For sometime (since the 1970s) we have known that there is something a bit...odd about Venus. Recently, the European Space Agency's Venus Express mission, which has spent more than 8 years studying Earth's planetary twin, collected data that revealed new information on the gigantic holes on the nightside of Venus' ionosphere. Scientists at NASA's Goddard Space Flight Center investigated these mysterious holes, and found evidence that the sun's magnetic field lines may be penetrating through the planet.
Unlike Earth, Venus doesn't have a magnetic field to protect it from the Sun's solar winds.
Ultimately, life on Earth needs this magnetic field because (occasionally) our sun will produce violent solar storms. Solar storms generally occur as a result of variations in the Sun’s magnetic field lines. When these field lines fluctuate, the matter they contain is released out into the solar system (and by “released,” I mean that it explodes from the Sun in a hellish firestorm). These super-heated particles blast from the Sun at speeds exceeding 600 miles per second (1,000 kms), and they can contain over 200 billion pounds of material (100 billion kilograms). This is bad news for anything that is in the path of the explosion.
In fact, our planet is constantly bombarded by a steady stream of high energy particles from the Sun. Without Earth’s magnetic field, the solar winds caused by the Sun would strip away our atmosphere, destroying our cellular structure and evaporating our oceans in the process.
In short, without its magnetic field, Venus is just a huge, unprotected rock sitting in space. Consequently, due to the strong solar winds that are emitted by our Sun, the planet's ionosphere streams behind it—trailing a thick path that is not unlike the tail of a comet; however, when these winds reach the planet, they can't quite penetrate Venus' ionosphere because it is so thick—but only on the day side.
Notably, Venus has a very slow rotational period. A year on the planet is 225 Earth-days long. Yet, a day lasts a staggering 116.5 days on Earth. One result of this slow rotational period is a thick ionosphere on the day side of the planet (and we mean thick; our landers can only survive on this harsh world for a few hours before being crushed by the immense atmosphere) and a thinner layer on the nightside. This occurs because Venus' local environment is characterized by a stream of electrons and protons (called plasma) that streams out from the Sun. As the embedded magnetic fields, which are carried on these winds, reach Venus they build up,. Some of this plasma shoots around the planet, but much of it is squished up against Venus, creating a one-sided pile of plasma on top of the (already super thick) ionosphere that is on the Sun-facing side.
Ultimately, this buildup makes a thin magnetosphere around Venus (much smaller than the one around Earth).
In order to determine what was causing the holes on the nightside, the Venus Express flew through the them, and the observations suggest that there are actually two holes. The lower density material in this region is stretching out from the planet's surface off into space. It seems that some magnetic structure causes the charged particles to be squeezed out of these areas.
Glyn Collinson, a space scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is first author of a paper on this work in the Journal of Geophysical Research, asserts that there are two possible causes for this squeezing.
1. The magnetic lines that travel from the Sun do not all wrap around the planet, some shoot through. "We think some of these field lines can sink right through the ionosphere, cutting through it like cheese wire," said Collinson. "The ionosphere can conduct electricity, which makes it basically transparent to the field lines. The lines go right through down to the planet's surface and some ways into the planet."
2. The magnetic fields from the solar system all drape themselves around the ionosphere; however, as this happens they collide with a pile up of plasma already at the back of the planet. When the two materials collide and content for space, it causes the required magnetic squeeze in the perfect spot