Ep. 599: Zodiacal Light

Pamela has told us in the most flowery terms about the diffuse dust across inner solar system. Leftover from the formation the inner planets. Well, it turns out, she was wrong. Super wrong. Time to update.

Download MP3 | Show Notes | Transcript

Show Notes

Serendipitous Juno Spacecraft Detections Shatter Ideas About Origin of Zodiacal Light (NASA)

South African Astronomical Observatory

Backscatter (Wikipedia)

Zodiacal Light (Swinburne University)

NASA’s Juno spacecraft

Sand and Dust Storms (World Meteorological Organization)

Mars Moons (NASA)

Martian dust storms parch the planet by driving water into space (Science Magazine)

Mars Exploration Rover – Opportunity (NASA)

Opportunity lost: NASA says goodbye to pioneering Mars rover (Nature)

Mars Volcanoes (Smithsonian Air and Space Museum)

Why volcanic ash is such a dangerous hazard to airplanes (Washington Post)

2010 eruption of Iceland’s Eyjafjallajökull (USGS)

Pamela’s Twitter

ABSTRACT: The OSIRIS-REx Touch-and-Go Sample Acquisition Event and Implications for the Nature of the Returned Sample (pdf)

Zodiacal light: All you need to know (EarthSky)


Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast Ep. 599: Zodiacal Light. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of The Universe Today, with me as always, Dr. Pamela Gay, senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey Pam, how are you doing? 

Dr. Pamela:                 I am doing well, I have a new microphone. It is identical to the old microphone. The microphone is dead. Long live the identical microphone.

Fraser:                         Right? This is the new something, same as the old something.   What’s happening? Five ninety-nine, we are one episode away from a completely irrelevant number, 600. 

Dr. Pamela:                 It’s still cool to know we’ve been ticking along here. What’s really starting to get to me is the number of people who are like, “Yeah, I started listening to you when I had my kid and they’re now a teenager.”

Fraser:                         Yeah, now they are a senior citizen, yeah

Dr. Pamela:                 Yeah.

Fraser:                         Yeah, we’ve had a couple of those emails or if someone’s like, “I started listening to you when I was a teenager and I just got my doctorate.”

Dr. Pamela:                 Yes, yes, or people coming up to us at conferences, this happened in Hawaii, “I started listening to you in high school, I’m now a post-doc.”

Fraser:                         Now a post-doc, yep, exactly. No, I don’t feel old, but thank you for bringing that up.

Dr. Pamela:                 But, it is a good excuse to, especially now that we’ve had this year’s AAS meeting and LPSC meeting, to basically say, “These are the things we’re now looking forward to,” so, that’s next week.

Fraser:                         But you know what? I’m just gonna say that, you, I hope seeing us do this 599 times, have some sense that there’s a stability going on that Pamela and I are in this for the long haul, that we’re going to keep bringing you space and Astronomy goodness for, I think as long as we live. You should join our Patrion.

Dr. Pamela:                 Yeah, we’re here until our voices –

Fraser:                         Give out.

Dr. Pamela:                 – breakdown.

Fraser:                         Exactly, and we re-joined the cosmos.

Dr. Pamela:                 Exactly.

Fraser:                         So go to patreon.com/astronomycast and you can just support the work that we do, and help make sure that we can get as much space and astronomy information freely available and educate as many people in the world about what’s going on in the cosmos.

Dr. Pamela:                 So, yeah, it’s awesome, help us do more awesome, thank you, that’s all.

Fraser:                         Thank you. Pamela has told us in the most flowery terms about the diffused dust across the inner solar system, leftover from the formation of the inner planets. Well, it turns out she was wrong, super wrong, time to update. And we’ll get into that at all the levels of Pamela’s wrongness, after this short break. And we’re back. So, Pamela.

Dr. Pamela:                 Yeah.

Fraser:                         Zodiacal Light.

Dr. Pamela:                 Yeah.

Fraser:                         Yeah, you’ve brought it up many times, and it is always about this cool idea that you can go out, take some pictures, you could see this leftover dust, from the formation of the solar system.

Dr. Pamela:                 Well, and also, I said from comets, from asteroids hitting into each other.

