“X-ray emissions have been detected from comets, Venus, Earth, Mars, Saturn, Pluto, Jupiter, and several of Jupiter’s moons,” said Dr. William Dunn, an astrophysicist in the Mullard Space Science Laboratory at University College London, and his colleagues.
“For Mercury, which is too close to the Sun to be observed by the Earth-orbiting X-ray observatories, in-situ X-ray instruments have provided detailed maps of the planet’s X-ray emissions.”
“Of the planets in the Solar System, only the ice giants, Uranus and Neptune, still remain to be detected in the X-ray waveband.”
“In this study, we will focus on the closer of these two bodies: Uranus,” they said.
In the study, they used data collected by NASA’s Chandra X-ray Observatory in 2002 and 2017.
They saw a clear detection of X-rays from the first observation, just analyzed recently, and a possible flare of X-rays in those obtained 15 years later.
“What could cause Uranus to emit X-rays? The answer: mainly the Sun,” they noted.
While the team initially expected that most of the X-rays detected would be from scattering of solar emission, there are tantalizing hints that at least one other source is present.
“One possibility is that the rings of Uranus are producing X-rays themselves, which is the case for Saturn’s rings,” the astronomers said.
“Uranus is surrounded by charged particles such as electrons and protons in its nearby space environment.”
“If these energetic particles collide with the rings, they could cause the rings to glow in X-rays.”
“Another possibility is that at least some of the X-rays come from aurorae on Uranus, a phenomenon that has previously been observed on this planet at other wavelengths,” they added.
“X-rays are emitted in Earth’s aurorae, produced by energetic electrons after they travel down the planet’s magnetic field lines to its poles and are slowed down by the atmosphere.”
“Jupiter has aurorae, too. The X-rays from Jovian aurorae come from two sources: electrons traveling down magnetic field lines, as on Earth, and positively charged atoms and molecules raining down at Jupiter’s polar regions.”
“However, we’re less certain about what causes auroras on Uranus. Chandra’s observations may help figure out this mystery.”