Seismology has long been an integral part of understanding Earth’s geology and climate. Recently, missions like InSight have provided valuable seismic data from the inside of Mars. However, when it comes to Venus, our closest sister planet, its inner workings have remained a mystery. With its sulfuric acid cloud and scorching surface temperatures, exploring Venus has posed significant challenges. Nevertheless, Siddharth Krishnamoorthy from NASA’s Jet Propulsion Laboratory and Daniel Bowman of Sandia National Laboratory believe that they have a solution – utilizing seismometers hanging from balloons.
Traditionally, seismometers have been deployed on the ground to detect seismic activity. However, an alternative type of seismometer, called an infrasound seismometer, has gained acceptance. Unlike regular seismometers, an infrasound seismometer monitors infrasound pressure waves created by seismic activity transmitted through a medium other than the ground, such as the atmosphere. Considering the substantial atmosphere present on Venus, this technology seems ideally suited for exploring the planet.
The high-altitude cloud layer of Venus shares similarities with the environment on Earth, leading to numerous ideas for creating “cloud cities” on Venus. While constructing an entire city is unnecessary for collecting infrasound data, a high-altitude balloon can serve the purpose effectively. This approach overcomes one of the most significant challenges in Venus exploration – developing materials that can withstand the harsh conditions on its surface. Unlike ground-based sensors, a balloon-mounted sensor can operate within reasonable temperature and pressure ranges, eliminating the need for additional development efforts.
A crucial question arises: how can seismic signals be transmitted from the ground to the sensors floating in Venus’ atmosphere? Earthquakes, or “venusquakes” in this context, generate deafening sounds that propagate through the atmosphere at low frequencies. Sensitive microphones, such as those deployed in the balloon, can capture these signals. A similar experiment carried out on Earth successfully detected signals from earthquakes of magnitude 7.3 and 7.5, despite being located 3,000 km away from the epicenter. Drawing inspiration from this experiment, researchers can develop a comparable system tailored for the unique environment of Venus.
Exploring Venus using balloon-mounted seismometers presents several challenges. First and foremost, no successful balloon mission to Venus has been achieved thus far, let alone one equipped with sensitive seismometers. Additionally, unlike the Earth experiment, where researchers had a “ground truth” to validate their seismic data, Venus lacks such external sensors. This means that scientists would have to speculate on the cause of specific patterns in the data, unsure whether they are venusquakes or simply disturbances to the balloon’s position.
Furthermore, while earthquakes above magnitude seven are considered significant on Earth, it remains unclear whether the seismometers could detect smaller quakes, even on our home planet. Venus may experience a comparable range of seismic activity or be even more active but with lower intensity, making the detection of weaker quakes a priority. While the JPL team managed to detect aftershocks with a magnitude as low as 4.2, the proximity of the balloon to the epicenter was significantly closer than several thousand kilometers.
Leveraging technologies developed on Earth for space exploration purposes is always a promising avenue. The utilization of seismometers hanging from balloons to explore Venus represents a novel application of these instruments. However, despite approximately a dozen planned missions to Venus in the near future, there are currently no specific plans to incorporate this innovative technology.
For now, the enigmatic inner workings of Venus will remain shrouded in mystery. While seismometers hanging from balloons offer a potential solution to unlocking these secrets, technical and logistical challenges must be addressed. Successfully launching a balloon mission to Venus, ensuring accurate data interpretation in the absence of ground truth references, and expanding the detection capabilities of seismometers all pose significant hurdles. Nonetheless, the allure of understanding our nearest sister planet’s interior workings will undoubtedly continue to spark curiosity and motivate future exploration efforts.
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