Fraser:                         Yeah, nope. All wrong.

Dr. Pamela:                 I was so wrong.

Fraser:                         I love it, I love it. It’s funny, we did this, we cover this topic over on the Weekly Space Hangout, and Moya McTier was the one who brought up the story and she was like, “Yeah, I found this story,” and I’m like, I couldn’t believe how important this is. This was the biggest news of the week, probably the biggest news of the month, in my opinion. And one of the big news stories of the year. And I think as amateur Astronomers, we are all about Zodiacal Light. So, to get that picture, it’s like one of those achievements, you get Aurora, you get Zodiacal Light.

Dr. Pamela:                 Have you succeeded?

Fraser:                         Never, no, I’ve never seen it, I’ve never taken a picture of it, never.

Dr. Pamela:                 Oh man, I’ve gotten to see it a few times. The most striking was, I was in South Africa at the observatory they have North of Cape Town in Sutherland, and a group of us had spent the night just watching the Southern sky rotate above us, and we thought dawn was coming, and it wasn’t the dawn, it was the Zodiacal Light becoming that much brighter as the angle between us, the dust and the sun got smaller and smaller.

And, it was really this striking column shooting up from the sky, and going in the angle tracing towards where all the planets were along the elliptical. It was really awesome.

Fraser:                         Oh, yeah, amazing, okay, all right. So, what is it?

Dr. Pamela:                 Well, observationally from Earth, it is the glow of backscattered light from the sun. So, when we look out in space, there’s this toroid of dust particles, a doughnut of dust particles, around the sun, and the sunlight going out past the earth, hits these dust particles and scatters back toward us.

Fraser:                         So, it’s like light pollution, so, like light pollution in the inner solar system.

Dr. Pamela:                 But it’s so faint, that a bright Jupiter can dry any of it out, and any amount of light pollution from cars, humans, streetlights, the moon, you can’t see it. So, you really do need to go to a dark sky park, an observatory of some kind, where you know there are actually dark skies and check the calendar to make sure there’s no moon first.

Fraser:                         All right, and then just to really rub this in one last time, what did you used to say a Zodiacal Light was?

Dr. Pamela:                 I used to say it was leftover dust, scattered from comets, tales from asteroids, colliding together, and other events that messed up our solar system.

Fraser:                         Right.

Dr. Pamela:                 I was wrong.

Fraser:                         And so, what do we now know is Zodiacal Light this week?

Dr. Pamela:                 This week?

Fraser:                         Yeah.

Dr. Pamela:                 And these are results that come from the Juno mission. The Juno spacecraft flew through the vicinity of the asteroids, flew through the vicinity of Mars, travelled on its way out towards Jupiter. And along the way, they were studying Zodiacal Light, dust particles in the most amazing way.

Fraser:                         Yeah, the way you would study bugs, as they smashed against your windshield.

Dr. Pamela:                 A little worse than that.

Fraser:                         Bugs made of metal.

Dr. Pamela:                 Yeah, they realized that the orbit of the dust particles that make up the Zodiacal Light, matches the orbit of Mars, and Mars or its moons or possibly its dust storms are somehow to blame, for the Zodiacal Light we see. 

Fraser:                         And so, this is the payoff, this idea that in fact, all of this Zodiacal Light, this dust that you see, just after sunset, just before sunrise is just Mars, dirt from Mars, filling this entire donut space. Now you mentioned a few possible sources of where this dust could be coming from, and we will get to that in one second, but first let’s have another break.

And we’re back. All right. So, let’s talk about what are the possible sources of this, because now if this sort of, and in fact it – yeah, we’ll talk about the possible sources and then we’ll think about the consequences of this, but you mentioned some briefly, let’s go through them one by one. It comes from the moons of Mars?

Dr. Pamela:                 Well, so let’s back up one step further to what we know.

Fraser:                         Okay.

Dr. Pamela:                 What we know is dust particles that – think sand storm dust, dust storm over Beijing, dust storm over the Sahara, dust storm over Tucson, dust, flying through the universe, specifically our solar system, at thousands and thousands of miles per hour, hit the giant solar panels on the Juno mission.

