Study indicates Venus has never had habitable conditions

3/12/2024 5:56

        Earth is an ocean world,
        with water covering about 71% of its surface. Venus, our closest
        planetary neighbor, is sometimes called Earth's twin based on
        their similar size and rocky composition. While its surface is
        baked and barren today, might Venus once also have been covered
        by oceans?
        
        The answer is no, according to new research that inferred
        the water content of the planet's interior - a key indicator for
        whether or not Venus once had oceans - based on the chemical
        composition of its atmosphere. The researchers concluded that
        the planet currently has a substantially dry interior that is
        consistent with the idea that Venus was left desiccated after
        the epoch early in its history when its surface was comprised of
        molten rock - magma - and thereafter has had a parched surface.
        
        Water is considered an indispensable ingredient for life, so
        the study's conclusions suggest Venus was never habitable. The
        findings offer no support for a previous hypothesis that Venus
        may have a reservoir of water beneath its surface, a vestige of
        a lost ocean.
        
        Volcanism, by injecting gases into a planet's atmosphere,
        provides clues about the interior of rocky planets. As magma
        ascends from an intermediate planetary layer called the mantle
        to the surface, it unleashes gases from deeper parts of the
        interior.
        
        Volcanic gases on Earth are more than 60% water vapor,
        evidence of a water-rich interior. The researchers calculated
        that gases in Venusian eruptions are no more than 6% water
        vapor, indicative of a desiccated interior.
        
        "We suggest that a habitable past would be associated with
        Venus' present interior being water-rich, and a dry past with
        Venus' present interior being dry," said Tereza Constantinou, a
        doctoral student at the University of Cambridge's Institute of
        Astronomy and lead author of the study published on Monday in
        the journal Nature Astronomy.
        
        "The atmospheric chemistry suggests that volcanic eruptions
        on Venus release very little water, implying that the planet's
        interior - the source of volcanism - is equally dry. This is
        consistent with Venus having had a long-lasting dry surface and
        never having been habitable," Constantinou added.
        
        Venus is the second planet from the sun, and Earth the
        third.
        
        "Two very different histories of water on Venus have been
        proposed: one where Venus had a temperate climate for billions
        of years, with surface liquid water, and the other where a hot
        early Venus was never able to condense surface liquid water,"
        Constantinou said.
        
        The Venusian diameter of about 7,500 miles (12,000 km) is
        just a tad smaller than Earth's 7,900 miles (12,750 km).
        
        "Venus and Earth are often called sister planets because of
        their similarities in mass, radius, density and distance from
        the sun. However, their evolutionary paths diverged
        dramatically," Constantinou said.
        
        "Venus now has surface conditions that are extreme compared
        to Earth, with an atmospheric pressure 90 times greater, surface
        temperatures soaring to around 465°C (869°F), and a toxic
        atmosphere with sulfuric acid clouds. These stark contrasts
        underscore the unique challenges of understanding Venus as more
        than just Earth's counterpart," Constantinou said.
        
        The story appears to have been different on Mars, the fourth
        planet from the sun.
        
        Surface features on Mars indicate it had an ocean of liquid
        water billions of years ago. No such features have been detected
        on Venus. Mars, according to research published in August based
        on seismic data obtained by NASA's robotic InSight lander, may
        harbor a large reservoir of liquid water deep under its surface
        within fractured igneous rocks, holding enough to fill an ocean
        that would cover its entire surface.
        
        While Venus has been studied less than Mars, new
        explorations are planned. NASA's planned DAVINCI mission will
        examine Venus during the 2030s from its clouds down to its
        surface using both flybys and a descent probe. Also during the
        2030s, the European Space Agency's EnVision orbital mission is
        due to conduct radar mapping and atmospheric studies.
        
        "Venus provides a natural laboratory for studying how
        habitability - or the lack of it - evolves," Constantinou said.