Engineers at NASA's Jet Propulsion Laboratory have developed and tested a method for recording tremors using instruments in balloons. In the same way, promising research vehicles, which will be located in the relatively safe upper layers of its atmosphere, can study the bowels of Venus. And it is not yet possible to place long-term seismometers on the surface of this planet.
JPL specialists conducted a series of experiments back in 2019, but the processing of their results took a long time. They recently published a scientific paper describing the method and analyzing the data obtained in the journal Geophysical Research Letters.
Tremors cause vibrations in the ambient air that can be picked up by instruments on aircraft. But this is in theory, but in practice this concept has never been fully tested until recently. And if on Earth humanity has an excellent opportunity to place many sensitive seismometers across the entire surface of the planet, then on other celestial bodies such a luxury may not be available.
The American Jet Propulsion Laboratory (JPL) has created a relatively simple apparatus for experimentally confirming the possibility of registering earthquakes in this way. It is a small piece of equipment with a highly sensitive barometer. Passing by it, acoustic waves cause a small jump in air pressure, which is recorded by the device.
JPL engineers decided to test their development in real conditions in July 2019. Then, between the fourth and sixth, a series of powerful earthquakes occurred near the city of Ridgecrest in the state of California. They were followed by about ten thousand aftershocks (repeated, weaker shocks) over a month and a half. Blocks of equipment with barometers were placed on four balloons of the "gelitrop" type.
These balloons are launched at dawn and gain altitude by heating the gas that fills them with the sun. By the evening, when the temperature of the balloon drops, it drops from 18-24 kilometers back to earth. Luck smiled at the scientists on July 22: an aftershock of magnitude 4, 2 was recorded by the instruments of two balls. However, on one, the signal-to-noise ratio turned out to be too bad, so his data had to be considered unrepresentative.
But the second barometer clearly caught the infrasound wave, which came to him 32 seconds later, after an earthquake occurred at a distance of about 80 kilometers from it. The ball at that moment was at an altitude of about 4.8 kilometers. This moment was the first time in history when tremors were recorded from a balloon. Although, of course, to understand their triumph, scientists had to analyze the data from the barometer for several months and compare them with the readings of ground seismometers using a variety of software.
Nevertheless, based on these results, NASA specialists will be able to develop new advanced models. And already they, in turn, will make it possible to create airborne devices for recording seismic vibrations. Both on Earth and on other planets with a dense atmosphere.
The importance of seismometers
Most of the information about the structure of our planet has been obtained by scientists through careful analysis of data from seismometers. By the way the waves propagate in the bowels of a celestial body, one can draw up a picture of their structure. Moreover, humanity managed to carry out similar experiments not only on Earth, but also on other celestial bodies - the Moon and Mars. Comparing the structure of different planets and their satellites, scientists get a more complete picture of the evolution of such objects and the structure of the world as a whole.
With Venus, however, there is a problem: on its surface the temperature exceeds 460 degrees Celsius (lead melts), and the pressure is 92 times higher than on Earth (the wind moves small stones and cuts them into pebbles, like water). Under such conditions, not a single Venusian research probe has been able to operate for much longer than two hours. And for full-fledged seismic observations, the sensor should function for several months, or better - years.
The alternative being developed by the Jet Propulsion Laboratory looks tempting. Balloons on Venus have already been tested in Soviet missions of the "Vega" series devices. Each of them, during the descent through the atmosphere, released two probes, which were balloons with a set of scientific equipment under them. These balloons drifted for 46 hours in the Venusian atmosphere at an altitude of about 54 kilometers.
In this region, conditions are quite close to those on Earth: the pressure is about half the atmosphere, and the temperature fluctuates between 27 and 43 degrees. That is, if desired, a long-lived research probe held on a balloon can be placed at this altitude. NASA plans to launch the first such device to Venus in 2030, as part of the DAVINCI + mission. It is not specified yet whether barometers will be installed on it.
But from the point of view of the convenience of registering earthquakes with atmospheric-based instruments, Venus is much more convenient than the Earth. Calculations by JPL engineers show that infrasonic waves will propagate at least 60 times more efficiently on the second planet from the Sun than in Earth's air. This means that even a device located at an altitude of about 50-60 kilometers will have a chance to record seismic vibrations. And this will already allow scientists to better understand the mysterious internal structure of Venus, about which mankind still has catastrophically little data.