Some of the largest solar panels out there, and chipped off pieces of the solar panels and those chipped off pieces, based on their size and their velocity, allowed scientists to determine the velocity mass energy combination of that dust. So, basically it’s like throwing small rocks.

Fraser:                         Yeah, flying through sandpaper. 

Dr. Pamela:                 Yeah, and then figuring out what hit you based on the chip that gets knocked off and where it lands.

Fraser:                         Right.  And so, was the damage to Juno more than scientists were expecting that it would face, going through this region of the solar system?

Dr. Pamela:                 It wasn’t significantly different, but it was different. We weren’t expecting to have things that had this kind of an orbit, and the pieces of dust were on average, a bit bigger than expected, but to be clear, Juno solar panels are fine.

Fraser:                         Right, right.

Dr. Pamela:                 They are huge, this was minimal damage. This was damaged in the name of science, I’m pretty sure everyone’s good with this. 

Fraser:                         Right, okay, okay. And so, now astronomers, based on these trajectories, based on the size, based on other factors, they were able to determine that this was material that had come from Mars?

Dr. Pamela:                 Comes from Mars, and this is because it has the same orbital characteristics, the same tilt relative to all the other planets. And the same eccentricity, even. So, it’s the same amount of not a circle as Mars orbits.

 Fraser:                        Same, amount of not a circle, that’s a great way of describing eccentricity. But yeah, it follows the same elliptical orbit around the sun as Mars does. And I think that angle is really important that each of the planets have, they largely follow the plane of the ecliptic, but each one is a little off, a little tilted away.

Dr. Pamela:                 Yeah, it’s a badly nested group of hula hoops.

Fraser:                         Right, the elliptical hula hoops.

Dr. Pamela:                 Yes.

Fraser:                         Bad loops that are badly nested.

Dr Pamela Gay:          Yes.

Fraser:                         So, all right, so now we’ve got this fairly convincing case that the dust does come from Mars, and then back to my original question, you mentioned three possibilities, let’s go through these one by one. So, what would it mean if this dust came from the moons of Mars?

Dr. Pamela:                 Well, if it came from the moon of Mars, this is actually not too bad of a thing to try and understand. Because these are little tiny moons, they don’t have a lot of gravity. If you hit them fairly hard, chunks are gonna fly off. And in fact, there are theories that describe the formation of the moons as being a cyclical process, where different objects over time have been torn apart and come back together.

So, this is actually reasonable, more information specifically about the composition of the moons, the composition of the dust is needed, Juno didn’t have the capabilities to do something like that.

Fraser:                         Wow.

Dr. Pamela:                 But, it’s completely reasonable that stuff would come from the moons, but it’s a lot of stuff, and they’re little tiny moons.

Fraser:                         Right.

Dr. Pamela:                 So, yeah. 

Fraser:                         That will be tricky, okay, so that’s the first possibility, is that you’ve got this stuff coming from the moons and so you can just imagine, they’re getting impacted, debris is flying off of the moons, making its way into space, but it seems like a surprising amount of dust.

Dr. Pamela:                 Yeah.

Fraser:                         Enough to give amateur astronomers something to chase after. It seems quite impressive. So, the next idea you mentioned was maybe Mars itself.

Dr. Pamela:                 Yeah, and so here, the science teams have actually mentioned the possibility that even though they can’t explain how it would happen, that the dust storms that periodically completely enshroud Mars, these are the same dust storms that are responsible for the death of the Opportunity rover, little Oppy when it’s – it was no longer able to get enough sunlight to keep itself warm, and talking with earth, these world in shrouding dust storms, we know they kick dust up into the upper most levels of Mars atmosphere.

But then the question becomes, when you have a world like this, is it possible that some of that dust is somehow put on escape trajectories? And they can’t really explain that, but what they’re seeing seems consistent with that particular type of dust just filling our solar system.

Fraser:                         And I think this is really impressive when you think about, as you said that these dust storms, these giant dramatic dust storms, that every few years will fill the entire planet, and it doesn’t seem unreasonable, and yet the atmosphere only goes so high, it’s not that thick and to hit escape velocity from Mars, has lower gravity seems impressive. 

Dr. Pamela:                 But this is a lot of material that had to hit escape velocities, admittedly, over the five, some odd billion years for our solar system.

