The quest for a new Earth: Insights from scientists on Venus’ atmosphere as illuminated by the Sun

In the last thirty years, astronomers have identified over 5,500 exoplanets orbiting stars similar to our Sun. Yet, from the outset, both the scientific community and the general public have been particularly interested in locating Earth-like planets, with the hope of discovering life elsewhere in the universe.

While the rocky planets of the solar system have been known for some time, the study of their atmospheres—key to the search for life—remains a significant challenge. The investigation of planetary atmospheres has a lengthy history.

To date, scientists have examined the expansive and inflated atmospheres of gas giants around distant stars. In these instances, astronomers observe a planet transiting its star, analyzing the star’s light as it filters through the planet’s dense atmospheric layer, comparing it to the star’s light when the planet is not in transit.

The disparity between these two measurements distinctly reveals the chemical makeup of the transiting planet’s atmosphere. While this analysis is achievable for gas giants, it becomes significantly more challenging when applied to rocky planets such as Earth.

The core issue lies in the contrasting destinies of Earth and its twin, Venus. Both planets are nearly identical in size and reside within the Sun’s habitable zone, enveloped by dense atmospheres. Yet, life flourishes on Earth, whereas Venus remains barren, likely having never hosted life at all.

Disappointment in the quest for a New Earth: unforeseen challenges

The atmospheric pressure on Venus exceeds that of Earth’s surface by over a hundred times, temperatures remain above 420 degrees Celsius, and the skies are deluged with sulfuric acid rain. Consequently, these twin planets present vastly divergent prospects for the emergence of life.

An important question emerges: Can scientists searching for a second Earth in distant planetary systems differentiate between rocky planets such as Earth and planets similar to Venus?

To find out, a team of researchers from Institute of Astrophysics (IA) decided to explore what insights into Venus’s atmosphere could be gleaned if the planet were not 40 million kilometers away, but rather situated in another system, several light-years distant.

A key aspect is the capability to differentiate between atmospheres primarily composed of nitrogen and those predominantly made up of carbon dioxide, like Venus’. Scientists utilized data from June 5 and 6, 2012, during Venus’ transit across the Sun’s disk, providing a chance to observe the planet’s passage against the backdrop of its (and our) star.

The observations enabled the determination of the impact Venus’ atmosphere has on solar radiation. Astronomers have deduced that with the advent of cutting-edge observatories such as the Extremely Large Telescope (ELT) and the Ariel Space Telescope, it will be feasible to observe and ascertain the atmospheric composition of Earth-sized exoplanets..

However, it appears that these methods may not suffice to accurately differentiate between Venus-like and Earth-like planets, potentially leading to substantial errors. Indeed, a planet discovered in a distant system, initially perceived as a second Earth, could in reality be akin to a second Venus.