Life on Io? An astrobiologist says it’s possible
Jupiter’s moon Io doesn’t top anyone’s list in the search for extraterrestrial life in our solar system. Io – our solar system’s most volcanically active place – is a hell world. Hundreds of sulfur volcanoes erupt there on a regular basis, covering the entire moon in hot lava and sulfur deposits. But some scientists are rethinking the possibility of life on this hostile world. It would most likely be underground, if it ever existed. Astrobiologist Dirk Schulze-Makuch recently wrote about his own perspective on this intriguing idea in Big Think on January 13, 2023.
He also tweeted on January 14:
There could be or could have been #life in the #subsurface of #Io (the "Pizza Moon") – an overlooked target for #astrobiology,
posted at BigThink, direct link at:https://t.co/xTtBFlpb5d#space #science #moon #planet #universe #sciencetwitter #exploration #alien #microbial
— Dirk Schulze-Makuch (@extreme_microbe) January 14, 2023
An inhospitable volcanic world
Life as we know needs heat, water and chemical nutrients. Io has at least one of those … heat. And lots of it, with all those volcanoes and subsurface magma. Maybe even a global magma ocean, according to a recent study. But water and nutrients would seem to be severely lacking.
The moon is covered in lava flows and sulfur dioxide deposits from ongoing eruptions. There’s also very little atmosphere, and the average surface temperature is -202 degrees Fahrenheit (-130 Celsius), while volcanic hotspots can reach a sizzling 2,900 degrees F (1,600 C). Scientists say that Io may have once had more water, perhaps even similar to the ocean moons Europa and Ganymede. But then it lost all or most of it over billions of years. As Schulze-Makuch wrote:
The moon’s surface is constantly being reworked, which means that we see no fresh impact craters. Early in its history, Io may have held as much water as Europa or Ganymede, since it formed in a region of the solar system where water ice was plentiful. In those early days, the combination of liquid water and geothermal heat could have led life to develop. However, due to Jupiter’s unforgiving radiation and tidal heating, Io subsequently lost most if not all of its water, and the surface became uninhabitable.
Not exactly the most welcoming place for life, at least as we know it here on Earth. Or is it?
Life on Io: Maybe not impossible after all?
These hostile conditions are what we see on the surface. But, what about below the surface? Europa and Ganymede are also desolate and unfriendly to life on their surfaces, but below their icy crusts are global, salty oceans. So what about Io?
As Schulze-Makuch noted, there may still be water and carbon (at least as carbon dioxide) underground. Io’s volcanoes emit sulfur dioxide, however, so that gas is likely more dominant.
But could microbes survive in Io’s subsurface, if they ever existed? On Earth, geothermal activity, as from volcanoes, provides energy sources for microbial life. The same could happen on Io, at least theoretically. On Io, reduced sulfur compounds, such as hydrogen sulfide, could provide some of the needed energy for biology. The underground environment could protect any organisms from the powerful radiation from Jupiter that hits Io. But it would also need to be warm enough and contain at least some moisture.
If there is not enough water, hydrogen sulfide may work as a substitute. Like water, it can dissolve organic compounds. It could also remain liquid in the possible conditions below Io’s surface, scientists say.
It’s all still a matter of conjecture at this point, but seemingly not impossible. Any life below Io’s surface would probably be quite different than anything on Earth. It would have evolved to survive the unique – and overall still quite hostile – conditions found there.
Life on Io could hide in lava tubes
Schulze-Makuch had earlier proposed at a conference in 2004 that microbes on Io might find a home in lava tubes. He also published a paper detailing this idea in 2009, in the Journal of Cosmology. Schulze-Makuch said:
At a 2004 conference in Iceland, followed by a paper six years later, I suggested that lava tubes could take over that function. They should be common on Io, given all the volcanic activity. Microbial growth is common in lava tubes on Earth no matter the location and climate, whether it’s ice-volcano interactions in Iceland or hot, sand-floored lava tubes in Saudi Arabia. Lava tubes are the most plausible cave environment for life on Mars, and caves in general are a great model for potential subsurface ecosystems.
As the paper also notes:
Lava tubes on Io may be an ideal habitat for any remaining microbial life, because they provide (1) protection from radiation, (2) insulation to keep temperatures sufficiently high and constant, (3) trap moisture and (4) provide nutrients such as sulfide and H2S that could be oxidized to sulfur dioxide or sulfates.
Juno and Io Volcano Observer
NASA’s Juno spacecraft has been studying Jupiter since 2016. While Jupiter itself is the main priority, Juno has also taken close looks at some of its larger moons, too, including Io. Indeed, Juno sent back some amazing infrared photos of Io’s erupting volcanoes on July 5, 2022. At the time, Juno passed about 49,700 miles (80,000 km) from Io’s surface. Later this year, it will pass by again, but this time at only about 930 miles (1,500 km) from the moon.
Juno should be able to provide more clues as to what is happening inside Io, as well as survey its surface in great detail.
Moreover, the proposed Io Volcano Observer (IVO) could do even more. It is currently under consideration for NASA’s Discovery Program. If selected, it will be a dedicated Io mission, making at least 10 close flybys over four years. Dipping as close as 120 miles (200 km) above the moon, IVO would image about 90% of Io’s colorful surface down to about 900 feet (300 meters) per pixel, and smaller areas down to an incredible 10 feet (3 meters) per pixel. It would also study the heat movement inside Io and take video of the erupting lava and plumes.
Keeping an open mind
Schulze-Makuch advises people to remain open-minded about the possibility of life on Io. It may be a long shot, but we could at least look for tentative evidence. He concludes the earlier paper saying:
Based on a consideration of possible life-sustaining solvents, organic building blocks, and energy sources, the plausibility of life on Io has to be considered low. Certainly, Europa and also Ganymede are the higher priority targets for astrobiology in the Jovian system. Nevertheless, there could conceivably be a habitable niche in the shallow subsurface, particularly in lava tube caves on Io, an idea which we can not dismiss without further investigation.
Bottom line: Could there be microbial life on Io? Jupiter’s hostile volcanic moon seems an unlikely home, but astrobiologist Dirk Schulze-Makuch says it’s not impossible.