Everyone has seen awe-inspiring pictures of Saturn鈥檚 rings.聽Less聽well聽known聽is that Jupiter has rings聽too,聽so faint they are聽normally all but invisible.聽The rings of Jupiter are just one of the聽little-known subjects that Heidi Becker has聽photographed聽over the past decade or so. She is a聽co-lead investigator聽on聽NASA鈥檚 Juno聽mission, which arrived at聽our solar system鈥檚 largest planet聽in 2016 and has been studying it in detail ever since.
Many of the most eye-catching聽images of聽Jupiter have been聽taken by the craft鈥檚 main camera,聽JunoCam. But聽that isn鈥檛 what Becker works with.聽She uses a special low-light聽detector聽that was never intended to take proper images聽for people to聽view.
Nonetheless, she聽has discovered she can use it to聽image dark and shadowy areas of the planet and its moons and to reveal things no other instrument can.聽That goes far beyond those聽feathery聽rings聽鈥撀爐o the dark sides of聽the planet鈥檚聽moons, mysterious聽craters聽and聽new kinds of lightning.聽New 女生小视频聽caught up with聽Becker to hear about the best pictures she聽has聽taken,聽and what we聽have learned from them.
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Joshua Howgego:聽When you were younger, you worked聽on the stage. How聽did you聽end up studying Jupiter?聽That鈥檚聽quite a transition.
Heidi Becker: Growing up, I was a dancer, and I also did a lot of experimental theatre in New York. But when I was in my early 20s, I had an injury to my knees, which made dancing not possible for me any more. But I was always fascinated by light and the stars. I was looking through a telescope聽on a聽visitor night at an amateur astronomy club in Connecticut, and the astronomer guiding us showed us the Orion Nebula. He described聽the nebula,聽the magnetic field lines, the gas that was collapsing,聽how it was聽a nursery for stars聽鈥撀爄t was so beautiful.聽It聽was聽the moment when聽I knew I wanted to go into that field.
You eventually wound up at NASA.
I decided to get a degree in physics and go on to optical sciences聽鈥� I was interested in cameras聽and light.聽Then,聽towards the end of聽my degree,聽I needed聽some聽extra money聽and got聽a聽part-time job at聽NASA鈥檚聽Jet聽Propulsion Laboratory,聽which ended up becoming a full-time job working on the effects of space radiation on electronics.聽One of my colleagues was an expert on star tracking and was聽involved in the proposal for Juno.
What is a star聽tracker聽and why are they聽so important?
The idea is that you keep track of the positions of the stars so that聽you know where you are聽in space. If you聽don鈥檛聽know that, you聽don鈥檛聽know where your data were collected.聽It鈥檚聽crucial to the science and聽for聽navigation.
The biggest challenge for Juno鈥檚 mission success at the time was: how do you have a star tracker on a spacecraft that is going to be constantly spinning 鈥� and that works in the harsh radiation environment around Jupiter?
A聽tiger team聽formed:聽a small group of experts aggressively trying to聽solve this problem.聽I joined this team, and聽we聽had聽only聽a few months to do a lot of unprecedented radiation testing on sensors that would go into our聽star聽tracker聽before Juno was approved. Most missions experience solar proton events and galactic cosmic rays, but聽not聽electrons travelling at聽relativistic聽speeds, which is what you get near Jupiter.聽So,聽there was no body of information about how a sensor from a camera would behave聽or聽degrade.聽We found a lot of odd places to simulate聽the environment.聽One was聽a cancer hospital聽in Paris聽鈥撀爐hey let us in at midnight to use their medical equipment to irradiate our sensor.
How did this go from being an instrument used for navigation to a聽science聽camera?
Juno鈥檚 star tracker is called a聽Stellar Reference Unit,聽or SRU. Its function is to take pictures of the dark sky and聽find聽known stars.聽Then the spacecraft figures聽out聽where it is pointing.
However, Juno flies where no one has flown before, and so [Juno principal investigator] 厂肠辞迟迟听叠辞濒迟辞苍聽asked me if there was any data聽we鈥檇聽be getting that we could use to understand the聽radiation聽environment. I聽was complaining one day to聽a colleague about how limited the information was that we could get from the SRU.聽They said,聽鈥淲ell, why don鈥檛 you just take a picture?鈥澛燗nd so,聽we reached an agreement that we would take about 20 pictures per orbit聽of Jupiter聽and聽transmit聽them to Earth 鈥� something we聽don鈥檛聽do with the SRU鈥檚 usual star images. These聽would just be images聽filled with the signatures of the聽surrounding radiation; it just looks like聽the snowy static you聽can聽get on a TV. What that shows us is the聽energy聽and concentration聽of聽high-energy聽penetrating particles聽around the spacecraft.
