Juno Flies By Jupiter

LULU GARCIA-NAVARRO, HOST:

It's time for another entry to Lulu's Log, stardate April 7, 2019, where we explore matters of space, the stars and the universe.

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GARCIA-NAVARRO: And explore is the right word today as the spacecraft Juno makes another flyby of Jupiter. Juno launched in 2011, took five years to get to Jupiter and has been orbiting that planet since 2016, making occasional flybys like the one this weekend. Steven Levin is a Juno project scientist with the Jet Propulsion Laboratory. And we're catching up with him at a conference in Vienna, Austria.

Good morning.

STEVEN LEVIN: Good morning.

GARCIA-NAVARRO: What are you looking for this time in this flyby?

LEVIN: So this particular flyby is actually an unusual one. We're turning sideways. So as we come down the planet from north to south, the spacecraft is rotating so that all the instruments look east to west.

GARCIA-NAVARRO: And why is that important?

LEVIN: So that's important because, in particular for the microwave radiometer instrument, by looking across, we'll get a three-dimensional picture so we get a very different view of Jupiter's atmosphere. It's a little tricky because our solar rays are not pointed at the sun for a couple of hours while we do that, so that's why we don't do this all the time. But it'll give us a completely different perspective of Jupiter for that instrument.

GARCIA-NAVARRO: And what are you hoping to find? Or do you know?

LEVIN: We're trying to understand Jupiter's atmosphere. We're interested in what it's made out of - how much water there is, how much ammonia there is, what the structure is. And so far, what we've found has been quite a puzzle. It's asymmetric. It's got a feature at the equator that looks different from everything off the equator. We see weather variations.

So now when we look sideways, we'll learn about some of those weather variations. We'll learn about how things might be varying with longitude instead of latitude. We thought Jupiter would be cylindrically symmetric. But Jupiter has surprised us in a lot of ways, and that could be one of them. And then we'll also get - I hope - a really nice 3D map of a strip of Jupiter.

GARCIA-NAVARRO: Why is Jupiter so mysterious? And why has it been so difficult to sort of understand what it is like there?

LEVIN: Well, to start with, before the spacecraft got there, Jupiter's a mystery because all we're seeing from Earth is the tops of the clouds. It's this giant planet. We've been studying it for centuries, but you can't see the interior. So when we got there with the spacecraft, we were all prepared to do a lot of measurements to learn about the interior of Jupiter. And basically, every way in which we looked at it threw us a curveball, showed us a surprise.

So we used gravity science. We measured how fast the spacecraft falls to learn about the interior. And we find that the dense core that we expected to find in the center of Jupiter is there, but it's not quite so small. It's larger, and there may be a second one. And we find that the belts and zones that we see go a few thousand kilometers deep. So Jupiter has been a surprise. And basically, we're re-learning the lesson that scientists learn all the time, which is every time you look at something in a new way, you find a surprise.

GARCIA-NAVARRO: And why is that important other than just curiosity? I mean, what can Jupiter tell us about Earth?

LEVIN: Jupiter can tell us about the formation of the solar system. You have to remember when you're thinking about this that Jupiter is not just the largest planet in the solar system. It's more than twice the mass of all the others combined, and it formed first. So if you want to understand, how did the planets form? - well, in some sense, they formed as the leftovers from Jupiter. So you really need to understand how Jupiter formed.

But to understand how it's formed, you need to know what it's made out of, in particular, water is really important because it probably formed from icy planetesimals. And you want to know, did they form really cold or closer to the sun than Jupiter is now or further out? But you want to know about the heavy metals as well - the heavier elements that sunk to the center of Jupiter and make its core. So by trying to understand how this one giant planet formed, we can learn a lot about how the whole solar system formed and, of course, about how the Earth formed and where we came from.

GARCIA-NAVARRO: That's Steven Levin, a project scientist with the Juno mission. Thank you so much.

LEVIN: Oh, my pleasure.

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