Finding life on a world in the outer Solar System — think Enceladus or Titan for starters — would be an extraordinary step forward. Martian microbes, if they exist, might be evidence of contamination, or we might be evidence of ancient contamination from Mars, given the ready exchange of materials between our planets in the last several billion years. But the outer system offers the possibility of discovering life that originated entirely separately from anything we know.
The problem is that we’re a long way from having built the spacecraft that can make these detections. That’s why places like Pitch Lake, on the island of Trinidad, are so useful. Other than the temperature, conditions here are about as close to what we might find on Titan as anything we know. The 114-acre lake is a cauldron of hot asphalt permeated with hydrocarbon gases and carbon dioxide. As you can see in the image below, it’s hardly a hospitable-looking place.
But this asphalt hell-hole defies expectation. As discussed in a recent article in Astrobiology Magazine, each gram of its black goo can harbor up to 10 million microbes. We’re looking at life that seem to feed off hydrocarbons and, while not breathing oxygen, respire with the aid of metals. Both bacteria and archaea are represented, some of the latter falling “…far enough away from known groups as to represent novel lineages.”
Image: Pitch Lake bubbles with hydrocarbon gases and carbon dioxide. Credit: Pitch Lake Research Group.
Those are the words of Steven Hallam (University of British Columbia), who is working with Dirk Schulze-Makuch (Washington State) on the project. The two scientists believe that the presence of life in Pitch Lake makes the hydrocarbon lakes of Titan look more astrobiologically promising than we have suspected. Moreover, some of Titan’s hydrocarbon reservoirs may be heated from below.
How does Pitch Lake stay alive? From the article:
Each sample contained a distinct microbial population. Most of the bacteria appear related to ones found in oxygen-depleted sediments, methane seeps or oil reservoirs…
Water levels in the asphalt are low, at or below the reported threshold for life on Earth, so the life the researchers found in the lake might be constrained to watery pockets within the surrounding asphalt, similar to what is seen bound in frozen lakes and glaciers in the McMurdoDry Valleys in Antarctica. The fact that E. coli gut bacteria can generate most of their own water and that fungus found in kerosene can extract water from light hydrocarbons could point to how life can survive even when little to no liquid water is available.
Studies like this give us a glimpse of the adaptations possible when life sustains itself with hydrocarbons and metals in asphalt. But even if we eventually find no life on Titan, we’re also getting insights into life on the early Earth before it adapted to oxygen. As to Schulze-Makuch, he is much in the news these days. We’ve already reported on his argument that the Viking lander may have found life on Mars in the 1970s (see his book We Are Not Alone), but his focus seems to be moving ever further out in the Solar System.
Some day we’ll know how far life can go in the natural laboratory that is Titan. For now, we’ll continue to seek out environments that are at the outer edge of adaptability, hoping to broaden our definition of ‘habitable zone.’