Solar Wind Explodes on Venus

As the solar wind flows around Venus, it creates similar space weather effects as it does near Earth. Credit: ESA/C. Carreau

In the grand scheme of the Solar System, Venus and Earth are almost the same distance from the Sun. Yet the planets differ dramatically: Venus is some 100 times hotter than Earth and its days more than 200 times longer. The atmosphere on Venus is so thick that the longest any spacecraft has survived on its surface before being crushed is a little over two hours. There’s another difference, too. Earth has a magnetic field and Venus does not — a crucial distinction when assessing the effects of the Sun on each planet.



“They are an amazing phenomenon,” says 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.”


When discontinuities in the solar wind remain in contact with a planet’s bow shock, they can collect a pool of hot particles that becomes a hot flow anomaly (HFA). An HFA on Venus most likely acts like a vacuum, pulling up parts of the planet’s atmosphere. Credit: NASA/Collinson

“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 says. “But a day on Venus is 243 Earth days.”




Rock morphology on Venusian surface from Venera, restored from 1975 data transmissions. The atmosphere on Venus is so thick that every spacecraft that has traveled to its surface has been crushed under the severe pressure in a matter of hours. Image Credit: Mitchell, ©

“These plasma particles are trapped in place,” says Sibeck. “They make a big puddle that gets bigger and bigger, sending out its own shock waves. Everything downstream from that bubble is going to be different than what’s upstream.”

Those downstream disturbances are what make HFAs interesting. These eruptions create global disturbances far beyond the mere local disruption of a hot plasma explosion. These eruptions of solar material can compress the entire magnetosphere around Earth for minutes at a time, shaking the particles along magnetic lines and causing them to fall into Earth’s atmosphere near the magnetic poles to create dayside aurora.

Understanding what the HFAs do in the non-magnetized Venusian environment, of course, would require direct observations that the current data sets from Venus Express do not provide. However Collinson and his colleagues have made some educated guesses. “At Earth, HFAs have a big effect, but don’t necessarily rule the roost,” says Collinson. “But at Venus, since the HFA happens right up next to the planet, it is going to have a more dramatic effect on the system.”


That HFAs can occur on a planet without a magnetic field suggests that they may well happen on planets throughout the Solar System, and indeed in other solar systems as well.