Exoplanet searches may be missing half the Earth-sized worlds orbiting other stars. A team using the international Gemini Observatory, the WIYN-3.5-meter Telescope at Kitt Peak National Observatory has discovered that there could be Earth-sized worlds hidden in binary star systems. This means that nearly half of all stars are located in binary systems. Astronomers may be missing many Earth-sized planets.It is possible that Earth-sized planets are more common than we thought. NASA Ames Research Center's twin telescopes, the international Gemini Observatory's NOIRLab Program, were used by astronomers to discover that many of the planet-hosting stars discovered by NASA's TESS exoplanet hunting mission [1] were actually pairs of stars, known as binary stars. This means that the planets orbit one of these stars. The team discovered that many planets of Earth size are hidden in two-star systems. Transit searches such as TESS's look for changes in light from stars when a planet passes by it [2]. It is more difficult to detect changes in the light of the host star when the planet transits due to the light coming from the second star.The team began by trying to find out if some of the exoplanet star host stars identified using TESS were actually unknown binary stellites. If they are not viewed at very high resolution, physical pairs of stars can be mistakenly thought to be single stars. The team used both Gemini telescopes to examine a selection of exoplanet host star samples in great detail. The astronomers used speckle imaging [3] to search for undiscovered stellar companions.The team used the Zorro and Alopeke instruments on the Gemini North telescopes in Chile, and Hawai’i respectively to observe hundreds of nearby stars TESS had identified for potential exoplanet host. They found that 73 stars were binary star systems, which had previously appeared as single points until Gemini was able to observe them at higher resolutions. This work was led by Katie Lester, NASA's Ames Research Center. "With the Gemini Observatory’s 8.1-meter telescopes we obtained extremely high resolution images of exoplanet hosts stars and detected stellar partners at very small separations," she said.Lester's team also examined 18 additional binary stars previously discovered among TESS exoplanet host hosts. They used the NN-EXPLORE Exoplanet, Stellar Speckle Imager(NESSI), on the WIYN 3.5 meter Telescope at Kitt Peak National Observatory. This is also a Program NSF's NOIRLab.After identifying binary stars, the team compared sizes of planets found in binary star systems with those in single-star system. The TESS spacecraft discovered that large and small exoplanets orbiting single star stars were found by the team. However, binary systems contained only large planets.AdvertisementThese results suggest that there could be a large population of Earth-sized planets lurking in binary systems, which might go undiscovered by the transit method used by TESS and other planet-hunting telescopes. Although some scientists suspected that transit searches could miss small planets within binary systems, the new study provides observational support and shows which exoplanet sizes are affected.Lester said, "We have demonstrated that it is harder to find Earth-sized worlds in binary systems," because smaller planets are lost in the glare from their parent stars. Steve Howell, a NASA scientist who is involved in speckle imaging research, said that their transits are "filled in" by the light from the companion stars.Lester stated that about half of the stars in binary systems are Earth-like.These missing worlds could mean that astronomers need to use many observational techniques before concluding that any binary star system does not have Earth-like planets. Lester explained that astronomers must determine whether a star's binary or single status before they can claim that there are no small planets in the system. If it is single, you can say there are no small planets. If the host is in binary, it would be impossible to determine if a small planet is hiding from the companion star or not. To figure this out, you would need to make more observations using a different technique.Lester and her coworkers also looked at how far apart stars were in binary systems that TESS detected large planets. The team discovered that stars in exoplanet hosting pairs were often farther apart than binary star not known to contain planets [6]. This could indicate that planets don't form around stars with close stellar companions.AdvertisementMartin Still, National Science Foundation Division of Astronomical Sciences Program Officer, stated that "This speckle imaging survey highlights the critical need to NSF telescope facilities in order to characterize new planetary systems and improve our understanding of planet populations."Howell stated, "This is an important finding in exoplanet research." The results will be useful for theorists to create models of how planets form in double-star systems.NotesTESS stands for Transiting Exoplanet Survey Satellite. It is a NASA mission that searches for planets around other stars. The spacecraft covers approximately 75% of the night sky. This mission was launched in 2018. It has already detected over 3500 potential exoplanets. More than 130 of these have been confirmed. The satellite observes exoplanets' host stars to find them. A transiting exoplanet causes some starlight to be blocked by the star, causing a subtle but noticeable dip in brightness.[2] One way to find exoplanets is through the transit technique. This involves looking for decreases in starlight that are consistent with a planet passing by or "transiting" starlight.[3] Speckle imaging allows astronomers see beyond the blurred atmosphere by making many fast observations in rapid succession. Combining these observations can cancel out the blurring effect caused by the atmosphere. This causes stars in the night sky and ground-based astronomy to twinkle.[4] Alopeke & Zorro, identical imaging instruments permanently mounted to the Gemini North & South telescopes. Their names, which mean "fox" respectively in Hawaiian and Spanish refer to their respective positions on Maunakea, Hawaii, and Cerro Pachn, Chile.[5] The transit method for observing binary systems was not able to detect planets twice as large or smaller than Earth, according to the team.[6] Lester's group discovered that the binary stars hosting exoplanets had an average separation of around 100 astronomical units. An astronomical unit refers to the distance between the Sun (or Earth) and the Sun. Binary stars without known host planets are usually separated by approximately 40 astronomical units.
