rhododendrons and lemurs
Modern Mars rovers use wheeled chassis and behave like rugged all-terrain machines. They excel on flat plains but struggle with rocky massifs and cave interiors, where critical clues about the planet’s geological past lie hidden. In response, researchers are designing animal-inspired robots to reach those inaccessible regions.
NeBula-SPOT draws on Boston Dynamics’ dog-like platform and is deployed to explore shallow cliffs and caves, including lengthy lava tubes. Its canine-inspired mechanics enable steady movement across rocks and uneven surfaces without hesitation.
Several units can operate as a coordinated swarm. If one unit loses contact with the ground, another linked by a tether can descend the cliff to continue the mission. A radioisotope thermoelectric generator powers one rover in the swarm, allowing exploration inside caves without sunlight. NeBula-SPOT has already undergone earthbound cave tests, where it creates three-dimensional maps and highlights areas worthy of closer inspection.
Despite their versatility, dog-like robots cannot scale very steep cliffs. Engineers are advancing a climbing solution in Robot LEMUR. It features numerous small hooked pads on each paw. When commanded, the pads compress toward the center and grip fine irregularities on stone surfaces with remarkable sensitivity.
That capability enables LEMUR to ascend rock faces vertically while instruments mounted on its underside can study rock composition and structure up close.
Earth tests have demonstrated LEMUR’s ability to detect ancient microbial fossil traces, such as stomatolites formed by cyanobacteria. It remains to be seen how the rover would reach challenging rocks after landing and how it would obtain energy. A practical approach could involve pairing a traditional wheeled Mars rover with a climber tasked to reach an especially informative location.
Aircraft carrier and submarine
Titan, Saturn’s largest moon, hosts seas of methane and other hydrocarbons, given surface temperatures around -180°C. Its hydrological cycle mirrors Earth’s in principle: methane evaporates, forms clouds, rains back as liquid, and cycles through rivers. To study this system, scientists have proposed an autonomous floating drone for Titan exploration. The TiME device (Titan Mare Explorer) resembled an inverted basin with masts and antennas and was designed to drift with Titan’s winds and atmospheric pressure, which is higher than Earth’s.
NASA originally favored the InSight mission concept for Mars, but the Titan idea persisted. The surface tool could be converted into a mini submarine to survey the seabed, periodically diving to map topography and composition while analyzing liquid, surface, and subsurface currents. The notion of replacing water with liquid methane as a potential biochemistry remains speculative; if methane-based life exists on Titan, investigators would seek traces on the seabed.
Alternatively, an autonomous “aircraft carrier” could host UAVs, replacing the submarine approach. This concept, proposed to the European Space Agency by researchers from the University of Paris, envisions small multicopters surveying large tracts of Titan from the air, with a main lander serving two roles: a charging station, a warming hub, and a laboratory for sample analysis. Both approaches remain in the concept and technology-development stage.
These ideas illustrate the breadth of exploration strategies under consideration for Titan and beyond.
Overalls
Neptune’s large moon Triton reveals a different kind of landscape. Smaller than Earth’s Moon and with roughly half gravity, it has shown signs of tectonic activity and dynamic terrain observed by Voyager 2 during its 1989 flyby. The eruptions observed on Triton appear not to involve silicate magma but water rich in ammonia, which acts as an antifreeze. Some regions may host lava-like lakes composed of a water-ammonia mixture, while the Moon’s surface remains frigid enough to approach absolute zero and harbors frozen nitrogen.
NASA’s Triton Hopper concept envisions a lander that, once it touches down, begins collecting nitrogen ice. A compact heat source vaporizes the isotope-rich material, producing pressurized gas that powers the propulsion nozzle. This thrust enables jumps up to about a kilometer high and five kilometers long, with the cycle repeating until energy or structural limits are reached.
Triton Hopper promises unprecedented mobility for a probe, enabling latitude-by-latitude movement to generate a detailed picture of the planet’s physical processes while testing a novel hopping mechanism. The project remains in a technology maturation phase, preparing for eventual demonstration.
Zeppelin-zeppelin
Venus presents a crushing challenge: a dense atmosphere and scorching surface make long-lived surface probes impractical. Elevating probes tens of kilometers above the surface reduces environmental stress, opening the door to flying payloads. Aircraft and airship concepts both offer advantages for Venus exploration, each with its own trade-offs.
VAMP, a collaboration between Northrop Grumman and LGarde, blends airplane and balloon ideas into a sleek, winged, hydrogen-filled airship idea. When inflated, it spans up to 50 meters in width. The heavy atmospheric pressure on Venus minimizes the volume needed to maintain buoyancy, allowing VAMP to hover around 55 kilometers altitude in its passive state.
With propellers engaged, VAMP can accelerate to around 100 km/h, lifting the craft into aircraft-like flight. In this mode, it can operate at altitudes 50–65 kilometers above Venus, examining a broad latitude while dipping through clouds. A suite of spectrometers and a weather station will enable study of Venus’s unusual atmosphere and potential microbe-hosting environments. Solar panels can power VAMP, and it can drift passively at night like a hot-air balloon.
Initial plans envisioned VAMP as part of the Russian Venera-D mission for the 2030s, but the partnership did not materialize due to shifting relations. The United States could undertake such a mission independently, though Venus research remains a lower priority for NASA compared with Mars and the outer solar system.