The biggest discoveries and achievements in space in 2019, from a mysterious layer outside our solar system to NASA's flight through the sun's atmosphere

In an August study, researchers calculated that Jupiter probably absorbed a young planet with 10 times the mass of Earth after a head-on impact.

The ancient collision would explain why Jupiter's core is less dense and more diffuse than scientists expected.

"Because it's dense, and it comes in with a lot of energy, the impactor would be like a bullet that goes through the atmosphere and hits the core head-on," Andrea Isella, an astronomer at Rice University and a co-author of the study, said in a press release. "Before impact, you have a very dense core, surrounded by atmosphere. The head-on impact spreads things out, diluting the core."

That's more than any other planet in the solar system.

Each of the newly discovered moons is about 3 miles (5 kilometers) in diameter, and 17 of them orbit in retrograde, or in the opposite direction of Saturn's rotation. One of them is now the farthest known moon of Saturn.

NASA is set to launch a new Mars rover in July 2020, and the European Space Agency plans to launch one as well. NASA and SpaceX, meanwhile aim to launch the first astronauts on the Crew Dragon in the first quarter of the year.