NASA has captured haunting sounds coming from the upper atmosphere of Venus during a close flyby of the Parker Solar Probe launched to study the sun.
The natural radio signal is helping scientists study the atmosphere of 'Earth's less hospitable twin,' according to the NASA team responsible for the probe.
The space agency captured the sounds while the Parker probe was making its 'closest-ever flyby' of the planet, travelling at just 517 miles above the surface.
NASA's Goddard space centre is running the solar probe, which made its third flyby of Venus on July 11, 2020, when it detected the radio signal and its eerie soundtrack.
The Venusian atmosphere appears to be changing, and it might explain why and how Venus and Earth are so different. MORE on NASA's Parker Solar Probe's discovery >> .https://t.co/OOCqth6epu— NASA_SLS (@NASA_SLS) May 3, 2021
The radio signal was detected during the Venus flyby while the probe was on its way back to study the sun, coming closer than any previous spacecraft.
The Parker Solar Probe was launched by NASA in 2018 to study our star and come within 4.3 million miles of the centre of the sun by 2025.
The probe detected a natural radio signal that revealed the spacecraft had flown through the planet's upper atmosphere, coming just 517 miles of the surface.
This was the first direct measurement of the Venusian atmosphere in nearly 30 years - and it looks quite different from Venus past, according to a new study of the data.
The new study found that Venus' upper atmosphere undergoes puzzling changes over a solar cycle - that is the Sun's 11-year activity cycle.
This marks the latest clue to untangling how and why Venus and Earth are so different, despite being born of similar process.
Earth and Venus are twin worlds, they are both rocky, and of a similar size and structure, according to NASA, but their paths diverged from birth.
Venus lacks a magnetic field, and its surface broils at temperatures hot enough to melt lead, it is so intense spacecraft sent to study it only last a couple of hours.
Studying Venus, inhospitable as it is, helps scientists understand how these twins have evolved, and what makes Earth-like planets habitable or not.
The Parker Solar Probe is flying close to Venus in a bid to leverage its gravity to slow down its sideway motion, allowing it to reach the sun and not overshoot the star.
26. NASA has just lost communications with the Mariner 5 spacecraft. It was able to collect information about interplanetary and Venusian magnetic fields, charged particles, plasmas, and the radio refractivity and UV emissions of the Venusian atmosphere. #NASA (December 4, 1967) pic.twitter.com/GR0mVZMv9E— Filip Bachorz (@BachorzFilip) December 13, 2017
The signal was detected on the third flyby, with each trip around the second planet helping the probe hit its target of coming 4.3 million miles of the solar centre.
Eventually, when it gets closer to the suns atmosphere the probe will be travelling at 430,000 miles per hour - making it the fastest human spaceship ever created.
'I was just so excited to have new data from Venus,' said Glyn Collison of NASA's Goddard Space Flight Center in Greenbelt, Maryland, the lead scientist on the study.
A Venus expert, Collinson has pored over all the Venus data available from this and previous missions like the NASA Pioneer Venus Orbiter or the ESA Venus Express.
One of Parker Solar Probe's instruments is FIELDS, named for the electric and magnetic fields it measures in the Sun's atmosphere.
During its seven minute flyby of Venus, the FIELDS instrument detected a natural, low-frequency radio signal coming from the upper atmosphere.
The shape and strength of the signal seemed familiar, but Collinson said he couldn't place it at first, then had a moment of recognition saying 'I know what this is!'
Collinson recognised the signal from his previous work with NASA's Galileo orbiter, which explored Jupiter and its moons before the mission ended in 2003.
A similar frown appeared when Galileo passed through the ionospheres of Jupiter's moons, and it is due to a layer of electrically charged gas in the ionosphere.
This sea of charged gases, or plasma, naturally emits radio waves that can be detected by instruments like FIELDS, explained NASA.
When Collinson and his team identified that signal, they realised Parker Solar Probe had skimmed Venus' upper atmosphere, something they called 'a pleasant surprise.'
The radio emission provided enough data to calculate the density of the ionosphere and compare it to measurements taken in 1992 by Pioneer.
When the Pioneer Venus Orbiter visited our sister world the sun was near its solar maximum - the stormy peak of its 11-year solar cycle.
Observations from Earth over the years that followed revealed changes were taking place on Venus as the Sun settled into its calm phase, solar minimum.
This ground based data revealed the bulk of the atmosphere remained the same, but the ionosphere was much thinner when the sun was at its least active, but this was impossible to prove without direct measurements from a spacecraft.
The observations from Parker Solar Probe's recent flyby, which occurred six months after the latest solar minimum, verify the puzzle in Venus' ionosphere.
'Indeed, Venus' ionosphere is much thinner compared to previous measurements taken during solar maximum,' according to a NASA spokesperson.
'When multiple missions are confirming the same result, one after the other, that gives you a lot of confidence that the thinning is real,' said Robin Ramstad, a study co-author and researchers at the University of Colorado, Boulder.
Understanding why Venus' ionosphere thins near solar minimum is one part of unraveling how Venus responds to the Sun.
Understanding this will help researchers determine how Venus, which was once so similar to Earth it may have been habitable and have flowing water, became the scorching world full of toxic air it is today.
For example, Venus' ionosphere is prone to leaking, meaning the escape of energised gases into space. Gathering data on this and other changes in the ionosphere is key to understanding how Venus' atmosphere has evolved over time.
To confirm the Earth-based readings took a mission to Venus, and decades later, a state-of-the-art mission to the Sun.
'The goal of flying by Venus is to slow down the spacecraft so that Parker Solar Probe can dive closer to the Sun,' said Nour E. Raouafi, Parker Solar Probe project scientist at the Applied Physics Laboratory.
'But we would not miss the opportunity to gather science data and provide unique insights into a mysterious planet such as Venus.'
Collinson likened the research to hitchhiking. Venus scientists were eager to piggyback off Parker Solar Probe's flyby for new data and views of Earth's twin planet. 'To see Venus now, it's all about these little glimpses,' he said.
The findings have been published in the journal Geophysical Research Letters.
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