By: HISTORY.com Editors

1974

U.S. space probe, Mariner, visits Mercury

Published: February 09, 2010Last Updated: May 27, 2025

The unmanned U.S. space probe Mariner 10, launched by NASA in November 1973, becomes the first spacecraft to visit the planet Mercury, sending back close-up images of a celestial body usually obscured because of its proximity to the sun.

Mariner 10 had visited the planet Venus eight weeks before but only for the purpose of using Venus’ gravity to whip it toward the closest planet to the sun. In three flybys of Mercury between 1974 and 1975, the NASA spacecraft took detailed images of the planet and succeeded in mapping about 35 percent of its heavily cratered, moonlike surface.

Mercury is the smallest planet in the solar system and completes its solar orbit in only 88 earth days. Data sent back by Mariner 10 discounted a previously held theory that the planet does not spin on its axis; in fact, the planet has a very slow rotational period that stretches over 58 earth days. Mercury is a waterless, airless world that alternately bakes and freezes as it slowly rotates. Highly inhospitable, Mercury’s surface temperature varies from 800 degrees Fahrenheit when facing the sun to -279 degrees when facing away. The planet has no known satellites.

Who Named the Planets?

Most are named after Roman gods and goddesses.

By: Elizabeth Nix

Timeline

Also on This Day in History

Discover more of the major events, famous births, notable deaths and everything else history-making that happened on March 29th

1865

Appomattox, the final campaign in the Civil War, begins

On March 29, 1865, the final campaign of the Civil War begins in Virginia when Union troops under General Ulysses S. Grant move against the Confederate trenches around Petersburg. General Robert E. Lee’s outnumbered Rebels were soon forced to evacuate the city and begin a desperate race west. Eleven months earlier, Grant moved his army […]

1945

Gen. George Patton takes Frankfurt

Gen. George S. Patton’s 3rd Army captures Frankfurt, as “Old Blood and Guts” continues his march east. Frankfurt am Main, literally “On the Main” River, in western Germany, was the mid-19th century capital of Germany (it was annexed by Prussia in 1866, ending its status as a free city). Once integrated into a united German […]

1:56m read

1951

The “Mad Bomber” strikes in New York

On March 29, 1951, a homemade device explodes at Grand Central Terminal in New York City, startling commuters but injuring no one. In the next few months, five more bombs were found at landmark sites around New York, including the public library. Authorities realized that this new wave of terrorist acts was the work of […]

1:40m read

1951

Rosenbergs convicted of espionage

In one of the most sensational trials in American history, Julius and Ethel Rosenberg are convicted of espionage for their role in passing atomic secrets to the Soviets during and after World War II. The husband and wife were later sentenced to death and were executed in 1953. The conviction of the Rosenbergs was the […]

2:36m read

1958

First reading of the Keeling Curve, which shows carbon dioxide levels in Earth’s atmosphere

In March of 1958, Dr. Charles David Keeling begins regularly measuring the amount of carbon dioxide in the atmosphere from the Mauna Loa Observatory in Hawai’i. Over the ensuing years, his research will reveal what is now known as the Keeling Curve: a graph of continuously-taken measurements showing the rapid accumulation of carbon dioxide. Previously, […]

1971

Lt. William Calley found guilty of My Lai murders

Lt. William L. Calley is found guilty of premeditated murder at My Lai by a U.S. Army court-martial at Fort Benning, Georgia. Calley, a platoon leader, had led his men in a massacre of Vietnamese civilians, including women and children, at My Lai 4, a cluster of hamlets in Quang Ngai Province on March 16, […]

1:56m read

1973

U.S. troops withdraw from Vietnam

The last U.S. combat troops leave South Vietnam as Hanoi frees the remaining American prisoners of war held in North Vietnam.

3:22m read

1974

Exiled writer Aleksandr Solzhenitsyn reunited with family

On March 29, 1974, prominent Soviet author, historian and political dissident Aleksandr Solzhenitsyn is reunited with his family after being exiled from his home country. Publication of The Gulag Archipelago, his detailed history of the Soviet Union’s vast system of prisons and labor camps, helped raise global awareness of the communist nation’s rampant political repression. Its […]

1:34m read

1982

Freshman Michael Jordan hits winning shot to give North Carolina NCAA title

On March 29, 1982, 19-year-old North Carolina freshman Michael Jordan makes a 16-foot jump shot with 15 seconds left to give the Tar Heels a 63-62 win over Georgetown for the NCAA Tournament championship. “To tell the truth,” Jordan tells reporters in New Orleans afterward, “I didn’t see it go in. I didn’t want to […]

1:36m read

Space Exploration

11 videos

Space Exploration

6 Ways the Space Race Transformed Everyday American Life

The launch of Sputnik in October 1957 sparked a space race that reshaped education, science, technology and everyday life.

Space Exploration

Earthrise: Behind the Famed Apollo 8 Photo

Earthrise is a photo taken by NASA astronaut Bill Anders on December 24, 1968, that gave people an awe-inspiring view of their home planet.

Space Exploration

The Rise and Fall of Planet Pluto

Look back at the controversial decision to give Pluto the pink slip and shrink the solar system from nine planets to eight.

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