Lightning on Venus and Earth may spark in much the same way despite vast differences in the atmospheres of the two planets, scientists say.
"Venus and Earth are often called twin planets because of their similar size, mass and interior structure," said Christopher Russell, lead author of the new lightning study and a professor at the University of California, Los Angeles. "The generation of lightning is one more way in which Venus and Earth are fraternal twins."
Russell and his colleagues used new data from Venus Express to show that lightning is similar in strength on Earth and Venus at the same altitudes on both worlds.
"We have analyzed 3.5 Earth-years of Venus lightning data using the low-altitude Venus Express data (10 minutes per day)," Russell said. "By comparing the electromagnetic waves produced at the two planets, we found stronger magnetic signals on Venus, but when converted to energy flux we found very similar lightning strength."
The data also show that lightning is more prevalent on the planet's dayside than at night, and occurs more often at low latitudes, where the solar input to the atmosphere is strongest.
These results will help scientists better understand the chemistry, dynamics and evolution of the atmospheres of the two neighboring planets. Russell will present the findings tomorrow (Sept. 23) at the European Planetary Science Congress in Rome.
Lightning on Venus
Previous missions to Venus, including the Soviet Venera spacecraft, NASA's Pioneer Venus orbiter and the robotic Galileo spacecraft, have detected optical and electromagnetic waves from the cloud-covered planet that could be produced by lightning. [ Photos: Lightning on Earth ]
Ground-based telescopes have also captured evidence of lightning flashes on Venus, but from a theoretical standpoint, the topic has been controversial.
Since the atmospheres of Venus and Earth are so different, some scientists have claimed that Venusian lightning is unlikely if it exists at all. The clouds of Venus are much like smog clouds on Earth, which typically do not generate lightning.
The European Space Agency's Venus Express probe currently orbiting the planet has since shed some light on how the two worlds are, in fact, more similar than previously thought.
Tracking Venus lightning
To track Venusian lightning , the Venus Express probe is equipped with a magnetometer that monitors the planet's magnetic field at altitudes between 124-310 miles.
The instrument has picked up low-frequency radio waves that last for a split second and are thought to come from electrical discharges.
"Short, strong pulses of the signals expected to be produced by lightning were seen almost immediately upon arrival at Venus, despite the generally unfavorable magnetic-field orientation for entry of the signals into the Venus ionosphere at the altitude of the Venus Express measurements," Russell explained.
When clouds form, on Earth or Venus, the energy that the sun has deposited into the air can be released in the form of a very powerful electrical discharge.
As cloud particles collide in the atmosphere, electrical charges are transferred from the larger ones to the small. The large particles fall, while the small particles are carried upward. This separation of charges leads to lightning strikes.
Science of lightning bolts
Studying how lightning is generated in a planet's atmosphere is important because the phenomenon can raise the temperature and pressure of a small portion of a world's overall atmosphere to a very high degree, enabling molecules to form. This would otherwise not occur at standard atmospheric temperatures and pressures.
The process has led some scientists to speculate that lightning may have helped life arise on Earth.
On Earth, approximately 100 discharges of lightning occur every second, but the number of flashes at any single location is much lower.
Similarly, on Venus scientists are not able to see the entire planet, so they must estimate the total occurrence rate with some assumptions about how far Venus Express's instruments can see.