Fraser:                         But that would also mean, I mean, we know that back in the day, Mars was a water world that like the earth had water on it, it had cooler temperatures, it didn’t have just these constant blowing dust storms. And yet over time, the planet died, the dust storms kicked up, and so, this Zodiacal Light is not a mark of the creation of the solar system, it’s a memory of the death of Mars. An ongoing reminder that Mars is a dead world.

Dr. Pamela:                 And it could be an ongoing reminder, that it’s a world that’s gotten knocked about pretty violently over the eons, and we know that whatever it was that hit the earth and killed the dinosaurs, creating the Chicxulub crater. The shockwaves from that sent, dirt, rubble, and very dead dinosaurs that escape velocities out of our atmosphere.

Fraser:                         Yeah, and I mean, we have some situations that are somewhat similar, like when you think about, say, the rings of Saturn, although the source of most of the rings of Saturn aren’t known, we know that the E-ring, has material that has been blasted out by the, ice volcanoes on Enceladus, and have gone into orbit around Saturn, and so you’ve got this source of dust, that is being sprayed into a ring and so there’s a similar version of that.

All right, well, we’ll continue to search for a possible source of this dust in a second, but first let’s have another break. And we’re back. So, those both seem to have problems, and what was the third idea?

Dr. Pamela:                 I don’t remember actually stating –

Fraser:                         Oh, did you not?

Dr. Pamela:                 – a third.

Fraser:                         Okay.

Dr. Pamela:                 No.

Fraser:                         Yeah, I thought it was just Mars getting smashed by asteroids in the past and that being turned into –

Dr. Pamela:                 So, that is a true thing, but we incorporated in there.

Fraser:                         – Okay, all right.

Dr. Pamela:                 But so, here’s the thing, this is a data release of, we saw this dust, we cannot fully explain the dust yet. We realized from the orbit of the dust, that it seems to originate from Mars and another factor that’s consistent with this, is there was a sharp cut off in the distribution of the dust as the spacecraft got closer to Jupiter, to that region of space where Jupiter’s gravitational influence would have said, “I don’t want any of this dust to dust to other places.”

So, the distribution dynamically, is consistent with Mars, Mars, Mars. And this allows us still at this point, without knowing the chemistry of it, to dream big. And so, reading this, I was like, “I wonder if it could have come at all from past volcanism,” and there’s these giant volcanoes.

Fraser:                         That is an awesome idea.

Dr. Pamela:                 Yeah, and they did not say that. This is me as a scientist, looking at what are all the possibilities, desperately wanting chemistry.  

Fraser:                         Well, desperately wanting super volcanoes. 

Dr. Pamela:                 Well, there’s that too.

Fraser:                         Yeah.

Dr. Pamela:                 It’s a known phenomenon people.

Fraser:                         Right.

Dr. Pamela:                 I like volcanoes.

Fraser:                         But I wonder if you had an Olympus Mons erupting, would it be throwing lava into solar orbit?

Dr. Pamela:                 Well, it wouldn’t be throwing lava, but it could be throwing –

Fraser:                         Dust.

Dr. Pamela:                 – ash.

Fraser:                         Right. Wow.

Dr. Pamela:                 And these are the things I still need to figure out. And volcanic glass, as was experienced by a few too many aircraft, when the unpronounceable Iceland volcano, went off in 2010, it is nasty shreddy stuff. And this is to the point where I wanted to bring these scientists on for an interview, and basically go, “Okay, how about – tell me, I wanna know. “

Fraser:                         How about this? How about that? How about this?

Dr. Pamela:                 Right. Because, on our world Etna is able to fountain lava a kilometre up into the air. We saw the Icelandic volcanoes able to shoot things six kilometres up into the air. And we have so much more gravity. So, what is possible?

Fraser:                         On that note, if you want, adorable volcano pictures, you should follow Pamela’s Twitter feed, she put, it was like Etna yesterday, I think.

Dr. Pamela:                 Yeah.

Fraser:                         Yeah, yeah, you’re quite the volcano fan.

Dr. Pamela:                 I stan for my volcanoes.

