Earth-like planets may be lurking in the glare of binary star systems
Double star systems may be concealing a population of potentially habitable Earth-sized planets in their combined glare, according to the results of a newly published study. Roughly half of all stars are thought to exist in binary systems, in which two massive stellar bodies orbit around a common center of mass.
Earth is unique, as it's the only planet known to be capable of hosting life. Because of this fact, astronomers on the hunt for extraterrestrial life prize the discovery of Earth-sized worlds more than any other.
Naturally, size is not the only factor affecting a world’s habitability. Any number of circumstances could render a planet thoroughly incapable of hosting life, such as its orbital characteristics or the hostile nature of its parent star. However, finding a world with a similar size and composition as Earth is considered to be a promising place to start, and often worthy of followup observations.
According to the new study, astronomers undertaking large-scale stellar surveys may be failing to discover many Earth-sized worlds that are embedded in binary star systems.
The scientists behind the study sought to discover how many stars in a sample of data collected by NASA’s TESS exoplanet hunting mission were actually part of a double star system. They also hoped to shed light on whether it was likely that the intense light from the stars was capable of obscuring the presence of hitherto unknown Earth-like worlds.
The Transiting Exoplanet Survey Satellite (TESS) was launched on April 18, 2018 with a mission to survey 200,000 of the brightest stars in close proximity to our Sun, in search of alien worlds. TESS detects these worlds by watching for minute dips in light that occur as a planetary body passes across the face of its parent star relative to Earth. This is known as the transit method.
Whilst it's an excellent technique for identifying potential exoplanet-hosting stars en mass, it doesn’t always paint the entire picture. For example, what may appear as a single star in the TESS survey could in reality be two stars orbiting very close together. It is estimated that half of all stars form such a system.
The researchers used the twin telescopes of the Gemini Observatory in Hawaii and Chile, and the WIYN 3.5-meter Telescope at the Kitt Peak National Observatory in Arizona, to collect high-resolution data on a batch of stars from the TESS catalog that are known to host exoplanets.
A grand total of 517 stars were followed up on by the team, using a method known as speckle imaging. This technique involves taking multiple images one after the other, and combining the shots in order to mitigate the blurring effect brought on by Earth’s dense atmosphere.
By reducing this disturbance, the astronomers were able to identify 73 "stars" in the TESS catalog that were in reality binary star systems. The astronomers then went on to compare the relative sizes of exoplanets orbiting stars in binary systems with their counterparts that orbit in single star systems.
It was discovered that both large and small planets orbited lone stellar bodies, but that only larger planets were present in the binary star systems observed by the team. This suggests that the extra light emitted by the companion star in a binary system is effectively erasing the dip in light that would ordinarily be observed when smaller planets, including potentially habitable ones the size of Earth, transit across the face of their star.
"Their transits are 'filled in' by the light from the companion star," explains Steve Howell of NASA's Ames Research Center, who co-authored the new paper. "Since roughly 50 percent of stars are in binary systems, we could be missing the discovery of, and the chance to study a lot of Earth-like planets."
It was also discovered that binary stars which orbited with a greater degree of separation were more likely to host exoplanets than those from the TESS catalog that were observed to orbit extremely close to one another. This suggests that the turbulent regions of space surrounding closer orbiting stars are inhospitable to the formation of planets.
The paper has been published in the Astronomical Journal.