Ganymed
Key facts
- What it is
- Largest near-Earth asteroid (Amor group)
- Size
- About 35 km across
- Discovered
- 1924, by Walter Baade
- Spacecraft
- Not yet visited
- Orbit group
- Amor
- Average distance from the Sun
- 2.66 au (about 400 million km)
- Time to go round the Sun
- 4.4 years
- Closest and farthest from the Sun
- 1.24 to 4.09 au
- Tilt of its orbit
- 26.7°
- Closest its orbit comes to Earth's
- 51,000,000 km (133 times the Moon's distance)
- Spins once every
- 10.3 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.
Ganymed is the largest known near-Earth asteroid, about 35 kilometres across. It is not to be confused with Ganymede, the largest moon of Jupiter: the asteroid's name is spelt the German way, without the final e.
Walter Baade discovered it on 23 October 1924 at the Hamburg Observatory in Bergedorf, Germany. It is an S-type asteroid, made of stony silicate minerals and metal, and its orbit is long and stretched. At its farthest from the Sun it reaches out into the main asteroid belt, while at its closest it comes inside the orbit of Mars and approaches the orbit of Earth.
Near-Earth asteroids are defined by how close they come to the Sun: any asteroid whose orbit takes it within 1.3 times Earth's distance from the Sun counts. Ganymed meets that definition, but its path never brings it very near our planet. Its closest possible approach to Earth's orbit is around 50 million kilometres, more than a hundred times the distance to the Moon. When it does pass close by astronomical standards, it becomes bright enough to see with a small telescope and is a popular target for radar studies.
Ganymed is a good reminder that the label near-Earth describes an orbit, not a danger. Being the largest in its class, it would be easy to track, and nothing in its path is a concern. Studying large near-Earth asteroids like this one helps scientists understand how bodies are steered out of the main belt into the inner Solar System over millions of years.