So,聽at that stage聽the pictures聽weren鈥檛聽exactly going to be much to look at鈥�
Before Juno arrived at Jupiter, there was a lot of talk on the team about Jupiter鈥檚 ring system. It wasn鈥檛聽clear how well the other cameras would be able to see it.聽The main camera,聽JunoCam,聽is designed for bright light, to聽take beautiful pictures of the cloud tops in sunlight.聽That made me wonder if we could do it with the SRU. And that started this cascade of聽searching for聽different types聽of opportunities within the system that were low light, because聽that first ring聽image聽was so successful.
What did we聽know聽about the聽rings聽before you photographed them?
It was known that there is this ring system. There are different parts to it, and it was thought that the rings are fed by dust coming from meteoroid impacts on its four inner moons that orbit at the same radius as the rings: Amalthea, Thebe, Metis and Adrastea. However, there were very limited observations of the rings, because many previous missions have approached it equatorially, or from the side, making it hard to see.
Those聽previous聽observations also raised this laundry list of mysteries about the rings. The New Horizons spacecraft聽observed聽bright clumps of material following Adrastea,聽and聽it鈥檚聽not known if those are other small moons, or whether something hit Adrastea, and for聽a brief moment聽in time, there were little pieces trailing it. Other observations show that the rings聽were聽brighter at certain longitudes, and聽it鈥檚聽not clear why.
I can see how they would be awkward to photograph. How did you manage it聽and what did you see?
Because聽we鈥檙e聽flying so close to Jupiter,聽we had聽the opportunity to look straight down on the rings聽and聽see the distribution of the dust.聽When you let Jupiter鈥檚 shadow get cast across part of the image, you see that sharp boundary between dust and darkness. So,聽if聽you鈥檙e聽trying to find a very dim signal from very diffuse,聽faint聽dust, it becomes a little easier,聽because you get that contrast.聽That鈥檚聽a trick聽we鈥檝e聽been using a lot. We took the first聽ring image聽in 2016,聽and聽we鈥檝e聽done as many as we can since then.
Why is it important to study rings?
罢丑别测鈥檙别听濒颈办别 mini laboratories for planetary formation or even solar system formation. You start with a great big ball of gas that accretes and turns into a star or a planet. Knowing how the dynamics of that work in the rings around planets like Jupiter gives聽us a framework for understanding how that works聽on larger scales.聽We鈥檙e聽finding that Jupiter鈥檚 rings are a聽part聽of a聽highly interconnected system. It involves those inner moons, the inner radiation belts of Jupiter, which are very strange and very non-uniform, the magnetic fields. All of this is very mysterious,聽and聽there may be other聽influences聽from Jupiter itself.
You have taken so many other great pictures.聽Tell聽me about Ganymede.
Our closest approaches聽to聽three of聽Jupiter鈥檚 moons 鈥撀燝anymede, Europa and then Io聽鈥撀爓ere on the night side.聽Jupiter was our light bulb,聽and the geometry was such that聽it聽shone聽on just聽a particular region聽of the surface聽of Ganymede.聽We were flying past extremely quickly, tens of kilometres per second, which meant that for each of those moons, the SRU could take only one picture.聽We had to get it right.聽But it worked. The SRU took Juno鈥檚聽highest-resolution image of Ganymede,聽and the special lighting conditions revealed an incredible amount of previously unseen features. This聽has allowed聽us to massively improve the geologic map of that region of Ganymede.
One of the things聽we聽identified聽is聽an intriguing聽spray of聽ejected material.聽Ganymede聽has聽a very large聽crater called聽Tros.聽But聽many kilometres away聽from the聽crater is this聽streak of聽ejecta that we saw聽in the shape of a ray.聽It聽sort of looks聽as though it could have come from聽Tros聽crater, but the weird thing is that there is this聽very old, dark terrain in between.聽So,聽did it come from there? Or is it a comet? Or what?
That sounds like a real mystery.聽If it聽was聽an impact crater, wouldn鈥檛 you expect it聽to聽spread out in聽a sort of a聽circle?
In a star pattern, yeah. It鈥檚 very strange. We鈥檝e brought it to the attention of the JUICE team [another mission due to study Jupiter]聽because I think once聽they鈥檙e聽there and doing this amazing survey聽of Ganymede,聽it鈥檇聽be interesting if they can figure out what it is.
