Coronagraphs onboard the orbiting Solar and Heliospheric Observatory (SOHO) tracked the fast-moving cloud as it billowed into space:

NASA’s STEREO-A spacecraft, which has a partial view of the sun’s farside, identified the source of the blast as active sunspot AR2665, familiar to readers of Spaceweather.com who watched the behemoth cross the Earthside of the sun earlier this month. STEREO-A observed an intense flash of extreme UV radiation from the sunspot’s magnetic canopy:

The intensity of the flash suggests (but does not prove) that the underlying flare might have been the most intense kind: X-class.

If this explosion had occurred 2 weeks ago when the huge sunspot was facing Earth, we would be predicting strong geomagnetic storms in the days ahead. Instead, the CME is racing away from our planet … and directly toward Mars. Compared to Earth, the Red Planet is currently on the opposite side of the sun, and apparently in the crosshairs of this CME. Mars rovers Curiosity and Opportunity might be observing the effects of a solar storm later this week.

Coincidentally, yesterday’s farside explosion occurred on the 5th anniversary of another significant farside event: The Solar Superstorm of July 23, 2012.  That superstorm, which has been compared to the historic Carrington Event of 1859, could have caused widespread power blackouts if it had not missed our planet.

Sunspot AR2665 will be back on the Earthside of the sun a little more than a week from now. If the sunspot remains active, it could bring a new round of geomagnetic storms and auroras to our planet in early August.

Source: Spaceweather.com