by neufer » Sun Dec 30, 2018 6:38 am
Chris Peterson wrote: ↑Sat Dec 29, 2018 9:11 pm
Ann wrote: ↑Sat Dec 29, 2018 5:46 pm
... the background light in the APOD appears to be "too scattered" and "ambient", as if the sunlight had been scattered all over the place by a nice Earth-like atmosphere. That obviously can't be the case though, can it, Chris?
Of course, there can be no atmosphere around this body (bodies). It lacks the mass to hold an atmosphere, and it's too far from the Sun to be outgassing. I can't tell what we're supposed to see in this image. Is all that glow the Milky Way? Is the Sun blocked by the probe? If so, why do we see anything at all on the sides of the bodies facing the viewer?
Really, I can live without these artist interpretations. I don't think they ever come very close to reality.
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20181220 wrote:
New Horizons scientists puzzled by lack of a 'light curve' from their Kuiper Belt flyby target
Credits: NASA/JHUAPL/SwRI
<<NASA's New Horizons spacecraft is bearing down on Ultima Thule, its New Year's flyby target in the far away Kuiper Belt. Even though scientists determined in 2017 that the Kuiper Belt object isn't shaped like a sphere – that it is probably elongated or maybe even two objects – they haven't seen the repeated pulsations in brightness that they'd expect from a rotating object of that shape.
"It's possible that Ultima's rotation pole is aimed right at or close to the spacecraft," said Marc Buie, also of the Southwest Research Institute. That explanation is a natural, he said, but it requires the special circumstance of a particular orientation of Ultima.
"Another explanation," said the SETI Institute's Mark Showalter, "is that Ultima may be surrounded by a cloud of dust that obscures its light curve, much the way a comet's coma often overwhelms the light reflected by its central nucleus." That explanation is plausible, Showalter added, but such a coma would require some source of heat to generate, and Ultima is too far away for the Sun's feeble light to do the trick.>>
https://en.wikipedia.org/wiki/Ring_system wrote:
10199 Chariklo, a [238 km wide]
centaur, was the first minor planet discovered to have rings.
It has two rings, perhaps due to a collision that caused a chain of debris to orbit it. The rings were discovered when astronomers observed Chariklo passing in front of the star UCAC4 248-108672 on June 3, 2013 from seven locations in South America. While watching, they saw two dips in the star's apparent brightness just before and after the occultation. The observations revealed what is likely a 19-kilometer -wide ring system. In addition, astronomers suspect there could be a moon orbiting amidst the ring debris. If these rings are the leftovers of a collision as astronomers suspect, this would give fodder to the idea that moons (such as the Moon) form through collisions of smaller bits of material. Chariklo's rings have not been officially named, but the discoverers have nicknamed them Oiapoque and Chuí, after two rivers near the northern and southern ends of Brazil.
A second [~238 km wide] centaur, 2060 Chiron, is also suspected to have a pair of rings. Based on stellar-occultation data that were initially interpreted as resulting from jets associated with Chiron's comet-like activity, the rings are proposed to be 324 km in radius. Their changing appearance at different viewing angles can explain the long-term variation in Chiron's brightness over time.
A ring around Haumea, a [1630 km wide] dwarf planet and resonant Kuiper belt member, was revealed by a stellar occultation observed on 21 January 2017. This makes it the first trans-Neptunian object found to have a ring system. The ring has a radius of about 2,287 km, a width of ≈70 km and an opacity of 0.5. The ring plane coincides with Haumea's equator and the orbit of its larger, outer moon Hi’iaka (which has a semimajor axis of ≈25,657 km). The ring is close to the 3:1 resonance with Haumea's rotation, which is located at a radius of 2,285 ± 8 km. It is well within Haumea's Roche limit, which would lie at a radius of about 4,400 km if Haumea were spherical (being nonspherical pushes the limit out farther).
