Astronomers discover largest collection of rogue planets in our galaxy

This artist's impression depicts a rouge planet drifting through space. (NOIRLab/NSF/AURA/J. da Silva)

Astronomers have recently discovered the largest collection of free-floating planets in our galaxy.

The cluster includes between 70 and 170 free-floating or rogue planets, which are planets that are drifting in space without orbiting around a star.

“We did not know how many to expect and are excited to have found so many,” said astronomer and study author Nuria Miret-Roig in a press release.

Miret-Roig and her colleagues published their findings in the journal Nature Astronomy on Wednesday. They examined data collected over the past 20 years from numerous telescopes and observatories, including the European Southern Observatory, the NOIRLab in Arizona, the Subaru Telescope in Japan and the Canada-France-Hawaii Telescope in Hawaii.

Because rogue planets by definition don't orbit a star, astronomers say they are extremely difficult to spot. Most rogue planets have been discovered through "microlensing" events, which is when a planet aligns with a background star for a brief moment and forms a silhouette.

However, scientists say microlensing events are extremely rare. Instead, the researchers found that many of these planets are hot enough to glow and could be directly captured with sensitive cameras.

“We measured the tiny motions, the colours and luminosities of tens of millions of sources in a large area of the sky,” said Miret-Roig in the release. “These measurements allowed us to securely identify the faintest objects in this region.”

These planets are approximately 420 light-years away from Earth, located within the Scorpius and Ophiuchus constellations. Their masses are also similar to that of Jupiter's.

It remains unclear how these rogue planets form. Some astronomers believe these planets form after the collapse of a gas cloud that is too small to become a star. Others say they could have been regular planets that were kicked out their solar system.

“There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,” noted study leader Herve Bouy in the release.