For many decades, seismology has been our trusty companion on Earth, unravelling the mysteries of our planet's depths. More recently, missions such as InSight have extended this insight to the enigmatic interior of Mars. Yet, while we've been delving into the geology and climate of various celestial bodies, Venus, often called our closest sister planet, has remained a cryptic enigma.
Facing the formidable challenges of Venus – with its sulphuric acid clouds and blistering surface temperatures – Siddharth Krishnamoorthy from NASA's Jet Propulsion Laboratory and Daniel Bowman of Sandia National Laboratory are embarking on an innovative solution: seismometers suspended from balloons.
The concept might initially raise eyebrows – after all, aren't seismometers supposed to be rooted on solid ground to detect seismic activity?
Indeed, traditional seismometers are ground-bound. However, a different variant, the infrasound seismometer, is gaining traction. This device tracks infrasound pressure waves arising from seismic events transmitted through a medium apart from the ground, such as an atmosphere.
Venus, with its abundant atmosphere, emerges as a prime candidate for this technology. Remarkably, nestled within its cloud layer lies an environment akin to Earth's – a tempting location for potential "cloud cities."
For this purpose, constructing entire cities isn't necessary; a high-altitude balloon could aptly host the infrasound sensors. This offers a solution to one of Venus' most significant hurdles – developing materials that can withstand its harsh surface conditions. NASA has invested substantial resources in devising radiation-hardened sensors capable of enduring the planet's extreme pressure and temperature. Nonetheless, a sensor suspended in more moderate conditions eliminates the need for additional bespoke materials.
But how will signals traverse from the ground to these atmosphere-faring sensors? Earthquakes, or "venusquakes," emanate thunderous sounds that ripple through the atmosphere at low frequencies. Sensitive microphones housed within the balloon can capture these vibrations.
A similar experiment on Earth, situated 3,000 km from earthquakes of magnitude 7.3 and 7.5, demonstrated this feasibility. This experiment can guide researchers in adapting a comparable system for Venus, considering its distinct atmospheric conditions.
However, significant challenges persist.
Firstly, launching balloon missions to Venus remains an uncharted territory.
Secondly, the Earth experiment had corroborating data from other sources to confirm earthquake occurrences. On Venus, where such validation is absent, interpreting data patterns becomes a complex task. The source could be a venusquake, or perhaps the balloon's motion caused the pattern.
Moreover, while our Earth considers earthquakes above magnitude seven significant, it's uncertain whether these seismometers can detect less potent quakes, even on our own planet. The JPL team managed to register aftershocks down to magnitude 4.2, but the balloon was much closer at that point.
The notion of adapting Earth-developed technologies for space exploration is commendable, and this application of seismometers underscores such innovation. However, despite nearly a dozen forthcoming missions to Venus, there are no immediate plans to incorporate these features. For now, delving into the enigmatic depths of our sister planet's interior must remain on hold.
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