Earth-like planets may be more common than we ever imagined

In a study led by Dr. Lujendra Ojha of Rutgers University, scientists report that Earth-like planets with potential to harbor liquid water could be about 100 times more common than previously believed.

The research, published in the journal Nature Communications, is a game-changer for our understanding of the universe. It also opens an intriguing new chapter in the search for extraterrestrial life.

“It was estimated that around one rocky planet around every 100 stars would have liquid water,” Dr. Ojha said at the Goldschmidt geochemistry conference held in Lyon, France.

“The new model shows that if the conditions are right, this could approach one planet per star – so we are a hundred times more likely to find liquid water than we thought.”

With at least 100 billion stars in our Milky Way galaxy, this study dramatically broadens the potential stage for the existence of life. As Dr. Ojha put it, “that represents really good odds for the origin of life elsewhere in the universe.”

Many stars could host Earth-like planets 

Traditionally, scientists have considered Earth-like exoplanets with surface water bodies like oceans, lakes, and rivers to be scarce.

However, this new research suggests that many stars could indeed host planets. They only need the right geological conditions to sustain liquid water beneath their surface.

Our own solar system provides examples of subterranean oceans. Enceladus, one of Saturn’s moons, as well as Europa and Ganymede, which are moons of Jupiter, are believed to harbor saltwater oceans encased within icy shells. Even dwarf planets like Pluto and Ceres, and potentially several moons of Uranus, are believed to possess underground oceans.

Liquid water is essential 

Dr. Ojha emphasized the significance of water for life as we know it. He said, “We know that the presence of liquid water is essential for life.”

This research sheds light on the potential for liquid water to exist in places that hadn’t been seriously considered before. “This significantly increases the chances of finding environments where life could, in theory, develop.”

This groundbreaking conclusion comes from a closer look at how planets, seemingly frozen on their surface, could have liquid water oceans beneath their crust.

A couple of primary mechanisms make this possible. First, the heat from radioactivity within the planet’s core can warm the water enough to prevent it from freezing. This is similar to what we observe in Antarctica and the Canadian Arctic. Also, the gravitational effects of the larger planets they orbit can prevent freezing.

Red dwarf stars 

The researchers also highlighted the role of red dwarf stars, the most abundant star type in the Milky Way. They found that a significant percentage of planets orbiting red dwarf stars could produce their own heat. 

“We found that when one considers the possibility of liquid water generated by radioactivity, it is likely that a high percentage of these exoplanets can have sufficient heat to sustain liquid water – many more than we had thought,” explained Dr. Ojha.

Wet moons

Furthermore, the experts drew attention to the solar system’s wet moons. Their interiors are continuously churned due to the strong gravitational effects from the large planets they orbit. This is similar to the lunar influence on our Earth’s tides but on a grander scale.

Enceladus and Europa are considered top contenders for life in our solar system. Several space agencies have already launched missions to explore these intriguing moons.

Notably, the European Space Agency’s JUICE (Jupiter Icy Moons Explorer) mission, which commenced in April 2023, is slated to orbit Ganymede following numerous flybys of Europa and Callisto.

NASA is not far behind with its Europa Clipper. This mission is set to launch in October 2024 and conduct 32 flybys of Europa from 2030.

More about Earth-like planets 

An Earth-like planet, also referred to as a “terrestrial” or “telluric” planet, is a planet that is similar to Earth in key characteristics. These include size, mass, and composition.

They are primarily composed of rock and metal, and have solid surfaces. The term “Earth-like” often suggests a similarity not only in physical properties but also in potential habitability.

Key characteristics 

Size and mass

Earth-like planets are usually close to Earth in size and mass. Too large, and the planet might become a gas giant. Too small, and it may not be able to hold onto an atmosphere.

Location in the habitable zone

The planet should ideally be located in its star’s habitable zone (often referred to as the “Goldilocks Zone”). This is where conditions might be just right – not too hot, not too cold – for liquid water to exist on the planet’s surface.

Rocky composition

Earth-like planets are composed mainly of silicate rocks or metals. They have a hard surface that can potentially support oceans, continents, and life as we know it.

Presence of an atmosphere

A significant atmosphere can help regulate temperature and protect the planet from stellar radiation and meteor impact.

Surface water

The presence of liquid water is a critical aspect of “habitability.” As we currently understand, every life form we know on Earth requires water to survive.

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