Space

Powerful comet activity pushes back solar wind

The event captured in three chronological images – the image on the left was captured at 13:06 GMT, middle 13:24 GMT and right 13:42 GMT
The event captured in three chronological images – the image on the left was captured at 13:06 GMT, middle 13:24 GMT and right 13:42 GMT
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This image captured April 12 shows the origin of the jet on the comet's nucleus in a small red circle
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This image captured April 12 shows the origin of the jet on the comet's nucleus in a small red circle
Chart showing the diamagnetic cavity detected by Rosetta on July 29
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Chart showing the diamagnetic cavity detected by Rosetta on July 29
Chart showing levels of gasses in 67P's coma during the event, compared to ordinary levels (the black line) recorded two days earlier
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Chart showing levels of gasses in 67P's coma during the event, compared to ordinary levels (the black line) recorded two days earlier
The event captured in three chronological images – the image on the left was captured at 13:06 GMT, middle 13:24 GMT and right 13:42 GMT
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The event captured in three chronological images – the image on the left was captured at 13:06 GMT, middle 13:24 GMT and right 13:42 GMT

Rosetta has detected apowerful jet of activity emitted from the comet67P/Churyumov–Gerasimenko (67P). The force of the outburst, whichis believed to be travelling at 10 m per sec (32 ft per sec), wasstrong enough to temporarily repel the solar wind – a constant streamof charged particles emanating from the Sun, that work to convey ourstar's magnetic field across the solar system.

Both comet andspacecraft made their closest approach with theSun, otherwise known as perihelion at 02:03 AM GMT. The Rosetta science team expectedextreme comet activity in the weeks following perihelion, and notethat outgassing activity would be unpredictable even before, but thesheer power of the recent activity display appears to have caught theteam by surprise.

"This is the brightest jet we’ve seen so far,"states OSIRIS team member Carsten Güttler, of the Max PlanckInstitute for Solar System Research, Göttingen, Germany. "Usually,the jets are quite faint compared to the nucleus and we need tostretch the contrast of the images to make them visible – but thisone is brighter than the nucleus."

Rosetta, which is in the process of transitioning to a saferorbit of 300 km (186 miles), was able to detect the outburstfrom a distance of 186 km (116 miles) witha number of its onboard instruments. While being showered in theejected dust particles, ROSINA, theelement of the probe's scientific suit designed to map the comet'satmosphere and ionosphere, recorded significant structural andcompositional deviations in 67P's coma.

This image captured April 12 shows the origin of the jet on the comet's nucleus in a small red circle
This image captured April 12 shows the origin of the jet on the comet's nucleus in a small red circle

The orbiter's OSIRIS camera captured a sequence of images of 67Pduring the episode, first capturing the jet at 13:24GMT, with theoutgassing subsequently appearing to subside a mere 18 minutes later.However, whilst the jet itself may have been short-lived, its effectslingered for some time after, with Rosetta's GIADA instrumentrecording 30 dust hits on the spacecraft per day, a significantincrease from the standard 1-3 per day usually recorded.

As the event unfolded, the gas and dust being expelled from the cometpushed back the solar wind. Due to the fact that the comet itself isnot magnetized, Rosetta was able to make detailed studies of how thissolar wind interacted with 67P using its onboard Plasma ConsortiumMagnetometer, as any magnetic field readings detected could only beattributed to the solar wind.

"The solar windmagnetic field starts to pile up, like a traffic jam, and eventuallystops moving towards the comet nucleus, creating a magneticfield-free region on the Sun-facing side of the comet called a'diamagnetic cavity'," explains Charlotte Götz, science teammember for Rosetta's magnetometer instrument at the Institute forGeophysics and extraterrestrial Physics, Braunschweig, Germany.

The effect only lasted for a few minutes, but managed to push thesolar wind back as far as 186 km (116 miles) from 67P's nucleus, withthe event providing a valuable insight into the power of the comet'sactivity as it nears perihelion.

Source: ESA

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