10 More Moons for Jupiter

Sometimes stuff gets in the way when you are looking for
faint Kuiper belt objects near the edge of the solar system. That is what happened to a team of scientists using the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. The huge 520-megapixel camera attached to the telescope also had Jupiter in its view leading to the discovery of 10 new moons for the largest planet in the solar system.


An additional year of observations verified the orbits of the moons and their status was confirmed by the International Astronomical Union on July 17th, 2019.

The moons are all less than 3 km in diameter and orbit Jupiter much further out than the large primary moons. The moons of Jupiter have been classified into a few groups:

  • The inner group of primary or Galilean moons (purple),
  • The prograde group that orbit Jupiter in the same direction as Jupiter’s rotation (blue), and
  • The retrograde group that orbit in the opposite direction to Jupiter’s rotation (red).

The newly discovered moons mostly fall into the above groups with 2 in the prograde group and 7 in retrograde group.

One outlier orbits in the same direction as Jupiter’s rotation but is located within the retrograde group. This outlier has tentatively been named “Valetudo” after Jupiter’s great-granddaughter. Its orbit with the retrograde group is unstable and a collision is likely at some point.

The new discovery brings Jupiter’s total up to 79 moons – the most of any planet in our solar system. Four moons of Jupiter were discovered by Galileo: Io, Europa, Ganymede, and Callisto. They are among the largest satellites in the Solar System and are easily visible in a small telescope or even binoculars (if they are supported or held steady enough).

Image of the Galilean Moons through a 100 mm refractor from Dec 2013. Image Credit: RASC Vancouver member, Ken Jackson

Jupiter is currently located about 20 degrees above the horizon, due south, at 10:00 pm PDT. Come out to Starry Nights at SFU’s Burnaby Campus on Friday, July 26th from 09:00 pm to midnight to get your own look at the Galilean moons (weather permitting) – Io slips in behind Jupiter at 09:30 pm but Europa, Ganymede, and Callisto will appear as tiny points of light with Europa on one side and Ganymede & Callisto lined up on the other side.