Astronomers have detected X-rays from Uranus for the first time, a result that may help scientists understand the mysterious icy giant planet in our solar system and help astronomers better understand the growing number of exotic objects in space, such as growing black holes. (NASA)
Astronomers have used NASA’s Chandra X-ray Observatory to detect Uranus’ X-rays for the first time, a result that may help scientists understand the mysterious ice-giant planet in our solar system and help astronomers better The results may help scientists understand the mysterious ice-giant planet in our solar system and help astronomers better understand how the growing number of strange objects in space, such as growing black holes, emit X-rays.
There are nine planets in our solar system, and Uranus, the seventh planet from the Sun, has two sets of rings around its equator, and is four times the diameter of Earth.
Because Voyager 2* (Voyager2) is the only spacecraft ever to visit Uranus, astronomers currently have to rely on telescopes closer to Earth (such as the Chandra and Hubble space telescopes, not Voyager 2) to learn about the distant, cold planet made almost entirely of hydrogen and helium, NASA reports.
Researchers using Chandra observations on Uranus in 2002 found that X-rays could be clearly detected, and obtained flares of X-rays that could occur in 15 locations in a re-observation years later, in 2017.
The images in this article show the results of superimposing a 2002 Chandra X-ray image of Uranus (pink) with an optical image from the Keck-I telescope obtained in another study in 2004, which showed the planet in roughly the same direction as the original in the 2002 Chandra observation.
What causes Uranus to emit X-rays? The answer from astronomers is “the Sun”.
Astronomers have observed that both Jupiter and Saturn scatter X-ray light from the Sun in a similar way to the way the Earth’s atmosphere scatters sunlight. Although the authors of the latest study of Uranus initially expected that most of the detected X-rays might also come from scattering (of sunlight X-ray light), there is at least one other source of X-rays, and if further observations confirm the researchers’ suspicions, they may be useful in understanding the mysterious planet Uranus.
There is also the possibility that Uranus’ rings themselves produce X-rays, as is the case with Saturn’s rings. Uranus is surrounded by charged particles in its nearby space environment, such as electrons and protons, and if these energetic particles collide with each other and Uranus’ rings, they could cause the rings to glow in X-rays.
Another possibility is that at least some of the X-rays come from the aurora on Uranus, a phenomenon that has been observed before at other wavelengths on the planet.
On Earth, we can see the brilliantly colored light in the sky called “auroras,” which are usually produced when energetic particles interact with the atmosphere, and X-rays are emitted in Earth’s auroras by energetic electrons that travel along the planet’s magnetic lines of force to its poles and are slowed down by the atmosphere.
Jupiter also has auroras, and X-rays from auroras on Jupiter have two sources: electrons traveling along magnetic field lines and positively charged atoms and molecules scattered in Jupiter’s polar regions, but scientists lack knowledge of what causes auroras on Uranus, and Chandra’s observations may help unravel this mystery.
Astronomers have shown great interest in observing Uranus through X-rays because of its unusual spin axis and magnetic field direction compared to other planets.
While the other planets in our solar system have their spin and magnetic field axes almost perpendicular to their orbital planes, Uranus’ spin axis is almost parallel to its path around the Sun. In addition, as Uranus tilts to its own side, its magnetic field tilts out of intensity and away from the center of the planet, which causes its auroras to become unusually complex and variable.
If the source of X-rays from Uranus can be identified, it could help astronomers better understand how the increasingly exotic objects in space, such as growing black holes and neutron stars, emit X-rays.
The study, authored by astronomers from the United States, the United Kingdom, France and China, is published in the latest issue of the Journal of Geophysical Research and is available online.
*Editor’s note: Voyager 2, a NASA unmanned interplanetary spacecraft launched on August 20, 1977, is still operational as of 2020 and is the longest-running space probe ever, being the first spacecraft to visit Uranus and Neptune.
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