When NASA’s New Horizons mission flew by Pluto last year, it sent back images that recalled a past era – a time when a few photos of initial reconnaissance could drastically change our sense of an entire celestial body. For The Moon and Mars, these initial glimpses happened decades ago; satellites of the gas giants, like Europa, Enceladus, and Titan were ready for their close-ups next. And after that? Well, it seemed as if the geologically active, charistmatic targets in our Solar System were spoken for. As illuminating as subsequent investigations have been – and to be sure, there are fundamental aspects of all of these bodies that still await discovery – at least we knew what kind of world we were dealing with.
That all changed with Pluto. Expectations were low, given the outer Solar System’s reputation as an icy wasteland, but when initial photos showed potential cryovolcanoes and recent resurfacing, the questions came fast and furious. Many of them centered around the heart-shaped feature a thousand kilometers across located at 25 degrees north latitude.
How hot is too hot for life to survive? Ever since microbes were discovered squirming around in hydrothermal springs several decades ago, the limit of heat-loving (thermophilic) organisms has been a moving target. The current record-holder is “strain 121,” an archaeon isolated from the Mothra hydrothermal vent deep beneath the surface of the northeast Pacific Ocean; suitably enough, it can grow at a blistering temperature of 121 °C.
There are some physical limitations of biological activity at high temperature. Enzymes unfold, as rapid molecular bond vibrations tear intricate molecular structures apart, obliterating their functional capabilities. Individual amino acids lose their “handedness” as geometrical arrangements of molecular structures equilibrate with heat; since all known biological amino acids are “right-handed,” organisms must spend a lot more energy re-shaping amino acids to fit the template. DNA bases “A” and “G” falter at exponentially higher rates as the temperature goes up, leading to murderous rates of mutations.
Despite these assessments of biomolecule stability and the search for the thermal outliers, there haven’t been a lot of systematic studies of how habitability at seafloor sites changes with temperature. Sure, an impressive organism or two can eke out a living at 121 °C in the lab, but is that also true in the real world, where conditions could be much more variable? And are viable communities around continuously up to that thermal limit?
In 2007, the Mars Exploration Rover (MER) Spirit came across a slightly raised platform, roughly pentagonal in shape and 90 meters across, which scientists named Home Plate. The rocky outcrop had a base of solidified ash, with nearby deposits of gas-filled basalts. Next to the plateau, nubby, nodular chunks of rock showed up, and light-colored soil just beneath the surface was exposed by the rover’s wheels. Mineralogical spectra of the bright soil were beamed back to Earth, revealing, to the scientists’ surprise, that it was composed almost entirely of silica.
When the geological puzzle pieces were assembled, two main options emerged: Home Plate may have been a volcanic fumarole, spewing sulfuric acid at basaltic rocks and leaving silica behind, or it could signify the remnants of a mineral rich hot spring, whose silica-saturated water generated the knobby rocks. Either way, water and heat were likely involved, and the discovery led to an onslaught of new questions and exciting plans for further studies.
But then, the Spirit rover went silent, forcing MER scientists to get creative. To pursue the Home Plate mystery, they’ve scoured the Earth for mineralogical signals most similar to those found on Mars. By determining the conditions that best recapitulate the martian data, the thinking goes, we might be able to piece together the events of Mars’ ancient past.
Astronauts flying long-duration missions in space have been known to suffer substantial health effects: they grow nauseous, lose bone density, and watch their muscles atrophy. These large, human-scale changes are pretty easy to observe, as trillions of cells’ responses to microgravity are compiled into the physiological response of one organism. But what’s happening at the cellular scale? How do single-celled life forms respond when launched into space?
Gravity is an aspect of life that we – and all other organisms on our planet – have taken for granted for all but the last 50 years of our 3+-billion year evolutionary journey. This makes it hard to think about ways in which gravity could be hard-wired into biology, as it never represented an actionable variable for evolutionary pressures.
By taking life into space, biologists are seeing how gravity affects the cellular environment in fundamental ways. It’s been suspected for years: past experiments have shown that microbial cultures tend to form biofilms more easily, and pathogens become stronger. But a genetic, mechanistic understanding of these processes hadn’t been explored.
