Key Facts


21P/Giacobini-Zinner is a mid-sized comet whose orbit features a relatively short period, low inclination, and is controlled by Jupiter's gravitational effects. NASA JPL has classified 21P/Giacobini-Zinner as a "Near Earth Asteroid" due to its orbit's proximity to Earth, but it is not considered potentially hazardous because computer simulations have not indicated any imminent likelihood of future collision.

21P/Giacobini-Zinner orbits the sun every 2,390 days (6.54 years), coming as close as 1.01 AU and reaching as far as 5.99 AU from the sun. Its orbit is highly elliptical. 21P/Giacobini-Zinner is about 2.0 kilometers in diameter, making it larger than 99% of asteroids, comparable in size to Mount Everest.

No Close Approaches

21P/Giacobini-Zinner's orbit is 0.02 AU from Earth's orbit at its closest point. This means that there is a 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

21P/Giacobini-Zinner's orbit is determined by observations dating back to May 1, 2011. It was last officially observed on Jan. 30, 2020. The IAU Minor Planet Center records 1,987 observations used to determine its orbit.

Accessibility and Exploration

This comet 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 21P/Giacobini-Zinner:



   or view a random object

Orbital Elements

  • Epoch: 2458063.5 JD
  • Semi-major axis: 3.5 AU
  • Eccentricity: 0.7105
  • Inclination: 32.0°
  • Longitude of Ascending Node: 195.41°
  • Argument of Periapsis: 172.81°
  • Mean Anomaly: 313.61°

Physical Characteristics

  • Diameter: 2.00000 km
  • Magnitude: 13.1

Derived Characteristics

  • Orbit Period: 2,390 days (6.54 years)
  • Avg. Orbit Speed: 15.93 km/s
  • Aphelion Distance: 5.99 AU
  • Perihelion Distance: 1.01 AU

Map Comparison

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Orbit Simulation

Sky Map

The position of 21P/Giacobini-Zinner 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 21P/Giacobini-Zinner 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.