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Space probe reveals more about mysterious holes of Venus

Paul Sutherland, Feature writer
Sep 15, 2014, 14:14 UTC

Sen—Europe’s Venus Express spacecraft has helped scientists learn much about the second planet from the Sun. Latest findings reveal more about mysterious giant holes that form in a layer of its atmosphere called the ionosphere.

Though Venus is a similar-sized, rocky world to our own, it could hardly be more different. It has a dense poisonous atmosphere with such high pressure that the few probes that have made it to the surface have been swiftly crushed.

Another difference is that, unlike Earth, Venus has no magnetic field. This means that the solar wind, a stream of charged, heated gas flowing in from the Sun, has nothing to deflect it at a safe distance. Instead it bombards the Sun-facing side of Venus and wraps itself around the electrically charged ionosphere.

Venus Express has spent the last eight years in orbit about the world dubbed Earth’s “evil twin”, following its launch on 9 November, 2005. An earlier NASA probe, called Pioneer Venus Orbiter, was sent to the planet in 1978 and was first to note the solar wind’s effect on the ionosphere, stripping the atmosphere away to form a kind of tail, rather like a comet’s. But it also observed the first hole.

Glyn Collinson is a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who has led a team study of the phenomenon. Their work is pubished in the Journal of Geophysical Research. 

Collinson said: “When Pioneer Venus Orbiter moved into orbit around Venus, it noticed something very, very weird—a hole in the planet’s ionosphere. It was a region where the density just dropped out, and no one has seen another one of these things for 30 years.”

Venus Express changed that. Despite the fact that the European Space Agency (ESA) probe is currently in a polar orbit that is much higher than Pioneer’s was, the newer spacecraft has recorded similar holes in the ionosphere.

A video illustrates the nature of the mysterious holes of Venus. Credit: NASA Goddard

It has also shown that they are a common occurence at Venus. NASA’s orbiter only saw the the holes at times when the Sun was especially active. Venus Express, however, has shown that the holes form throughout the solar cycle, even when activity is low. It also revealed that they penetrate deeper into the atmosphere than had been realised. 

Venus Express’s onboard instruments detected a jump in the field strength as it flew through the ionospheric holes, as well as very cold particles flowing in and out of the holes, though at a lower density than in the rest of the ionosphere.

This leads Collinson to believe that the holes are actually tubes of lower density material, stretching far out into space, rather like toothpaste squeezed from a tube. He believes that this is due to some magnetic structure, but their exact nature is not yet clear.

He said: “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.”

Collinson suspects the phenomenon is similar to one found on the Moon where magnetic field lines from the Sun go through its mantle and right to the iron core that is thought to lie at its heart.