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Astronomers used NASA’s Chandra X-ray Observatory to detect X-rays from Uranus for the first time. This result could help scientists learn more about this enigmatic giant ice planet in our solar system.
Uranus is the seventh planet from the sun and has two sets of rings around its equator. The planet, four times the diameter of the earth, rotates on its side and is different from all other planets in the solar system. Since Voyager 2 was the only spacecraft ever flown with Uranus, astronomers are currently relying on telescopes much closer to Earth, such as Chandra and the Hubble Space Telescope, to learn more about this distant and cold planet, the consists almost entirely of hydrogen and helium.
In the new study, the researchers used Chandra observations recorded in Uranus in 2002 and then in 2017. They saw clear evidence of x-rays from the recently analyzed first observation, and a possible flare of x-rays from the fifteen preserved years later. The main graphic shows a 2002 Chandra X-ray image of Uranus (in pink) overlaid on an optical image from the Keck-I telescope captured in a separate 2004 study. The latter shows the planet in roughly the same orientation as it was during the Chandra observations in 2002.
What could cause Uranus to emit X-rays? The answer: mainly the sun. Astronomers have observed that both Jupiter and Saturn scatter X-rays emitted by the Sun, much like the Earth’s atmosphere scatters sunlight. While the authors of the new Uranus study initially expected that most of the X-rays detected would also be from scattering, there is tantalizing evidence that at least one other X-ray source is present. If further observations confirm this, it could have fascinating implications for understanding Uranus.
One possibility is that the rings of Uranus themselves generate x-rays, which is the case with Saturn’s rings. Uranus is surrounded by charged particles such as electrons and protons in its nearby space environment. When these energetic particles collide with the rings, they can cause the rings to glow in X-rays. Another possibility is that at least some of the X-rays are from aurors on Uranus, a phenomenon previously observed on this planet at other wavelengths.
On Earth, we can see colorful light shows in the sky called aurors, which occur when high-energy particles interact with the atmosphere. X-rays are emitted in Earth’s aurors and created by energetic electrons after they are dragged down the planet’s magnetic field lines to its poles and slowed down by the atmosphere. Jupiter has aurors too. The X-rays from aurors on Jupiter come from two sources: electrons that travel across magnetic field lines as they do on Earth, and positively charged atoms and molecules that rain in Jupiter’s polar regions. However, scientists are less sure what is causing aurors on Uranus. Chandra’s observations might help solve this mystery.
Uranus is a particularly interesting target for X-ray observations because of the unusual orientation of its spin axis and magnetic field. While the axes of rotation and magnetic field of the other planets in the solar system are almost perpendicular to the plane of their orbit, the axis of rotation of Uranus runs almost parallel to its path around the sun. While Uranus is tilted on its side, its magnetic field is tilted a different amount and is offset from the center of the planet. This can make the aurors unusually complex and variable. Identifying Uranus’ X-ray sources could help astronomers better understand how more exotic objects, such as the ocean, are in space. B. growing black holes and neutron stars emit X-rays
An article describing these results appears in the latest issue of the Journal of Geophysical Research and is available online. The authors are William Dunn (University College London, Great Britain), Jan-Uwe Ness (University of Marseille, France), Laurent Lamy (Paris Observatory, France), Grant Tremblay (Center for Astrophysics | Harvard & Smithsonian), Graziella Branduardi- Raymont ( University College London), Bradford Snios (CfA), Ralph Kraft (CfA), Z. Yao (Chinese Academy of Sciences, Beijing), Affelia Wibisono (University College London).
NASA’s Marshall Space Flight Center administers the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science from Cambridge, Massachusetts and flight operations from Burlington, Massachusetts.
Photo credit: X-ray: NASA / CXO / University College London / W. Dunn et al. Optical: WM Keck Observatory
Read more from NASA’s Chandra X-ray Observatory.
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http://www.nasa.gov/chandra
Last updated: April 1, 2021 Publisher: Lee Mohon
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