New Delhi: The James Webb Space Telescope (JWST) has discovered salt clouds surrounding a cold, planetary-mass companion known as the ‘Pink Planet’, providing
the first direct evidence for an atmospheric phenomenon theorised over 15 years ago. The object, designated as GJ504 b, orbits a Sun-like star about 57 lightyears from the Earth. The object was discovered in 2013, and is estimated to contain 25 times the mass of Jupiter, placing it on the boundary between a gas giant and a brown dwarf, an exotic object that is formed just like a star, but does not accumulate sufficient mass to sustain nuclear fusion.
The conventional methods used to hunt exoplanets favour the discovery of large worlds in close orbits around small stars. Most exoplanets that have been directly imaged have temperatures between 540°C and 1,100°C. GJ504 b is measured to be around 290°C, about the temperature of a baking oven, which is considered a low temperature for giant exoplanets. This low temperature is because of the advanced age of the object, which is estimated to be between 2.5 billion and four billion years. Giant planets cool over time. Because GJ504 b is so cold and faint, ground-based telescopes could not isolate its light from the host star, even in observations that lasted through the night.
What the spectra revealed
Using Webb, the international research team was able to capture the light of the companion in just two hours. Advanced data-processing techniques were applied to remove the glare of the host star, revealing the spectrum of the object for the first time. This spectrum showed a rich molecular mix including water vapour, methane, carbon dioxide and ammonia. The data aligned with astrophysical models when researchers introduced clouds into simulations. Out of three cloud types tested, salt clouds provided the best fit. These clouds cloak the deeper layers of the atmosphere, subduing the chemical signatures of underlying molecules. A paper describing the research has been published in The Astronomical Journal.
