Venus analogues used to gain insights into Earth’s future

Researchers from the University of California – Riverside have compiled a list of Venus analogues to gain valuable insights into Earth’s future.

Scientists are the closest they have ever been to finding Earth’s twin through the compilation of all known information on Venus analogues. If Earth’s twin is located, it could reveal valuable insights into Earth’s future, and our risk of developing a runaway greenhouse climate as Venus did.

The team began with more than 300 known terrestrial planets orbiting other stars, called exoplanets. This list was narrowed down to the five most likely to resemble Venus in terms of their radii, masses, densities, the shapes of their orbits, and most significantly, distances from their stars.

The paper, ‘The Demographics of Terrestrial Planets in the Venus Zone,’ published in The Astronomical Journal, also ranked the most Venus-like planets in terms of the brightness of the stars they orbit. This would increase the likelihood that the James Webb Space Telescope would get more informative signals regarding the composition of their atmospheres.

What is the Venus zone?

Venus floats in a nest of sulfuric acid clouds, has no water, and features surface temperatures of up to 900°F. The team are using the Webb telescope to observe the possible Venus analogues to try and gain insight into ever different to today’s Venus.

“One thing we wonder is if Venus could once have been habitable,” said Colby Ostberg, lead study author and UC Riverside PhD student. “To confirm this, we want to look at the coolest of the planets in the outer edge of the Venus zone, where they get less energy from their stars.”

Proposed by UCR astrophysicist Stephen Kane, the Venus Zone is similar to the concept of a habitable zone. This is a region around a star where liquid surface water could exist.

“The Venus Zone is where it would be too hot to have water, but not hot enough that the planet’s atmosphere gets stripped away,” Ostberg explained. “We want to find planets that still have significant atmospheres.”

The importance of finding a Venus analogue with a similar mass

It is crucial to find a Venus analogue with a similar planet mass to our Venus because mass affects how long a planet is able to maintain an active interior, with the movement of rocky plates across its outer shell known as plate tectonics.

Image depicts divergent evolutionary pathways of Earth and Venus after formation. © O’Rourke, JG, Wilson, CF, Borrelli, ME, et al.

“Venus has 20% less mass than Earth, and as a result, scientists believe there may not be any tectonic activity there. Therefore, Venus has a hard time taking carbon out of its atmosphere,” Ostberg stated. “The planet just can’t get rid of it.”

Volcanic activity is evidence of an active planet interior, and recent research suggests that Venus still has active volcanoes. “The large number of Venus analogues identified in our paper will allow us to test if such volcanic activity is the norm amongst similar planets, or not,” said Kane, who co-authored the study.

The Webb telescope will allow scientists to observe Venus analogues in more detail

The observations made from the Webb telescope could reveal biosignature gases in the atmosphere of a Venus analogue, such as methane, methyl bromide, or nitrous oxide. These could all signal the presence of life.

“Detecting those molecules on an exoVenus would show that habitable worlds can exist in the Venus Zone and strengthen the possibility of a temperate period in Venus’ past,” Ostberg said.

These observations will complement NASA’s two upcoming missions to Venus: the DAVINCI mission and the VERITAS missions. The DAVINCI mission will measure gases in the Venusian atmosphere and the VERITAS mission will allow 3D reconstructions of the landscape.

These observations will help answer Kane’s ultimate question posed in the work, which attempts to understand the Earth-Venus divergence in climate: “Is Earth weird or is Venus the weird one?”

“It could be that one or the other evolved in an unusual way, but it’s hard to answer that when we only have two planets to analyse in our solar system, Venus and Earth. The exoplanet explorations will give us the statistical power to explain the differences we see,” Kane said.

If the Venus analogues appear to have great similarities to Venus, it would show the outcome of Venus’ evolution is common.

“That would be a warning for us here on Earth because the danger is real. We need to understand what happened there to make sure it doesn’t happen here,” Kane said.

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