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The Europa Clipper finally took off! It'll reach this icy, water-filled moon of Jupiter in 2030. But it won't orbit that moon. Instead, it will fly by Europa 44 times, tracing out these wonderful tracks.
Why not orbit Europa? There's too much radiation that close to Jupiter, and the Clipper can collect data much faster than it can transmit it to Earth. If it orbited Europa it would fry before it could tell us very much!
Thus, the Clipper will spend most of its time farther from Jupiter, transmitting data to Earth. Using gravity assists from 2 other moons, it will occasionally swoop down, zip past Europa, and make more measurements.
In its 3½ year life, the Europa Clipper will get 2.8 megarads of radiation from Jupiter. This is about 280 times the amount that would kill you! Jupiter is pretty, but don't try to live nearby.
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Here is the path the Europa Clipper will take on its journey from Earth to Jupiter. Gravity boosts from Mars and Earth will speed it up enough to reach Jupiter.
The Sun's gravity is powerful, but we've learned how cleverly steal energy from planets to help spacecraft escape its attraction!
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Here is the path the Europa Clipper will take once it reaches Jupiter. The orbit of Europa is shown in aqua - the goal is to swing past that 44 times before the spacecraft dies. But to make the Clipper follow its crazy path, the gravity of Jupiter's moons Callisto and Io will be needed!
Callisto's orbit is shown in yellow, and Io is shown in red.
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@johncarlosbaez BOUNCE Bounce bounce bounce bounce
@johncarlosbaez that looks like an etch-a-sketch on mushrooms
@johncarlosbaez Phoenix's animations are so common we got a question on Space StackExchange on what they're made with. Turns out it's bespoke software they made themselves; wonderful of them to share
EDIT: found it after I got home https://space.stackexchange.com/a/65104/11262
@ChateauErin - interesting! I didn't know about Phoenix.
Btw, your post was "filtered" from my notifications, probably due to the spam problems at mastodon.social. I had to deliberately work to see it.
@johncarlosbaez thanks for letting me know; I'll move instances some day, but I chose unwisely maybe :(
@johncarlosbaez thoroughly blowing my mind on how the spacecraft uses the gravity of other planets to slingshot it's way to Jupiter so it can observe Europa without being fried
@JamesAkers - humans are so cool in some ways... so annoying in other ways.
@johncarlosbaez Thank you for posting this. I was looking just for this type of image yesterday when I heard of the launch.
Spaceflight is just so wild to me. Nothing is stationary and there no straight lines. Also, Jupiter is soooo far away. Wow.
@vegetarianzombie - yeah, it's an amazing journey.
Wikipedia is good for this sort of image.
@johncarlosbaez what are the main mechanisms that make Jupiter radiate so much? I assume all gas giants tend to be like this?
@TTimo @meercat0 @johncarlosbaez Jupiter's magnetosphere has particularly intense radiation belts because of Io.
The volcanoes on the moon eject gas, which gets ionized and forms the Io plasma torus.
Orbiting just outside the torus; Europa is so heavily irradiated that its surface glows in the dark.
Ganymede and Callisto orbit further out and are not so thoroughly cooked.
@michael_w_busch @TTimo @johncarlosbaez Thank you for detailed explanation
@michael_w_busch @TTimo @meercat0 @johncarlosbaez And we’re looking at Europa to see if it is habitable by humans? I must have heard wrong.
@VirginiaHolloway @TTimo @meercat0 @johncarlosbaez Nowhere on Europa is habitable for humans.
The ocean under the ice shell might be habitable for some variety of life.
But Clipper alone cannot answer that. What it will do is tell us things like just how thick the ice is.
(There was a proposal to send a lander with Clipper, but it would not have lasted long on the surface before the radiation fried it.)
@VirginiaHolloway - we are not looking to see if Europa is habitable by humans. We are looking for hints that it could have life of its own, hidden away in oceans under the ice. We're not even sure those oceans exist, but there are a lot of clues that they do!
They might look like this. The ice might be 10 to 15 miles thick (that's 15 to 25 kilometers). This is a cross-section of Europa drawn by an artist:
@TTimo @johncarlosbaez Jupiter has the strongest, largest magnetosphere of all the planets in the whole solar system; it even reaches into the inner system and directly interacts with the solar magnetosphere. This gives Jupiter the monster version of Van-Allen belts. The inner jovian moons pass through these belts. Io is the most extreme, its volcanic eruptions moving so much plasma into space, that it creates a radiation channel between Jupiter and its radiation belts.
@datenwolf @TTimo @johncarlosbaez Peak radiation is even higher a little further in, at Amalthea and Metis.
