During an in depth flyby of the planet Venus in July 2020, NASA’s Parker Solar Probe detected one thing odd.
As it dipped simply 833 kilometers (517 miles) above the Venusian floor, the probe’s devices recorded a low-frequency radio sign – a telltale signal that Parker had skimmed by the ionosphere, a layer of the planet’s higher ambiance.
This was the primary time an instrument had been capable of document direct in situ measurements of Venus’ higher ambiance in practically three many years, and the info recorded provides us a brand new understanding of how Venus adjustments in response to cyclic adjustments in the Sun.
“I was just so excited to have new data from Venus,” mentioned astronomer Glyn Collinson of NASA’s Goddard Space Flight Center.
Venus is a captivating world to us right here on Earth. It’s so just like our personal planet in dimension and composition, however so crucially completely different: a poisonous, scorching scorching hell-world that’s possible fully inhospitable to life as we all know it.
How the 2 planets might have developed into such radically completely different beasts is of deep curiosity to planetary scientists and astrobiologists looking for different liveable worlds on the market in the Milky Way.
Yet missions to discover Venus have been comparatively few. There’s not a lot level sending landers; they cannot survive the planet’s 462 diploma Celsius (864 diploma Fahrenheit) floor.
Sending orbiting probes can be thought-about problematic, as a result of extremely thick ambiance of carbon dioxide and sulfuric acid rain clouds that make it laborious to inform what’s occurring on the floor.
For these causes, Venus hasn’t been a well-liked goal for devoted missions in a while (Japan’s Akatsuki orbiter being the latest exception), and numerous our latest knowledge has come piecemeal, from devices with different main aims, just like the Parker Solar Probe.
As Parker conducts its mission to check the Sun in shut element, it has been utilizing Venus for gravity help maneuvers – slingshotting across the planet to change velocity and trajectory. It was on one in all these gravity help flybys that the probe’s devices recorded a radio sign.
Collinson, who has labored on different planetary missions, famous an odd familiarity that he could not fairly place in the form of the sign.
“Then the next day, I woke up,” he mentioned. “And I thought, ‘Oh my god, I know what this is!'”
It was the identical form of sign recorded by the Galileo probe when it skimmed by the ionospheres of Jupiter’s moons – a layer of ambiance, additionally seen on Earth and Mars, the place photo voltaic radiation ionizes the atoms, ensuing in a charged plasma that produces low-frequency radio emission.
Once the researchers realized what the sign was, they had been in a position to make use of it to calculate the density of the Venusian ionosphere, and examine it to the final direct measurements taken, all the best way again in 1992. Fascinatingly, the ionosphere was an order of magnitude thinner in the brand new measurements than it was in 1992.
The crew believes that this has one thing to do with photo voltaic cycles. Every 11 years, the Sun’s poles swap locations; south turns into north and north turns into south. It’s not clear what drives these cycles, however we do know that the poles swap when the magnetic discipline is at its weakest.
Because the Sun’s magnetic discipline controls its exercise – corresponding to sunspots (short-term areas of sturdy magnetic fields), photo voltaic flares, and coronal mass ejections (produced by magnetic discipline traces snapping and reconnecting) – this stage of the cycle manifests as a interval of very minimal exercise. It’s referred to as the photo voltaic minimal.
Once the poles have switched, the magnetic discipline strengthens, and photo voltaic exercise rises to a photo voltaic most earlier than subsiding once more for the subsequent polar swap.
Measurements of Venus from Earth advised that Venus’ ionosphere was altering in sync with the photo voltaic cycles, rising thicker at photo voltaic most and thinner at photo voltaic minimal. But with out direct measurements, it was troublesome to substantiate.
Well, guess what? The 1992 measurement was taken at a time near photo voltaic most; the 2020 measurement near photo voltaic minimal. They had been each according to the Earth-based measurements.
“When multiple missions are confirming the same result, one after the other, that gives you a lot of confidence that the thinning is real,” mentioned astronomer Robin Ramstad of the University of Colorado, Boulder.
Exactly why the photo voltaic cycle has this impact on Venus’ ionosphere is unclear, however there are two main theories.
The first is that the higher boundary of the ionosphere may very well be compressed to a decrease altitude throughout photo voltaic minimal, which prevents atoms ionized on the day facet from flowing to the evening facet, ensuing in a thinner evening facet ionosphere. The second is that the ionosphere leaks into house at a quicker charge throughout photo voltaic minimal.
Neither of those mechanisms may very well be dominated out by the Parker knowledge, however the crew hopes that future missions and observations may be capable to make clear what is going on on. In flip, that might assist us achieve a greater understanding of why Venus is the best way it’s, in comparison with Earth.
Maybe it is about time for an additional Venus mission, eh?
The analysis has been printed in Geophysical Research Letters.
Credit for high picture: Venus throughout Parker’s July 2020 flyby. (NASA/Johns Hopkins APL/Naval Research Laboratory/Guillermo Stenborg and Brendan Gallagher)