U.S. space agency researchers successfully used balloons to detect earthquakes in the California desert.

The experiment tested whether similar balloons could be sent to Venus to study that planet's seismic activity. NASA recently announced plans to launch two future missions to Venus.

The NASA scientists got the chance to carry out the test in July 2019, when a series of powerful earthquakes struck the area around Ridgecrest, California. The main earthquake took place on July 4 and had a magnitude of 6.4, the United States Geological Survey reported in May. Several other large quakes hit the area within days and more than 10,000 aftershocks were reported over the next six weeks.

The experiment involved four large sun-powered balloons designed to fly at altitudes of 18 to 24 kilometers. The team attached instruments to the balloons that measure changes in air pressure. The equipment is used to detect sound waves that rise up from beneath the surface during earthquakes and aftershocks.

The researchers say that by studying seismic wave activity of a rocky planet, like Earth, they can learn more about how that planet developed and about its current state.

Venus is also a rocky planet. It is our closest neighbor in the solar system and the second closest planet to the sun. It is similar in structure to Earth, but a little smaller. But unlike Earth, Venus has an extremely hot surface temperature and a very dense atmosphere. Such conditions make it difficult for spacecraft to survive in Venus' atmosphere or on its surface.

Scientists have long thought about the possibility of studying seismic activity on Venus. They want to learn more about how the planet developed such extreme conditions.

The researchers, from NASA's Jet Propulsion Laboratory (JPL), think they can send balloons like the ones tested in California on a mission to Venus. The experiment -- which also involved scientists from the California Institute of Technology (Caltech) --was recently described in a study in Geophysical Research Letters.

Scientists from JPL and Caltech have been developing their balloon-based method since 2016. But the heavy earthquake activity in the California desert in July 2019 gave them a good chance to test their equipment in the field.

Seismic energy from earthquakes is transmitted into the atmosphere and produces sound waves. These waves are detected by ground-based seismic stations. But the JPL team reported it was able to detect, for the first time, earthquake related seismic activity from its balloons.

One of the balloons detected seismic sound waves seconds after a 4.2 magnitude aftershock was confirmed by ground-based detection stations. At the time, the balloon was about 4.8 kilometers above the Earth.

The researchers hope the balloons will permit new studies of seismic activity on Venus to provide information about the planet's interior. For example, they say this method could help them learn why the surface of Venus stays hot enough to melt lead. It may also lead to discoveries of liquid, such as water or oil, on the planet.

Jennifer M. Jackson is a professor of mineral physics at Caltech's Seismological Laboratory who helped lead the research. She said in a statement that much of our understanding about Earth's interior comes from the study of seismic activity happening deep inside the planet. The method could also be possible with Venus.

"Observations of seismic activity...would strengthen our understanding of rocky planets. But Venus' extreme environment requires us to investigate novel detection techniques."

The researchers say they plan to continue flying balloons over seismically active areas to improve their ability to identify seismic events over wide areas from the air. They also plan to add more instruments and fly more balloons at the same time. This could permit them to identify where earthquakes happen without the need for confirmation from ground stations.

I'm Bryan Lynn.

Bryan Lynn wrote this story for VOA Learning English, based on reports from NASA, Geophysical Research Letters and the U.S. Geological Survey. Mario Ritter, Jr was the editor.