Rock-Hidden Water: A Lifeline for Planets Orbiting Hostile Stars

 Planets orbiting red dwarf stars may regain life-sustaining conditions by safeguarding water within their rocky interiors. Even if their surfaces lose water due to intense stellar radiation, these planets can rely on groundwater to rehydrate.

Red dwarf stars' habitable zones are prime targets in the quest for extraterrestrial life. However, these stars experience a highly volatile youth, marked by plasma bursts far more powerful than those from our Sun, which could jeopardize the habitability of surrounding planets.

Planets may lose their surface water during these violent phases, especially when lacking an atmosphere for protection. While this phase is brief for larger stars like the Sun, red dwarfs experience it for an extended period, casting doubt on the habitability of planets in their vicinity.

Nonetheless, recent research suggests that water trapped within planets can resurface and replenish lost water. As the star's volatility subsides, volcanoes may transport water stored in rocks back to the surface.

Researchers developed a model to estimate the presence of water-rich minerals within a planet. These minerals, similar to sponges, absorb water, shielding it from the star's radiation and charged particles. Once the star's activity diminishes, water returns to the surface, refilling oceans.

The planet's size determines the proportion of water-transporting minerals, with most water stored in the upper mantle (just below the crust). Here, pressure and temperature conditions foster the formation of wadsleyite and ringwoodite, minerals adept at absorbing water. Additionally, this layer is accessible to volcanoes, enabling water transportation to the surface via eruptions.

This model could help astronomers comprehend how planets orbiting tumultuous stars become potentially habitable after periods of heightened stellar activity. This knowledge is crucial for the search for extraterrestrial life, as red dwarfs are both the most abundant and longest-lived stars in the Milky Way.

Red dwarfs' lifespans are estimated to exceed the universe's current age of 13.7 billion years. Given their prevalence, they are an enticing target for exoplanet-hunting telescopes. However, consensus regarding the habitability of these planets remains elusive. This new research, published in Monthly Notices of the Royal Astronomical Society, offers promising insights for the pursuit of life within these systems.

Source: MNRAS, University of Cambridge