Venus Lightning Debate Gets Lit

FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman in for Ira Flatow. Later in the hour, we’ll take you to an art exhibition focusing on HIV and AIDS and hear about a saltwater threat to city water supplies along the lower Mississippi River, including New Orleans. But first, a trip to Venus– the planet is already a dangerous place.

It’s blazing hot. It has bone crushing pressure and sulfuric acid clouds. The longest any spacecraft has survived on the surface is thought to be around two hours. But if you went there, would there also be lightning to worry about? That question has been a topic of electric debate among scientists for some 40 years.

Now, here on Earth, there are signs of lightning beyond just a flash in the sky. The lightning’s effects show up in the radio spectrum at very low frequencies. They’re called whistler waves.

[WHISTLER WAVE SOUND]

No, that’s not a Star Wars sound effect. This is the real sound of whistler waves collected by the Van Allen Probes mission near Earth. Thank you, NASA and the University of Iowa. Missions to Venus have detected whistler waves there, too, and they were thought to be evidence of lightning, maybe a lot of lightning. But now a paper published in the Journal Geophysical Research Letters, based on data from the Parker Solar Probe, argues that the whistler waves on Venus may have a different cause, throwing some cold water, or hot sulfuric acid, on the “Venus has lightning” theory.

Joining me now to talk about that finding is research scientist Dr. Harriet George and space plasma physicist Dr. David Malaspina. They’re both at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. Welcome to the show.

HARRIET GEORGE: Hi, great to be here.

DAVID MALASPINA: Thank you.

FLORA LICHTMAN: Harriet, is this finding sending a jolt through the Venus researcher community?

HARRIET GEORGE: I do think it’s been a little bit of a jolt. It’s, obviously, been debated for quite a long time now. And this is really going against what we really thought these whistle waves were telling us. So it is a bit of a surprise to everyone involved, I think.

FLORA LICHTMAN: Are people in the “lightning on Venus” camp, are they like shook by this?

HARRIET GEORGE: I’d say we’re a bit startled, yes.

FLORA LICHTMAN: So why is this a matter of hot debate? Why do people care about whether there’s lightning on Venus?

HARRIET GEORGE: Well, there’s a few reasons why we care. One of the first really big reasons is that lightning is very dangerous. We don’t want to spend huge amounts of money to send a probe over to Venus just have it get hit by lightning and short out before it gives us the data that we need. So finding out if there’s lightning, how much of it there is on Venus is really important to protecting those space missions that could go over there.

FLORA LICHTMAN: I feel like that’s just one of many, many threats to any spacecraft on Venus.

HARRIET GEORGE: One of many, but it’d be one that it’s nice not to have to deal with. We also really care about lightning from an atmospheric perspective because lightning can only happen if you have really huge number of charged particles build up in the clouds. And knowing whether Venus has those charged particles in the clouds is something that atmospheric scientists really care about. And the wavelength that lightning occurs at can also tell us a lot about the molecules that make up the atmosphere because that wavelength depends on the particles in Venus’s atmosphere. So we can also get a lot of information about what Venus is like from that.

FLORA LICHTMAN: What do you need to create lightning, David? Do we know if– is wind important?

DAVID MALASPINA: Yeah, so to build up some of those collections of charged particles on Earth, the mechanisms that we know about, for example, are regions where there’s a lot of dust. This also happens on Mars. You can get lightning strikes associated with dust storms. You can also get them in regions of high wind, where the clouds move rapidly over the surface or past each other, where they can differentially charge. Now, it’s really unknown whether those conditions exist on Venus, and lightning would be an indicator that they do.

FLORA LICHTMAN: So if it’s there, it tells us things about the planet that we don’t already know, and that’s why people care about it.

DAVID MALASPINA: Or, if it’s not there, that also gives us information about the planet because it tells us that these circumstances that we expect or are familiar with on Earth may not be there on Venus.

FLORA LICHTMAN: Harriet, this might be a stupid question. But is there a way to directly observe lightning on Venus? Could you look for flashes?

HARRIET GEORGE: Not a stupid question at all. People have been looking for those flashes for quite a while. The Japanese Akatsuki Mission has actually got a camera on it that’s specifically designed to look for lightning. So this Akatsuki spacecraft is orbiting around Venus, trying to take photos of lightning flashes that could be happening. And actually, in the first three years of their operation, they didn’t see any lightning flashes, which is another indicator that lightning either isn’t happening or isn’t very common.

FLORA LICHTMAN: Well, what is causing the whistler waves if it’s not lightning, Harriet?

HARRIET GEORGE: We think that it could be an explosive process happening in the magnetic environment around Venus, where magnetic field lines in the space plasma surrounding the planet break apart and then snap back together. When this happens, a process called reconnection, it fires off beams of electrons. And we know from observations on Earth that these electron beams can generate whistler waves. So we think that a similar process could have happened over at Venus and could be responsible for all or some of these whistler waves that have been seen over the decades.

FLORA LICHTMAN: Electron beams, would you see those or feel those on Venus if you were on that planet?

HARRIET GEORGE: If you were standing on the surface, you probably wouldn’t be able to feel these electron beams because you’d be shielded by the very thick atmosphere. But if you’re a floating out in space, then you probably could get pinged by them.

FLORA LICHTMAN: David, this is data from the Parker Solar Probe. What is the Solar Probe doing looking at Venus?

