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The Neptune System Up Close

How lucky we are to live during the era of the James Webb Space Telescope! Webb has merely begun its decades-long mission (hopefully, it will do two decades), and already, it is returning outstanding data from objects near and far: distant galaxies, Einstein rings, exoplanets, atmospheric transits, nebulas, etc. The list is already impressive. (At the time of writing, one of JWST’s instruments seems to be having an issue, but more on that in a later post).

As I’ve mentioned before, one thing that I am most interested in with JWST is the images returned of planetary objects in our Solar System, or our ‘family’ so to speak. Given the nature of Webb (highly sensitive to light) and its position (L2), we will not get ‘entire family shots’ like the ones provided by Voyager 1 (Pale Blue Dot series), Cassini (The day the Earth smiled) or Messenger (Inside Out). This is, of course, because planetary objects within the inner Solar System, such as our planet, Venus, Mercury, or Near-Earth Asteroids, are far too close to the Sun and pointing the telescope towards them would blind the sensors.

When it comes to objects further away, though, it’s all up for grabs. We recently saw a beautiful infrared image of Jupiter and a close-up image of Mars showing some surface features. The red planet is the closest object Webb can image at the moment, and while Mars is extensively studied by numerous satellites and surface assets, additional data is always welcome.

But it is the images of the more distant planetary bodies that I am looking forward to see. Those objects are rarely studied with such high resolution as visiting them are rare affairs. Case in point: Neptune. We recently received this wonderful image of the planet furthest away from us taken by Webb’s Near-Infrared Camera (NIRCam), and, it's just... Wow!

Look at those atmospheric storms! The moons! Triton is bright like a star! The rings are so clear and sharp! This is the first time we see the Neptune system with such detail for over thirty years, and it once again shows that we need to go back as it is a fascinating place.

In the image, we can see seven of Neptune’s fourteen icy moons, although Nereid (3rd most massive) and Halimede (10th most massive) are missing - most likely hiding behind the planet - while Triton, the massive Pluto-size retrograde moon, is shining like a beacon; unsurprisingly given its absolute magnitude of -1.2. Will Webb be able to take more detailed shots of Triton, revealing large-scale surface features? Unfortunately, not. We will have to wait for a flyby mission or an orbiter to reveal more of this potential ocean world (less than 40% of its surface was imaged by Voyager 2).

The planet’s thin rings are beautifully revealed here. They were confirmed when Voyager 2 flew past the planet and are tricky to capture due to their low reflectivity. However, since Webb works in infrared, the rings are shown here in all their glory, with the three main rings - Adams, Le Verrier, and Galle - clearly visible.

The planet itself is seen in infrared (gone is the characteristic bluish tint), revealing atmospheric storms occurring in high-altitude clouds. Since methane absorbs infrared light, lower cloud structures will not be seen in Webb’s images. Nevertheless, I hope that with time, JWST will be able to show dynamic images of such storms moving across the planet or the change in the position of the rings as the planet makes its long orbit around the sun.

All in all, this image of the Neptune system is truly mesmerizing – it has now become my wallpaper. And yet, this is still the beginning of what will become a truly remarkable family photo album. We now await shots of Uranus and its moons and rings, distant Pluto with its moon system, other Kuiper belt objects, asteroid belt objects, centaurs, scattered disc objects, etc. The list of interesting objects within the outer Solar System to study is long, and two decades of Webb observing them will be more than what I could have hoped for.

We live in exceptional times! Onwards and upwards.


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