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. Scientists have discovered 12 previously unknown moons orbiting Jupiter, and one of them is a real oddball. While hunting for the proposed Planet Nine, a massive planet that some believe could lie beyond Pluto, a team of scientists, led by Scott Sheppard from the Carnegie Institution for Science, found the 12 moons orbiting Jupiter. With this discovery, Jupiter now has a staggering 79 known orbiting moons -- more than any other planet in the solar system.
"These are tiny--these are 1-3 km in size," says Amanda Bosh, Senior Lecturer in the Department of Earth, Atmospheric, and Planetary Sciences at MIT, who was not involved in the research. "That's why they haven't been discovered before because they are so small and so faint." To understand the discovery, it helps to separate out the moons into groups. First up: the two that were discovered last year. Both are located in a group of moons travelling around Jupiter in the same direction as the planet's rotation (in technical terms, they have a prograde orbit).
Sometimes a search for one thing presents the chance to look for something else. If you're like me, that something else is usually something small: Rummaging in the couch cushions for the TV remote might prompt you to dig for spare change. But if you're astronomer Scott Sheppard, the second bird occasionally turns out to be a doozy. Like, say, a dozen previously unknown moons orbiting Jupiter, the discovery of which was announced Tuesday by the International Astronomical Union. "We just wanted to be as efficient as possible," says Sheppard, an astronomer at the Carnegie Institution for Science in Washington, DC.
Astronomers have spotted an incredibly rare'backwards' asteroid. Asteroid 2015 BZ509, also known as Bee-Zed, orbits the Sun in the opposite direction to the planets. It takes 12 years to make one complete orbit around the Sun - roughly the same time as Jupiter travelling in the opposite direction. Researchers predicted it two years ago, and have now been able to prove their theory was correct. Co-orbital bodies that orbit the Sun in the same direction as a planet can follow trajectories (blue curves with arrows) that, from the perspective of the planet, look like tadpoles, horseshoes or'quasi-satellites' It is estimated that only 82 of the more than 726,000 known asteroids are orbiting the'wrong way'.
There's an asteroid in Jupiter's lane that orbits the sun in the wrong direction – and it may have been doing so for more than a million years. The asteroid 2015 BZ509 was discovered in 2015, orbiting near Jupiter but in the opposite direction. Like Jupiter and the other asteroids tied to its orbit, which are called Trojans, it takes 12 Earth years to orbit the sun. It is the only asteroid we know of that shares a planet's orbital space while moving in the opposite, or retrograde, direction. Paul Wiegert at the University of Western Ontario and his colleagues examined this strange orbit to figure out why BZ509 doesn't crash head-on into Jupiter.