Dramatic outbursts have been witnessed on Rosetta’s comet as it gets ever closer to the Sun. The growing activity has proven so powerful that the comet has managed to push away incoming solar wind unleashed by our nearest star.
Comet 67P/Churyumov-Gerasimenko reaches perihelion on Thursday, the moment in its 6.5-year orbit when it is closest to the Sun. Recently, the increasing solar energy has been warming up the comet’s frozen ices, turning them to gas, which pours out into space and drags dust along with it.
With parts of the comet previously cast in years of darkness soon to be flooded with sunlight, the period around perihelion is very important for the Rosetta team as they wait for the comet’s activity to peak, not just on approach, but weeks after it speeds away from the Sun. Sudden and unpredictable eruptions can occur at any time.
The comet’s most recent outburst, which occurred on 29 July and takes the form of a jet, was registered by several of Rosetta’s instruments from their vantage point 186 kilometres (115.57 miles) from Comet 67P’s surface. The eruption from the nucleus illustrates a change in the structure and makeup of the gaseous coma environment that surrounds both the comet’s nucleus and the Rosetta spacecraft. The instruments have also uncovered increased levels of dust impacts.
More surprisingly though, Rosetta has found that the outburst – which emerged from the side of the comet’s neck, known as the Anuket region – has pushed the solar wind magnetic field from around the nucleus, according to a sequence of images taken by the spacecraft’s camera, OSIRIS. “This is the brightest jet we’ve seen so far,” says Carsten Güttler, an OSIRIS team member based at the Max Planck Institute for Solar System Research in Göttingen, Germany. “Usually, the jets are quite faint compared to the nucleus and we need to stretch the contrast of the images to make them visible – but this one is brighter than the nucleus.”