June 15, 2024

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Jupiter’s Moon Io Could Play Host To Life

Jupiter’s Moon Io Could Play Host To Life

It was many years ago now when David Bowie asked if there was life on Mars. Since then, we’ve concluded there isn’t, much to everyone’s disappointment. That left scientists the world over to start looking elsewhere for new lifeforms for us to talk to, conquer, or play bridge with. Or perhaps more likely, look at under a microscope.

The latest candidate for hosting nearby life is Jupiter’s moon, Io. Let’s take a look at what makes Io special, and what we might hope to find there.

The Pizza Moon

When it comes to places to search for life, Io hasn’t really been at the top of the list. Other moons of Jupiter, like Europa and Ganymede, have been considered far more likely candidates. That’s largely down to the fact that those moons play host to subsurface oceans. Given that we know life and water are so closely intertwined here on Earth, that has guided our search elsewhere. Saturn’s moon Enceladus has also been considered a strong contender, for a plume of methane erupting from its surface. It too plays host to subsurface oceans which could theoretically host life.

Io’s volcanic eruptions can be huge in scale, as seen by Galileo in 1997.

Io, in comparison, is a hot and volcanic place. New data collected by NASA’s Juno spacecraft suggests that despite this rugged, unhospitable exterior, Io could still host living things. On a recent flyby, Juno got within 80,000 km of the so-called “pizza moon,” and a future pass will get as close as 1,500 km. That’s set to update our knowledge of the moon significantly. Before Juno, our last visit to Io was with the Galileo spacecraft, over 20 years ago.

In size, Io is roughly comparable to the Earth’s moon, also known as “The Moon”. Io is wracked by volcanic activity though, with active lava flows on the surface, with mountain ranges and plains interspersed with calderas left over from volcanic eruptions. Being so distant from the Sun, Io can be very cold, at up to -130 °C in places. It’s nevertheless is an energetic place, with eruptions capable of shooting lava hundreds of kilometers from the surface.

In fact, near areas of volcanic activity, temperatures can reach up to 1,600 °C.  The lava is kept hot and flowing thanks to the tidal forces experienced by Io, thanks to Jupiter itself and nearby moons Europa and Ganymede. It’s possible that the small moon may have once held water, like Europa or Ganymede, as ice was once common in its part of the solar system. However, a combination of radiation from Jupiter and the unrelenting tidal heating have likely long since driven away most of the water on Io, if any was once present.

Theories about life on Io center around the materials present and its unique environment. It’s believed that geothermal heat on the moon, combined with sulfur compounds, could serve as an energy source for simple microbial life. However, it’s unlikely these microbes would live on the surface, where temperatures are often well below freezing and radiation abounds. Instead, they could lurk within lava tubes beneath the surface. In fact, lava tubes commonly play host to microbes on Earth, all around the globe, so it’s conceivable that the same thing could happen on a distant rock far away in the solar system.

The difficulty for life on Io hinges on whether or not there is any water left on the desolate moon. Water serves as a solvent, and is involved in all manner of basic life processes for organisms on Earth. It’s abundant here, and the absence of water in an environment here largely coincides with an absence of life.

Lava tubes are conduits underground through which lava once flowed. It’s possible that lava tubes on Io could host life in much the same way they do on Earth. Credit: Frank Schulenburg, CC-BY-SA-3.0

If water isn’t present, though, alternatives could exist. Hydrogen sulfide (H2S) is one possibility, with some similarities to the chemical behavior of water. It exists in a liquid form from -86 °C to -60 °C. Given the temperature profile on Io, liquid H2S could form in areas beneath the surface, particularly if subsurface channels were warmed by lava flows. Life could potentially exist in a spore-like form, where it springs to life when at the right temperature and in the right solvent environment, and going dormant when conditions aren’t so suitable. Bacteria on Earth can behave in such ways, so it’s not inconceivable for life to develop in this way elsewhere.

Of course, it’s all speculation at this point. The primary focus is on theories as to whether life could be on Io, rather than investigating if it currently is there or not. Proving the latter is a difficult task, and one that would likely require new space missions with a focus on doing the hard science necessary. Perhaps, though, a future generation will be the first to discover life teeming just beneath the scorched surface of the distant Pizza Moon.

Featured image: “Full Disk Views of Io” by NASA.