Stars may often act as flashlights in space, shining beams of light on objects that would otherwise stay hidden in the dark, but undiscovered planets can be obscured by their glare.
We only see our solar system as the norm because we live here. Beyond our cosmic territory, about half of star systems are binary (and our own might have been once), so experiencing a sunrise or sunset on one of their planets would be like standing on Tatooine. Sci-fi realness aside, we might not know many of these planets even exist, since new research has found that previous exoplanet searches were possibly missing out on many Earth-like planets in these binary systems.
About half of all stars being in binary systems might mean that the glare of these systems has been making it impossible to see up to half of existing planets close in size to Earth. Such planets could be far more common that previously thought, and some of them might even be habitable.
“In exoplanet systems containing binary host stars, there is an observational bias against detecting Earth-size planet transits due to transit depth dilution caused by the companion star,” said astronomers from NASA’s Ames Research Center in a study led by Katie Lester and recently published in Solar and Stellar Astrophysics.
TESS had originally found these star systems, but identifying them as binary needed especially hi-res vision. This is why Lester and her team used the twin telescopes at the Gemini Observatory of the National Science Foundation’s (NSF) NOIRLab to determine which apparently single pinpoints of light observed by TESS were actually coming from two stars at once. TESS, like other telescopes scouring the universe for exoplanets, uses the transit method to find them. When a planet’s orbit takes it in front of the star (at least from the telescope’s point of view), and it transits that star, TESS sees a dimming in that star’s light.
What can make the transit method problematic is that some planets may not be large enough to block enough light from a binary star system for it to register as a transit. It doesn't help when binary stars that are close together are easily mistaken for just one star. Depending on the size and brightness of their stars, even larger planets could pass by unnoticed. The astronomers instead relied on speckle interferometry. This technique involves math, hardware and advanced tech that allow Earthbound telescopes to reach the diffraction limit — the maximum resolution that the telescope can observe at without image quality being affected.
The speckle instruments ‘Alopeke on Gemini North in Hawai’I and Zorro on Gemini South in Chile reach the diffraction limit by taking thousands of quick-exposure images that visually “freeze” the atmosphere. These are then further finessed by mathematical intervention and processed through specialized software to produce images clear enough to rival a space telescope. Space telescopes get such an amazing view because they don’t have Earth’s atmosphere in the way. Speckle images make space appear as it would if Earth had no atmosphere.
Because of speckle imaging, Lester and her team were able to get such a clear view of binary stars that would have otherwise been too close together to tell apart.
“Other imaging studies have suggested this dearth of very closely separated binaries in systems which host exoplanets, but incompleteness at small separations makes it difficult to disentangle unobserved companions from a true lack of companions,” they said in the study.
Known binary star systems were also given a second look with the WIYN Telescope at Kitt Peak National Observatory, also under the NSF NOIRLab program. While it had previously been suspected that the glare of binary stars could be keeping transiting planets from being seen, this is the first study to provide actual observational evidence of that. Knowing whether a star is single or binary could give away whether there are any small planets in a system. When they are in transit of a binary system, its intense light could easily swallow them.
So, aliens? Too soon for that, but we could at least end up finding other Earths that may have what it takes for some form of life to survive out there.