James Webb Space Telescope directly studies an exoplanet’s surface for the 1st time: ‘We see a dark, hot, barren rock’ – Image for illustrative purposes only (Image credits: Pexels)
Astronomers achieved a milestone in exoplanet science when the James Webb Space Telescope captured the first direct infrared spectrum from the surface of LHS 3844 b, a super-Earth 48.5 light-years from our solar system. This rocky world, 30 percent larger than Earth, hurtles around its cool red dwarf star every 11 hours, locking one side in perpetual daylight at scorching temperatures around 1,000 Kelvin.[1][2] The findings reveal a barren landscape devoid of atmosphere, offering the clearest glimpse yet into the geology of worlds beyond our own.[3]
Probing a Tidally Locked Super-Earth
The James Webb Space Telescope’s Mid-Infrared Instrument, or MIRI, targeted the planet’s hot dayside during its brief orbital passage behind the star. Researchers measured the faint infrared glow – mere parts per million compared to the star’s brightness – across wavelengths from 5 to 12 micrometers. Data from the earlier Spitzer Space Telescope helped refine the analysis.[1]
LHS 3844 b’s extreme proximity to its star, just three stellar diameters away, ensures tidal locking: one hemisphere forever faces the stellar blaze while the other remains in shadow. This setup allowed scientists to isolate dayside emission, free from atmospheric interference. The international team, led by Laura Kreidberg of the Max Planck Institute for Astronomy, published their results in Nature Astronomy.[3]
Unveiling a Dark, Rocky Crust
Spectral analysis pointed to a surface rich in magnesium and iron, possibly featuring minerals like olivine, akin to Earth’s mantle or lunar basalt. Solid expanses of basaltic or magmatic rock provided the best match, ruling out brighter powders or grains. The dark hue likely stems from space weathering – stellar radiation and micrometeorite bombardment that infuses iron and carbon into the regolith.[1]
“Thanks to the amazing sensitivity of JWST, we can detect light coming directly from the surface of this distant rocky planet. We see a dark, hot, barren rock, devoid of any atmosphere,” Kreidberg stated. No signs of volcanic gases like sulfur dioxide appeared, tilting evidence toward a weathered, inactive crust rather than fresh lava flows.[2]
| Feature | LHS 3844 b | Earth | Moon/Mercury |
|---|---|---|---|
| Size | 1.3 Earth radii | 1 Earth radius | Smaller rocky bodies |
| Surface | Dark basalt/mantle-like | Silicate crust (granite) | Dark regolith |
| Atmosphere | None | Thick N2/O2 | Negligible |
| Dayside Temp | ~1,000 K | ~288 K avg | Up to 700 K (dayside) |
Absence of Air and Water Shapes a Harsh Reality
Without an atmosphere, LHS 3844 b endures unrelenting cosmic rays and impacts that grind rock into fine regolith, much like the Moon’s surface. Sebastian Zieba, a key researcher now at the Center for Astrophysics, noted the implications: “Since LHS 3844 b lacks such a silicate crust, one may conclude that Earth-like plate tectonics does not apply to this planet, or it is ineffective. This planet likely only contains little water.”[3]
The lack of a granite-like crust further underscores limited water and tectonic recycling, processes essential for Earth’s diverse geology. Two scenarios emerged: a surface of relatively fresh dark rock from past volcanism, or prolonged weathering over eons of inactivity. The absence of volcanic markers favors the latter, evoking Mercury’s weathered exterior.[1]
Geological Clues to Distant Worlds
This study marks a shift from atmospheric hunts to surface geology, validating techniques long tested on solar system asteroids. By comparing spectra to rock libraries from Earth, the Moon, and Mars, the team constrained compositions with unprecedented precision. Future observations will exploit emission angles to distinguish rough regolith from smooth slabs.[2]
Kreidberg expressed optimism: “We are confident the same technique will allow us to clarify the nature of LHS 3844 b’s crust and, in the future, other rocky exoplanets.” As JWST continues its survey under program GO 1846, similar bare-rock worlds may yield insights into how planets form and evolve without protective envelopes.[3]
These revelations challenge assumptions about super-Earths, many of which bake near their stars. LHS 3844 b stands as a stark reminder: not all larger rocky planets foster habitable conditions. Yet each barren detail sharpens the hunt for those that might.