Jupiter's moon count reaches 79, including tiny 'oddball'

Astronomers are still finding moons at Jupiter, 400 years after Galileo used his spyglass to spot the first ones.

The latest discovery of a dozen small moons brings the total to 79, the most of any planet in our solar system.

Scientists were looking for objects on the fringes of the solar system last year when they pointed their telescopes close to Jupiter's backyard, according to Scott Sheppard of the Carnegie Institute for Science in Washington. They saw a new group of objects moving around the giant gas planet but didn't know whether they were moons or asteroids passing near Jupiter.

"There was no eureka moment," said Sheppard, who led the team of astronomers. "It took a year to figure out what these objects were."

This April 3, 2017 image made available by NASA shows the planet Jupiter. A team of astronomers is reporting the recent discovery of a dozen new moons circling the giant gas planet. That brings the number of moons at Jupiter to 79, the most of any planet. (NASA, ESA, and A. Simon (GSFC) via AP, File)

They all turned out to be moons of Jupiter. The confirmation of 10 was announced Tuesday. Two were confirmed earlier.

The moons had not been spotted before because they are tiny. They are about one to two kilometers (miles) across, said astronomer Gareth Williams of the International Astronomical Union's Minor Planet Center.

And he thinks Jupiter might have even more moons just as small waiting to be found.

"We just haven't observed them enough," said Williams, who helped confirm the moons' orbits.

The team is calling one of the new moons an 'oddball' because of its unusual orbit. Sheppard's girlfriend came up with a name for it: Valetudo, the great-granddaughter of the Roman god Jupiter.

Valetudo is in Jupiter's distant, outer swarm of moons that circles in the opposite direction of the planet's rotation. Yet it's orbiting in the same direction as the planet, against the swarm's traffic.

"This moon is going down the highway the wrong way," Sheppard said.

Scientists believe moons like Valetudo and its siblings appeared soon after Jupiter formed. The planet must have acted like a vacuum, sucking up all the material that was around it. Some of that debris was captured as moons.

"What astonishes me about these moons is that they're the remnants of what the planet formed from," he said.

Telescopes in Chile, Hawaii and Arizona were used for the latest discovery and confirmation.

Galileo detected Jupiter's four largest moons, Io, Europa, Ganymede and Callisto in 1610. The latest count of 79 known planets includes eight that have not been seen for several years. Saturn is next with 61, followed by Uranus with 27 and Neptune with 14. Mars has two, Earth has one and Mercury and Venus have none. 

TOKYO (AP) — Japan’s first moon lander has survived a third freezing lunar night, Japan’s space agency said Wednesday after receiving an image from the device three months after it landed on the moon.

The Japan Aerospace Exploration Agency said the lunar probe responded to a signal from the earth Tuesday night, confirming it has survived another weekslong lunar night.

Temperatures can fall to minus 170 degrees Celsius (minus 274 degrees Fahrenheit) during a lunar night, and rise to around 100 Celsius (212 Fahrenheit) during a lunar day.

The probe, Smart Lander for Investing Moon, or SLIM, reached the lunar surface on Jan. 20, making Japan the fifth country to successfully place a probe on the moon. SLIM on Jan. 20 landed the wrong way up with its solar panels initially unable to see the sun, and had to be turned off within hours, but powered on when the sun rose eight days later.

SLIM, which was tasked with testing Japan's pinpoint landing technology and collecting geological data and images, was not designed to survive lunar nights.

JAXA said on the social media platform X that SLIM's key functions are still working despite repeated harsh cycles of temperature changes. The agency said it plans to closely monitor the lander's deterioration.

Scientists are hoping to find clues about the origin of the moon by the comparing mineral compositions of moon rocks and those of Earth.

The message from SLIM came days after NASA restored contact with Voyager 1, the farthest space probe from earth, which had been sending garbled data back to earth for months.

An U.S. lunar probe developed by a private space company announced termination of its operation a month after its February landing, while an Indian moon lander failed to establish communication after touchdown in 2023.

This image provided by SLIM official X account @SLIM_JAXA shows a part of the moon surface taken by Japan’s first moon lander called SLIM on Tuesday, April 23, 2024. Japan’s first moon lander has survived a third freezing lunar night, Japan’s space agency said Wednesday, April 24, after receiving an image from the device three months after it landed on the moon. (SLIM official X account @SLIM_JAXA via AP)