Key Facts


Riema is a mid-sized asteroid orbiting between Mars and Jupiter within the inner portion of the asteroid belt. NASA JPL has not classified Riema as potentially hazardous because its orbit does not bring it close to Earth.

Riema orbits the sun every 1,020 days (2.79 years), coming as close as 1.90 AU and reaching as far as 2.06 AU from the sun. Riema is about 4.6 kilometers in diameter, making it larger than 99% of asteroids, comparable in size to the San Francisco Bay.

The rotation of Riema has been observed. It completes a rotation on its axis every 3.59 hours.

Riema's spectral type E (Tholen) / Xe (SMASSII) indicates that it is likely to contain iron, nickel, and cobalt.

No Close Approaches

Riema's orbit is 0.91 AU from Earth's orbit at its closest point. This means that there is a very wide berth between this asteroid and Earth at all times.

Orbital simulations conducted by NASA JPL's CNEOS do not show any close approaches to Earth.

Images and Observations

Riema's orbit is determined by observations dating back to Aug. 13, 1923. It was last officially observed on July 4, 2023. The IAU Minor Planet Center records 5,166 observations used to determine its orbit.

Accessibility and Exploration

This asteroid is not considered a viable target for human exploration by the NHATS study.

Similar Objects

These objects have orbits that share similar characteristics to the orbit of Riema:



   or view a random object

Orbital Elements

  • Epoch: 2460200.5 JD
  • Semi-major axis: 1.979 AU
  • Eccentricity: 0.0397
  • Inclination: 26.87°
  • Longitude of Ascending Node: 163.36°
  • Argument of Periapsis: 349.13°
  • Mean Anomaly: 161.06°

Physical Characteristics

  • Diameter: 4.60500 km
  • Magnitude: 12.55
  • Albedo: 1.000
  • Spectral type (Tholen): E
  • Spectral type (SMASS): Xe

Derived Characteristics

  • Orbit Period: 1,020 days (2.79 years)
  • Avg. Orbit Speed: 21.11 km/s
  • Aphelion Distance: 2.06 AU
  • Perihelion Distance: 1.90 AU
  • Rotation Period: 3.59 hours
  • Approx. Composition: iron, nickel, and cobalt.

Map Comparison

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Orbit Simulation

Sky Map

The position of Riema is indicated by a ◯ pink circle. Note that the object may not be in your current field of view. Use the controls below to adjust position, location, and time.

Size Rendering

The above comparison is an artistic rendering that uses available data on the diameter of Riema to create an approximate landscape rendering with Mount Everest in the background. This approximation is built for full-resolution desktop browsers. Shape, color, and texture of asteroid are imagined.