Washington: Researchers have observed a type of space weather outburst on Venus, which are quite common on Earth.
As the solar wind rushes outward from the sun at nearly a million miles per hour, it is stopped about 44,000 miles away from Earth when it collides with the giant magnetic envelope that surrounds the planet called the magnetosphere.
Most of the solar wind flows around the magnetosphere, but in certain circumstances it can enter the magnetosphere to create a variety of dynamic space weather effects on Earth.
Venus has no such protective shield, but it is still an immovable rock surrounded by an atmosphere that disrupts and interacts with the solar wind, causing interesting space weather effects.
A recent study has found clear evidence on Venus for a type of space weather explosion called a hot flow anomaly. These anomalies, also known as HFAs, cause a temporary reversal of the solar wind that normally moves past a planet.
An HFA surge causes the material to flood backward, said David Sibeck, a scientist at NASA``s Goddard Space Flight Center in Greenbelt, Md., who studies HFAs at Earth and is a co-author on the paper.
“They are an amazing phenomenon,” said Sibeck.
“Hot flow anomalies release so much energy that the solar wind is deflected, and can even move back toward the sun. That’s a lot of energy when you consider that the solar wind is supersonic – traveling faster than the speed of sound – and the HFA is strong enough to make it turn around.”
Observing an HFA on Venus will help scientists tease out how space weather is similar and different at this planet so foreign to our own.
With no magnetic field to interact with, space weather at Venus is milder than that at Earth, but occurs much closer to the surface.
“Hot flow anomalies average one a day near Earth,” says Goddard scientist Glyn Collinson and the first author on the new paper.
“They’ve been seen at Saturn, they may have been seen at Mars, and now we’re seeing them at Venus. But at Venus, since there’s no protective magnetic field, the explosion happens right above the surface of the planet.”
The search for this kind of space weather on Venus began in 2009 when NASA’s Messenger satellite, which is actually a mission to study Mercury, spotted what may well have been an HFA at Venus.
But Messenger’s instruments could only measure a suggestive magnetic signature, not detect the temperature of the material inside, a necessary measurement to confirm the heat of a “hot” flow anomaly.
For further evidence, Collinson turned to a European Space Agency spacecraft called Venus Express.
Venus Express was not designed to study space weather phenomena per se, but it does have instruments that can detect magnetic fields and the charged particles, or plasma, that make up the solar wind.
Collinson began to search for the telltale signatures of an HFA through a few days worth of data.
“That may not sound like much,” he said.
“But a day on Venus is 243 Earth days.”
Collinson looked for a pattern of magnetic change that would indicate the spacecraft traveled through one of these gigantic explosions. Envision what a bullet might experience if shot through a hot air balloon – a moment of heat in an otherwise fairly temperature-consistent journey. In this case, the heat comes with other characteristics as well: The boundaries show an abrupt change in the magnetic fields, and the inside is less dense than the outside.
Given a set of instruments that were not specifically designed to find this signature, the search turned up quite a long list of potential, but not conclusive, events.
But his work eventually paid off. A combination of magnetic and plasma data shows that a Venusian hot flow anomaly did indeed take place on March 22, 2008.
The study has been published online in the Journal of Geophysical Research.