Free-Floating Planets (FFP), also known as “Rogue Planets,” were first discovered in 2000 by astronomers searching the Orion Nebula. Since then, hundreds of FFP candidates have been identified, and scientists predict there may be billions across the Milky Way. This means they outnumber stars by 20 to 1, and habitable planets by 25 or more. Research has also shown that most of these planets may come with moons of their own.
This was determined by LMU physicist Dr. Giulia Roccetti in a previous study, where he found that gas giants taken from their star centers can retain some of their “exomoons”. In a new study, Roccetti and researchers from the Ludwig-Maximilians-University Munich (LMU) and the Max Planck Institute for Extraterrestrial Physics (MPG) investigated hydrogen as a possible thermal trap that could ensure the habitability of some of these exomoons. Their research shows that if there is enough hydrogen in the atmosphere, these moons can last for billions of years!
The idea of exomoon habitation comes directly from what we know about moons in our Solar System. Many of the moons of Jupiter, Saturn, Uranus and Neptune are believed to have internal oceans, which remain warm when warm. In fact, the strong gravitational interaction between these moons and their gas giants caused their rocky interiors to oscillate, releasing heat and energy.
This heat, along with the minerals necessary for life, seeps into the oceans inside the moon through hydrothermal vents near the edge of the mantle. For decades, astronomers have hoped to get a closer look at “Sea Earths,” so named because they contain more water than all of Earth’s oceans combined. However, things would work differently for exomoons orbiting FFPs, as the ejection process would change their paths.
The waves caused by the ocean currents would deform the body of the moon by compressing its interior and generating heat through friction. This heating would be enough to maintain oceans on these moons, despite the fact that they do not have a star to draw heat and energy from them. However, maintaining this temperature on the surface of the moon depends on the presence of an atmosphere that contains enough heat gases.
On Earth, carbon dioxide (CO2) is a greenhouse gas, which helps our atmosphere retain heat, and drives anthropogenic Climate Change. According to the research team, previous studies have found that CO2-rich atmosphere can support habitable conditions for up to 1.6 billion years. However, for exomoons orbiting FFPs, extreme cold can cause CO2 to cool, thus allowing the heat to escape.
The team envisioned another heat trap in the form of an atmosphere rich in molecular hydrogen. Although this element is highly visible in heat, under high pressure, friction between atoms allows it to absorb heat. In addition, hydrogen remains stable at very low temperatures, including those present in the interstellar medium (ISM). In fact, the “Ocean Worlds” in the ISM may support life in surface oceans rather than inland oceans, as observed here at home.
*This is an artist’s rendering of a habitable exomoon orbiting a giant planet. Credit: NASA GSFC/Jay Friedlander and Britt Griswold*
The findings may also provide insight into the origins of life. For example, tidal disruption that deforms the moon’s interior can also cause a “water cycle,” where water evaporates and refreezes. These cycles are thought to be the key to making the complex molecules that would eventually give rise to life. In this regard, ocean energy would not only provide heat but could also drive chemical change in the bodies around the Rogue Planets.
David Dahlbüdding, doctoral researcher at LMU and lead author of the study, explained:
Our partnership with Prof. Braun helped us realize that the birth of life does not need the Sun. We found a clear connection between these distant moons and the first Earth, where the abundance of hydrogen radiation from an asteroid impact would have created conditions for life.
These findings provide good ideas for scientists engaged in the investigation of life in the Universe (aka abiogenesis). Given how common FFPs are in our galaxy and the fact that these moons can provide stable habitation for billions of years, interstellar space may be teeming with life. The findings may also shed light on how life has been distributed throughout the universe (panspermia).
But above all, they reveal that life may exist in the darkest regions of the Universe, challenging the long-held idea that habitable worlds only exist around stars.
Read More: IDW
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