During its third flight to Venus, NASA’s Parker solar probe recorded natural radio emissions in the Venusian atmosphere. The discovery confirms that the upper atmosphere of Venus is undergoing significant changes in accordance with the 11-year cycle of the Sun, providing new insights into this mysterious – and completely hostile – Earth-like planet.
The Parker solar probe is designed to explore the Sun, but some of its best work to date revolves around Venus. Launched in 2018, the spacecraft uses the gravity of Venus to get closer to the Sun. These flies will eventually place Parker 6.9 million kilometers from our host star, allowing the probe to explore the solar winds and the corona.
These gravitational aids proved fruitful, as Parker’s instruments were skillfully used to study Venus. The data obtained from the probe recently allowed astronomers capture our first full view of the orbital ring of Venus and – quite unexpectedly – peek through the clouds and visualize the healthy surface of the planet.
And now, like new research published in Geophysical Research Letters, Parker was able to detect natural radio emissions from the Venusian atmosphere. Venus expert Glyn Collinson of the Heliophysics Research Department at NASA’s Goddard Space Flight Center is leading the new study.
Parker testified on July 11, 2020, when performing his third flight to Venus. It is only logical that astronomers use these moments to study the planet, as we still have much to learn about this planet, which is very similar to ours in terms of its size, chemical composition and location in the solar system. But in a way, while the Earth is boiling with life, Venus is a burning hole.
A possible reason for this big difference is that Earth has a protective magnetic field and Venus does not. Our magnetic field can contribute to habitability by preventing the atmosphere from leaking into space. At least that’s the theory. By this logic, Venus, without a magnetic field, must have an atmosphere that flows into space during periods of intense solar activity. The problem is that observations made by ground-based telescopes show the opposite, revealing thinner ionospheres – the very top of the atmosphere – during periods when the Sun is least active. He presented a basic puzzle.
That is why the third flight of Venus, in which Parker reached a distance of 833 km from the Venusian surface, was so important because scientists were not entirely sure about the reliability of remote sensing data. For a period of seven minutes, the probe measures the upper atmosphere of Venus, which it does with the help of its onboard instrument FIELDS (this instrument will later be used to study the electric and magnetic field of the Sun). Unlike the radio in your car, this instrument simultaneously scans frequencies across the entire radio frequency spectrum.
At first, Collinson didn’t know what to do with Parker’s new data, but then he remembered seeing something similar to NASA’s Galileo orbiter, which explores Jupiter and its moons. The frown-like signal found by Parker was just like the signal caught by Galileo as the probe zipped through the ionospheres of Jovian’s satellites.
Parker Solar Probe, Colinson realized that he had actually traveled through the atmosphere of Venus, providing the first direct measurement of the Venusian atmosphere in nearly 30 years. Parker had detects natural low-frequency radio emissions that are associated with planetary ionospheres – an atmospheric region full of plasma or charged gases.
These radio emissions allowed Collinson to calculate the density of the ionosphere of Venus, or at least the part of the ionosphere studied by Parker. His team compared these findings to data recorded by NASA’s Pioneer Venus Orbiter.
When the Pioneer spacecraft visited Venus in 1992, the Sun was close to its maximum activity point in its 11-year solar cycle. “The cool thing about Parker is that his overflight happened six months after the solar minimum,” Collinson explained in a telephone interview that allowed him to “kill the ionosphere” during that period, he said.
“We were able to mathematically prove significant differences between this atmosphere and the one that Pioneer saw many years ago,” Collinson added.
As the data show, the atmosphere of Venus seems to be significantly thinner than previous measurements made during the solar maximum, which actually confirms the observations made by ground-based telescopes.
“By measuring the frequency of this emission, we can directly calculate the density of the ionosphere around Parker, finding that it is far less dense than previous missions,” the scientists wrote in their report. “This supports the theory that the ionosphere of Venus varies considerably during the 11-year solar cycle.”
In fact, the team “was able to confirm what we had previously assumed from remote sensing measurements,” Collinson explained.
So a very good result, because this “deviation was expected”, Collinson said, but planetary scientists already have a big mystery: Why is this happening? Venus appears to be prone to leakage, leading to the escape of plasma into space, but not during periods when the Sun is most active.
“It tells us that we really don’t have a good understanding of how the closest sister on Earth works,” Collinson said. “This is an indication that there is an Earth-like planet that is undergoing huge changes in its upper atmosphere, revealing mechanisms that we do not fully understand.”
Collinson said the new data provided a “painful idea of how Venus works,” and now we need to compare that to how things work here on Earth. That way we could understand “what makes the planet habitable and why we’re here,” not Venus, he said.
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