PROVIDENCE, R.I. [Brown University] — Venus floats in a nest of sulfuric acid clouds, has no water, and its surface temperatures are hot enough to melt lead. Despite being such a scorching wasteland, however, the planet is often referred to as Earth’s sister because of similarities in size, mass, density and volume.
Earth and Venus, which both formed about 4.5 billion years ago, now sit on opposite ends of habitability. This leaves astronomers with a giant question: Is Venus Earth’s past or Earth’s future?
To answer that, a team of researchers — including Brown University planetary scientist Jim Head — have proposed using the James Webb Space Telescope to search other solar systems for a planet with similar attributes to Venus. If found, such a planet could serve as an analog to Earth, revealing valuable insights into its planetary future.
“It’s all about trying to understand why Earth and Venus are so different now,” said Head, a professor of geological sciences at Brown. “We have Venus to look at here, but there are solar systems out there in which we can actually compare all these different things that we want to know. It's a whole new parameter of space to explore.”
The proposal is described in a new paper in the Astronomical Journal. In the study, authors from the University of California, Riverside and Brown identify five Venus-like planets from a list of more than 300. These terrestrial planets orbiting other stars, called exoplanets, were selected because they were the most likely to resemble Venus in terms of their radii, masses, densities, the shapes of their orbits and distances from their stars.
The researchers rank the Venus-like planets depending on the brightness of the stars they orbit to increase the odds that the Webb Telescope gets the clearest view of them, enabling researchers to pull key signals from them regarding the composition of their atmospheres.
The five planets all orbit regions called the Venus Zone, which was coined by astrophysicist and study co-author Stephen Kane from U.C. Riverside. The Venus Zone encompasses the region around a star where it’s too hot for a planet to have water but not too hot for it to have no atmosphere. It is similar to the concept of a habitable zone, which is a region around a star where liquid surface water could exist.
The research team proposes the planets identified in the paper as targets for the Webb telescope in 2024. Webb is NASA’s most ambitious telescope to date and is enabling scientists not only to look into the deep past of the universe but to peer into the atmospheres of exoplanets for telltale signs of what the planet is like.
Studying exoplanets in the Venus Zone could give astronomers a better understanding of whether Venus was ever habitable. The Webb observations the researchers propose, for example, may reveal biosignature gases in the atmosphere such as methane, methyl bromide or nitrous oxide, which could signal the presence of life. The researchers also explain in the paper that they hope to see through the observations whether Venus’s lack of plate tectonics is common and whether the planet’s volcanic activity is normal.
These observations will be complemented by NASA’s two upcoming spacecraft missions to Venus, both led by Brown University graduates. The DAVINCI mission, with James Garvin as its principal investigator, will measure gases in the Venusian atmosphere. Garvin graduated from Brown in 1978 with a bachelor's degree in computer science and applied math before returning to earn a Ph.D. in geological sciences in 1984. The VERITAS mission, led by Suzanne Smrekar who graduated from Brown in 1984 with a bachelor's degree in geophysics, will enable 3D reconstructions of the landscape.
Combined, the findings will help lead to a better understanding of the Earth-Venus divergence, which could serve as a dire warning for where Earth is heading, the researchers said.
The study was led by Colby Ostberg, a U.C. Riverside Ph.D. student. The research was supported by the NASA Habitable Worlds Program.