The Sun's "Stealth" Explosions

Scientists Figure Out the Sun's Mysterious "Stealth" Explosions

Unmasking stealth coronal mass ejections.

NASA's Goddard Space Flight Center/ARMS/Joy Ng, producer
 
By David Grossman

The sun regularly shoots material out into the void of space, and the largest of these blasts are known as coronal mass ejections, or CMEs. A team of scientists led by the Space Sciences Laboratory at University of California, Berkeley has developed a model that simulates the evolution of stealth CMEs, which explode into space with no warming.

CMEs are usually telegraphed in advance. The warning varies; sometimes there's a bright flash of a flare, other times a burst of heat or a flurry of solar energetic particles. A standard CME also moves fast, with a speed of 1,800 miles per second leaving the sun. NASA describes stealth CMEs as having a "rambling gait" in comparison, flying at 250 to 435 miles per second, roughly the same speed as the constant stream of charged particles that flows from the sun known as solar wind.

Using the space agency's Solar Terrestrial Relations Observatory (STEREO) and Solar and Heliospheric Observatory (SOHO), the scientists made a model of the sun's magnetic fields. They discovered that the sun's rotation is crucial to the mystery of stealth CMEs.

A star like the sun is not a solid body of mass like Earth or Mars. It rotates unevenly, faster at the equator than the poles. That differential in rotation makes the sun's magnetic fields stretch and spread at varying rates. This pulling and stretching creates enough energy to produce a stealth CME in about two weeks, the scientists discovered. The rotation stresses the magnetic fields until they are warped into a strained coil of energy. "When enough tension builds," NASA says, "the coil expands and pinches off into a massive bubble of twisted magnetic fields — and without warning — the stealth CME quietly leaves the sun."

A stealth CME can moderately disturb the Earth's magnetic fields, but it's unlikely that we'll ever be directly affected by one. But understanding the weather of the sun —beyond "always hot"— can help us predict space weather elsewhere, which will come in handy as we look past the Moon and start traveling deeper into the solar system.

Source: NASA