Far from the Sun, near the outer limits of our solar system, the ice giant Uranus slowly orbits its distant parent star. For the first time, astronomers have seen X-rays emanating from this distant world.
The Chandra X-ray observatory, launched in 1999, examines the Universe in X-rays, highly-energetic wavelengths of electromagnetic energy most commonly associated with diagnosing broken bones.
“NASA’s Chandra X-ray Observatory is a telescope specially designed to detect X-ray emission from very hot regions of the Universe such as exploded stars, clusters of galaxies, and matter around black holes. Because X-rays are absorbed by Earth’s atmosphere, Chandra must orbit above it, up to an altitude of 139,000 km (86,500 mi) in space,” NASA describes.
A new study of observations shows this world — literally — in a new light.
Seeing through the X-ray mystery
X-rays have been seen before, radiating from the gas giants of the solar system, Jupiter and Saturn. On those worlds, most X-ray emissions are the result of scattering of X-ray radiation from the Sun, while a percentage are generated in aurorae — similar to northern and southern lights.
“Measuring the energy of the X-rays can tell us the elemental composition of Mercury’s surface. Jupiter’s and Saturn’s atmospheres scatter and reflect X-rays released by the Sun. Saturn’s rings also fluoresce and this is actually the brightest part of the planet when seen in X-rays. X-ray auroras have so far only been detected at Jupiter and the Earth,” Affelia Wibisono of University College London states.
Researchers studying data collected by the Chandra spacecraft in 2002 and 2017 found X-ray emissions centered on the ice planet Uranus. Analysis of the data suggests this display may result from the same conditions that drive displays on Jupiter and Saturn.
However — an intriguing possibility exists that a portion of this display has another cause.
Uranus is bathed in electrons and protons, filling space around the icy planet. One idea holds these charged particles might interact with material in the rings of Uranus, producing X-rays. A similar process is known to take place in the rings of Saturn.
Another possibility is that X-rays are produced in aurora at the poles of Uranus. These displays, the result of charged particles interacting with an atmosphere, are known to produce other wavelengths of electromagnetic radiation. On Earth, X-rays are produced in aurorae as charged particles, drawn to Earth by our planet’s magnetic field, are slowed as they pass through our atmosphere.
If either of these ideas are confirmed, the discovery of the nature of X-rays from Uranus could alter our understanding of this icy world.
Whose side are you on?
So far, just one spacecraft — Voyager 2 — has visited this distant icy world. Astronomers, therefore, rely on observatories (such as the Hubble Space Telescope and Chandra) on and near the Earth to study this planetary target.
Unlike the other planets in our solar system, Uranus rotates on its side, although why it does so remains a mystery. This planet, like the Sun, is composed mainly of hydrogen and helium.
The magnetic fields of Uranus are tilted in relation to the axis on which the planet rotates, and this field is centered away from the middle of this icy globe. These conditions could create intricate displays of auroras at the poles of Uranus.
Analysis of the study was published in the Journal of Geophysical Research: Space Physics.
By learning more about the processes driving X-rays from Uranus, researchers hope to learn more about other X-ray sources including black holes and neutron stars.
This article was originally published on The Cosmic Companion by James Maynard, founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat. You can read this original piece here.