@60sRefugee @datenwolf @TTimo @meercat0 - For now I'll just quote Wikipedia:
Jupiter's internal magnetic field is generated by electrical currents in the planet's outer core, which is theorized to be composed of liquid metallic hydrogen. Volcanic eruptions on Jupiter's moon Io eject large amounts of sulfur dioxide gas into space, forming a large torus around the planet. Jupiter's magnetic field forces the torus to rotate with the same angular velocity and direction as the planet. The torus in turn loads the magnetic field with plasma, in the process stretching it into a pancake-like structure called a magnetodisk. In effect, Jupiter's magnetosphere is internally driven, shaped primarily by Io's plasma and its own rotation, rather than by the solar wind as at Earth's magnetosphere. Strong currents in the magnetosphere generate permanent aurorae around the planet's poles and intense variable radio emissions, which means that Jupiter can be thought of as a very weak radio pulsar. Jupiter's aurorae have been observed in almost all parts of the electromagnetic spectrum, including infrared, visible, ultraviolet and soft X-rays.
The action of the magnetosphere traps and accelerates particles, producing intense belts of radiation similar to Earth's Van Allen belts, but thousands of times stronger. The interaction of energetic particles with the surfaces of Jupiter's largest moons markedly affects their chemical and physical properties. Those same particles also affect and are affected by the motions of the particles within Jupiter's tenuous planetary ring system. Radiation belts present a significant hazard for spacecraft and potentially to human space travellers.
@johncarlosbaez Why is there that much radiation emanating from Jupiter?
Juice my beloved
@johncarlosbaez “Why not orbit Europa? There's too much radiation that close to Jupiter, and the Clipper can collect data much faster than it can transmit it to Earth. If it orbited Europa it would fry before it could tell us very much!”
Thanks! That’s helpful, and makes sense!
Maybe
@astrodicticum wants to talk about that in an upcoming podcast?
@johncarlosbaez Given the radiation levels, I submit that Elon Musk and his followers should consider moving to Europa instead of Mars. I'm sure those big strong alpha males can handle it.
@Pepperbike @johncarlosbaez
Yeah, gamma radiation should be NO PROBLEM for alpha males like them! 
@Pepperbike @johncarlosbaez Finally, I know what “alpha” refers to. 
@johncarlosbaez But why is Jupiter so radioactive?
@johncarlosbaez What is the... process by which Jupiter emits radiation?
@errant - That's a fun question! I'll just quote Wikipedia:
Jupiter's internal magnetic field is generated by electrical currents in the planet's outer core, which is theorized to be composed of liquid metallic hydrogen. Volcanic eruptions on Jupiter's moon Io eject large amounts of sulfur dioxide gas into space, forming a large torus around the planet. Jupiter's magnetic field forces the torus to rotate with the same angular velocity and direction as the planet. The torus in turn loads the magnetic field with plasma, in the process stretching it into a pancake-like structure called a magnetodisk. In effect, Jupiter's magnetosphere is internally driven, shaped primarily by Io's plasma and its own rotation, rather than by the solar wind as at Earth's magnetosphere. Strong currents in the magnetosphere generate permanent aurorae around the planet's poles and intense variable radio emissions, which means that Jupiter can be thought of as a very weak radio pulsar. Jupiter's aurorae have been observed in almost all parts of the electromagnetic spectrum, including infrared, visible, ultraviolet and soft X-rays.
The action of the magnetosphere traps and accelerates particles, producing intense belts of radiation similar to Earth's Van Allen belts, but thousands of times stronger. The interaction of energetic particles with the surfaces of Jupiter's largest moons markedly affects their chemical and physical properties. Those same particles also affect and are affected by the motions of the particles within Jupiter's tenuous planetary ring system. Radiation belts present a significant hazard for spacecraft and potentially to human space travellers.
@johncarlosbaez that is such a cool solution to this problem
@johncarlosbaez Old man Jupiter wants to be a star but can't quite make it. Close enough to be a bad neighbor, though!
@johncarlosbaez What's the radiation dose around Jupiter like? Is there a simple radial drop off or is it more like a belt region with a safer low and high orbit space?
@Michkov - that's a really fun question! Here are a few pictures with links to more info.
https://eos.org/research-spotlights/two-moons-and-a-magnetosphere
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@Michkov - this looks very different, showing the flow of electric current.
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https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter#Co-rotation_and_radial_currents
@Michkov - This is supposed to show the radiation levels.
I would need to study all this to understand it better!
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@johncarlosbaez Thanks, it looks like crazy complicated problem, but looking at the 3 diagrams, either close in at the equator or far out with a decent inclination seems to be OK at first glance. The primary radiation type is the plasma particles in the current I assume?
@Michkov - yes. I'll quote an article which points out something interesting: the enormous eruptions of Jupiter's volcanic moon Io play a big role!
"Any charged particles in the space around Jupiter will experience the planet’s strong magnetic field and get accelerated to high energies. These negatively charged electrons and positively charged ions of hydrogen (i.e., protons), oxygen, and sulfur form Jupiter’s radiation belts. The source of the protons is some combination of particles escaping from Jupiter’s ionized atmosphere (the ionosphere) and particles leaking in from the solar wind. The dominant particle source, however, is the volcanic moon Io, which dumps a ton per second of sulfur dioxide gas into space where the molecules are broken up and ionized. These processes around the moon drive million-amp currents between Io and Jupiter’s ionosphere, where they excite intense aurorae on the planet. "
https://www.astronomy.com/science/what-is-the-source-of-jupiters-radiation/