Exozodiacal Light Could Hinder Direct Imaging of Earth-Like Exoplanets

Artist rendering of exozodiacal light viewed from an imaginary planet. ESO/L. Cal├žada

Finding life on exoplanets in a star's habitable zone would, arguably, be the biggest event that has ever happened in human history. Unfortunately, an international team of astronomers using the Very Large Telescope discovered exozodiacal light around nearby stars, which would make imaging Earth-like exoplanets in those systems quite difficult. Steve Ertel from ESO and the University of Grenoble in France was lead author of the paper, which was published in the journal Astronomy & Astrophysics

Zodiacal dust can be generated by comet disintegration, collisions between asteroids or small planetary bodies, and through general space weathering of these bodies. When the tiny dust particles reflect sunlight or become heated enough to glow on their own, it produces a faint white light that can be widely seen throughout the solar system. When this phenomenon occurs in solar systems outside of our own, it's called exozodiacal dust. 

Ertel’s team studied the exozodiacal dust near the habitable zones of 92 nearby stars, including 14 known to have exoplanets. Observations were made in near-infrared wavelengths using the Very Large Telescope’s Interferometer (VLTI). In order to produce a contrast high enough to view the dust, the VLT was given additional light from the four 1.8 meter Auxiliary Telescopes, allowing it to be ten times more powerful than any other similar instrument in the world. 

“If we want to study the evolution of Earth-like planets close to the habitable zone, we need to observe the zodiacal dust in this region around other stars,” Ertel said in a press release. “Detecting and characterizing this kind of dust around other stars is a way to study the architecture and evolution of planetary systems.”

Radiation from the star tends to push the tiny particles of zodiacal dust away, and a disc is formed past the habitable zone. It was assumed that the amount of dust in the clouds would decrease as the star and its system grew older, as there would be fewer asteroids to collide and create the dust. Interestingly, the stars with the brightest exozodiacal light came from older stars.

This blinding exozodiacal light could be problematic for future studies of each star’s potential planetary system. As if the glare from the star’s light wasn’t bad enough, the dust exacerbates that glare, becoming 1000 times brighter than zodiacal light in our solar system. The 14 stars known to have exoplanets all have extremely bright exozodiacal dust near the habitable zone, which will make it very difficult to directly image those planets. Further studies of the dust are needed to better understand its properties. This is necessary to find a way to circumvent it in order to image potential Earth-like planets in the habitable zone.

“The high detection rate found at this bright level suggests that there must be a significant number of systems containing fainter dust, undetectable in our survey, but still much brighter than the Solar System’s zodiacal dust,” adds co-author Olivier Absil from the University of Liège in Belgium. “The presence of such dust in so many systems could therefore become an obstacle for future observations, which aim to make direct images of Earth-like exoplanets.”

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