[quote="Chris Peterson" post_id=288431 time=1546117878 user_id=117706]
[quote=Ann post_id=288430 time=1546105617 user_id=129702]
... the background light in the APOD appears to be "too scattered" and "ambient", as if the sunlight had been scattered all over the place by a nice Earth-like atmosphere. That obviously can't be the case though, can it, Chris?[/quote]
Of course, there can be no atmosphere around this body (bodies). It lacks the mass to hold an atmosphere, and it's too far from the Sun to be outgassing. I can't tell what we're supposed to see in this image. Is all that glow the Milky Way? Is the Sun blocked by the probe? If so, why do we see anything at all on the sides of the bodies facing the viewer?
Really, I can live without these artist interpretations. I don't think they ever come very close to reality.[/quote][quote=" http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20181220"]
New Horizons scientists puzzled by lack of a 'light curve' from their Kuiper Belt flyby target
Credits: NASA/JHUAPL/SwRI
<<NASA's New Horizons spacecraft is bearing down on Ultima Thule, its New Year's flyby target in the far away Kuiper Belt. Even though scientists determined in 2017 that the Kuiper Belt object isn't shaped like a sphere – that it is probably elongated or maybe even two objects – they haven't seen the repeated pulsations in brightness that they'd expect from a rotating object of that shape.
"It's possible that Ultima's rotation pole is aimed right at or close to the spacecraft," said Marc Buie, also of the Southwest Research Institute. That explanation is a natural, he said, but it requires the special circumstance of a particular orientation of Ultima.
[size=115]"[b][i][color=#0000FF]Another explanation[/color][/i][/b]," said the SETI Institute's Mark Showalter, "[b][i][color=#0000FF]is that [u]Ultima may be surrounded by a cloud of dust[/u] that obscures its light curve, much the way a comet's coma often overwhelms the light reflected by its central nucleus.[/color][/i][/b]" That explanation is plausible, Showalter added, but such a coma would require some source of heat to generate, and Ultima is too far away for the Sun's feeble light to do the trick[/size].>>[/quote][quote=" https://en.wikipedia.org/wiki/Ring_system"]
10199 Chariklo, a [238 km wide] [url=https://en.wikipedia.org/wiki/Centaur_(minor_planet)]centaur[/url], was the first minor planet discovered to have rings. [b][u][color=#0000FF]It has two rings, perhaps due to a collision that caused a chain of debris to orbit it.[/color][/u][/b] The rings were discovered when astronomers observed Chariklo passing in front of the star UCAC4 248-108672 on June 3, 2013 from seven locations in South America. While watching, they saw two dips in the star's apparent brightness just before and after the occultation. The observations revealed what is likely a 19-kilometer -wide ring system. In addition, astronomers suspect there could be a moon orbiting amidst the ring debris. If these rings are the leftovers of a collision as astronomers suspect, this would give fodder to the idea that moons (such as the Moon) form through collisions of smaller bits of material. Chariklo's rings have not been officially named, but the discoverers have nicknamed them Oiapoque and Chuí, after two rivers near the northern and southern ends of Brazil.
A second [~238 km wide] centaur, 2060 Chiron, is also suspected to have a pair of rings. Based on stellar-occultation data that were initially interpreted as resulting from jets associated with Chiron's comet-like activity, the rings are proposed to be 324 km in radius. Their changing appearance at different viewing angles can explain the long-term variation in Chiron's brightness over time.
A ring around Haumea, a [1630 km wide] dwarf planet and resonant Kuiper belt member, was revealed by a stellar occultation observed on 21 January 2017. This makes it the first trans-Neptunian object found to have a ring system. The ring has a radius of about 2,287 km, a width of ≈70 km and an opacity of 0.5. The ring plane coincides with Haumea's equator and the orbit of its larger, outer moon Hi’iaka (which has a semimajor axis of ≈25,657 km). The ring is close to the 3:1 resonance with Haumea's rotation, which is located at a radius of 2,285 ± 8 km. It is well within Haumea's Roche limit, which would lie at a radius of about 4,400 km if Haumea were spherical (being nonspherical pushes the limit out farther).[/quote]