Chandra: Saturn Reflects Sun's X-Rays

May 25, 2005

When it comes to mysterious X-rays from Saturn, the ringed planet may act as a mirror, reflecting explosive activity from the sun, according to scientists using NASA's Chandra X-ray Observatory.
The findings stem from the first observation of an X-ray flare reflected from Saturn's low-latitudes, the region that correlates to Earth's equator and tropics.

Dr. Anil Bhardwaj, a planetary scientist at NASA's Marshall Space Flight Center (MSFC), Huntsville, Ala., led the study team. The study revealed Saturn acts as a diffuse mirror for solar X-rays.

Counting photons, particles that carry electromagnetic energy including X-rays, was critical to this discovery. Previous studies revealed Jupiter, with a diameter 11 times that of Earth, behaves in a similar fashion. Saturn is about 9.5 times larger than Earth. It is twice as far from Earth as Jupiter.

"The bigger the planet and nearer to the sun, the more solar photons it will intercept; resulting in more reflected X-rays." Bhardwaj said. "These results imply we could use giant planets like Jupiter and Saturn as remote-sensing tools. By reflecting solar activity back to us, they could help us monitor X-ray flaring on portions of the sun facing away from Earth's space satellites."

Massive solar explosions called flares often accompany coronal mass ejections, which emit solar material and a magnetic field. When directed toward Earth, these ejections can wreak havoc on communications' systems from cell phones to satellites.

Even as the research appeared to solve one mystery, the source of Saturn's X-rays, it fueled long standing questions about magnetic fields. Of the three magnetic planets in our solar system, Jupiter and Earth emit two general types of X rays, auroral emissions from polar regions and disk emissions from low latitudes. No research has observed unambiguous signatures of auroral X-ray emissions on Saturn.

"We were surprised to find no clear evidence of auroral X-ray emissions during our observations," Bhardwaj said. "It is interesting to note that even as research solves some mysteries, it confirms there is much more we have to learn."

The research appeared in the May 10, 2005 issue of Astrophysical J. Letters. the research team also included Ron Elsner of MSFC; Hunter Waite of the University of Michigan, Ann Arbor; Randy Gladstone of the Southwest Research Institute, San Antonio, Texas; Thomas Cravens of the University of Kansas, Lawrence; and Peter Ford from the Massachusetts Institute of Technology, Cambridge.

Source: NASA