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Comment by grecy | Hacker News Reader

Can Webb image Europa?

As others have said, you're looking at the image. We'll have to wait for a bit before we get some really good images of Europa. From Google:

NASA's Europa Clipper is the first dedicated mission to explore a world with a global ocean, other than Earth. The spacecraft is scheduled to launch in October 2024 and will arrive at Europa in 2030. The mission will study Europa's surface and interior to determine if it has the ingredients to support life. The spacecraft will make about 50 close flybys of Europa while orbiting Jupiter.

Also see some of the images from Juno if you want a better look at the moon.

> scheduled to launch in October 2024 and will arrive at Europa in 2030

wow, when you see dates like this it really puts things into perspective! a six year trip! any idea of how much of the trip is acceleration vs. deceleration?

Not exactly what you're asking, but it might be helpful to know that they're not planning to take a direct flight there. NASA is planning to use gravity assists off of Mars in Feb 2025 and Earth in Dec 2026. They can launch it MUCH more cheaply that way but it'll take about 3 years longer than a direct flight.

There's an animation of the planned trajectory on Wikipedia: https://en.wikipedia.org/wiki/File:Animation_of_Europa_Clipp...

> Can Webb image Europa?

The implication by the presence of "Europa Carbon Dioxide Distribution" (NIRCam and NIRSpec IFU) images on the NASA release is that yes, it can.

Yes, the NIRCam images in the article are from the Webb telescope.

The article is very precise:

"Both teams identified the carbon dioxide using data from the integral field unit of Webb’s Near-Infrared Spectrograph (NIRSpec). This instrument mode provides spectra with a resolution of 200 x 200 miles (320 x 320 kilometers) on the surface of Europa, which has a diameter of 1,944 miles, allowing astronomers to determine where specific chemicals are located."

Wikipedia article about the NIRSpec:

https://en.wikipedia.org/wiki/NIRSpec

There’s an image of Europa from Webb in the article.

It's less clear than I'd expected. Is that image deliberately downscaled so as to not reveal the true capabilities of the telescope optics?

No, moons are not very big.

No, I doubt it.

Europa is fairly small and very far away.

For reference, the best photos we had of Pluto prior to the fly-by were from the Hubble telescope, and were even grainier.

In addition to moons being big and far away, the specific instrument here (a spectrograph) is not very high resolution-- at least spatially. For each "pixel", it measures the brightness of many wavelengths of light.

Is this post trying to imply they found aliens and are hiding them?

No, just some black monoliths on the surface ;)

No. JWST is not a spy satellite. Everybody gets the images as measured. Different instruments have different resolutions.

Not reveal the true capabilities? Is this an RPG reference?

It's as designed:

"Both teams identified the carbon dioxide using data from the integral field unit of Webb’s Near-Infrared Spectrograph (NIRSpec). This instrument mode provides spectra with a resolution of 200 x 200 miles (320 x 320 kilometers) on the surface of Europa, which has a diameter of 1,944 miles"

Webb has two main instruments and one of them is not very high resolution (but I think it’s the one that gets good spectral data). When you browse the raw Webb images on the nasa website you see a mix of high res and low res images and they are each attributed to one of the two instruments.

You can probably even find the raw data for the image on one of NASA's sites soon if not already available. This isn't a spy satellite where there's a strategic need to hide the capabilities of the optics. If anything, it's more valuable to show off the capabilities because of how it's somewhat of a prestige project.

No, they're quite open about the capabilities of the optics (see https://webb.nasa.gov/content/forScientists/faqScientists.ht...). It's just that Europa is very far away.

Webb's mirror system has an angular resolution of about 0.1 arcseconds. Earth is currently about 630 million km from Europa (Webb is only 1.5 million km away from earth). Because the sine of theta is approximately equal to theta for values of theta near zero, you can get the diameter of a 0.1 arcsecond cone at x km from Earth by multiplying by 0.00000485 = sin(2pi/3603600).

0.1 0.00000485 * 630000000 = 305 km

The article says the pixels are about 320 km, so the math works out pretty close (for astronomy).

Those magnificent images of black holes and galaxies that are way more distant, but also way way bigger. This isn't downscaled when you compare it to gorgeous, sharper images like those at [1], a 340 light-year wide multi-image mosaic of the Tarantula Nebula, which is "only" 161000 light years away, that width is 1/500th the distance and Europa's width is 1/20,000th the distance.

In space, intuition about distances that you've built up from using your eyeballs on human-scale terrestrial objects just doesn't work, you've got to do the math.

[1]: https://www.nasa.gov/feature/goddard/2022/a-cosmic-tarantula...

This reply is why I love the audience on HN. Thank you for your detailed comment.

For the conspiracy theorists: this is the same reason why we can't just point Webb at the moon and get pictures of the lunar landing sites. In terms of arcseconds of the Webb's FOV, the moon landing site is much smaller than these distant galaxies (which blows my mind just how big those distant "objects" are).

We can image the lunar landing sites with lunar orbiters, though. Footsteps and all!

https://www.nasa.gov/mission_pages/LRO/news/apollo-sites.htm...

Right -- they are a bit closer than Webb :D

You obviously mean the fake lunar orbiters. And those footsteps are not human anyway, it's the Moonfoot. /s :)

Not just that, its infrared sensors require shielding from Earth/Moon (let alone Sun) heat to function as designed, and it would mostly see the dark side of the moon anyway.

Thanks for the detailed comment, that is incredibly helpful info.

I wish every website I visited had comments of this quality…

This is why I only read Hacker News these days.

Nice! Yeah, some things in the sky are actually way bigger than one might think. The first time I saw this composite of the moon and andromeda it kind of blew my mind.

https://i.stack.imgur.com/gMZb3.jpg

It’s probably a mental trick but once you know where the Orion Nebula is you can also just barely make it out with the naked eye.

https://www.reddit.com/r/Astronomy/comments/aecbbl/the_orion...

This is what it looks like ‘live’ through an 11” telescope if you try to hold your phone with your hands lol, and you can see the ‘fuzziness’ of it, not the color:

https://imgur.com/a/nt6FdLV

Only if your IP address has been listed as suspicious. For the rest of us, we see an non-manipulated image.

I’m not sure, it’s the sensor that worries me. The sensor isn’t even big enough to image uranus.

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