Launched in 2018 to study the Sun's atmosphere, NASA’s Parker Solar Probe uses Venus' gravity to orbit closer and closer to the Sun. On July 11, 2020, the spacecraft flew through Venus' upper atmosphere for the first time in 30 years. During the fly-by, the probe detected a low-frequency radio signal coming from Venus' atmosphere when dipped 517 miles above the planet's surface, reports Victor Tangermann for Futurism.
The find gives researchers a new understanding of how Venus's atmosphere changes with the Sun's 11-year solar cycle, reports Passant Rabie for Inverse. The study, published in Geophysical Research Letters, may also give researchers an insight into why Venus evolved to be inhospitable, despite being similar in size and structure to Earth.
The radio signal was detected with an instrument aboard the probe called FIELDS, named for its ability to measure electric and magnetic fields in the Sun's atmosphere, reports Ashley Strickland for CNN. FIELDS recorded the seven-minute-long radio signal, but when Glyn Collinson, a researcher at NASA's Goddard Space Flight Center, analyzed the data, he noticed an odd shape in the signal that looked familiar. The signal was similar to a radio wave registered by NASA's Galileo probe when it flew through the ionospheres of Jupiter's moons, reports Michelle Starr for Science Alert. Ionospheres are electrically charged layers of gas or plasma located in the upper atmosphere of planets. The charged plasma emits radio waves that can be detected, reports Inverse.
Using the detected radio wave, Collinson and his team calculated the density of Venus' ionosphere and compared it to measurements taken back in 1992 by the Pioneer Venus Orbiter, NASA explains in a press release. The measurements in 1992 were taken when the Sun was near the peak of its stormy solar cycle, or solar maximum. During the sun's solar cycle, its magnetic field flips every 11 years when it is at its weakest, reports Science Alert. When the poles switch, increases in solar activity, such as solar flares and sunspots, occur.
After comparing the measurements, the researchers found that Venus' ionosphere was thinner than when it was in 1992 during a solar maximum. In contrast, the new measurements were taken six months after the sun's solar minimum, CNN reports. The find suggests Venus' ionosphere is influenced by the sun's solar cycle and becomes thinner during the solar minimum than it is during the solar maximum.
"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 study co-author Robin Ramstad, a postdoctoral researcher at the University of Colorado, Boulder, in a statement.
Understanding how the sun affects Venus' ionosphere can help researchers find how the planet evolved to have a leaking ionosphere and became the hot, scorching planet it is today.
"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 John Hopkins University's Applied Physics Laboratory, in a statement. "But we would not miss the opportunity to gather science data and provide unique insights into a mysterious planet such as Venus."