The search for life beyond Earth has inspired many strategies, from examining microfossils with elemental analyzers, to sequencing putative genetic material, or studying the composition of distant exoplanets. But a recent paper from Jay Nadeau, a Scientific Researcher at the California Institute of Technology, proposes a surprisingly new approach of looking for life by, well, looking for it.
Nadeau and her colleagues suggest that “rapid and meaningful” cell movement is “an unambiguous biosignature that makes no assumptions about the chemical composition of the organisms under study.” They propose using a microscope to track particles moving through a field of view, but the two qualifiers are critical: after all, dust grains that move by diffusion, or are pushed by wind or water currents, can easily be mistaken for cells.
“Rapid” movement can be explored using the Stokes-Einstein equation to determine how fast a non-living sphere might move through water. A sphere one millionth of a meter (a micron) in diameter moves about 0.01 microns per second; microbes of the same size can swim at 10 to 100 microns per second. “Meaningful” movement distinguishes a putative cell from its medium: under controlled conditions, abiotic diffusing particles tend to move in a straight line, while microbes tumble around in wandering paths, occasionally with a chemical target in mind.
Natural gas is an increasingly important energy source, as vast reservoirs are being accessed through fracking, coal exploitation, and, in the not-too-distant future, subseafloor hydrate ice mining. But how exactly all of this fuel is being made deep underground is not very well known; figuring out will tell geologists how carbon moves through the planet and whether or not we should depend on natural gas reserves as a long term energy source.
Methane is the dominant ingredient of natural gas, a result of complex, gooey organic molecules being chopped up into smaller pieces by industrious microbes or the pressure cooker burial of geological activity. The microbial instigators are members of the archaeal domain, producing methane from just a few precursors: carbon dioxide, methanol, methylamines, and dimethylsulfide.
Growth rate is a fundamental aspect of life, a metric that can separate biology’s winners and losers. Even a small advantage can lead to complete dominance in short order, given the exponential scaling patterns of biological growth. Calculating growth rate is pretty straightforward when you’re looking at plants or animals, where it’s possible to measure an organism’s mass with relative ease. But what about microbes? How can minuscule changes in a cell’s mass be measured when the whole organism weighs just a picogram (10-12 grams)?
Over the last few years, physicists, biologists, and nanoscale engineers have joined forces to tackle this question. One camp has examined cells under the microscope, tracking their expanding diameters over time, but this method makes broad assumptions about cell geometry and takes a long time. A different approach pioneered by Scott Manalis, a Professor of Biological Engineering at MIT, combines microfluidics and resonating cantilevers to calculate a cell’s mass as it flows through tiny channels just three microns across.
Mountain gorillas are big business in the Virungas, the majestic volcanic mountain range that is shared between the Democratic Republic of the Congo and Rwanda. And nowhere is this more evident than in Musanze (also known as Ruhengeri), the gateway to Volcanoes National Park in northwest Rwanda.
Musanze is a mecca of gorilla conservation: The Dian Fossey Gorilla Fund International and The International Gorilla Conservation Program are based here. The local university has a specialized ecotourism degree program, and loitering students eagerly practice their English and touristic salesmanship on passing mzungus. Gorilla statues and profiles are the default logo, for everything from the Gorillas hotel to the local tennis club.
“These animals are everything to us,” says Felix Sibomana, a guide who escorts tourists on any number of park excursions, from cave tours to mountain climbs to gorilla treks. “Everyone comes here for this special experience, and we can’t let that gift be wasted.” Official estimates suggest that 85% of the tourism industry is gorilla-centric, and the sector grew by 34% from 2014 to 2015. Last Tuesday, for example, all 91 of Volcanoes National Park’s allotted gorilla tracking permits were sold, for $750 each, bringing in a cool $68,250. In one day.
Things are a bit different a few kilometers to the west; Virunga National Park in the Democratic Republic of the Congo had just six tourists, each paying $400.
There are two obvious reasons for the discrepancy: community buy-in and the broader economic context. Ever since a 2005 revenue-sharing initiative started feeding 5% of national park revenue back into adjacent villages, more than $1.8 million has bolstered hundreds of community development projects, from road construction to small business loans. On the other hand, this positive feedback loop of conservation and ecotourism – more pristine environments generating more revenue, encouraging local populations to keep the ecosystem intact – has yet to complete a full revolution in Virunga, though recent implementation of a mixed model incorporating strategic exploitation and practical conservation seems to be making headway.
