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HEAPOW: Uranus X-rayed (2021 Apr 12)

Uranus was identified as a planet in 1781 by astronomer William Herschel, the first planet to be discovered in modern times. Herschel proposed naming the planet in honor of King George III, the "mad king", and many other names were propsed for the planet, but the suggestion of Uranus (the Greek god of the sky) by astronomer Johann Bode was eventually adopted (ensuring the planet's place as the butt of mischievous schoolboy humor for centuries). Uranus is an unusual planet, a ringed ice giant whose rotational axis lies nearly in the plane of the planet's orbit, making it appear as if the planet is rotating on its side. This weird orientation produces extreme seasons and storms as the planet revolves in its 84 earth year orbit. Though poorly understood, ice giants like Uranus (and its cousin Neptune) are fairly common in identified planetary systems outside the solar system. Now the Chandra X-ray Observatory has shown, for the first time, that Uranus is a source of X-ray emission. The image above shows an X-ray image obtained by Chandra's High Resolution Camera of the planet (in purple) superimposed on an optical image of Uranus from the Keck observatory. The origin of this X-ray emission is not yet known. Likely much of the emission is produced by X-rays from the Sun being reflected by the planet's atmosphere, but emission from polar aurorae or X-rays from the interaction of charged particles with ice in the rings of Uranus (a process that produces X-ray emission from comets) might also contribute.

X-ray: NASA/CXO/Univ College London/W Dunn et al; Optical: Keck Observatory

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Astronomers have detected X-rays from Uranus for the first time, using NASA's Chandra X-ray Observatory. This result may help scientists learn more about this enigmatic ice giant planet in our solar system.

Uranus is the seventh planet from the Sun and has two sets of rings around its equator. The planet, which has four times the diameter of Earth, rotates on its side, making it different from all other planets in the solar system. Since Voyager 2 was the only spacecraft to ever fly by Uranus, astronomers currently rely on telescopes much closer to Earth, like Chandra and the Hubble Space Telescope, to learn about this distant and cold planet that is made up almost entirely of hydrogen and helium.

In the new study, researchers used Chandra observations taken in Uranus in 2002 and then again in 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 fifteen years later. The main graphic shows a Chandra X-ray image of Uranus from 2002 (in pink) superimposed on an optical image from the Keck-I Telescope obtained in a separate study in 2004. The latter shows the planet at approximately the same orientation as it was during the 2002 Chandra observations. ...

Blog: What We Found When We X-rayed Uranus

• JGR: Space Physics 126(4):2020JA028739 (Apr 2021) DOI: 10.1029/2020JA028739