Variable X-ray radiation likely drives helium escape from exoplanet LHS 1140 b

LHS 1140 b is a rocky planet orbiting within the habitable zone of a Red dwarf star. Previous observations detected helium escaping from the planet as it transited, or passed in front of, its host star. Because stars emit high-energy radiation that can strip away planetary atmospheres, researchers analyzed whether fluctuations in the star's X-ray and ultraviolet output could explain the changing levels of escaping helium.

Using the XMM-Newton space telescope, observers monitored the system for 18 hours. They detected significant fluctuations in the star's X-ray brightness, with levels varying by a factor of up to 8.5 during the observation period. No such variability was found in the ultraviolet or visible light spectra.

Comparing this data to earlier measurements from 2018, the long-term X-ray output of the star appears stable over the years. However, the 2018 data lacked the sensitivity to detect the rapid, short-term fluctuations observed in 2026. Models suggest that these brief bursts of X-ray activity or small stellar flares are the most likely drivers of the observed changes in helium escape.

Key findings
- X-ray flux from the star LHS 1140 shows significant short-term variability, varying by a factor of 8.5 during an 18-hour window.
- No variability was detected in the ultraviolet or visible light emissions from the star.
- Long-term X-ray activity of the host star appears consistent with measurements taken in 2018.
- Short-term X-ray fluctuations or small flares are likely responsible for the observed variations in atmospheric helium escape on LHS 1140 b.

Scientific study

Variable X-ray flux may explain variable helium escape from the habitable-zone exoplanet LHS 1140b (external link)