Musanze has also been buoyed by the region’s most dynamic economy: Rwanda has boasted a mean annual GDP increase of 7.7% over the last 15 years (compared with the DRC’s 4.7%). With other opportunities and the infrastructure to enable mobility, it’s easier to dissuade people from pillaging the forest. But in the villages surrounding Virunga National Park north of Goma in the DRC, there are no obvious alternatives: if you want a more prosperous life, farm expansion – at the expense of untouched jungle – is the most straightforward option.
So if the bad news is that Virunga is just starting its journey toward community-supporting ecotourism, the good news is that the model seems to work, for people and gorillas alike. Over the last 35 years, the mountain gorilla population has nearly doubled to 880 – they’re still designated as “critically endangered,” but things are certainly moving in the right direction.
Another factor in the resurgence is a bushwhacking team of veterinarians known as the Gorilla Doctors. Dr. Julius Nziza works with the group; splitting his time between Kigali’s Department of Veterinary Services and the Gorilla Doctors’ Musanze office, Nziza is always on call. Humans, it turns out, are a triple threat to mountain gorillas, instigating bodily harm through hunger (snares used to trap bushmeat), hatred (machete or bullet wounds from poachers), or love (cuddle-seeking tourists can transmit human diseases – especially the flu – for which the gorilla’s immune system is woefully unprepared).
When Nziza’s phone does bring news of an ailing gorilla, it’s likely a call from a tracker or a ranger. “They spend every day with the family, so they will tell us if they see an abnormal situation,” he explains, “like if an animal is coughing a lot, or lethargic.” According to Nziza’s estimates, the Doctors have saved approximately a hundred animals since the group’s inception in 1986.
Maintaining a dedicated team of doctors for the mountain gorillas may seem like a capricious luxury, particularly in a region where human health is far from optimized. But given their outsized importance as an economic engine, “every individual matters,” says Nziza. “And these technical medical tools are helping to sustain the population.”
Getting a job as a ranger at Virunga National Park, the contentious jungle set among steaming volcanoes in the eastern Democratic Republic of the Congo, is not easy.
Innocent Mburanumwe should know – as the Warden of the Park’s southern sector, he oversees 140 rangers and helps pick each new crop through an intensive selection process. First are the challenges of brute force: running several miles while carrying a heavy pack, and climbing 14,000-foot mountains in less than a day. There are tests of survival skills and orienteering through one of the most dense forests on the planet. Then come the more nuanced abilities: marksmanship, spotting small camoflauged objects through binoculars, and an exam to identify and describe various animals and plants. And finally, there’s the interview, where the selection panel tries to get to the root of the most important question: how much do you really care? Is this just a job to you, or something more, something for which you’re willing to risk your life?
Steering the clattering camo-green truck over the pitted lava flows that pass as roads in Virunga National Park, southern sector warden Innocent Mburanumwe looks intently out the windows, scouring the landscape for unusual activity. Six rangers sit on padded benches in the truck’s bed, equipped with an intimidating aresenal of rusting weapons.
Driving north out of Goma, the largest city along the eastern margin of the Democratic Republic of the Congo, the road marks the park’s boundary. On the left, the dense forest cascades over itself in layers of green; on the right, parallel terraces of manioc, maize, and beets climb the hills, a rising tide that strands trees like marooned survivors.
Mburanumwe slams the brakes. He’s following the gaze of a crowd of passing women to a shouting match in the distance. Mburanumwe and five rangers dismount and trot toward a nearby berm while one stays with the vehicle and keeps watch. Remarkably, a Virunga sentry posted along this section of the road is on hand to give a report: three men from the nearby village had planned to cut down several of the park’s trees – for building supplies, for charcoal – but the sight of our truck careening toward them was a sufficient deterrant. “They have run off,” Mburanumwe says as he climbs back into the driver’s seat, “but I’m sure they will be back, and hopefully we can stop them again, convince them to not go into the park.”