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July 18, 2018
The moons that have just been identified around Jupiter are all small. Jupiter's new moons were observed for the first time in 2017.
Twelve new moons were discovered around Jupiter. The planet now has 79 known satellites, a record among the planets of our solar system, said Tuesday an American team of astronomers.
Jupiter and Ganymede. Image Credits: NASA/Hubble/STScI
The moons that have just been identified are all small. If Jupiter has large satellites like Ganymede (the largest in the solar system with a diameter of 5268 km), those who have just been spotted are only between 1 km and 4 km in diameter. This is tiny compared to the diameter of Jupiter, which borders on 143'000 km.
Researcher Scott Sheppard of the Carnegie Institution for Science has called one of these new moons a "strange ball" because of its size: just under one kilometer in diameter, making it "probably" the smallest satellite of Jupiter. Its orbit is also "different from that of all other known Jupiterian moons," said the astronomer.
It takes about a year and a half for this "strange ball" to circle Jupiter, whose inclined orbit intersects those of a cloud of other moons moving in the opposite direction of the rotation of Jupiter.
"It's an unstable situation," said Sheppard. "Frontal collisions can quickly dislocate satellites and reduce them to dust." The "strange ball", like two recently discovered moons, turns in the same direction as Jupiter.
Images above: Images taken in May 2018 with Carnegie's 6.5-meter Magellan telescope at the Las Campanas Observatory in Chile. Lines point to Valetudo, the newly discovered "oddball" moon. Images Credits: Carnegie Institution for Science.
Astronomers have proposed to christen it "Valetudo", named after the great-granddaughter of the Roman god Jupiter, goddess of health and hygiene.
Half ice, half rock
It takes about a year for the nearest satellites to circle the planet, compared to two years for those more distant. All these moons could be fragments resulting from collisions between larger cosmic bodies.
Image above: This image shows the different groupings of moons orbiting Jupiter, with the newly discovered moons displayed in bold. The "oddball" moon, known as Valetudo, can be seen in green in a prograde orbit that crosses over the retrograde orbits. Image Credits: Roberto Molar-Candanosa, courtesy of Carnegie Institution for Science.
"Jupiter is like a big vacuum, so this planet is massive," said Scott Sheppard. "These objects started spinning in orbit around Jupiter rather than being rushed against it. We think these are objects halfway between rocky asteroids and icy comets. Probably half ice, half rock.
Discoveries by Galileo
The Italian astronomer Galileo discovered in 1610 the first four moons of Jupiter. The team of astronomers behind the recent discovery was not looking for new Jupiter satellites, but they appeared in the field of their telescopes as they searched for planets beyond Pluto.
Artist's view of Galileo spacecraft. Image Credit: NASA
The new moons were observed for the first time in 2017 for a Chile-based telescope operated by the US National Astronomical Observatory. It took a year to confirm the trajectory of their orbits using several other telescopes in the United States and Chile.
Old Data, New Tricks: Fresh Results from NASA’s Galileo Spacecraft 20 Years On
Carnegie Institution for Science: https://carnegiescience.edu/
NASA Galileo mission: https://www.jpl.nasa.gov/missions/galileo/
Images (mentioned), Text, Credits: ATS/NASA/Orbiter.ch Aerospace/Roland Berga.
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