On Thursday, the European Space Agency (ESA) announced that its Venus Express spacecraft had discovered that Venus, the second-closest planet to the Sun, has an ozone layer.

Scientists say that ozone on a planet may indicate the presence of life.

The ozone found on Venus is at far too small of a concentration to indicate that it derived from life there. But comparisons with ozone levels on Earth could help set parameters to determine the likelihood of life elsewhere.

'By chance'

Scientists from ESA made the determination after analyzing measurements from instruments aboard the Venus Express craft.

"We have been able to identify the signature [of the gas]," Franck Montmessin, an ESA researcher, told Deutsche Welle.

On-board instruments measured changes in wavelength of starlight passing through Venus' rather thick atmosphere.

"It was a bit by chance," Montmessin said. "We carefully looked at the spectra, and we saw some unexpected features," he explained.

The finding built on discovery of ozone on Mars, which "was more obvious," Montmessin added.

Other scientists were excited by these findings.

Anja Bauermeister, an astrobiologist at the German Aerospace Center, who was not part of the new ESA findings, told Deutsche Welle that she thinks the data are trustworthy, in particular since the measurements were taken so close to the planet.

Life on Venus?

With the addition of Venus, scientists now know there are three planets in our solar system with ozone: Mars, Earth and Venus.

On Earth, living organisms produce oxygen, which ultraviolet light breaks down in the upper layers of the atmosphere. These may combine with other oxygen molecules to become ozone. The ozone layer absorbs radiation, regulating the temperature on the planet.

As for life - possibly microbial - on Venus, Bauermeister said, "There is speculation."

These tiny, simple forms of life could have occurred shortly after the planet was formed, and if so, then most likely in drops of water in clouds of the upper atmospheric layers.

But the greenhouse effect on Venus, due in part to its lacking a thick ozone layer, has effectively prevented it from being hospitable to life.

"Conditions on Venus are really too harsh - people say it's basically like hell: hot, acidic," Montmessin said.

Ozone on Venus is nowhere near levels indicating that it originated from life. Rather, the Venusian ozone layer is likely a result of sunlight breaking up carbon dioxide in the planet's atmosphere.

'Biosignatures'

Ozone may, however, act as a "biosignature" - an element indicating the presence of life.

"If we find ozone on an exoplanet, we can't just jump for joy and say 'yoo-hoo! We've found life!'," Bauermeister said.

Exobiologists and astronomers say that the presence of ozone, especially in combination with oxygen and carbon dioxide, is a decent indicator of a higher probability that life may exist on a planet.

Bauermeister noted that methane, together with oxygen, is also a good biosignature. But the best one, she explained, is nitrous oxide, since it's a direct byproduct of life.

However, nitrous oxide is extremely difficult to measure in light spectrums, she added.

Further probes

Montmessin said the ozone signatures were found quite high in the atmosphere, at about 100 kilometers from the surface of the planet.

The ability for the Venus Express to probe the Venus atmosphere is limited, due to a thick layer of sulphuric acid.

"One could send balloons into the Venusian atmosphere" to probe it further, Montmessin said, adding that this has been done in the past.

In any case, he said, "we need to go back to Venus and use other types of measurements to see if there are types of complex organisms there."

Author: Sonya Angelica Diehn
Editor: Cyrus Farivar