Life on Mars does it exist? Depending on when you last checked in with news about the Red Planet, you could probably be convinced either way. As we discover more and more about the composition and planetary dynamics of Mars, there has been cause for both elation and disappointment regarding the likelihood that organic life could manage to eke out a living on the planet.

The pendulum swung back toward the no side today with the release of a study examining how a special kind of salt on Mars interacts with ultraviolet radiationthere. Martian soil islaced with perchlorates, an ioncomposed of one chlorine and four oxygen atoms, and which binds to a number of different elements to form various compounds. Its classified as a salt, and was initially cause for celebration among extraterrestrial hopefuls because it drastically lowers the freezing point of water, meaning that liquid H20 might conceivably exist on the surface. It can also be used to produce rocket fuel and oxygen, another plus for future settlers.

It turns out that these perchlorates are actually highly toxic to life when bathed in UV radiation that pummels Mars. Researchers from theUnited Kingdom Centre for Astrobiology at the University of Edinburgh exposed a strain of bacteria commonly found on spacecraft to levels of perchlorates and UV light found on the Red Planet and found that nearly all of them were dead within a minute. They tried this with several different kinds of perchlorate, and found similar results every time. Adding in additional environmental factors found on Mars like low temperatures, additional minerals found on Mars and a lack of oxygen also failed to keep the bacteria alive.

This was a bit surprising for the researchers because the strain of bacteria used,Bacillus subtilis, belongs to a genus that actually does fine in the presence of perchlorates, as studies of the microbesinterrestrial environmentshave confirmed. These findings were initially good news for researchers looking for extraterrestrial life, as they suggested that some forms of life could survive in Martian analogue conditions.

Theres more to Mars than just the soil though, and when the Edinburgh researchers added in a few more Mars-like factors UV specifically the bacteria died in short order. They think this happens because the UV light breaks apart the perchlorate molecules into more reactive ions that wreak havoc on living cells. This hypothesiswas backed up by the observation that low temperatures, which slow down chemical reactions, extended the lifespan of the bacteria in the perchlorates but still resulted in them dying. If they cant survive there, it significantly lowers our chances of finding life on Mars life that looks similar to organisms on Earth at least. The researcherspublished their findingsThursday inNature Scientific Reports.

While its a blow to the possibility of finding life on Mars, there is at least one upside to the news: NASA regularly worries about the possibility of contaminating other planets with Earthly bacteria, even going so far as tocrash probes into Saturnso that they dont hit the planets moons. If Mars is so hostile to bacteria that they cant even make it a minute on the surface, our fears of contamination could be pretty much resolved.

This article originally appeared on Discover.

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Mars may be more toxic to life than we thought - Astronomy Magazine