A new study of Venus reveals a strange and surprising green glow in the night sky, while separate research seems to have solved a 20-year-old question about whether lightning strikes on the cloud-shrouded planet.

For two decades, scientists have argued about whether the atmosphere of Venus produces lightning. During two flybys, the Cassini spacecraft detected no signatures of Earth-like electrical discharges.

"If lightning exists at Venus, it is either extremely rare, or much different than terrestrial lightning," said University of Iowa physicist Donald Gurnett.

On Earth, the crackle of lightning can be heard on an AM radio. Cassini easily detected such signals on an Earth flyby, but heard nothing as it looped around Venus in 1998 and again in 1999. The craft used the planetary flybys to get gravity boosts that helped propel it toward Jupiter and Saturn.

Gurnett told SPACE.com he was "very certain" of the results, which appear in the Jan. 18 issue of the journal Nature.

Missions in the 1970s found low-frequency electrical activity in the clouds of Venus, but Gurnett suspects the activity represents something like "sprites," discovered recently above Earth's clouds. Sprites are similar to lightning, but they travel upward from clouds into the ionosphere, and they involve far less electricity.

Gurnett didn't zap all hopes for lightning on Venus. He said there might be some cloud-to-cloud lightning, which is weaker than the typical bolts that strike the ground in a terrestrial thunderstorm.

The glow surprised Slanger and other scientists, who did not expect Venus to have the right chemistry to produce the phenomenon. How it is generated is not fully understood, but Slanger says it results when pairs of oxygen atoms collide to form an oxygen molecule, the energy of which is transferred to a third atom, which releases light energy that is -- you guessed it -- green.

But there's a little problem with that theory. Venus has virtually no molecular oxygen in its carbon dioxide choked atmosphere.

What little oxygen that is created -- when sunlight interacts with the carbon dioxide -- develops on the dayside. That oxygen then circulates. Venus' upper atmosphere rotates more rapidly than the surface, transporting oxygen atoms swiftly around the planet. "Within a few hours of formation, the oxygen atoms move to the dark side of the planet," Slanger explains.

Thick clouds around Venus have long frustrated scientists trying to understand the atmosphere of our nearest planetary neighbor.

"The new observations should help to unravel the unusual oxygen chemistry and dynamics of the upper atmosphere of Venus," writes NASA's David Crisp in the January 19 issue of the journal Science, where the study is presented.

On Earth, a similar green glow exists in addition to a related phenomenon, the multi-colored northern and southern lights known as aurorae. These lights are created when charged particles from the solar wind excite gas molecules in the upper atmosphere, mostly near the poles.

Venus shows no evidence of aurorae, Slanger said. The main reason is that Venus does not have a strong magnetic field, which on Earth traps and concentrates the charged solar particles that fuel the colorful lights.

Observations of Venus in the 1970s showed no evidence of the nighttime green glow, either, leading scientists to assume that it would only be found on planets with Earth-like atmospheres -- those rich in oxygen and having the potential to support life. It has therefore been considered as a possible signature for potentially habitable places outside the solar system.

But Slanger points out that the discovery of a green glow on Venus means other planets that exhibit it might, like Venus, contain very little oxygen.

"In this way, information gained from another planet enables us to say more about our own, and will help us to interpret what we may see in the future outside the solar system."

Slanger collaborated with David Huestis and Philip Cosby, also of SRI, as well as the Keck Observatory's Thomas Bida, who is now at the Lowell Observatory.

Click here to learn more about Venus and its climate.