You also made an amazing discovery about a new type of lightning鈥�
Well, at聽a聽certain point in our mission,聽we started approaching Jupiter from the night side.聽The聽very first picture that we took聽was聽a really exciting聽moment. At that point in the聽mission, the closest approach to Jupiter was always at 2 or 3聽in the morning, California time. So,聽I would wake up instinctively and聽look at my computer聽鈥撀爏ort of like聽a mother with a baby that needs to be fed in the middle of the night. And the picture came down, and we could see the cloud tops at high resolution on the night side.聽The reason for that was because they were illuminated by moonlight from Io. And there were聽little flashes of light in the image that were lightning in the cloud tops.
Were聽you聽the first to see that image in the middle of the night?
Absolutely. When聽you鈥檙e聽the first person seeing some part of nature for the first time聽鈥� in this case聽before others wake up聽鈥撀爄t鈥檚聽an incredibly intimate and聽awe-inspiring moment.聽It鈥檚聽one of the things about what I do that is rarefied and precious.聽I think I聽put my hands on the screen and said聽鈥淥h, my God鈥�,聽because it was such high-resolution imagery.
What was new about this lightning?
Lightning has been seen by every mission that orbited or flew past Jupiter on its night side.聽We know that the larger聽the聽flashes we saw on the cloud tops,聽the deeper it originated in the atmosphere.聽Ever since聽the聽Voyager聽mission聽[in 1979],聽we鈥檝e seen lightning coming from a particular depth in the atmosphere, where the conditions allow water to exist in a liquid,聽solid and gaseous state, which is the condition that on Earth is necessary for most lightning and thunderclouds.聽So,聽scientists聽were聽content with the fact that lightning on Jupiter was very聽Earth-like.
When I analysed聽the lightning I saw,聽I found it聽was聽coming聽from above the water cloud,聽where it聽is too cold for liquid water to exist.聽I remember one scientist,聽who is a real expert on Jupiter鈥檚 lightning,聽saying to me: 鈥淭his is a problem.鈥澛燘ut really, it was a discovery.聽It was a different kind of lightning that聽doesn鈥檛聽occur on Earth.
Right at the time that this discovery was made,聽we聽were finding that Jupiter鈥檚 atmosphere聽wasn鈥檛聽as well-mixed as we had always thought聽鈥� there were these pockets of聽missing聽ammonia 鈥撀燼nd聽Juno鈥檚 atmospheric scientists were聽developing ideas to explain why.聽The theory was that, at聽a certain聽high region in the atmosphere, you have high-energy storms that聽are聽throwing up water ice crystals and interacting with the ammonia gas聽at a specific altitude,聽which can聽act聽like an antifreeze聽and create聽liquid ammonia-water聽droplets. These droplets聽get tumbled around in thunderstorms, forming an icy crust,聽and would eventually form into hailstones. These hailstones could grow and聽fall deep into Jupiter鈥檚 atmosphere,聽taking the聽ammonia聽with them聽and creating the missing pockets of ammonia scientists previously measured.聽So,聽when I saw lightning coming from聽exactly the region where this was predicted to happen, it was聽evidence聽that these high-altitude storms may聽actually exist.
What are you excited about snapping in your next photograph?
We鈥檙e聽doing a lot of imaging of Jupiter鈥檚聽aurora聽on the night side of the planet.聽We鈥檙e聽interested in the vertical structure of the aurora, and what is happening at different depths in the atmosphere. And there聽has been a lot of imaging of the aurora at infrared and ultraviolet wavelengths, but聽some of the chemistry聽cannot be seen at those wavelengths.聽Visible cameras can see them, though, so聽we聽have this unique, close vantage point,聽and聽we鈥檙e聽in the middle of a campaign聽of investigating this.
If you could take a picture of anything in the Jupiter system,聽what would you go for?
When we did the Jupiter shine trick with Europa, we found a region that聽we nicknamed the聽platypus [above],聽which聽looks like the ice shell has been disrupted and where there could be聽liquid water聽very close聽to the surface.聽There鈥檚聽a theory that proposes that if you have聽liquid water聽close to the surface,聽it can cause聽the ice shell above it to collapse聽and create a sinkhole.聽As聽it鈥檚聽in the process of refreezing, you might have big ice blocks that shoot up from the water. Our photograph makes聽it look a lot like that is going on there.聽So,聽if I could聽do anything, I would聽probably fly聽back there, even closer, and see if we could prove that聽鈥� I think that would be聽very cool.
