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Venus may be a (slightly) gentler place than some scientists give it credit for.

In new research, space physicists听at CU Boulder have jumped into听a surprisingly long-running debate in solar system science: Does lightning strike on the second planet from the sun?

The team鈥檚 results add strong new evidence suggesting that, no, you probably wouldn鈥檛 see bolts of lightning flashing from Venus鈥� thick, acidic clouds鈥攐r, at least, not very often.

鈥淭here鈥檚 been debate about lightning on Venus for close to 40 years,鈥� said Harriet George, lead author of the new study and a postdoctoral researcher at the (LASP). 鈥淗opefully, with our newly available data, we can help to reconcile that debate.鈥�

She and her team in the journal Geophysical Research Letters.

The research takes a deep dive into one of the most mysterious, and inhospitable, bodies in the solar system. Venus is about the same size as Earth, but its dense, carbon dioxide-rich atmosphere has led to a runaway greenhouse effect. Anyone standing on the ground would face searing temperatures of 900 degrees Fahrenheit and crushing atmospheric pressures. No spacecraft has ever survived for more than a few hours on the planet鈥檚 surface.听

To explore this extreme world, the researchers turned to a scientific tool that wasn鈥檛 designed to study Venus at all: NASA鈥檚 , which launched in 2018 as part of a seven-year mission to investigate the physics of the sun's听corona, or outermost atmosphere, and the solar wind. Parker Solar Probe was designed, built and is now operated by the Johns Hopkins Applied Physics Laboratory, which leads the mission for NASA.

In February 2021, the spacecraft swooped around Venus at a distance of roughly 1,500 miles. In the process, its instruments picked up dozens of what scientists call 鈥渨histler waves鈥濃�攑ulses of energy that, on Earth at least, can be kicked off by bolts of lightning. The team鈥檚 data showed that Venus鈥� whistler waves may not actually originate from lightning, but rather from disturbances in the weak magnetic fields that envelop the planet.

The , which failed to detect radio waves generated by lightning strikes coming from Venus.听The research was led by Marc Pulupa of the University of California, Berkeley.

David Malaspina, a co-author of the new study, said the findings show just how little humans know about one of our nearest neighbors.

鈥淚t鈥檚 very rare that new scientific instruments make it to Venus,鈥� said Malaspina, assistant professor at LASP and the Department of Astrophysical and Planetary Sciences. 鈥淲e don鈥檛 get a lot of chances to do this kind of interesting research.鈥�

Dark and stormy nights

Much of the debate around Venus and lightning dates back to 1978 when a NASA spacecraft called entered into orbit around Earth鈥檚 hotter, angrier twin. Almost immediately, the spacecraft began picking up the signals of whistler waves hundreds of miles above the planet鈥檚 surface.

For many scientists, these signals were reminiscent of a familiar phenomenon from Earth: lightning.

George explained that, on Earth, whistler waves are often鈥攂ut not always鈥攃reated by lightning. Lightning strikes, she said, can jostle electrons in the planet鈥檚 atmosphere, which then launch waves that spiral out into space. These waves create whistling tones that early radio operators on Earth could hear using headphones, hence the name 鈥渨histlers.鈥澨�

If Venus鈥� whistler waves have a similar origin, then the planet might be a monster of lightning, experiencing roughly seven times more strikes than Earth. Scientists have also spotted lightning on Saturn and Jupiter.

鈥淪ome scientists saw those signatures and said, 鈥楾hat could be lightning,鈥欌�� George said. 鈥淥thers have said, 鈥楢ctually, it could be something else.鈥� There鈥檚 been back and forth about it for decades since.鈥�

A brush with Venus

Parker Solar Probe could offer scientists an opportunity to resolve the debate for good.

George said that the spacecraft will skim by Venus seven times during its mission, using these flybys to draw closer and closer to the sun. In 2021, during its fourth such maneuver, the probe got remarkably near to the planet鈥攑assing into the shadow cast behind Venus, a prime spot to go looking for whistler waves.

To find those signals, George, Malaspina and their colleagues used Parker Solar Probe鈥檚 , a set of electric and magnetic field sensors that stick out from the spacecraft. (A team at CU Boulder and LASP designed and built the Digital Fields Board, which analyzes signals from the FIELDS sensors).

When the researchers analyzed a set of those whistlers, however, they noticed something surprising: Venus鈥� whistler waves were headed the wrong way. 听They seemed to be moving down toward the planet, not out into space like you鈥檇 expect from a lightning storm.

鈥淭hey were heading backward from what everybody had been imagining for the last 40 years,鈥� Malaspina said. 听

What is causing these backward whistlers isn鈥檛 clear. George and Malaspina suspect that they may emerge from a phenomenon called magnetic reconnection鈥攊n which the twisting magnetic field lines that surround Venus come apart then snap back together with explosive results.

For now, the researchers say they need to analyze more whistlers to completely rule out lightning as a cause. They鈥檒l get their next chance in November 2024 when the Parker Solar Probe makes its final pass by Venus, dropping down to less than 250 miles above the surface鈥攂rushing the top of the planet鈥檚 鈥渟oupy鈥� atmosphere, Malaspina said.听

鈥淧arker Solar Probe is a very capable spacecraft. Everywhere it goes, it finds something new.鈥�

Co-authors of the new study include Robin Ramstad at LASP; Stuart Bale and Shannon Curry of the University of California, Berkeley;听Yingjuan Ma of the听University of California, Los Angeles; and Kathrine Goodrich and Dylan Conner of West Virginia University.