Advancing solar blasts filmed for first time

 作者:楚呃     |      日期:2017-06-02 05:02:23
By David Shiga (Image: NASA/NRL) A video showing an explosion of solar plasma advancing from the Sun to the Earth’s orbit has been captured for the first time, thanks to observations made by NASA’s STEREO mission. Mission scientists say the spacecraft should dramatically improve the ability to predict the arrival at Earth of solar storms, which pose a threat to astronauts and satellites. The two STEREO (Solar Terrestrial Relations Observatory) spacecraft blasted into space on 26 October 2006 (see Twin probes enter space to spy on the Sun). They are designed to help scientists determine what causes the outbursts of solar plasma, or charged particles, and to better understand how the plasma clouds evolve as they move towards Earth’s orbit. Now, the mission has captured the first video of such an outburst, called a coronal mass ejection (CME), as it advances from the Sun to Earth’s orbit. Other spacecraft such as SOHO have obtained videos of CMEs – but only in the immediate vicinity of the Sun. The video shows a pair of CMEs that were ejected from the Sun on 24 and 25 January 2007, as they rocket outwards at 1200 kilometres per second. They slowed down to 800 kilometres per second before disappearing from view, taking about two days to reach the distance of Earth’s orbit. Light and dark streaks are visible at the centre of the frame. These are wisps of dust shed by Comet McNaught, which had a close encounter with the Sun on 12 January. The black trapezoid at left is part of the STEREO camera, which hides the Earth to reduce the glare from the sunlight it reflects. STEREO project scientist Michael Kaiser says the spacecraft will allow scientists to predict the arrival time of CMEs at Earth much more accurately than has previously been possible. Current predictions of arrival times have an uncertainty of 12 hours. “We’re hoping to cut drastically into that, down to maybe a couple of hours,” Kaiser says. Data from STEREO is being fed 24 hours a day to the National Oceanic and Atmospheric Administration (NOAA), which forecasts space weather. The two spacecraft are slowly drifting in opposite directions ahead and behind Earth in its orbit around the Sun. By April,