New data collected from the atmosphere of Venus could reveal why Earth’s ‘twin’ grew up so differently.
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Whilst NASA’s Parker Solar Probe may have been launched with the primary mission of learning more about the Sun, that hasn’t stopped from delivering information about some of the solar system’s other inhabitants.
In particular, the craft, which recently became the fastest object ever created by humans, has been delivering some stunning discoveries about Venus — the planet in the solar system that most resembles Earth.
During its third swing past Venus on July 11, 2020, the Parker Solar Probe detected a natural radio signal that indicates it had passed through Venus’ upper atmosphere.
This is significant because it is the first direct measurement of this planet’s atmosphere for 3 decades. Surprisingly, the Venusian atmosphere appears significantly different from how it has appeared in the past. The new observations seem to demonstrate that the upper atmosphere of Venus undergoes some mysterious changes during the solar cycle — the Sun’s 11 year period of activity.
The observations are detailed in a new paper published in the journal Geophysical Research Letters. Lead author Glyn Collison of NASA’s Goddard Space Flight Center is one of the foremost experts on the second planet from the Sun. Whilst he has extensively examined data from previous Venus missions such as the European Space Agency’s (ESA) Venus Express and NASA’s Venus Orbiter, the data from Parker presents a special opportunity for Collinson.
“I was just so excited to have new data from Venus. To see Venus now, it’s all about these little glimpses.”
Glyn Collison, Lead Author
The discovery joins a series of recent exciting findings concerning the planet and could give astronomers and planetary scientists an idea of why the Earth and Venus are similar in many ways whilst being radically different in others.
Earth and Venus: Twins but not Identical
The fact that Venus is so similar to Earth — the two planets being born in similar circumstances with a similar size and structure — and yet lacks the conditions necessary to support life makes it an ideal laboratory for the study of habitability.
A great deal of research into Earth’s habitability has pointed at the fact that its magnetic field is vital for life as it prevents the atmosphere from being stripped away by solar activity.
This assumption has been somewhat challenged by the fact that despite having no protective magnetic field Venus has been able to maintain its atmosphere, even at times when the Sun is particularly active.
In order to investigate this further, scientists have sought to make detailed observations of Venus’ atmosphere ‘up close.’ That’s precisely what the Parker Solar Probe’s flyby has allowed.
The third pass by Venus by the craft represents its closest approach to the planet, bringing it to within just 520 miles of the Venusian surface. The probe uses these flybys to use Venus’ gravity to adjust speed for its journey to the Sun.
The probe had just 7 minutes to collect data on Venus’ atmosphere and as it did so one of its instruments picked up a low-frequency radio emission. This signal was naturally generated by the Venusian planetary ionosphere — the ‘buffer’ that separates a planet’s space environment from its atmosphere which is created by extreme ultraviolet radiation from the Sun.
Fortunately, that has enough time for it to pick up a telltale and familiar signal.
A FIELDS Trip to Venus
The low-frequency radio signal was detected by the Parker Solar Probe’s FIELDS instrument. This is a device, comprising of three magnetometers — devices that can measure the direction, strength, or relative change of a magnetic field at a particular location — was designed to make measurements of the magnetic fields in the solar corona.
This small blip in the data collected by FIELDS was immediately spotted by Collinson who connected the shape and strength of the signal to a similar pattern in data collected from Jupiter’s moons by the Galileo orbiter.
The blip revealed that the Parker Solar Probe had indeed brushed Venus’ upper atmosphere, revealing radio emission originated from the ionosphere a plasma cloud consisting of charged particles that naturally emit radio waves. Its similarity to the Galileo data is because that mission touched the ionosphere of the Jovian moons.
The NASA team was able to decode the radio signal and use it to calculate the density of the ionosphere at the point the probe passed through — something that has not been done since 1992 when the Pioneer Venus Orbiter also obtained data from the Venusian ionosphere.
These earlier measurements were taken at a time when the Sun was at solar maximum — the peak of its activity — whilst these new observations from FIELDS come just after a solar minimum. Whilst data from ground-based telescopes have shown that Venus’ atmosphere has remained unchanged as the Sun returned to solar minimum, comparing these datasets shows that the ionosphere has not been so calm.
The NASA team can see that the Venusian ionosphere seems to be much thinner when the Sun is less active, changing thickness as the Sun’s activity fluctuates. This could be significant to our understanding of how atmospheres are lost as this is the region responsible for gases seeping into space.
The fact that the ionosphere of Venus thins at solar minimum and leaks gases into space gives planetary researchers a picture of how the planet’s environment has changed and a good idea of how a world so similar to Earth became so toxic.
Collinson describes the study of Venus as a hitchhiker piggybacking on the Parker Solar Probe’s primary mission to study 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,” concludes Nour E. Raouafi, Parker Solar Probe project scientist at the Applied Physics Laboratory, Johns Hopkins, Laurel, Maryland, who operate the mission. “But we would not miss the opportunity to gather science data and provide unique insights into a mysterious planet such as Venus.”
Collinson. G. A., Ramstad. R., Glocer. A., Wilson III. L., Brosius. A., , ‘Depleted Plasma Densities in the Ionosphere of Venus Near Solar Minimum From Parker Solar Probe Observations of Upper Hybrid Resonance Emission,’ Geophysical Research Letters, [https://doi.org/10.1029/2020GL092243]