Astronomers Discover a Recent Class of Molten Planet: L 98-59 d

Astronomers have identified a new type of exoplanet – a planet orbiting a star outside our solar system – characterized by a permanent ocean of magma and significant amounts of sulfur stored deep within. This discovery, published in Nature Astronomy, challenges existing classifications of small planets and offers insights into planetary formation and evolution.

What is L 98-59 d?

The exoplanet, known as L 98-59 d, orbits a small red star approximately 35 light-years from Earth. It was initially identified in 2019, but recent observations from the James Webb Space Telescope (JWST) and ground-based observatories have revealed its unusual composition. L 98-59 d is about 1.6 times the size of Earth and has a notably low density.

A Planet Unlike Any Other

Previously, astronomers categorized small planets as either rocky ‘gas-dwarfs’ with hydrogen atmospheres or water-rich worlds with deep oceans and ice. Yet, L 98-59 d doesn’t fit neatly into either category. Researchers found significant amounts of hydrogen sulfide in its atmosphere, suggesting a composition rich in heavy sulfur molecules.

Magma Ocean and Sulfur Storage

The research indicates that L 98-59 d possesses a mantle likely composed of molten silicate – similar to lava on Earth – and a global magma ocean extending thousands of kilometers beneath the surface. This vast molten reservoir allows the planet to store extremely large amounts of sulfur within its interior over geological timescales. The magma ocean similarly contributes to the planet’s ability to retain a thick, hydrogen-rich atmosphere containing sulfur-bearing gases like hydrogen sulfide.

Implications for Planetary Science

This discovery suggests that current models for classifying small planets may be too simplistic. The findings highlight the diversity of planetary compositions and the potential for previously unrecognized types of exoplanets to exist. The chemical exchanges between the planet’s molten interior and atmosphere over billions of years have shaped its current observable characteristics.

What Does it Smell Like?

The atmosphere of L 98-59 d contains gases such as water, sulfur dioxide, and hydrogen sulfide. Hydrogen sulfide, particularly when burned, can smell like rotten eggs.

Future Research

Further observations and analysis of exoplanets like L 98-59 d will be crucial for refining our understanding of planetary formation and the potential for habitability beyond our solar system. The James Webb Space Telescope will continue to play a vital role in these discoveries.