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The Sun’s stormy surface

An image captured by NASA's SOHO spacecraft shows storms brewing on the Sun.

A flare and a storm brewing on the surface of the Sun.

Magnetic storms from the Sun bombard Earth with charged particles that can interfere with electronics systems and satellites. This image, captured by NASA’s Solar Terrestrial Relations Observatory (STEREO) Ahead spacecraft on February 12, 2010, shows one such storm (albeit a very small one) brewing on the solar surface.

Two active regions glow brightly in this ultraviolet image of the Sun. A small flare rises from the active area on the left. Flares are intense explosions on the Sun that blast radiation into space. This one paints a white line across the left horizon of the Sun.

The active area on the right churns with magnetic loops. Arcs of charged particles rise from the surface and are drawn back down again in the magnetic field. A video showing a sequence of STEREO observations, including this one, reveals that a small coronal mass ejection (CME) burst from this region a short time after this image was taken. Like a flare, a CME sends charged particles and energy into space, but CMEs are larger solar storms that both last longer and carry a larger cloud of particles and magnetic field into space than do flares.

Artist's impression of the twin STEREO Sun-monitoring spacecraft.

Artist's impression of the twin STEREO Sun-monitoring spacecraft.

Both flares and coronal mass ejections can create space weather if aimed at Earth. The charged particles from large storms blast Earth’s magnetic field, which acts as a shield. The charged particles interacting with Earth’s magnetic field generate intense and beautiful aurora, but they can also be destructive. Solar storms in the past have damaged power grids, causing blackouts, and harmed and destroyed satellites.

STEREO is one of several NASA missions studying the Sun. STEREO was launched to help scientists better understand coronal mass ejections. An improved understanding of solar storms will improve space weather forecasts, which will help limit the damage they cause on Earth.

NASA image courtesy the STEREO science team. Text adapted from information issued by the STEREO science team and Holli Riebeek.

Mars is losing its air

Mars

The solar wind is slowly stripping Mars of its atmosphere.

Space physicists from the University of Leicester are part of an international team that has identified the impact of the Sun on Mars’ atmosphere.

Writing in the AGU journal Geophysics Research Letters, the scientists report that Mars is constantly losing part of its atmosphere to space.

The new study shows that pressure from solar wind pulses is a significant contributor to Mars’s atmospheric escape.

The researchers analysed solar wind data and satellite observations that track the flux of heavy ions leaving Mars’s atmosphere. The authors found that Mars’s atmosphere does not drift away at a steady pace; instead, atmospheric escape occurs in bursts.

The researchers related those bursts of atmospheric loss to solar events known as co-rotating interaction regions (CIRs). CIRs form when regions of fast solar wind encounter slower solar wind, creating a high-pressure pulse. When these CIR pulses pass by Mars, they can drive away particles from Mars’s atmosphere.

The authors found that during times when these CIRs occurred, the outflow of atmospheric particles from Mars was about 2.5 times the outflow when these events were not occurring. Furthermore, about one third of the material lost from Mars into space is lost during the impact and passing of CIRs.

The study should help scientists better understand the evolution of Mars’s atmosphere.

Professor Mark Lester, Head of the Department of Physics and Astronomy at the University of Leicester said: “The main reason it happens at Mars and not at Earth is the lack of a magnetic field produced by [Mars]…”. Earth has a strong magnetic field that protects its atmosphere.

“One other aspect of this work is that the observations were made during a very quiet period in the eleven year solar cycle and so we would expect the effect of these and other large scale disturbances to be higher at other times in the solar cycle.”

Adapted from information issued by the University of Leicester.