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We knew that, if the Webb telescope could make it to the L2 Lagrange Point in one piece and deploy properly, this would be an exciting season for astronomers–but, even so, the parade of stunning new images from outer space are marvelous and demand comment. Today’s treasure is a picture of Planet Neptune and its moons as imaged by the near-infrared camera on Webb. The ice giant Neptune is made of strange cold things with a great pall of methane gas over them. Methane gas is very opaque to infrared light (which it absorbs) and so the planet looks like a frosty, haunted bowling ball with glass rings.

Ever since Pluto got demoted to “dwarf planet”, Neptune is the outermost world of our solar system. Yet the great gas giants…or even the trans-Neptunian objects like Eris and Haumea get all of the attention. No space craft has even visited Neptune since Voyage II rolled by in 1989 (the first and last time a probe entered the Neptune system).

Aside from the spectral rings, the image shows some bright sparks in a line along Neptune’s Tropic of Capricorn (which is not called that, but you get the idea). These bright spots are caused by high altitude methane clouds which are made of methane ice (which reflects infrared light better than methane gas does).

The full Webb photo has a striking focal point! Pulling back we see that Neptune’s largest and strangest moon Triton outshines the giant world it orbits. This is because Triton (which is named for the Greco-Roman deity Neptune’s merman super-son) is covered in a sheet of frozen nitrogen which reflects 70% of the sunlight which strikes it–so Triton glows like an aquamarine star in this photo. Ultimately Triton might well turn out to be be more interesting than Neptune: it is the only large moon in the solar system with a retrograde orbit (an orbit opposite of the planet’s rotation). Such an unusual orbit suggests that the moon was a little world captured by the ice giant long ago.

Triton is larger than Pluto and is one of five moons in the solar system known to be geologically active (the others being Io, Europa, Titan, and Enceladus). Voyager II spotted geysers of nitrogen gas venting from the moon. Clearly cryovolcanic activity is taking place below the strange patchwork of old ice (as explained in this confusing yet compelling map/diagram) and lakes of liquid water may exist below the moon’s crust.

I am going to keep staring at images of our strange far-off neighbor world, but I can’t wait to see what Webb photographs next!

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