Five Exoplanets Resembling Venus Could Tell Us If Earth's Twin Was Once Habitable: Study

If the scientists are successful in locating an analogue to Venus, the planet could reveal valuable insights into Earth's future.

Scientists have published the first paper compiling all known information about Exoplanets similar to Venus, and are the closest they have ever been to finding an analogue of Earth's twin. If the scientists are successful in locating an analogue to Venus, the planet could reveal valuable insights into Earth's future. Also, scientists will be able to determine if Earth is at a risk of developing a runaway greenhouse climate as Venus did.

The study, led by researchers from the University of California, Riverside, was recently published in The Astronomical Journal. The scientists identified more than 300 exoplanets, and then whittled the list down to the five planets most likely to resemble Venus in terms of their radii, masses, densities, the shapes of their orbits, and distances from their stars. These five planets could tell us if Earth's twin was once habitable. 

The study ranked the most Venus-like planets in terms of the brightness of the stars they orbit. This increases the likelihood of the James Webb Space Telescope getting more informative signals regarding the composition of the planets' atmospheres.

Webb can explore if things were ever different for Venus

Venus is covered with sulphuric acid clouds, has no water, and features surface temperatures up to 480 degrees Celsius. These temperatures are hot enough to melt lead. Webb's observations of these possible Venus analogues, or "exoVenuses" could help scientists determine if things were ever different from Earth's twin. 

In a statement released by the University of California, Riverside, Colby Ostberg, the lead author on the paper, said one thing researchers wonder is if Venus could once have been habitable. To confirm this, the team wants to look at the coolest of the planets in the outer edge of the Venus Zone, where the planets get less energy from their stars. 

What is the Venus Zone?

The Venus Zone is a region where Venus-like planets could exist, and is a concept proposed by Stephen Kane, an astrophysicist from the University of California, Riverside, in 2014. 

Ostberg said that the Venus Zone is where it would be too hot to have water, but not hot enough that the planet's atmosphere would get stripped away. He said that researchers want to find planets that still have significant atmospheres.

Since mass affects how long a planet is able to maintain an active interior, it is important to find a planet similar to Venus in terms of planet mass. A planet with plate tectonics is said to have an active interior.

According to Ostberg, Venus has 20 per cent less mass than Earth. Therefore, scientists believe there may not be any tectonic activity there. 

Volcanic activity is another aspect of an active planet's interior. NASA's Magellan spacecraft recently found evidence that suggests Venus still has active volcanoes. 

Kane, who co-authored the study, said the large number of Venus analogues identified in the paper will allow researchers to test if such volcanic activity is the norm amongst similar planets.

Webb may find biosignatures signalling the presence of life in exoVenuses

Webb will likely observe these planets in 2024. With the help of Webb, scientists will not only be able to determine if exoVenuses have atmospheres, but also find out what they are made of. 

According to the study, Webb may reveal biosignature gases such as methane, methyl bromide or nitrous oxide in the atmosphere of an exoVenus, signalling the presence of life.

Ostberg said that if such molecules are detected on an exoVenus, it would prove that habitable worlds can exist in the Venus Zone. Also, the finding will strengthen the possibility of a temperate period in Venus' past.

Significance of the study

NASA's two upcoming missions, the DAVINCI mission and VERITAS mission will provide further insights into Venus. The DAVINCI mission will measure gases in the Venusian atmosphere, and the VERITAS mission will enable three-dimensional reconstructions of the landscape.

A question which Kane poses in most of his work is whether Earth is weird or is Venus the weird one. The observations made by Webb, the DAVINCI mission and VERITAS mission could answer this question.

If the planets compiled in the paper are too similar to Venus, it would suggest that the evolution of Venus is common, and would be a warning for people on Earth, because if the planet is not taken care of, it may have the same plight as Venus in the future.