Why does Earth support life, while Venus and Mars—and for all we know, any other planet in the universe—do not?
“It’s one of the most fundamental questions in all of science: Why are we here? And it’s what Endurance is after,” said Glyn Collinson, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and principal investigator for NASA’s Endurance mission.
The Endurance mission will try to measure the Earth’s global electric potential, or how strongly the Earth’s electric field “attracts” electrically charged particles into our air. This electric potential is expected to be very weak, making it difficult to measure – and this is one of the reasons why the Earth can sustain life. The Endurance launch window from the small town of New Alesund in Svalbard, Norway, will open on May 9.
Earth is a water planet, and this is one of the main reasons why life can exist on it. However, billions of years ago you could say something similar about Venus. Scientists believe that Venus was once much wetter than it is today, but for reasons we still do not fully understand, it has dried up. Finding out the causes can point to a key difference from Earth and reveal the hidden ingredient of the planet’s fitness for life.
In 2016, the Venus Express mission of the European Space Agency discovered the key to the solution. The spacecraft has discovered an electric potential of 10V around the planet, which means that positively charged particles are drawn away from its surface. Like a planetary vacuum cleaner, this electric potential can suck out components of water, such as positively charged oxygen, which is cleaved from hydrogen atoms under the influence of intense sunlight. Eventually, this electric potential could play a role in diverting Venus’ water into space.
However, these discoveries, made on Venus, raised questions about the Earth. The electric potential of Venus is created by the ionosphere – an electrically charged outer layer of its atmosphere. But the Earth also has an ionosphere. So does the Earth have such an electric potential, and if so, why does our water still exist?
We think one of the reasons Earth may be habitable is because we have this very weak electrical potential,” Collinson said. The Endurance team estimates a strength of about 0.3 volts, some 25 times weaker than on Venus and so weak it has foiled all previous attempts at measurement. “It’s not even as strong as a watch battery—but it should be there,” Collinson added.
Rising into the air, the Endurance mission measures electrons emanating from the Earth’s atmosphere as part of a gradual process of exiting the atmosphere that has been going on for billions of years. These electrons leave the Earth at a certain, predictable rate, but they need to be slightly slowed by the Earth’s global electrical potential. The instruments will try to measure this subtle deceleration effect to find out how strong it is.
If all goes according to plan, it will be the first measurement of the Earth’s global electrical potential.