How rainbows help search for life on other planets

These rare and mesmerising effects are caused by the interaction of light with ice crystals or water droplets in the atmosphere. And, as scientists suggest, similar phenomena may occur on other planets outside the solar system, The Conversation reports.

On Earth, phenomena such as halos, parhelia (or "solar dogs"), glories and rainbows are well-studied. For example, rainbows only occur in the presence of spherical liquid droplets - ordinary rain. And "sun dogs" appear because of light refraction in horizontally orientated hexagonal ice crystals high in the atmosphere.

Scientists note that each of these forms of light indicates certain physical parameters of the atmosphere: composition, shape and orientation of particles, temperature and even the presence of electric or magnetic fields.

The atmospheres of other planets, including exoplanets, also contain crystalline aerosols. For example, on Io (a satellite of Jupiter) it is sodium chloride, and on Mars it is carbon dioxide crystals. These particles can form similar optical effects, especially when winds, magnetic fields and radiation pressure are involved.

The study suggests that on giant planets with dense and active atmospheres, like so-called hot Jupiters, crystals are lined up by winds of up to 18,000 kilometres per hour, like sailboats under a squall. This orientation of the crystals could theoretically create stable optical phenomena.

Scientists have already detected quartz crystals in the atmosphere of exoplanet WASP-17 b using the James Webb Telescope. These elongated particles are particularly sensitive to wind flow, making visual effects possible.

Although the human eye cannot see such phenomena on other planets, JWST instruments make it possible to record their spectral traces. For example, using glorius observations, scientists have detected persistent clouds on the exoplanet WASP-76 b despite the extreme heat - on one side of the planet, the temperature is hot enough to melt iron.