'Sparkles' could be heating the Sun's atmosphere
Sen— Scientists studying images of the Sun's atmosphere captured by a NASA camera may have discovered why the star's atmosphere is so much hotter than its surface.
The images were taken last July by NASA's High Resolution Coronal Imager (Hi-C). The results of the study are being announced today by Professor Robert Walsh at the Royal Astronomical Society's National Astronomy Meeting taking place this week in St Andrews, Scotland.
The innovative camera was sent into space for just over ten minutes. Launched aboard a NASA suborbital sounding rocket from the White Sands Missile Range in New Mexico on July 11 2012, the Hi-C flight lasted 620 seconds.
Hi-C set its sights on a magnetically-active sunspot region and snapped away every few seconds of its brief mission, capturing 165 images in the extreme ultraviolent light, the higher energy wavelength being optimal for viewing the hot solar corona.
The international team of scientists studying the images, led by astronomers at the University of Central Lancashire (UCLan) in the UK, found dynamic bright dots - dubbed 'sparkles' by the team - which switch on and off at high speed and release huge amounts of energy into the corona.
Each sparkle is about 680 km across and typically lasts around 25 seconds, and releases at least 1024 (one million million million million) Joules of energy -- about 10,000 times the yearly energy consumption of the UK. The sparkles provide evidence that enormous amounts of energy are being added into the corona and may then be released violently to heat the plasma.
According to the study, these enormous releases of energy into the corona could solve the mystery as to why the Sun's corona - at two million degrees Celsius - is around 400 times hotter than its photosphere (surface).
The study also found small clumps of electrified gas (plasma) speeding along 'highways' in a Coronal Mass Ejection (CME). The highways are about 450 km across and shaped by the Sun's magnetic field. These clumps have a temperature of about one million degrees Celsius and travel at about 80 km per second. The finding of these highways improves our understanding of CMEs - eruptions of bubbles of magnetic field and gas from the solar atmosphere.
CMEs travel with speeds of up to 2,000 km per second and send charged particles into the Solar System - these take between 1 and 4 days to reach Earth where they can cause damage to electrical infrastructure. CMEs can also pose a threat to satellites and astronauts. The discovery of these solar highways will enable scientists to understand better the driving force behind CMEs, and improve prediction of when they might take place.
Professor Walsh, a solar physicist and Director of Research at the University of Central Lancashire (UCLan), commented: “I’m incredibly proud of the work of my colleagues in developing Hi-C. The camera is effectively a microscope that lets us view small scale events on the Sun in unprecedented detail. For the first time we can unpick the detailed nature of the solar corona, helping us to predict when outbursts from this region might head towards the Earth.”
The UCLan team worked with scientists from NASA and the Lebedev Physical Institute of the Russian Academy of Sciences in Moscow. Dr Jonathan Cirtain, senior heliophysicist at NASA's Marshall Space Flight Center and principal investigator for the Hi-C mission, observed: “Our team developed an exceptional instrument capable of revolutionary image resolution of the solar atmosphere. We took advantage of the high level of solar activity to focus in on an active sunspot and obtained these remarkable pictures.”
Hi-C is one of a number of missions sent to explore the Sun. NASA recently launched its latest explorer, IRIS (Interface Region Imaging Spectrograph) which aims to further our understanding of the Sun's surface and atmosphere.