Venus's deadly atmosphere may aid in our search for habitable planets.

 

 (Image credit: Mark Garlick/Science Photo Library/Getty Images)

Venus, despite being lethal, has a lot to teach us.

Since both planetary entities are roughly the same size and mass, the planet Venus is frequently referred to as "Earth's twin." However, Venus has been observed to be far less hospitable and somewhat of a hellscape than Earth, which is teeming with all forms of life, both big and small. This is a result of its crushing surface pressures of 90 times that of the Earth and its scorching surface temps of up to 900 degrees Fahrenheit (482 degrees Celsius).

Venus displays a phenomenon known as a runaway greenhouse effect, in which solar radiation that reaches the surface is confined and gradually raises pressure and temperature. But why is it crucial to understand how Venus and Earth diverged, and how did Venus' climate get so out of control and hostile? In a recent study, a group of scientists headed by the University of California, Riverside (UC Riverside) aim to provide answers to these questions.

Colby Ostberg, a PhD candidate at UC Riverside and the study's lead author, said in an email to Space.com, "Since Mars has been the centre of attention in the solar system for a long time, it is usually forgotten that Venus is actually the most similar planet to Earth in terms of size and mass." "Additionally, previous studies have demonstrated that Venus's surface could have remained livable for up to a billion years ago, indicating that the solar system may have once contained two habitable planets. We can control the conditions that result in uninhabitable planets by understanding what led Venus to transform into the hellscape it is today. By determining which exoplanets should or should not be targeted in atmospheric observations with JWST or other future facilities, this will also be essential for the hunt for life in the universe.

 

The exoVenuses, or exoplanets that are located inside the Venus Zone (VZ) or the runaway greenhouse limit of their parent star's orbit, were the focus of the study's atmospheric analysis. Astronomers hope to better comprehend Venus' runaway greenhouse effect as well as its past by using exoVenus atmospheres as analogues.

Oxygen is frequently regarded as a possible exoplanet biosignature since it is almost entirely produced by photosynthetic life on Earth at present, according to Dr. Eddie Schwieterman, co-author of the research and Assistant Professor of Astrobiology at UC Riverside. He spoke with Space.com via email. "However, a prolonged runaway greenhouse is one possible abiotic method of accumulating oxygen in a planetary atmosphere. UV photons from the star break up water as it enters the higher atmosphere, causing the lighter hydrogen to escape and the heavier oxygen to be retained.

There are other oxygen sinks, but if they run out, oxygen could pile up in the atmosphere. Early in their lives, M dwarf stars—the first targets for planetary characterization with JWST—are extremely bright. This extremely bright period would accelerate the loss of atmosphere to space. Abiotic oxygen accumulation on exoplanets is unknown, but we would anticipate that it would be more prevalent on Venus Zone worlds than on planets that are farther from their stars. We might be advised against interpreting life on temperate planets if we scan Venus Zone planets, where life is improbable, and discover a lot of them have oxygen. On the other hand, it would be encouraging to locate oxygen biosignatures on Earth-like worlds inside the habitable zone if we do not discover oxygen-rich Venus Zone planets.

An artist's representation of the 'habitable zone,' the range of orbits around a star where liquid water may exist on the surface of a planet.  (Image credit: Erik A. Petigura)

A catalogue of 317 confirmed terrestrial (rocky) exoplanets that orbit within the VZ, including those found using either transit or non-transit detection techniques, was created by the researchers using planetary and stellar data from the NASA Exoplanet Archive. However, they determined that these candidates were not good Venus analogues due to the loss of atmosphere they experience from their high temperatures and solar energy they receive, also known as incident flux. They estimated that the largest population of exoVenuses exists closer towards the VZ's inner boundary. Eight of these will be viewed by the James Webb Space Telescope (JWST), including GJ 357 b, GJ 1132 b, TRAPPIST-1 b, TRAPPIST-1 c, TOI-776 b, TOI-776 c, LTT 1145 A bL 98-59 b., and others.

According to Dr. Stephen Kane, a professor of planetary astronomy at UC Riverside and a co-author of the study, "the most important targets are those that have multiple terrestrial planets within the Venus Zone." These systems enable us to conduct comparison planetary research on planets that are of a similar age and most likely have comparable bulk abundances. L 98-59 and TRAPPIST-1 are two examples of such systems, both of which enable us to study the impacts of M dwarf activity on planetary atmosphere retention.

 

An artist's depiction of the seven planets in the TRAPPIST-1 system. (Image credit: NASA/JPL-Caltech)

Studying the planet Venus itself is a crucial component for carrying out this investigation. The most current information is, regrettably, from NASA's Magellan mission in the 1990s. The researchers do, however, name a number of proposed and approved missions to Venus, including VERITAS and DAVINCI+ from NASA, Venera-D from the Russian Federal Space Agency, and EnVision from the European Space Agency.

These missions will all offer the most recent information on Venus' atmospheric structure and composition, as well as high-resolution surface maps that may corroborate recent findings that Venus is volcanically active. These missions could, however, also advance our understanding of exoplanets by enhancing the models used to forecast the climates of exoVenuses.

"NASA's VERITAS discovery mission to Venus will be crucial to research into Venus and exoVenus as well as our knowledge of the Earth. However, the launch was postponed by three years in November 2022, which will have a significant effect on a number of disciplines outside of Venusian science. In order to shorten its delay, it is crucial that the scholarly community supports VERITAS and emphasises its significance.

Sadly, it doesn't appear to be the situation. The financing for VERTIAS decreased from a projected $56.7 million to just $1.5 million in NASA's most recent budget request, frustrating the project's team.

Reference: space.com