Water Microhabitats in Oil Show Potential for Extraterrestrial Life
An international team of researchers has found extremely small habitats that increase the potential for life on other planets while offering a way to clean up oil spills on our own.
Looking at samples from the world’s largest natural asphalt lake, they found active microbes in droplets as small as a microliter, which is about 1/50th of a drop of water.
“We saw a huge diversity of bacteria and archaea,” said Dirk Schulze-Makuch, a professor in Washington State University’s School of the Environment and the only U.S. researcher on the team. “That’s why we speak of an ‘ecosystem,’ because we have so much diversity in the water droplets.”
Writing in the journal Science, the researchers report they also found the microbes were actively degrading oil in the asphalt, suggesting a similar phenomenon could be used to clean up oil spills.
“For me, the cool thing is I got into it from an astrobiology viewpoint, as an analog to Saturn’s moon, Titan, where we have hydrocarbon lakes on the surface,” said Schulze-Makuch. “But this shows astrobiology has also great environmental applications, because of the biodegradation of oil compounds.”
Schulze-Makuch and his colleagues in 2011 found that the 100-acre Pitch Lake, on the Caribbean island of Trinidad, was teeming with microbial life, which is also thought to increase the likelihood of life on Titan.
The new paper adds a new, microscopic level of detail to how life can exist in such a harsh environment.
“We discovered that there are additional habitats where we have not looked at where life can occur and thrive,” said Schulze-Makuch.
Analyzing the droplets’ isotopic signatures and salt content, the researchers determined that they were not coming from rain or groundwater, but ancient sea water or a brine deep underground.
In 2011, Schulze-Makuch speculated on the possibility of extreme life on Jupiter’s Io, the volcanic epicenter of our Solar System. Io, the innermost of Jupiter’s large satellites with plumes of matter rising up to 186 miles (300 km) above the surface.
In the image below two sulfurous eruptions are visible on Io from the robotic Galileo spacecraft that orbited Jupiter from 1995 to 2003. At the image top, over Io’s limb, a bluish plume rises about 140 kilometers above the surface of a volcanic caldera known as Pillan Patera.
In the image middle, near the night/day shadow line, the ring shaped Prometheus plume is seen rising about 75 kilometers, or about 46 miles, above Io while casting a shadow below the volcanic vent. The plume is visible in every image ever made of the region dating back to the Voyager flybys of 1979, presenting the possibility that this plume has been continuously active for at least 18 years.
“Everyone right away tends to categorically exclude the possibility of life on Io,” said astrobiologist Dirk Schulze-Makuch at Washington State University. Conditions on Io might have made it a friendlier habitat in the distant past. If life did ever develop on Io, there is a chance it might have survived to the present day, Schulze-Makuch suggested.
“Life on the surface is all but impossible, but if you go down further into the rocks, it could be intriguing,” he said. “We shouldn’t categorize it as dead right away just because it’s so extreme.”
Computer models suggest Io formed in a region around Jupiter where water ice was plentiful. Io’s heat, combined with the resulting possibility of liquid water, could have made life plausible.
“There must have been quite a lot of water on Io shortly after formation, judging from the amount of water ice on Europa and Ganymede,” said Schulze-Makuch.
Jupiter’s radiation would have stripped this water from Io’s surface, perhaps within 10 million years. At this point life could have retreated underground, where water might still be abundant, and geothermal activity and sulfur compounds could provide microbes with sufficient energy to survive.
Although no organic molecules have been detected on the moon’s surface, that does not mean they do not exist underground, Schulze-Makuch said. Any organic compounds that once existed on the surface or that may today still emanate from the subsurface — which probably were naturally present in this region of space during Io’s formation — would get quickly destroyed by Jupiter’s radiation.
The many lava tubes thought to exist on Io could serve as an especially favorable environment for life, Schulze-Makuch suggested, by protecting organisms from radiation. The lava tubes also could provide thermal insulation, trapping moisture and providing nutrients such as sulfurous compounds. Microbes are common in lava tubes on Earth, from ice and volcano zones in Iceland to hot sand-floored tubes in Saudi Arabia, and lava tubes are the most plausible cave environment for life on Mars, he added.
The primordial soup that any life on Io might have originated from was likely based on water, but the solvent of choice for organisms there might have drastically changed later on as the moon transformed. Hydrogen sulfide is one choice, as it is reasonably abundant in Io’s shallow subsurface and remains liquid from negative 123 to negative 76 degrees F (-86 to -60 degrees C), falling within the environmental conditions that would prevail there. While it is not especially efficient as a solvent for ions, it does dissolve many substances, including many organic compounds. Other possibilities include sulfur dioxide and sulfuric acid.
“I’m exploring with colleagues whether sulfur compounds could work as solvents of life,” Schulze-Makuch noted. Given the wild extremes Io can swing through as it orbits Jupiter, one possible survival strategy for life in this challenging environment would be to remain dormant most of the time, only reverting back when nutrients were rich. “It’d be much easier for life to take a beating if it goes dormant regularly,” Schulze-Makuch said.
- R. U. Meckenstock, F. von Netzer, C. Stumpp, T. Lueders, A. M. Himmelberg, N. Hertkorn, P. Schmitt-Kopplin, M. Harir, R. Hosein, S. Haque, D. Schulze-Makuch.Water droplets in oil are microhabitats for microbial life. Science, 2014; 345 (6197): 673 DOI: 10.1126/science.1252215