Rather than delay their work, the researchers chose to pivot to studying moons of Jupiter which had flown into their gaze. Sheppard's discovery brought the total number of objects orbiting Jupiter to 79 - but he said one discovery stood out in particular. The latest count of 79 known planets includes eight that have not been seen for several years. This tells us something about the timing of the formation of these moon families, which, in turn, tells us something new about the formation of the Solar System.
This image shows the different groupings of moons orbiting Jupiter, with the newly discovered moons displayed in bold. He and his team have been photographing the skies with some of today's best telescope technology, hoping to catch sight of this mysterious ninth planet.
Two of the newly discovered moons orbit much closer to Jupiter and have a prograde orbit, meaning that they orbit in the same direction as the planet.
As part of that search, Sheppard was using the 4-meter Víctor Blanco Telescope in Chile in March of past year and realized that Jupiter was right near the part of the sky he wanted to search.
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. Jupiter is not in the frame and is off to the upper left.
"Valetudo's going down the highway the wrong way, so it's very likely it will collide with these other objects".
12 new moons spotted around Jupiter - but one may destroy them all
Astronomers group Jupiter's moons by their distance from the planet as well as their orbital direction. But the newly discovered moons are tiny, ranging from 1 to 3 kilometers in diameter.
Two of the new discoveries are part of a closer, inner group of moons that orbit in the prograde, or same direction as the planet's rotation. If moon circles a planet in the opposite direction of a rotating planet, that orbit is retrograde.
Most of the moons are the size of large asteroids, measuring between one and three kilometers (about two-thirds of a mile to two miles) in diameter.
Valetudo might be the last fragment of a larger moon that was destroyed by the retrograde moons, and its path means it too might eventually get demolished.
The curious find might shed light on how many of Jupiter's current moons were formed.
The moons are remnants of what was out there, born in the disc of gas and dust around Jupiter after the planet formed and then captured and pulled into Jupiter's orbit. It's small - less than one kilometer in diameter - with a prograde orbit that crosses the outer retrograde moons. Sheppard expects there could be even more small moons lurking out there.
"Our other discovery is a real oddball and has an orbit like no other known Jovian moon", Sheppard explained.
Finding lots of these small moons also tells us about conditions in the early solar system.
If Planet Nine exists, it could be the runt of the giant planets, Sheppard said. The planet must have acted like a vacuum, sucking up all the material that was around it. The new moons are faint, so researchers haven't been able to spot features on their surfaces or clues to what they're made of. It's also the smallest known moon of Jupiter, scientists said.