Earth-Sized Planets May Be Hiding in Space in 'Major' Exoplanet Finding

Astronomers believe there could be many more Earth-sized planets than previously thought because they may be lurking in the glare of what are known as double-star systems.

The finding comes after researchers from NASA and U.S. universities teamed up to find out whether some exoplanet host stars may actually be binary stars—two stars in orbit around one another.

In recent years, astronomers have been searching for exoplanets using the Transiting Exoplanet Survey Satellite (TESS).

TESS is an Earth-orbiting satellite that works by looking at stars and measuring their brightness. When this brightness dims, it suggests that a planet has passed in front of a star and temporarily blocked out some of its light.

In this way, TESS can detect planets orbiting stars outside of our solar system and also give clues as to how big these planets are. This planet detection method is called transit photometry.

However, it can be difficult for TESS to tell the difference between one large star and two smaller ones in close orbit around one another. According to Steve Howell from NASA's Ames Research Center, who was involved in the study, around 50 percent of stars are in binary systems.

To solve this, scientists selected hundreds of stars that TESS had previously looked at that were believed to host potential exoplanets. They then used telescopes at the Gemini Observatory in Hawaii and Chile to peer as closely at the stars as they could with high resolution.

They found that 73 of the exoplanet host stars were actually binary systems.

Afterwards, the team realized that TESS had only detected large planets when it looked at binary systems, but detected both large and small planets when it looked at single-star systems.

This suggested the possibility that small planets, such as those that are Earth-sized, have not been showing up in TESS observations of binary star systems.

The study was published on the pre-print website arXiv, meaning it has not been peer-reviewed. Kathryn Lester from NASA's Ames Research Center, who led the study, said this is because the planets are getting hidden by the brightness of their two stellar hosts.

She said in a statement: "We have shown that it is more difficult to find Earth-sized planets in binary systems because small planets get lost in the glare of their two parent stars."

Howell said the study represented "a major finding in exoplanet work" and added that "we could be missing the discovery of—and the chance to study—a lot of Earth-like planets."

James Kirk, an astronomer at the Center for Astrophysics at Harvard & the Smithsonian who was not involved in the study, told Newsweek the study demonstrated observational bias against detecting Earth-sized planets in these two-star systems.

He said: "This result will help inform models of planet formation and dynamical evolution in binary star systems, while the potential implications of this study on our understanding of the occurrence rate of Earth-sized planets are profound."

This article has been updated to provide more information about the role of James Kirk.

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An illustration shows a mock-up of an exoplanet. Some small exoplanets may be hard to detect if they have two host stars. Getty Images