Updated:
Original:
Year
1974
Month Day
March 29

U.S. space probe, Mariner, visits Mercury

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. 

Tags
terms:
Space

FACT CHECK: We strive for accuracy and fairness. But if you see something that doesn't look right, click here to contact us!

ALSO ON THIS DAY

U.S. withdraws from Vietnam

Two months after the signing of the Vietnam peace agreement, the last U.S. combat troops leave South Vietnam as Hanoi frees the remaining American prisoners of war held in North Vietnam. America’s direct eight-year intervention in the Vietnam War was at an end. In Saigon, some ...read more

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 ...read more

The "Mad Bomber" strikes in New York

On this day in 1951, a homemade device explodes at Grand Central Station 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 ...read more

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. ...read more

Patton takes Frankfurt

On this day, 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 ...read more