Every planet in the solar system has its peculiarities, but Uranus is truly one of a kind.
Not only is it tilted sideways, so its axis of rotation is almost parallel to its orbital plane, it smells awful, it leaks everywhere, its magnetic field is a complete mess and it has rings unlike any other planetary rings in the solar system. .
But wait, there’s more. About 20 years ago, astronomers turned their instruments to take X-ray emissions from Saturn, Uranus and Neptune. Unlike every planet before it, Uranus saw a flash.
For the first time, we have detected X-rays emanating from the strangest ball of the Solar System, and it is not entirely clear where they come from or what they mean.
Observations about and discoveries about Uranus – and Neptune, for that matter – are quite difficult to make, compared to the rest of the Solar System. These two planets are really a long way away, and little sin has ever ventured into their icy environment.
In general, we rely on telescopes close to home to take a quiz there – telescopes that are optimized to look at things farther away than Uranus or Neptune, so the details can be a bit vague.
The new discovery is based on observations made using the Chandra X-ray Observatory, a space telescope in orbit around the Earth. The first set of observations was taken in 2002, and then two more sets in 2017. When a team of astrophysicists led by William Dunn of the University College London were finally able to analyze the 2002 observational data, they found clear evidence of X-rays of Uranus.
The 2017 observation. (NASA / CXO / University College London / W. Dunn et al; WM Keck Observatory)
That Uranus should emit X-rays is not so surprising; X-rays have been detected that are emitted from many solar system bodies, including comets, Venus, Earth, Mars, Saturn, Pluto, Jupiter and even some of Jupiter’s moons. It is also not surprising that we have not detected them so far, given the problems that the distant planet has studied.
The strange part is that we do not know the full picture of Uranus’ X-rays.
There are a few options. Most of the X-rays in the solar system come naturally from the sun, which is known to scatter when it hits Jupiter and Saturn’s clouds. This is probably also happening on Uranus, although the team’s calculations indicate more X-rays than this process could calculate.
Based on other objects in the solar system, we have some clues as to what could be the potential source of this excess. Saturn’s rings are one such example, known to thrive in X-rays generated by energetic particles that interact with oxygen atoms in the rings.
Although Uranus’ rings show off less than Saturn’s, radiation belt studies have found a higher intensity of energetic electrons around Uranus. If it interacts with atoms in the rings, it can cause a similar X-ray fluorescence.
Another process that produces X-rays in the solar system is aurora. It occurs when energetic particles interact with a planetary atmosphere. On Earth, it produces a breathtaking display of dancing green light in the sky, but it is known to occur on other planets as well; Jupiter, Mars, Saturn and even comets can have auroras.
In most cases, a magnetic field plays a role in the generation of auroras; the particles are accelerated along magnetic field lines before being deposited in the atmosphere.
It is possible that a similar process is taking place on Uranus, generating auroras in the higher atmosphere. However, if it is because the magnetic field of Uranus is such a mess from outside the axis, these auras may be much more complex than we have ever observed in the solar system.
Longer Chandra observations in the future could help scientists map the locations of the X-ray emissions in Uranus, which will help find out what causes them. However, more detailed observations that could characterize the fluctuations in emissions are not possible with our current generation of instruments.
Upcoming observatories, such as Athena from ESA, or Lynx from NASA, will be better able to tell us what’s going on. It can help us not only better understand Uranus’ atmosphere and magnetic field, but also gain a deeper understanding of X-ray sources around the universe.
The team’s research was published in JGR Space Physics.