Astronomy

propeller-based system of equivalent

thrust. The design also generates much

less turbulence, making it ideal for

research and observation of a host of

marine conditions.

Engineers at the Swiss Federal

Institute of Technology in Zurich are

currently testing a nautical robot that

incorporates four fins inspired by those

of the cuttlefish. Called Sepios, the

28-inch-long (70 cm) remotely operated

underwater vehicle (ROV) exhibits a high

degree of maneuverability, along with the

capability for precise multidirectional

travel in tight spots.

Researchers at Canada’s Dalhousie

University have combined forces with

McGill University and York University to

create the AQUA robot. This aquatic

vehicle is a hybrid, with the capacity to

walk along the seabed as well as to

“swim” using its legs.

Yet another approach, under study

at the Jet Propulsion Laboratory, uses

a buoyant robot that f loats against

the underside of ice, crawling or

wheeling along upside down. There

are many options available for underwa-

ter exploration, but considering the

vast geological differences between the

various watery worlds in our solar sys-

tem, no single submersible vehicle is

equipped to effectively explore every

wet environment.

Challenges at Titan

While Europa’s ice crust presents a bar-

rier to its ocean (as does the crust of the

geyser-spouting moon Enceladus, which

orbits Saturn), one moon in the solar sys-

tem has seas on its surface.

Saturn’s Mercury-sized moon Titan is

shrouded in an orange haze. Since the

1960s, researchers have suspected that

conditions on Titan’s surface were at the

triple point of methane: Methane could

exist as a gas, a liquid, and a solid (ice).

Earth’s surface is at the triple

point of water, and it was tempting to see

Titan as a cryogenic version of Earth’s

coastal regions, with surf breaking on

alien shores. But the actual conditions

there were not known in detail. Studies

for landing probes often included a

spectrum of designs to accommodate

thick or thin atmospheres, and surfaces

ranging from rock or ice to snowbanks

and liquid ponds.

With the arrival of the Cassini orbiter

and the European Huygens probe in

2004, the true nature of Titan’s unique

landscape became clear. Vast lakes of

methane and ethane, rivaling the Black

Sea in extent, wash across the northern

hemisphere, with another huge body —

Ontario Lacus — in the south. The larg-

est of Titan’s hydrocarbon oceans is

Kraken Mare, followed closely by Ligeia

Mare. To Johns Hopkins University

Applied Physics Laboratory’s Ralph

Lorenz, it seems a perfect place for a sub-

marine: “There are some aspects about

Titan’s methane bodies that are actually

easier for a submarine [than terrestrial

seas] because hydrocarbons are not elec-

trically conductive, so you don’t need to

worry so much about exposed connec-

tors. There’s a possibility that you can

send a radio signal through the liquid,

which is something you can’t do very

easily on Earth. You might be able to

have higher bandwidth. We know that at

least one of Titan’s seas is very radio

transparent, because we bounced Cassini

radar off the bottom of it.”

But despite its advantages, Titan

presents a new set of challenges for

50 ASTRONOMY • JULY 2018

SquidROV, currently

under development

at the University

of Edinburgh,

is a biomimetic

submarine

propulsion

system that uses a

glassfish-style fin

to get around. In

addition to being

more efficient than

a propeller-based

system, SquidROV

(shown upside

down, below)

also creates less

turbulence.

UNIVERSITY OF EDINBURGH