Apollo
Key facts
- What it is
- Near-Earth asteroid (namesake of the Apollo group)
- Size
- About 1.5 km across
- Discovered
- 1932, by Karl Reinmuth
- Spacecraft
- Not yet visited
- Orbit group
- Apollo
- Average distance from the Sun
- 1.47 au (about 220 million km)
- Time to go round the Sun
- 651 days
- Closest and farthest from the Sun
- 0.65 to 2.29 au
- Tilt of its orbit
- 6.4°
- Closest its orbit comes to Earth's
- 3,900,000 km (10 times the Moon's distance)
- Spins once every
- 3.1 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Apollo was the first asteroid found whose orbit crosses Earth's. Karl Reinmuth discovered it at Heidelberg on 24 April 1932, when it passed about 10 million kilometres from Earth. It then went unseen for more than forty years, because its orbit had not been measured well enough to predict where to look. It was found again in 1973.
The Apollo group of asteroids is named after it. An Apollo asteroid crosses Earth's orbit, and its average distance from the Sun is greater than Earth's, so it takes longer than a year to go round. This is the largest group of near-Earth asteroids. Most of the meteorites whose orbits have been worked out from fireball cameras came from Apollo-type orbits, and the small asteroids that have hit Earth soon after being discovered were mostly Apollos too.
Apollo itself is about 1.5 kilometres across. In 2005 radar observations revealed that it has a small moon, only about 80 metres wide.
Apollo has also helped scientists measure a subtle effect of sunlight. A spinning asteroid absorbs sunlight and gives off the heat again, and that tiny push can change both its spin and its orbit over time. Careful observations over many years showed that Apollo's spin is speeding up, one of the first detections of this effect, called YORP.
Crossing Earth's orbit does not mean being on a collision course. Orbits are tilted at different angles, so most of the time an Apollo asteroid passes far above or below the point where Earth is. Apollo itself has been tracked for more than fifty years, and its path is very well known.
Coming close to Earth
Its next passes within about 30 million km of Earth, worked out from its orbit. Each one is a safe miss.
| Date | Distance | In Moon distances |
|---|---|---|
| 13 Nov 2046 | 5,300,000 km | 14 |
| 13 May 2048 | 7,400,000 km | 19 |
| 17 Nov 2071 | 16,000,000 km | 41 |
| 20 May 2073 | 20,000,000 km | 51 |
| 5 Nov 2080 | 15,000,000 km | 38 |
| 12 May 2082 | 5,000,000 km | 13 |