A composite image of Uranus, combining data from the optical and X-ray wavelengths. X-ray: NASA/CXO/University College London/W. Dunn et al; Optical: W.M. Keck Observatory
For the first time, researchers have discovered X-rays being emitted by the planet Uranus.
The X-rays were detected using the NASA Chandra X-ray Observatory, by looking at previous observations of the planet from 2002 and 2017. Researchers found that the first set of observations showed clear evidence of X-rays, and there was a possible burst of X-rays in the later observations as well. From this data, they combined the findings with previous optical observations of Uranus to produce the image above.
The image shows the blue and white visible-light observations, which were captured using the Keck-1 Telescope at the W. M. Keck Observatory in Hawaii. Imposed on top are the X-ray observations in pink, captured using the Chandra X-ray Observatory.
As for where these X-rays are coming from, the answer is complicated. We know that X-ray emissions from Jupiter and Saturn are caused by the planets scattering sunlight, and a similar effect is seen on Uranus. But this scattering only explains part of the emissions — so where are the rest of the X-rays coming from? Scientists are still figuring that out.
“Our calculations suggest that Uranus was producing more X-rays than it should if the planet was only scattering the sun’s X-rays,” NASA guest blogger Affelia Wibisono wrote about the findings, “so could there be at least one other process at play and what are they? Are Uranus’ rings fluorescing like Saturn’s? Or could this oft-forgotten world have X-ray aurorae like Jupiter and the Earth? More observations of Uranus by Chandra and other X-ray telescopes are needed before we can give a definitive answer.”
The possibility that the X-rays could be related to auroras is an intriguing one, as auroras on Earth are created when particles traveling magnetic field lines interact with the atmosphere. Uranus has an unusual magnetic field, and the planet rotates almost entirely on its side — that is, it is “tipped over” relative to its orbit. But the magnetic field is tipped over by a different amount than the tilt of the planet. “This may cause its auroras to be unusually complex and variable,” NASA writes in a post. “Determining the sources of the X-rays from Uranus could help astronomers better understand how more exotic objects in space, such as growing black holes and neutron stars, emit X-rays.”