Involves

Moment

Venus opens the road to Mercury

Venus, February 5, 1974; Mariner 10 turns toward the inner planet

NASA's Mariner 10 passed Venus on February 5, 1974, gathering images and measurements while using the encounter to redirect its trajectory toward Mercury. Venus was both a scientific target and a means of reaching another world. The spacecraft then made its first Mercury encounter on March 29.

Spacecraft
Mariner 10
Encounter
February 5, 1974
Next target
Mercury

The caveat

Popular descriptions call the maneuver a slingshot, which can imply a simple speed boost. The actual change depends on the reference frame and geometry. Mariner 10's achievement was a carefully designed transfer, not a universal recipe for accelerating whenever a planet is nearby.

Mariner 10 became the first mission to use an interplanetary gravity assist to reach another planet. It later returned for additional Mercury flybys. The route demonstrated that a mission could be designed around encounters that altered its orbit rather than treating every planet as the endpoint of a direct journey.

How it connects

Mariner 10 used Venus as a turning point on the way to Mercury.

This moment appeared in Borrowing motion from a planet, the Involves connection for September 9, 2026, which asked: How can a spacecraft change course without carrying all the fuel for the turn?

Check yourself

What role did Venus play for Mariner 10?

It was a scientific target and a flyby that redirected the mission toward Mercury. Exactly. Mariner 10 studied Venus and used its gravity before the first Mercury encounter.

What the sources establish

  • Mariner 10 flew past Venus on February 5, 1974, before reaching Mercury on March 29, using the first interplanetary gravity assist.

Sources