In 2017, scientists spotted an oddly shaped visitor in our solar system that was accelerating in an unexplainable way.
The object, called 'Oumuamua, was unusually long and skinny, like a cigar, and had a reddish hue.
Planetary scientists now say the interstellar object is "pancake" or dish-shaped.
Oumuamua is actually an icy comet, not an alien spaceship, and researchers now have a good idea of why it's been speeding up.
As the sun heated the comet, the icy object released a particular gas, accelerating its trajectory.
Jennifer Bergner and Darryl Seligman wrote in Nature that interstellar comets should do this.
Oumuamua is the first ever observed visitor from outside our solar system and didn't behave like other comets.
Bergner and Seligman believe the comet accelerated by releasing hydrogen into space.
When radiation hits water ice, it produces hydrogen, which then became trapped on or just beneath the comet's surface.
When sunlight hit 'Oumuamua, it released the gas, producing sufficient force to power its acceleration.
Oumuamua was too small to outgas from a thin shell like a comet several kilometres across.