On July 20, 1969, the bulkily space-suited figure of astronaut Neil Armstrong descended the ladder of Apollo 11’s lunar lander, planted his boot in the Moon's gray dust, and declared: "That's one small step for a man, one giant leap for mankind." This first visit to Earth's natural satellite—the culmination of NASA's Apollo 11 mission—was a seminal moment in the history of human space exploration (Fig. 1). See also: Moon; Space flight

Since its landing in 2012, NASA’s Curiosity rover has been analyzing Martian soils and rocks for evidence that the Red Planet could have supported life in its past. So far, Curiosity has found carbon, hydrogen, oxygen, phosphorus, sulfur, methane, and organic molecules. In addition, Curiosity has found evidence of surface water and groundwater. All these discoveries suggest favorable chemistry and conditions for supporting life, although not evidence of life. Most recently, scientists reported in the journal Geophysical Research Letters (September 2017) the discovery of the element boron, which may have acted as a stabilizer for the molecular precursors of life. See also: Boron; Mars Science Laboratory; Robot rover Curiosity lands on Mars; Prebiotic organic synthesis; Space probe

On February 6, 2018, the Falcon Heavy rocket passed its first launch test, lifting off from NASA’s Kennedy Space Center in Florida atop a bright pillar of fire. Built by the California-based, private aerospace company SpaceX, the Falcon Heavy is the most powerful launch vehicle since NASA’s Saturn V took humans to the Moon nearly a half-century ago. The Falcon Heavy is also the strongest rocket ever debuted by the commercial space sector. In recent years, private industry has started to play a major role in the access and utilization of space, a realm that had long been only available through governmental agencies. See also: Astronautical engineering; Moon; Rocket; Rocket propulsion; Space flight

In 2017, the U.S. National Aeronautics and Space Administration (NASA), along with partner space agencies around the world, created Artemis, a lunar exploration program. Named after the Greek goddess of the Moon and twin sister to Apollo—the namesake of the series of NASA missions that first put astronauts on the Moon in 1969—the Artemis missions will also lay the groundwork for eventually sending humans to Mars. With the new Space Launch System rockets and Orion spacecraft developed for Artemis, NASA plans on studying the Moon, establishing U.S. leadership in deep-space exploration, expanding U.S. commercial partnerships, and inspiring a new generation to pursue science, technology, engineering, and math (STEM) careers, among other goals. The first Artemis mission, designated Artemis I, launched November 16, 2022 after a series of weather delays postponed its original late-August launch date. Plans call for continued launches over the next several years. Artemis I served as an uncrewed demonstration of the complete mission profile including launch, lunar orbit, re-entry in Earth’s atmosphere, descent, oceanic splashdown, and recovery. The mission concluded on December 11, 2022, after 25 days in space. See also: Astronautical engineering; Astronautics; Mars; Moon; Space flight

The New Horizons space probe, launched on January 19, 2006, was designed to fly by Pluto and to study that body and its satellites. On July 14, 2015, after a 9½-year journey, New Horizons reached the vicinity of Pluto, flying only 12,500 km (7800 mi) above the surface of that body at 7:49 AM EDT. At that time, Pluto was 31.9 astronomical units (au) from Earth, or about 4.8 × 10⁹ km (3.0 × 10⁹ mi), and signals from New Horizons, travelling at the speed of light, took 4 hours 25 minutes to reach Earth. See also: Pluto; Space probe

In the summer of 2014, a search conducted with the Hubble Space Telescope identified 5 small Kuiper Belt objects as potential second destinations for the New Horizons spacecraft after its flyby of Pluto, which would take place on July 14, 2015. This field of candidate objects was subsequently winnowed to 3 and then 2. On August 28, 2015, NASA announced that it had selected one of these objects, formally designated 2014 MU69 and informally known as PT1 (for Potential Target 1), as the potential next destination of New Horizons, subject to a detailed assessment before official approval of the mission extension by NASA. New Horizons will perform a series of 4 maneuvers in late October and early November 2015 that will set it on course to fly by PT1 about January 1, 2019, nearly 13 years after the launch of the space probe. New Horizons will then be 43.4 astronomical units (au) from the Sun, about 11 au (1.6 × 10⁹ km or 1.0 × 10⁹ mi) further from the Sun than it was during the Pluto flyby. See also: Hubble Space Telescope; Kuiper Belt; New Horizons at Pluto; Pluto