forum has been closed.
Comment Sorting
by: Yoshi from: Sapporo
November 10, 2013 8:02 PM
Hi, Norimaki and Barrie, it is very kind of you to answer me. Now I understand centrifugal force working on the moon from the earth would explain the reasons of my qestions. Probably the core and magma once active are also lopsided to some extent toward the earth side. So, maybe the temperature is higher and volcanic activity is more active on the near side.

I am sorry but one more question comes up again. How come the moon rotates at the same period as its revorution?

by: Barrie Templeton from: Calgary, Alberta
November 10, 2013 9:24 AM
If I remember correctly, the moon is believed to have been ripped from the earth, and both rocks returned to spherical shapes due to centrifugal forces. If this theory is still valid, it might explain the thinner crust on the near side, and also may be the reason why it always puts the same face to the larger orb. If you have an out-of-balance ball, such as an old softball which has become lopsided, it will, when thrown, tend to put one side more toward the ground as it flies. This may be difficult to observe due to rather short travel times, but should be measurable with proper instruments such as slow-motion cameras. If the thinner-crust side is also the part that was attached to the planet prior to ejection, I believe the thinness is self-explanatory, as that area would have been hotter because of its proximity to the magma in the earth's core.

by: Norimaki Senbei from: Tokyo
November 09, 2013 6:31 PM
The moon is orbiting around the Earth without rotating on its axis, so outward force which is called "centrifugal force" works on only the far side. That's the cause of the difference of the thickness of the crust.

by: Yoshi from: Sapporo
November 08, 2013 8:10 PM
Thank you VOA for interesting stories every time. I did not know diameters of craters are different between the near side and far side. I understand how it might occur by your explanation.

After that, I would like to ask how come the crust is thinner and temperature is higher on the near side than the far side. In adission, how come volcanic activity was more on the near side?

Featured Videos

Your JavaScript is turned off or you have an old version of Adobe's Flash Player. Get the latest Flash player.
Amnesty Accuses Saudi Coalition of ‘War Crimes’ in Yemeni
Henry Ridgwell
October 12, 2015 4:03 PM
The human rights group Amnesty International has accused the Saudi-led coalition of war crimes in airstrikes against Houthi rebels in Yemen. Henry Ridgwell reports the group says hundreds of civilians have been killed in strikes on residential areas.

Video Amnesty Accuses Saudi Coalition of ‘War Crimes’ in Yemen

The human rights group Amnesty International has accused the Saudi-led coalition of war crimes in airstrikes against Houthi rebels in Yemen. Henry Ridgwell reports the group says hundreds of civilians have been killed in strikes on residential areas.

Video No Resolution in Sight to US House Speaker Drama

Uncertainty grips the U.S. Congress, where no consensus replacement has emerged to succeed Republican House Speaker John Boehner after his surprise resignation announcement. Half of Congress is effectively leaderless weeks before America risks defaulting on its national debt and enduring another partial government shutdown.

Video New Art Exhibit Focuses on Hope

Out of struggle and despair often comes hope. That idea is behind a new art exhibit at the American Visionary Art Museum in Baltimore, Maryland. "The Big Hope Show" features 25 artists, some of whom overcame trauma and loss. VOA’s Deborah Block reports.

Video Columbus Day Still Generates Controversy as US Holiday

The second Monday of October is Columbus Day in the United States, honoring explorer Christopher Columbus and his discovery of the Americas. The achievement is a source of pride for many, but for some the holiday is marked by controversy. Adrianna Zhang has more.

Video Anger Simmers as Turks Begin to Bury Blast Victims

The Turkish army carried out new air strikes on Kurdistan Workers Party (PKK) targets on Sunday, a day after the banned group announced a unilateral cease fire. The air raids apparently are in retaliation for the Saturday bombing in Turkey's capital Ankara that killed at least 95 people and wounded more than 200 others. But as Zlatica Hoke reports, there are suspicions that Islamic State is involved.

Video Bombings a Sign of Turkey’s Deep Troubles

Turkey has begun a three-day period of mourning following Saturday’s bomb attacks in the capital, Ankara, that killed nearly 100 people. With contentious parliamentary elections three weeks away, the attacks highlight the challenges Turkey is facing as it struggles with ethnic friction, an ongoing migrant crisis, and growing tensions with Russia. VOA Europe correspondent Luis Ramirez reports.

Video Afghanistan’s Progress Aided by US Academic Center

Recent combat in Afghanistan has shifted world attention back to the central Asian nation’s continuing civil war and economic challenges. But, while there are many vexing problems facing Afghanistan’s government and people, a group of academics in Omaha, Nebraska has kept a strong faith in the nation’s future through programs to improve education. VOA’s Greg Flakus has more from Omaha, Nebraska.

Video House Republicans in Chaos as Speaker Favorite Withdraws

The Republican widely expected to become the next speaker of the House of Representatives shocked his colleagues Thursday by announcing he was withdrawing his candidacy. The decision by Majority Leader Kevin McCarthy means the race to succeed retiring Speaker John Boehner is now wide open. VOA National Correspondent Jim Malone reports.

Video German, US Officials Investigate Volkswagen

German officials have taken steps to restore some of the reputation their car industry has lost after a recent Volkswagen diesel emissions scandal. Authorities have searched Volkswagen headquarters and other locations in an effort to identify the culprits in the creation of software that helps cheat on emission tests. Meanwhile, a group of lawmakers in Washington held a hearing to get to the bottom of the cheating strategy that was first discovered in the United States. Zlatica Hoke reports.

Video Why Are Gun Laws So Hard for Congress to Tackle?

Since taking office, President Barack Obama has spoken out or issued statements about 15 mass shootings. The most recent shooting, in which 10 people were killed at a community college, sparked outrage over the nation's gun laws. But changing those laws isn't as easy as many think. VOA's Carolyn Presutti reports.

Video In 'He Named Me Malala,' Guggenheim Finds Normal in Extraordinary

Davis Guggenheim’s documentary "He Named Me Malala" offers a probing look into the life of 18-year-old Malala Yousafsai, the Pakistani teenager who, in 2012, was shot in the head by the Taliban for standing up for her right to education in her hometown in Pakistan's Swat Valley. Guggenheim shows how, since then, Malala has become a symbol not as a victim of brutal violence, but as an advocate for girls’ education throughout the world. VOA’s Penelope Poulou has more.

Video Paintable Solar Cells May Someday Replace Silicon-Based Panels

Solar panels today are still factory-manufactured, with the use of some highly toxic substances such as cadmium chloride. But a researcher at St. Mary’s College, Maryland, says we are close to being able to create solar panels by painting them on a suitable surface, using nontoxic solutions. VOA’s George Putic reports.

VOA Blogs