Low-density planets struggle to hold on to their atmospheres when they’re blasted with high-energy radiation from a close-by host star. New observations have caught a view of one such escaping atmosphere using a powerful tracer: helium.
Atmosphere on the Run
When a planet orbits close to its star, incoming ultraviolet radiation can heat and puff up the planet’s atmosphere, extending it so far that the gravitational pull of the planet can no longer hold it in. The mass loss that results from this process dramatically shapes the population of short-period exoplanets — so understanding atmospheric escape is critical to our understanding of planetary evolution.
As a star’s light filters through a planet’s atmosphere on its way to Earth, the atmosphere absorbs certain wavelengths depending on its composition. [European Southern Observatory]But measuring a planet’s escaping atmosphere is challenging! At high altitudes, the atmosphere is thin and low-pressure, which means that most of the spectral signatures of this escaping mass — produced during transits when the planetary atmosphere absorbs background stellar light — are faint.
In 2018, however, a new discovery provided some hope: the first detection of helium in an exoplanet atmosphere.
Letting Helium Lead
Why is helium helpful? When a ...