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Comment by bloopernova | Hacker News Reader

I wish we were capable of sending manned missions to the gas giants. Uranus and Neptune are such mysterious and beautiful worlds, I'd really like to see them up close with my own eyes, however dim such an image would be.

Maybe if we make it past the ecosystem collapse, one day people will take the Grand Tour in person. (Jupiter, Saturn, Uranus, Neptune)

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It wouldn't be too dim, your eyes have remarkable dynamic range. Brightness is experienced more like sound, with sensory capacity of many orders of magnitude, than a physical scalar sense like weight or distance.

Wikipedia says [1] the solar radiation on Uranus is 3.4-4 W/m^2. Imagine lighting up a square meter of wall with a 3W pocket inspection light, or a mood-lit room with just a few 8W bulbs. Reading might be a little bit of a strain after a while, but I think your eyes would quickly adjust.

When New Horizons was going past Pluto, Nasa put out the #PlutoTime website [2]. Pluto is about 30 AU from Earth, Uranus is about 20 AU out, so at a particular moment around twilight - when it's bright enough to walk around without artificial lighting and to take a photo - it will be as bright as it is on Uranus. The widget is dead, but it's still accessible through archive.org. Unfortunately, it's no longer accurate, it seems to be linked to the time and date when the site was archived. I'm neither a web dev nor an astronomer, but I exported the JS and it seems to provide reasonable results:

https://jsfiddle.net/9btumsj6/

Anyone have an idea of what solar_angle should be to simulate Uranus or Neptune? Apparently, when the sun is -1.5 degrees below the horizon here, that's about right for Pluto illumination. Just reducing the angle by three from -1.5 to -0.5 changes the time by about 6 minutes of twilight...

[1] https://en.wikipedia.org/wiki/Sunlight#Intensity_in_the_Sola...

[2] https://web.archive.org/web/20150827083531/http://solarsyste...

Thank you for a very interesting comment, I appreciate the work you put into it.

The problem that most people aren't even aware of is that Jupiter(and maybe others? I'm actually not sure) is throwing a massive amount of radiation around - getting anywhere close to it would kill any human very quickly. It's a huge factor in any proposed missions to its moons - like, it would be awesome to explore Europa, the concept is fascinating, but its surface is deadly due to radiation coming from Jupiter.

Yeah, the radiation was partly why I wrote "capable of sending people". You'd probably need quite a few metres of water ice surrounding your livable space if you don't want to get fried.

Which makes me wonder: if a ship was covered in, say, 10 metres of ice, would the top layer get irradiated and thus need to be replaced every so often? I wonder if it was left exposed to space, would the water ice sublimate away? Then "all" you'd need to do is replace the top layer.

Humans safe behind ice while robots do the work isn't quite as romantic as The Expanse but it'll get the job done!

What is even the benefit of being physically located right next to Jupiter, if you have to stay enclosed in 10 meters of ice at all times? Sure, you have an hour lag or so to communicate from Earth, but that seems easier to solve than all the problems of shipping humans around.

given that the moons are tidally locked, is it going to be safer on the far sides?

Sure! It still leaves the issue of getting there, and you can't stay in the shadow of a moon the whole way there.

The radiation doesn't come from Jupiter but from its magnetosphere. The radiation comes from belts, like Earth's Van Allen belts, but much stronger. The Galilean moons are all inside the magnetosphere and Io is in the middle of the strongest belt.

On the other hand, Europa has its thick ice surface shielding a lot of that radiation, making for an absolutely fascinating place to visit.

I recall from the New Horizons media blitz that noon on Pluto is roughly the brightness of dawn or dusk, so the image of these planets should be bright enough!

Agree. The more I see of Uranus the more mysterious it seems. Like it’s got to be much more complex than we imagine.

"Like it’s got to be much more complex than we imagine."

That is, how it usually is ..

I wouldn't mind taking a closer look, but being inside of a gas giant seems questionable given the pressure. I've heard astronomers compare the atmosphere of some gas giants to the density of a 7-11 slurpee... and that sounds terrifying.

The Grand Tour is a hard one, and was only possible due to a convenient alignment of the planets that does not happen frequently. For example, if Jupiter is on one side of its orbit while Saturn is on the 180° opposite point of its orbit, that's a really long way to go between destinations on the tour. I think going on a Grand Tour where you had to skip one of the planets due to a misalignment would be like going to Disneyland and never seeing Mickey. Even if you saw all of the other characters, it would still feel like you missed something.

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