Building a base on Europa has always seemed unrealistic due to the intense radiation that is believed to exist there. But that is not the case, says John Leif Jørgensen from DTU in Denmark, one of the co-investigators on NASAs Juno mission. DTU has provided NASA with the instruments that measure the radiation around the Jovian system and recent data from Junos close flyby of Europa shows that - when you get close enough - there is as little radiation at Europa as there is on the surface of the Earth.

I am the host of a Danish radio show about spaceflight and I learned this today when I interviewed professor John Leif Jørgensen on my show. I tweeted about the interview and people asked if I could transcribe and translate the part of the interview about the new data that suggest that the radiation levels close to Europa are benign.

So that is what I have done. At the end of this post you will find a link to the show and a link the Twitter thread I also made abut this.

Enjoy:

The host starts by asking what it is John Leif Jørgensen and the team found out about Europa. John Leif Jørgensen starts out by talking about how we can see intense radiation around Europa with space based telescopes and how Europa is the most likely candidate for life elsewhere in the solar system. He then talks about last weekends flyby of Europa.

15:02

As we fly past [Europa] we can hear it crackle and boom with radiation, it is only barely we can hold on with our instruments and measure how powerful the radiation is because there is so much of it. When we then get closer to the moon, then suddenly the radiation starts to die out. It gets weaker and weaker and at closest approach there is nothing left. As in, at the surface of the Earth, absolutely nothing. And as we came out the other side it rose again. That was a surprise, it was not what we had expected. Everybody expected it would howl and boom as we came close and therefore nobody has ever planned to make a lander on this moon, despite it is the only one where we can look for life. The moon is covered by a thin layer of ice, it is minus 200 degrees [Celsius] out there, so the surface is frozen, but within it is melted and it has an ocean. It is in there could be found life if it exists. So our surprise was of course enormous but what is even more surprising is what we can gain from this. It means that we can in fact build a base, a moon base on Europa. So all those movies you’ve seen with nasty radiation on the surface of Europa is actually a lie.

The host then comes with some facts about the fly by and then asks if he has understood correctly that the breakthrough in the discovery is that it opens new possibilities for missions to Europas surface.

16:58

Yes, there is in fact a place- a series of natural phenomena that work together to- you can in fact land on the surface, there’s no radiation - it is like here on Earth. That means it completely changes the picture we had. We’ve made many analysis with NASA about landing on this moon but we could see that our spacecraft would be grilled by the intense radiation within the first two to three months and it takes a lot longer to drill through the ice. But with this discovery it changes the picture completely. It means we can land on this icy moon and be there without harm. That is the big surprise. The place where Galileo [the space probe] flew past it didn’t enter the same radiation belt as we did, it was quick to move through. So they didn’t measure this. It is the first time we realize this is how it is.

The host interrupts and says that is weird how you, with space based telescopes can see the radiation around Europa from afar and then when you get close enough, there is no radiation whatsoever. He then asks what the explanation for that could be.

18:10

It is actually quite simple. You only need some high school level physics and maybe some theory of relativity, then it is quite obvious. Everybody, when we presented this to each other – we have science meeting every time we fly past Jupiter – everybody sat and said ‘my god have we been stupid, why haven’t we realized this before?’. [*laughs*] But that’s how it is with mother nature. The thing is that the moon itself is capable of stopping the radiation such that it protects itself. It’s actually quite funny. But now we have learned that.

The hosts reads aloud a message that a listener has sent in via SMS. The listener asks if Europa has a magnetic field and the host asks if that could be the explanation.

19:00

That was actually one of the purposes for us to fly so close, it was to determine of there was just a little bit of a magnetic field, because, we had some time ago flown past the other moon further away, Ganymede, which is the biggest moon of the solar system. It has, in fact, a rather powerful magnetic field itself. It is at least comparable to Jupiter’s magnetic field at that place where the moon is. But here [at Europa] it [the magnetic field] was completely passive, there is definitely not any magnetic field that we can see. However, we can of course see all the usual things we can see at the Earth with field aligned currents [feltlinje rettede strømme] that get trapped by Jupiters magnetic field, but there is definitely no magnetic field from the moon. So that means, the only thing there is, it is passive as a piece of iron relative to a magnet.

The host says that he didn’t quite understand how there then could be no radiation close to Europa. John Leif Jørgensen interrupts

20:02

[*laughs] Maybe I should wait until I have published this in Science or Nature- [*laughs*] it is a bit surprising that people for 40 years have been telling each other that the radiation on the surface of this moon is absolutely lethal for everything, even electronics and other materials are being shot to pieces, and when we then go there, we see it is completely different. Give me some time to publish it first, the data is not more than a week old

The host interjects that this leads him on to the next question, which is about how certain John Leif Jørgensen is about the data and what it indicates.

20:43

There is no doubt. The place we have gone wrong [in the understanding that Europa has intense radiation on the surface] is the way a moon interacts with the magnetic field of its host planet. It is that fallacy have been led to. For your listeners curiosity, let me explain, this is quite complex, but let me say the following; the moon Europa revolves around Jupiter like our own moon does around the Earth. It [Europa] moves rather quickly, it takes only a little less than a week to come all the way around. The thing to notice is that Jupiter itself is very different than the Earth. It whirls around its own axis. In fact a rotation only takes 10 hours. That means that the magnetic field from Jupiter actually catches up to the moon [Europa] and that means that it pushes the plasma - the ionized gasses there are at the distance of the moon – ahead such that the bow wave- sorry, the stern wave of the ship is actually in front. That is the picture you should have [in your mind]. It is in that environment the particles move. It is actually not so- I do understand people make the mistake.

The host says he might have to wait to read the results when they are published to really understand it.

22:11

It is so simpler [*laughs*] it is simple but it is such a pity, afterwards you think ‘damn, how stupid I’ve been’. The worst thing is that here we are sitting with the world elite, it is the same people that made the probes to Saturn and Pluto and Mercury and Venus and Mars. It is those people and then we sit there and think ‘damn’. But that’s how it is.

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Links

The show from today where I did the interview with John Leif Jørgensen:

https://www.radio4.dk/program/den-nye-rumalder/?gid=42467&title=dart-missionen-gav-asteroide-et-kmpe-skub

The Twitter thread I did afterwards:

https://twitter.com/Tschnn/status/1580524165794185216