NASA Sees First X-Rays From Uranus

Chandra X-ray observations of Uranus from 2002 (in pink) superimposed on an optical image from the Keck-I Telescope obtained in a separate study in 2004. Image credit: X-ray: NASA/CXO/University College London/W. Dunn et al; Optical: W.M. Keck Observatory

NASA reports the first detection of X-rays from Uranus thanks to NASA’s Chandra X-ray Observatory. The seventh planet of the solar system is together with Neptune classified as an Ice Giant and until now these were the only two planets from which x-rays had not been detected.

The new work, published in the Journal of Geophysical Research Space Physics, looked at three observations performed by Chandra over the last two decades. One from August 7, 2002, and two over November 11 and 12, 2017. The detection became apparent only when the data was re-analyzed recently. The older observations clearly show a signal and in the more recent one, the signal might be hinting at a flare.

Three observations are not much but they are providing some new insight into Uranus. The team believes that most of the X-rays seen don’t come from Uranus but some might. The main source of this light is none other than the Sun. Just like the Earth’s atmosphere scatters visible light, so does the atmosphere of the giant planets in the solar system, like Jupiter and Saturn, they all scatter X-rays.

The researchers believe that the same process is also happening on Uranus. But there might be something more. There are hints that some of the x-rays observed are not simply scattered from the Sun but are produced by the planet.

One possible source could be the rings of Uranus. While not as spectacular as Saturn’s own, the planet possesses rings made of dark particles between a few microns to a fraction of a meter (a few feet) across. Saturn’s rings emit x-rays so it could be possible that the same happens here.

The alternative is aurorae. Northern and southern lights are not exclusive to Earth where they are caused by electrons hitting the atmosphere. On Jupiter charged atoms and molecules create a similar effect. It is not known what the exact mechanism behind Uranus’ aurorae is. But it could be a crucial clue in understanding this mysterious planet better.

As planets go, Uranus is way more complicated than we’d like it to be. It orbits on its side, so day and night don’t happen as it rotates on its axis. This is possibly due to a colossal impact in its past. And a consequence of this is its weird magnetic field. If we imagine the magnetic field like a bar magnet, we’d find that it doesn’t go through the center of the planet, like on Earth. It’s a bit off to the side. And it points in a completely different direction compared to its axis of rotation.

More observations will be necessary to understand where the X-rays from Uranus come from exactly.

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