by Ann » Sat Sep 07, 2024 5:29 am
johnnydeep wrote: ↑Fri Sep 06, 2024 3:53 pm
So, Neptune's atmospheric methane both absorbs infrared (getting warmer I suppose), and then also emits infrared that is visible to JWST here?
Or is it only the "High altitude clouds that reach above most of Neptune's absorbing methane" that we are seeing here? (And that also must be emitting IR visible to JWST?)
Neptune's atmosphere absorbs infrared light, thereby getting fainter at several infrared wavelengths:
But in the stunning Webb view, the planet's dark and ghostly appearance is due to atmospheric methane that absorbs infrared light. High altitude clouds that reach above most of Neptune's absorbing methane easily stand out in the image though.
So indeed, the high altitude clouds that look white in the JWST image probably can't contain (much, or any) atmospheric methane, or else they would be as faint as the rest of Neptune's atmosphere at the infrared wavelengths detected by JWST.
Britannica wrote:
Neptune is more than 50 percent farther from the Sun than is Uranus and so receives less than half the sunlight of the latter. Yet the effective temperatures of these two giant planets are nearly equal. Uranus and Neptune each reflect—and hence also must absorb—about the same proportion of the sunlight that reaches them. As a result of processes not fully understood,
Neptune emits more than twice the energy that it receives from the Sun. The added energy is generated in Neptune’s interior. Uranus, by contrast, has little energy escaping from its interior.
NASA has admitted that it fooled us with the cornflower-blue pictures of Neptune that were shown to the public after the Voyager 2 flyby. Neptune and Uranus are much the same pale cyan hue, and the processes that cause this color - atmospheric methane that absorbs infrared light - are much the same. But Neptune, unlike Uranus, produces appreciable amounts of its own heat. Don't ask me why, because Britannica doesn't know! Maybe Wikipedia does?
What I don't understand is why JWST makes Uranus look at least partly bluish-cyan and Neptune look "ghostly grayish white".
Also note that while we can see the rings of Uranus, Neptune and of course Saturn in the JWST images, the rings of Jupiter are not visible.
Wikipedia wrote: The Jovian ring system is faint and consists mainly of dust. It has four main components: a thick inner torus of particles known as the "halo ring"; a relatively bright, exceptionally thin "main ring"; and two wide, thick and faint outer "gossamer rings", named for the moons of whose material they are composed: Amalthea and Thebe.
The main and halo rings consist of dust ejected from the moons Metis, Adrastea and perhaps smaller, unobserved bodies as the result of high-velocity impacts.
Another oddity of the JWST images of the outer planets is that the rings of Saturn are very bright, but the disk of Saturn is exceptionally dark. Can anyone tell me why?
Ann
[quote=johnnydeep post_id=341114 time=1725637980 user_id=132061]
So, Neptune's atmospheric methane both absorbs infrared (getting warmer I suppose), and then also emits infrared that is visible to JWST here?
Or is it only the "High altitude clouds that reach above most of Neptune's absorbing methane" that we are seeing here? (And that also must be emitting IR visible to JWST?)
[/quote]
Neptune's atmosphere absorbs infrared light, thereby getting fainter at several infrared wavelengths:
[quote]But in the stunning Webb view, [b][color=#800000]the planet's dark and ghostly appearance is due to atmospheric methane that absorbs infrared light.[/color][/b] High altitude clouds that reach above most of Neptune's absorbing methane easily stand out in the image though.[/quote]
So indeed, the high altitude clouds that look white in the JWST image probably can't contain (much, or any) atmospheric methane, or else they would be as faint as the rest of Neptune's atmosphere at the infrared wavelengths detected by JWST.
[quote][url=https://www.britannica.com/place/Neptune-planet/Basic-astronomical-data#ref54299]Britannica[/url] wrote:
Neptune is more than 50 percent farther from the Sun than is Uranus and so receives less than half the sunlight of the latter. Yet the effective temperatures of these two giant planets are nearly equal. Uranus and Neptune each reflect—and hence also must absorb—about the same proportion of the sunlight that reaches them. As a result of processes not fully understood, [b][color=#0040FF]Neptune emits more than twice the energy that it receives from the Sun. The added energy is generated in Neptune’s interior. [/color][/b] Uranus, by contrast, has little energy escaping from its interior.[/quote]
NASA has admitted that it fooled us with the cornflower-blue pictures of Neptune that were shown to the public after the Voyager 2 flyby. Neptune and Uranus are much the same pale cyan hue, and the processes that cause this color - atmospheric methane that absorbs infrared light - are much the same. But Neptune, unlike Uranus, produces appreciable amounts of its own heat. Don't ask me why, because Britannica doesn't know! Maybe Wikipedia does?
[img3="Voyager 2/ISS images of Uranus and Neptune released shortly after the Voyager 2 flybys in 1986 and 1989, respectively, compared with a reprocessing of the individual filter images in this study to determine the best estimate of the true colors of these planets. Patrick Irwin"]https://www.popsci.com/wp-content/uploads/2024/01/05/neptune-uranus-composite-resized-2.jpg[/img3]
What I don't understand is why JWST makes Uranus look at least partly bluish-cyan and Neptune look "ghostly grayish white".
[img3="Uranus is the third planet from left and Neptune is at far right. Credit: JWST."]https://www.sciencealert.com/images/2023/07/GasIceGiants.jpg[/img3]
Also note that while we can see the rings of Uranus, Neptune and of course Saturn in the JWST images, the rings of Jupiter are not visible.
[quote][url=https://en.wikipedia.org/wiki/Rings_of_Jupiter]Wikipedia[/url] wrote: The Jovian ring system is faint and consists mainly of dust. It has four main components: a thick inner torus of particles known as the "halo ring"; a relatively bright, exceptionally thin "main ring"; and two wide, thick and faint outer "gossamer rings", named for the moons of whose material they are composed: Amalthea and Thebe.
The main and halo rings consist of dust ejected from the moons Metis, Adrastea and perhaps smaller, unobserved bodies as the result of high-velocity impacts.[/quote]
[img3="The main ring of Jupiter. The upper image shows the main ring in back-scattered light as seen by the New Horizons spacecraft. The fine structure of its outer part is visible. The lower image shows the main ring in forward-scattered light demonstrating its lack of any structure except the Metis notch. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute "]https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Jovian_main_ring_New_Horizons_050107_10.jpg/1920px-Jovian_main_ring_New_Horizons_050107_10.jpg[/img3]
Another oddity of the JWST images of the outer planets is that the rings of Saturn are very bright, but the disk of Saturn is exceptionally dark. Can anyone tell me why?
Ann