Life Under A Spanish Red River

NASA scientists will visit Spain April 10 through 12 to search for drilling sites where later this fall they plan to look for exotic life forms that may live underground near the Rio Tinto, a river in southwestern Spain.

During the Mars Analog Research and Technology Experiment (MARTE), scientists and engineers from NASA, U.S. universities and the Spanish Centro De Astrobiología (Center for Astrobiology) hope to show how robot systems could look for life below Mars’ surface. Bacteria may dwell beneath the surface, eating minerals derived from subsurface rocks that contain iron and sulfur.

acidophilic demateaceus fungi
Acidophilic demateaceus fungi (black fungi) from Rio Tinto.
Credit: Dr. Ricardo Amils Pibernat

Similar bacteria are in the very acidic Rio Tinto, and these microbes may play a role in producing acid in the river. Located in a region that legend claims was part of King Solomon’s mines, the Rio Tinto looks like deep, red wine, because iron is dissolved in the highly acidic river water. Mining activity at the Tinto River dates back at least 5,000 years

"The Rio Tinto area is an important analog to searching for life in liquid water, deep beneath the subsurface of Mars," said Carol Stoker, principal investigator of the three-year project and a scientist at NASA Ames Research Center in California’s Silicon Valley. "Beginning next fall, we plan to start drilling to explore for life in subsurface waters that are the source of the Rio Tinto," she said.

Core Science

The team plans to explore the area using a drill and science instruments designed for use in a Mars mission. Scientists at NASA facilities in the United States and at the Centro de Astrobiología in Madrid will remotely operate a robotic drill and life-detection instruments, and will interpret the results, all via satellite, to simulate the operation of a mission to search for life on Mars. At the same time, scientists at the drill site will conduct traditional core sample drilling and analysis to understand subsurface life forms at the site and to check the accuracy of the remote-control efforts to identify life forms, organic compounds and minerals.

As a simulation for remote planetary exploration, "the project could have a large impact, since a drilling system and many instruments and equipment developed specifically from the project are going to be tested outside a laboratory, (in) uncontrolled environmental conditions like high temperature, humidity, transport vibration, etc.," said Javier Gómez-Elvira, lead engineer for robotics for the Centro de Astrobiología. Because the science team will remotely operate all equipment and instruments, including the drill, many ‘lessons learned’ could result that could be used for a real Mars mission, Gómez-Elvira explained.

Drill Down

The subsurface is the key environment for searching for life on other planets, according to MARTE scientists. "Life needs liquid water and a source of energy," Stoker said. On Earth, most common life forms are at the surface, where sunlight provides the energy, but liquid water occurs rarely at the Martian surface, if at all. Liquid water is expected in the subsurface of Mars. So, NASA plans to use robotic drilling to search for subsurface life. "That is why we are testing the life search strategy in the Rio Tinto, where subsurface water and chemical energy are expected to support life," Stoker added.

Water sample from RT showing different eukaryotic cells and prokaryotes
Water sample from the river in which different eukaryotic cells (Heliozoa, diatoms, dinoflagelates) and prokaryotes (much more smaller) can be seen.
Credit: Dr. Ricardo Amils Pibernat

Scientists say evidence suggests the chemistry of the Rio Tinto and its biology may be a result of an underground, biologically-based, chemical reactor fueled by organisms that do not need oxygen gas to survive. MARTE scientists propose that such a system may exist in the subsurface of the Rio Tinto area, according to Ricardo Amils Pibernat, a biologist at the Centro de Astrobiología and a specialist on the biology of the Rio Tinto. If found, this type of life would represent an entirely new subsurface life system, he said.

Ricardo Amils Pibernat is the director of the laboratory of applied microbiology at the Center for Molecular Biology at the Autonomous University in Madrid. He says the water’s red color and average pH of 2 [highly acidic] is due to this natural abundance of sulfide. Pibernat believes that bacteria living in the river turn this sulfide into sulfuric acid, giving the river its low pH. Other bacteria oxidize the iron, giving the river its signature red color. Although both sulfur and iron naturally oxidize (or ‘rust’) when exposed to air, the bacteria act as catalysts, speeding up the reactions considerably.

Tinto_river_runs_red
Sulfide minerals on surface of ponded water, Rio Tinto region of Spain, July 2002
Credit: Carol Stoker, NASA Ames

It is not precisely known how bacteria oxidize the ferrous iron. Scientists believe the process relies on both chemical and biological forces working together. Pibernat’s team has collected about 1,300 different organisms, including archaea, yeast, fungi, and protists. The most abundant biomass in the river seems to be algae. Blooms of algae often coat the surface of the water, turning the red water green and producing bubbles of oxygen. Pibernat thinks it is strange how eukaryotic organisms like algae are able perform in such harsh conditions of acidity and heavy metal concentrations (Eukaryotes are organisms that have a DNA-holding nuclear membrane in their cells).

What’s Next

One of the largest deposits of sulfide minerals in the world is in the Rio Tinto region. Similar mineral deposits may well be found on Mars, according to the scientists. "There is a critical and immediate need for technology maturation for drilling that can be done during a field experiment on Earth to simulate a Mars mission," Stoker said. "It is crucial to prepare for Mars exploration by understanding the relevant terrestrial environments where life persists," she added.

Searching for life in the subsurface of another planet will not only require drilling, but sample extraction and handling, as well as new technologies to identify biomarker compounds and search for living organisms, according to Stoker and her colleagues. "A biomarker compound is like a signature left by life," she explained.

During the Rio Tinto campaign, the drill and the robotic system will bring cores of underground rock to the surface. There, a suite of remotely operated science instruments that simulate a Mars mission payload will analyze samples and search for signs of life or biomarkers. The Signs of Life Detector (SOLID) instrument, developed at the Centro de Astrobiología, will search for life in the samples using new technology derived from molecular biology. This instrument can detect not just whole organisms, but macromolecules or other life byproducts, said Gómez-Elvira.

Researchers from the Centro de Astrobiologia have suggested that the Tinto River also makes a good Europa analogy. Jupiter’s moon Europa is thought to have an acidic, salty ocean under its outer layer of ice. Thus, the Tinto River could represent a unique biological setting also to investigate the possibility of sulfur-based life on Europa.

"In addition to looking for evidence of subsurface life, we hope MARTE inspires students to pursue careers in science and engineering," Stoker said. "Because of the location in Spain, we’re hoping this experiment will be of particular interest to Hispanic students."


The NASA team also will meet with Spanish scientists in Madrid April 14 through 15 at the Centro De Astrobiología. The Astrobiology Science and Technology for Exploring Planets program at NASA Headquarters, Washington, is funding the project.