Tag Archives: Adrastea

Encyclopedia Entry #5 – Adrastea

This is the first in the Solar System Moons series.  Each entry will go through the moons of the solar system in alphabetic order.  This time, we will start with Adrastea.

Adrastea is also known as Jupiter XV.  The smallest of the inner moons of Jupiter, it was the first moon discovered by a spacecraft, Voyager 2.  It was discovered on July 8, 1979.  Very little is known about the surface of Adrastea, as it is very small and was not photographed very much at all.  It’s known to be tidally locked to Jupiter and orbit at the edge of Jupiter’s Main Ring.


  • Dimensions: 20 x 16 x 14 km
  • Mass: ≈ 2×1015 kg
  • Mean density: 0.86 g/cm³
  • Surface gravity: 0.0004 g
  • Albedo: 0.10±0.045
  • Temperature: ≈ 122 K
  • Mean orbit radius: 129000 km
  • Orbital period: 0.29826 d
  • Inclination: 0.03°
  • Eccentricity: 0.0015

Name Origin

Adrastea was named after the nymph who nursed the infant Zeus in Greek mythology.  This was in order to protect him from his father Cronus.

5 Interesting Facts

1. It was the first natural satellite to be discovered not by a telescope, but by a spacecraft.

2. It’s thought to be the main contributor to Jupiter’s rings.  It orbits at the edge of the Main Ring.

3. Very little is known about Adrastea, but if it’s like Amalthea, it’s thought to be composed mainly of water ice with a porosity of 10-15%, as its density is lower than water.

4. It’s one of only 3 moons that orbit its parent planet faster than the planet’s day.  The other two are Metis, the innermost moon of Jupiter and Phobos, the innermost moon of Mars.

5. As it lies within Jupiter’s synchronous orbit radius, it will eventually crash into Jupiter as its orbit decays.  However, as it appears to be just outside the Roche limit, it hasn’t been been broken up.

And that is Adrastea. It’s not a well-known moon, since it hasn’t been studied much at all.  The Galileo probe didn’t study it much, as you can see by the image taken by it.  It’s pretty fuzzy.  I hope you learned something about Adrastea.