NASA’s Parker Solar Probe may be focused on the Sun, but that doesn’t mean that space agency scientists will give up the opportunity to get the first live data from Venus’s atmosphere in nearly three decades. The spacecraft is currently swinging through space, using Venus’ gravity to bring it closer to the Sun each time, and in the process has been getting closer and closer to the planet’s surface.
In fact, on July 11, 2020, the Parker Solar Probe was “mere” 517 miles from the surface of Venus. This lowered it enough to scrape through the Venusian atmosphere, the first time that a spacecraft has been able to make a direct measurement of that region since the Pioneer Venus Orbiter in 1992.
At first, however, scientists did not realize the new data they had. It took Glyn Collison, from NASA’s Goddard Space Flight Center in Greenbelt, Maryland – familiar with all of the agency’s previous Venus mission data – to find what is described as a “thin frown” in the data. This was a natural low-frequency radio signal on the FIELDS instrument.
FIELDS consists of a trio of magnetometer and is designed to measure magnetic fields in the Sun’s corona. However, for seven minutes near Venus – which coincided with the Parker Solar Probe being at its closest point on the planet – FIELDS also recorded a signal. “A similar scowl appeared whenever the spacecraft passed through the ionospheres of Jupiter’s moons,” explains NASA.
In fact, it is the planet’s ionosphere – a thin layer of electrically charged gas at the very edges of Venus’s atmosphere – that it has detected. Thanks to this, it was possible to confirm the density of the ionosphere. The measurements of this can be compared to the findings of the Pioneer Venus Orbiter almost three decades ago.
In the process, it allowed an ancient mystery to be further explored. When the Pioneer Venus Orbiter took its measurements, the Sun was close to the highest peak in its solar cycle, known as the solar maximum. As it decreased towards the solar minimum in the following years, it seemed that Venus’ ionosphere became thinner. However, scientists only had Earth-based telescopes to observe these changes.
It is now clear from the findings of the Parker Solar Probe that the ionosphere is actually thinner. A new article published today documents the changes.
As to why this happens and why it is important, there is still some uncertainty. One of the reasons Venus is so interesting to researchers is that, in many ways, it is a close counterpart to Earth. Both are similar in size and structure, but Venus has no magnetic field and the surface temperatures are so extreme that the spacecraft lasted a few hours at most. Finding out how the magnetic field changes with the solar cycle can help to understand how the atmosphere on Venus – and planets like it – was destroyed, and can help to better understand other planets that are potentially hospitable to life.