The god of the boundless sea beyond the inner solar system is Neptune, the last known major planet from the sun.
Even though it is four times the diameter of Earth, Neptune is so small and faint that it wasn't discovered until 1846.
The only close-up view we have had in the last 30 years has been sent back from the farthest reaches of the solar system.
That's right, whoa. There is a lot happening on this distant planet.
There is a reminder that this shot is a combination of images taken in the long wavelength of light. This is a lot more fun to investigate because the physics of what we see is different.
Neptune is called an ice giant because it has a lot of molecule like methane, ammonia, and water inside, which planetary scientists call "ices" even though technically they are a weird form of high pressure liquid deep in the atmosphere. I have seen methane absorb red light and make the planet look a rich blue at the eyepiece, but it also absorbs IR light, so Neptune is not as bright as it could be.
It has methane ice clouds that are very reflective and bright. They appear at different latitudes above the cloud deck.
Neptune is similar to the other giant planets in that it has several rings made of ice particles that make them appear red, and that is visible in the image. There are a number of small moons around Neptune. Proteus is a little over 400 km in diameter and is one of the smallest. The shepherd moons are thought to be superposed on the rings because of Despina's and Galatea's gravity.
My friend and astronomer, who is an expert on Neptune, thinks another small moon, Hippocamp, can be seen, and has a labeled image with the ring names.
Here's a zoom-in on the Neptune system with some moons and rings annotated (Triton and Proteus are outside this field). I told NASA we also see Hippocamp, but they weren't confident. As someone whose spent decades studying the Neptune system in FAR worse images, I am confident. pic.twitter.com/XHMxV9oPFL— Dr Heidi B. Hammel (@hbhammel) September 21, 2022
It's very cool.
There's that brilliant teal star. Neptune's largest moon is called Triton. It is larger than our own Moon but smaller than the other one. It appears bright because it is covered in frozen nitrogen which is highly reflective and the lines going through it are caused by light bends around the three legs holding the secondary mirror. You can only see them when the light source is very small and Neptune has them but they are not visible in the picture.
Astronomers think that it may be a large Kuiper Belt object captured by the planet's gravity long ago. This isn't easy to do and the exact mechanism isn't known.
Some fainter inner rings can be seen in this close up shot of Neptune. There is a faint line at the equator. The atmosphere of Neptune is very different from ours in that the gases sink and warm up at the equator. The gas may be hotter than it is as it warms.
This one is so cool.
Almost all of the other things you see in the image are hundreds of millions or even billions of light years away. Neptune is the final big outpost of the solar system.
More observations will be made over time to track the moons, rings, and storms. Dr. Hammel says that we will be able to probe the planet's atmospheric composition in the near future. There is more to come.