DAVID MALASPINA: Right. So the Parker Solar Probe mission is designed to get as close to the Sun as physically possible to try to scoop up pieces of the outer solar atmosphere so we can understand how the Sun generates what’s known as the solar wind, or the stream of particles that’s continually coming off the Sun and all stars, really. Solar Probe has, during the course of its prime mission, 24 different orbits about the Sun. And those orbits get progressively closer to the Sun. And the way that’s achieved or the orbital dynamics that allow that to happen involve these close encounters with Venus such that we can shed angular momentum and allow the spacecraft to get ever closer to the Sun.

FLORA LICHTMAN: Is there another flyby planned for Venus? Are there more Venus questions that the Solar Probe might help us answer?

DAVID MALASPINA: So there is one more flyby planned of Venus in 2024. And that flyby will take us very close to the planet, something like or approximately 250 miles off the surface.

FLORA LICHTMAN: What will you be looking for?

DAVID MALASPINA: Well, we’ll be looking for lightning, Harriet and I, for sure. Other folks, of course, will be looking for different processes related to some atmospheric chemistry, some related to dust rings near the planet, some related to the electric and magnetic field environment near the planet.

FLORA LICHTMAN: So for you, the jury’s still out about the lightning.

DAVID MALASPINA: Well, I think there’s this 40-year-old mystery. One camp has been saying, hey, we see whistlers every time we go to Venus, and we know on Earth that whistlers are associated with lightning. And then another camp says, well, we haven’t seen any flashes that we can conclusively call lightning.

So where’s the resolution? Because neither of those observations is incorrect, it must be our interpretation. And so one of the things that Solar Probe allowed us to do was provide a new interpretation that allows both observations to be true but points to either a very low level of lightning on Venus or perhaps no lightning on Venus.

FLORA LICHTMAN: Which is the outcome you would prefer, the whole debate keeps going or it’s wrapped up neatly with a bow?

HARRIET GEORGE: It would be very nice to have it wrapped up neatly. But I also think it’s just a fascinating topic. So if the debate keeps going, then I’m allowed to keep on studying it.

DAVID MALASPINA: There are very few things in science that ever get wrapped up neatly with a bow.

FLORA LICHTMAN: That’s true. David, can looking at Venus tell us anything about planets elsewhere in the universe?

DAVID MALASPINA: Well, in our own solar system, we have Venus. And we have Earth. And we have Mars. It’s kind of our three data points for rocky worlds close to a star.

Earth, of course, we have a large and strong magnetic field that holds back the solar wind. And we also have an atmosphere that we can live in, that humans can survive in and we know life can propagate in. At Venus, we have a similar-sized planet, but we have no internal magnetic field. So the solar wind can buffet right up against the planet’s ionosphere, or the outer layers.

And then at Mars, there is no planetary magnetic field, but we know there used to be in the past. And so Mars at one point had an atmosphere that could support liquid water and is now gone. So as we look out toward exoplanets and make observations of other stellar systems– and of course, we’re looking for things like life or at least the ability for a planet’s atmosphere to support life– and we look toward what properties of a planet are required to hold on to an atmosphere, is one of those properties a magnetic field?

And so that’s an exciting question we can answer by comparing Venus and Earth. So as we explore processes like the atmospheric chemistry of Venus and the way the magnetic field can accelerate particles or generate waves like we’re doing with this study, those are important pieces of information that help us along the way answer the bigger question, eventually, of, is a planetary magnetic field necessary to protect a planet’s atmosphere against its star’s stellar wind?

FLORA LICHTMAN: That’s fascinating because I think, in the exoplanet conversation, I feel like we often talk about composition of gases. That’s the headline that I’m always looking for. But it’s interesting to think that there are other ingredients that we should be thinking about for what makes life possible.

DAVID MALASPINA: So composition of gases is the thing we can most directly observe at this point. But those composition of gases, of course, is very likely to be impacted by the star’s stellar wind and by the existence or nonexistence of a planetary magnetic field.

FLORA LICHTMAN: Hmm. So I like watching a good thunderstorm. It may not be happening on Venus. Where else in the solar system can I go?

DAVID MALASPINA: If we walk through the planets from the Sun outward, Mercury, of course, can’t have lightning related to the atmosphere because there’s no atmosphere on Mercury. If we go to Venus, that’s, of course, what we’re trying to address here in this study. And the answer is a solid maybe, leaning toward no or very rarely. At Mars, there’s documented evidence of lightning, especially associated with dust storms, even though the atmosphere is very thin.

On Jupiter, there’s copious evidence of lightning, both related to whistler waves and directly observing flashes. The same is true at Saturn. At Uranus, there are electromagnetic waves consistent with lightning strikes. But I do not believe that any optical flashes have been observed. And then out at Neptune, there’s a similar situation, where some whistler-like waves have been observed but no optical flashes yet. So I would say the jury is still out at Uranus and Neptune.

FLORA LICHTMAN: This is making me think that Earth is kind of cool. I don’t know. There’s something unique happening here. The next time I see lightning, I might– I should appreciate it.

DAVID MALASPINA: Earth is a special place in a lot of ways.

FLORA LICHTMAN: [LAUGHS] We’ve run out of time. I’d like to thank my guests, Dr. Harriet George and Dr. David Malaspina, both at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. Thank you both for talking with me today.

HARRIET GEORGE: Thank you so much for having us here.

DAVID MALASPINA: Thank you.

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