The orbit of a dozen previously unknown moons around Jupiter are shown here, including the "oddball" discovery, Valetudo.
Astronomers peering into the depths of the solar system in search of a presumed ninth planet far beyond Pluto happened to be looking past Jupiter during their observations and happened to discovery 12 new moons orbiting the giant planet.
Because of how many observations it takes to determine an object in space is actually in orbit around Jupiter, it took about a year to confirm that these were, indeed, new Jovian moons.
Not only that, but when the orbital characteristics (shape, tilt, and so on) are compared, these nine retrograde moons seem to fall into three groups; that implies that each group used to be a single moon that got smashed somehow, possibly a collision with another moon-sized body. It is more distant (for good reason!), more inclined, takes longer to orbit Jupiter than its siblings, and crosses the outer retrograde moons.
Two other new moons were found to be part of a closer group that orbits in the prograde, or same direction as Jupiter's rotation.
A head-on collision between two moons would "grind the objects down to dust", he added. Astronomers believe they were once all part of a larger moon that broke apart.
The small moon rotates at the distance of the retrograde moons, but it's traveling in the other direction. If the collisions had happened earlier, the moons would likely have interacted with dust and gas leftover from forming Jupiter and been dragged into the planet.
Using the Blanco 4-meter telescope at Cerro Tololo Inter-American in Chile, with its highly-sensitive Dark Energy Camera, however, gave the team a distinct advantage. That swells to 79 or so the number found circling the giant planet since Galileo spotted the first of them with a homemade telescope more than 400 years ago.
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The astronomers were not intentionally searching for new Jovian moons when they began observing.
The moons Sheppard spied are farther-flung and tiny, each no more than two miles in diameter. The team's goal was to scan the sky for evidence of a massive ninth planet in the outer solar system.
The moons are small, ranging from just one kilometre to three kilometres in width. Sheppard believes it could be Jupiter's smallest, and it has an orbit unlike any other moon around the planet.
"Our other discovery is a real oddball and has an orbit like no other known Jovian moon", said Scott Sheppard, lead scientist on the project and a staff scientist at the Department of Terrestrial Magnetism in Washington, D. C. They named it Valetudo, after a daughter of Jupiter and the Roman goddess of hygiene and personal health.
It is possible the various orbital moon groupings we see today were formed in the distant past through this exact mechanism. They exist in retrograde - going the opposite direction of Jupiter's spin rotation.
The newfound moons are small, between about 1 and 3 kilometers across.
"If we do find this planet in the next few years, it would be a pretty unbelievable discovery for astronomy". "We think these moons are an intermediate type of object, half-rock and half-ice". That makes it a powerful tool for surveying the night sky in search of faint objects.