Space Science & Space Physics Research Spotlight

Venus's Unexpected, Electrifying Water Loss

New research shows that an electric field surrounding Venus is stripping its atmosphere of water—and the same phenomenon may plague exoplanets scientists hope might be habitable.

Source: Geophysical Research Letters

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Billions of years ago, when the solar system was young, you might have mistaken Venus for Earth at a glance—both planets were home to life-sustaining water.

Venus lost that water long ago, and scientists generally place the blame on the solar wind. The electric field carried by the solar wind penetrated Venus’s ionosphere, stripping away its ions—including water group species like oxygen and hydrogen.

However, this isn’t the only way that Venus might have dried out. A different mechanism involves how an electric field could be generated from the movement of electrons, even while gravity pulls the ions downward. The field could make it easier for water’s constituent atoms to be lost to space: It could fling hydrogen ions away from the planet at escape velocity, and it might give a considerable boost to the heavier oxygen ions as well.

Now Collinson et al. have made the first definitive measurement of this electric field, and their results show it may indeed have played a larger role than previously thought. The results may even force scientists to downgrade prospects for water on exoplanets thought to be habitable.

The researchers used data from the European Space Agency’s Venus Express probe, which arrived at the planet in 2006 and operated until it ran out of propellant and sank into the atmosphere in 2014. The team chose orbits where the satellite flew over Venus’s North Pole on every orbit. This allowed the probe to measure the strength of the electric field associated with the planet’s magnetic field lines.

The authors were surprised to find just how much potential the electric field had: roughly 10 volts, strong enough to fling not only hydrogen ions but also oxygen atoms into space. For context, that’s at least 5 times stronger than the equivalent field in Earth’s ionosphere. The team suspects this could be because Venus is closer to the Sun and receives more ionizing radiation, and some preliminary modeling supports that conclusion.

If true, the discovery could be bad news for the dozens of potentially habitable exoplanets that NASA’s Kepler satellite has discovered. Although these planets are in the “Goldilocks zone”—situated at the right distance from their star to support water—in Kepler’s sample of systems, that zone tends to be closer to their stars because those planets are easier to detect. If they too have strong electric winds like Venus, they may be more likely to share its bone-dry, lifeless fate. (Geophysical Research Letters, doi:10.1002/2016GL068327, 2016)

—Mark Zastrow, Freelance Writer

Citation: Zastrow, M. (2016), Venus’s unexpected, electrifying water loss, Eos, 97, doi:10.1029/2016EO056037. Published on 20 July 2016.
© 2016. The authors. CC BY-NC-ND 3.0
  • wd73383

    No doubt human caused.

  • davidlaing

    This is clever, but there is a much more compelling argument that has been generally ignored. That is the fact that Earth has a massive natural satellite, Moon, that holds Earth’s rotational axis at 23.3 ± 1.2 degrees from a perpendicular to the plane of the ecliptic. No other planet in the Solar System, Venus included, has such a satellite. This stabilizing effect of Moon, of course, has effectively prevented Earth’s polar regions from 24/7 irradiation by Sun during the solstices, which would definitely have happened with obliquities close to 90 degrees, and which would definitely have led to the evaporation and dissociation of surface water, i.e., oceans. This is well-documented by the extremely high deuterium to hydrogen ratio of Venusian water as opposed to Earth water (hydrogen is twice as easily “strippable” to escape velocity than is deuterium). Venus and also Mars, which also has a much higher D/H ratio than Earth, were obviously placed in such a situation, probably several times in its past, and Earth wasn’t, so Venus and Mars lost their water, and Earth didn’t. Ergo, a massive natural satellite is prerequisite to the preservation of planetary water, and hence to the development of life on that planet.