For the first time, astronomers have successfully analyzed the surface of a rocky planet located nearly 50 light-years away, thanks to observations made by the James Webb Space Telescope (JWST). The planet, known as LHS 3844 b, has been described as airless, dark, and possibly composed of volcanic or weathered rock.
LHS 3844 b, which is approximately 30% larger than Earth, orbits its star every 11 hours and is tidally locked, meaning one side is perpetually exposed to the sun, heating up to around 725°C. This unique positioning allows researchers to gather detailed thermal data from the planet's dayside.
Using JWST's Mid-Infrared Instrument, scientists measured the heat emitted from LHS 3844 b as it passed behind its star. The results indicate a barren landscape reminiscent of Mercury or the Moon, lacking a significant atmosphere or Earth-like geological features. "The sensitivity of JWST enables us to detect light directly from the surface of this distant rocky planet," stated Laura Kreidberg, the principal investigator of the study.
A Planet with a Fixed Orientation
LHS 3844 b's rapid orbit means that it always presents the same face to its star, while the opposite side remains in darkness. The extreme temperatures on the dayside allow for a strong infrared glow, facilitating detailed observations. However, astronomers couldn't directly observe features like valleys or volcanoes; instead, they analyzed the light emitted as the planet slipped behind its star in a phenomenon known as a secondary eclipse.
During this event, a small amount of infrared light disappeared, revealing the planet's thermal emissions. The analysis of this data allowed researchers to infer that the surface is likely composed of iron- and magnesium-rich rocks, such as basalt, rather than granite, which is prevalent on Earth.
Understanding the Surface Composition
The study compared the observed spectrum from LHS 3844 b with laboratory measurements of various rocks and minerals, revealing that granite was not a suitable match for the planet's surface. Instead, the data pointed towards darker, volcanic materials. The findings suggest that LHS 3844 b lacks the geological processes associated with Earth-like plate tectonics, indicating a different evolutionary history.
The researchers are considering two scenarios: either the planet has a relatively fresh surface due to recent volcanic activity or it is geologically inactive, covered with darkened regolith formed over time. The absence of volcanic gases further leans towards the latter hypothesis.
A New Era in Exoplanet Studies
This groundbreaking research signifies a shift in the field of exoplanet science. JWST is moving beyond merely identifying rocky planets to categorizing them based on their surface characteristics. As astronomers continue to refine their techniques, they anticipate gaining further insights into the geological nature of LHS 3844 b and other rocky exoplanets in the future.
The findings were published in Nature Astronomy, highlighting a promising path for future explorations of exoplanet geology.