Observations of planet LHS 1140 b show no persistent signs of helium escape

Star system: LHS 1140 | Distance from the Sun: 48.8 light years

Recent observations of the temperate planet LHS 1140 b have provided new insights into its atmosphere. While previous data suggested the presence of helium escaping from the planet, detailed analysis of four planetary transits—the period when a planet passes in front of its star—reveals no consistent evidence of such activity, indicating that earlier detections may have been influenced by stellar changes or instrumental factors.

Researchers examined the light from the star LHS 1140 during transits of planets LHS 1140 b and c using the James Webb Space Telescope. By looking for the specific signature of metastable helium, they sought to track atmospheric loss, a process where a planet's outer gases are stripped away by stellar radiation.

The findings show that any helium signal is likely absent or below current detection thresholds. Instead, the team observed significant variability in the star’s own helium spectral lines. This behavior is typical for Red dwarfs, suggesting that the star's natural fluctuations, rather than planetary atmospheric escape, may explain previous contradictory results.

This analysis highlights the challenges in confirming atmospheric escape on distant worlds, as stellar activity can easily mimic the signal of a planetary atmosphere. Future observations will be necessary to definitively rule out rare, sporadic escape events and to clarify the impact of stellar variability on these measurements.

Key findings
- No evidence of helium absorption was detected for planet LHS 1140 b or LHS 1140 c during recent observations.
- Previous high-resolution detections of helium escape from LHS 1140 b are not supported by new, consistent data.
- The host star LHS 1140 exhibits substantial variability in its helium spectral lines, common for Red dwarf stars.
- Instrumental effects or seeing-dependent noise may have contributed to previous observations of potential helium signals.
- Any potential atmospheric escape from LHS 1140 b is likely an infrequent or rare event.

Scientific study

No Persistent Helium Absorption in LHS 1140 b: Four JWST/NIRISS SOSS Transits and Multi-epoch Stellar He I Variability (external link)