Fraser:                         So, I love this in so many ways, that you have this thing that you thought you knew where it came from, and now new evidence pops in that goes, “Nope, here’s the source.” And now the question is, what’s the mechanism? And now we’re back to hypotheses again.

Pamela Gay:               Yes.

Fraser:                         And there’s a few that the science-y, but again, they discover is that it’s not really their problem. “Hey, we found this thing, it came from Mars, next.” And now the scientific community goes at it, and they propose hypotheses. And you just proposed one, maybe it was volcanoes, maybe it was asteroid impacts, maybe it comes from whatever event created the Martian moons, maybe it’s further evidence of it, maybe it’s the – maybe it’s those dust storms.

Dr. Pamela:                 Maybe it’s those dust storms do cause craziness.

Fraser:                         Yeah, and so, now the question is trying to gather evidence, for each one of these possible hypotheses, trying to figure out ways that you can falsify them. This is just a beautiful example of science in action, this is how it works

Dr. Pamela:                 Well, and it also raises the question of, where did all the dust from all the colliding asteroids go? Because we know those suckers collide, because the asteroid Benu is essentially the consistency of a ball pit in orbit. It’s not a rubble pile in space. Unless the rubble is made of styrofoam, in terms of what the spacecraft experienced. The gravity is so low. I don’t know if you saw this, but Donte Loretta was saying, that the Cyrus Rex spacecraft would’ve gone meters in to the surface of Benu had they not been firing rockets with thrusters rather.

Fraser:                         Right. It just would’ve gone plunging into it, splashing into the rock of Bennu. That’s amazing.

Dr. Pamela:                 And so, the gravitational pull that Bennu exerts on all of its own rocks is like what earth exerts on ball pit balls.

Fraser:                         Yeah.

Dr. Pamela:                 Yeah, so, there’s a lot of stuff out there. And so, now we need to know where did it go? Maybe as Zodiacal dust will turn out to be a mixture of different things. There’s so many questions, so many questions.

Fraser:                         And so, before we go, you have seen it, you have taken pictures of it. If people want to get photographs, cause it’s still beautiful even though we have a new answer for it, if you want to capture an image of Zodiacal Light, as an amateur astronomer, astrophotographer, how should you go about it? 

Dr. Pamela:                 Well, right now is actually a really good time. The best times of year to see it are around the equinoxes. The same is true of Aurora. So, go out, I believe right now it’s evening, twilight is the best. Do double check me on that, and go out, look up in the Twilight. And the reason I’m saying double check is, I don’t remember which of the two hemispheres, it’s evening Twilight is best for.

And what you’re waiting for is that moment before the sun’s light starts to eliminate the sky. When the sunlight reflected off the dust creates a streak along the path that is filled with planets, the elliptic across the sky.

Fraser:                         Fantastic. Yeah, if you haven’t seen it, you should go out and try.


Fraser:                         You need dark skies. Yeah, and do you have some names for us this week?

Dr. Pamela:                 I do. So, as always, our show is brought to you, thanks to you. Your support allows us to pay our server costs, to pay Allie and Rich to edit our shows together, to pay Nancy, to make sure that we don’t get lost along the way, to have Beth doing all the social media work for us. It takes a team to do everything Fraser and I do, and to keep him and I on the straight and narrow and we do require herding.

Fraser:                         Hey, you noticed that our shows get start roughly on time every week? Yeah.

Dr. Pamela:                 We are now herded, which is excellent. So, this week I would like to thank the generous contributions of Matthew Horstman, Arthur Latz-Hall, Omar Del Rivero, Tim Gerrish, John, Paul L Hayden, Marco Iarossi, J. AlexAnderson, William Lauer, Jeremy Kerwin, Dustin A. Ruoff, Michelle Culle, Brian Kilby, Brent Kreinop, Marc Steven Rasnake, Roland Warmerdam, The Lonely Sand Person, Steven Coffey, Ronald McCoy, Aron Tannenbaum, Ruben McCarthy, Geoff MacDonald, Wayne Johnson, Iggy Hammick, Jordan Young and Catherine McCabe.Thank you so much, all of you, for everything you do to support us month after month.

Fraser:                         Thanks everyone.

Dr. Pamela:                 Bye-bye everyone.

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