Collins maintains lunar orbit

The gamma-ray signal was initially detected by instruments built to monitor nuclear explosions.

The detection later helped establish the study of transient cosmic gamma-ray sources.

The recorded burst had no precise sky position at detection; its meaning became clear only with later analysis.

Armstrong and Aldrin landed in the Sea of Tranquility while Collins remained in lunar orbit.

The landing prepared for direct observations and sample collection by human explorers on the Moon.

The landing was a milestone in human exploration of the solar system; the first steps took place later in UTC on 21 July.

The spacecraft became the first human-made object to orbit another planet.

Engine firing slowed Mariner 9 enough for capture by Martian gravity.

The new orbit enabled prolonged planetary study, although a global dust storm initially limited surface views.

Mariner 9 showed how staying in orbit could reveal much more than a single passing encounter.