OSIRIS-APEX

The OSIRIS-REx spacecraft, sent on to meet Apophis just after its close pass of Earth in 2029.

Key facts

Agency

NASA (United States)

Type of mission

Asteroid orbiter (extended mission)

Target

Asteroid 99942 Apophis

Launched

8 September 2016 (as OSIRIS-REx)

Status

On its way to Apophis

After dropping off its sample of Bennu in September 2023, the OSIRIS-REx spacecraft still had fuel and working instruments. It was renamed OSIRIS-APEX, for Apophis Explorer, and sent towards one of the best-known near-Earth asteroids.

Apophis

Apophis is about 340 metres across. When it was discovered in 2004, early calculations gave it a worrying chance of hitting Earth in 2029. Further tracking ruled that out, and in 2021 radar measurements removed any significant risk for at least the next century.

On 13 April 2029, however, Apophis will pass only about 32,000 kilometres above Earth's surface, closer than the satellites that orbit at the height of geostationary orbit. It will be visible to the naked eye from parts of Europe, Africa and western Asia as a moving point of light. An object this size passes so close only about once in several thousand years.

The plan

OSIRIS-APEX is due to reach Apophis just after that pass and spend about 18 months studying it. Earth's gravity may trigger small landslides, change its spin or even shake its surface. The spacecraft will look for those changes and then fire its thrusters close to the surface to stir up dust and expose what lies beneath, much as it did at Bennu.

Why it matters to meteorites

Apophis is an S-type asteroid, probably related to the LL chondrites, like Itokawa. It is a rare chance to watch a planet's gravity reshape a meteorite parent body in real time.

Key dates

See where this mission fits among all the others in the mission timeline.

Did you know?

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