'Flux ropes' discovered in Venus' atmosphere



`Flux ropes` discovered in Venus` atmosphere New York: Astronomers have spotted enormous magnetic entities - called flux ropes - stretching for hundreds of kilometres in Venus's upper atmosphere, above the poles.

The European Space Agency's Venus Express spacecraft observed the strange structures in Venus' atmosphere which has redrawn scientists' perceptions of the planet's magnetic environment.

Flux ropes have been seen before around other planets, including Earth. They transport superheated plasma gas from one side of the "rope" to the other.

On Earth, flux ropes form near the face of the planet opposite the Sun. The stream of charged particles known as the solar wind flows around the planet and creates a "magnetotail" of charged particles on the other side.

Periodic solar outbursts known as coronal mass ejections arise from a type of flux rope. The delicate structures sit on top of the Sun and transport matter and superheated gas from one part of the Sun to another.

Venus stands apart from most other planets in the solar system, however, because it has no magnetic field.

Study leader Tielong Zhang, in an email to the website said the ionosphere (or upper atmosphere) of Venus acts as an obstacle to the solar wind.

When Venus' atmosphere has a higher pressure than the incoming solar wind field, the ionosphere is considered "unmagnetised," meaning that it's free of all but the smallest magnetic field structures.

The ionosphere of Venus stays unmagnetised most of the time, until the solar wind reaches a higher pressure than the surrounding atmosphere and magnetises it.

In these conditions, relatively small flux ropes can form due to the higher speed of the solar wind rolling over the slower ionosphere, researchers said.

"The ionosphere is filled with these very small kilometres across - flux ropes," said Christopher Russell, a space physicist at UCLA and co-investigator of the study. Scientists determined that the flux ropes on Venus form from solar particles on the side of the planet facing away from the Sun, in the magnetotail.

"It seems to be associated with a process known as reconnection, which is magnetic field lines joining up together and forming a new magnetic configuration," Russell said.

Zhang noted that giant flux ropes were previously found in the atmosphere of Mars ? but only in the southern hemisphere. Mars, like Venus, does not have a planet-wide magnetic field.

"The observation and formation of the large flux rope at Mars might raise speculative questions related to the giant flux ropes at Venus," Zhang said, but added it was too early to draw direct links.

The findings were published in the journal Geophysical Research Letters.

PTI