Astronomy - USA (2019-09)

Hydrothermal vents

Liquid

ocean Ocean

currents

Ice

Ice fractures

Diapirs

Surface

Plume

Deposited material

from plume

Ice blocks

Charged particles

(radiation) Sunlight Impacts

6 miles

(10 km)

60 miles

(100 km)

Chaos,^ lineae

Rocky

interior

Extensional

features

34 ASTRONOMY • SEPTEMBER 2019

Entering orbit around Europa, the craft

will use nine instruments to investigate

the moon’s surface and interior. At closest

approach, Europa Clipper will speed by

just 3 miles (5 km) above the surface, low

enough to f ly through geyser bursts. A

mass spectrometer and dust mass ana-

lyzer will study particles ejected in the

bursts, while an ultraviolet spectrograph

will image the plumes from afar and iden-

tify their composition. Other instruments

will look for thermal signatures on the

surface to detect new bursts, while ice-

penetrating radar will measure the thick-

ness of the icy shell. A magnetometer will

measure the strength of the moon’s mag-

netic field to probe its interior. These data

will help scientists determine how deep

the ocean might be, as well as its salinity.

Proof in pictures

Ultimately, Europa Clipper will likely be

able provide proof of habitability, but not

signs of life. If selected, NASA’s proposed

Europa Lander will follow after Europa

Clipper and complement its mission by

searching directly for biosignatures on

the surface, as well as sampling the local

composition of the moon.

Perhaps the best way to capture conclu-

sive evidence of life on Europa is to take a

photo. Scientists think their best bet is to

equip the Europa Lander with a micro-

scope for imaging water and ice samples.

Jay Nadeau, a biophysicist at Portland

State University, and her collaborators are

testing autonomous microscopes robust

enough to withstand an interplanetary

journey. They’re also developing a method

of creating 3D images, similar to a holo-

gram, with a camera that can simultane-

ously focus at multiple distances to avoid

blurry images. However, such images gen-

erate a lot of data, and the proposed

lander’s power supply and communica-

tions bandwidth for sending information

back to Earth is limited. With multiple

instruments vying for those necessities,

Nadeau suspects they’ll have enough

bandwidth to send back only a few 3D

pictures. “There’s not much data you can

send back from the mission, so we’re going

to need a computer algorithm to say, ‘This

picture is actually interesting and we’ll

send it back to Earth,’” Nadeau says.

The first missions will likely only be

able to take surface samples, which

would show life that has been preserved

THESE TWO VIEWS of Europa’s trailing side show the moon in natural color (left) and false color to
enhance variations in the terrain. Bluer and whiter regions are covered in particles of water ice; redder areas
are contaminated by minerals from the moon’s interior or delivered by impacts. Several long, thin fractures —
some more than 1,850 miles (3,000 km) long — are visible across the surface. Also easy to distinguish on the
moon’s lower half is the bright Pwyll crater, a 31-mile-wide (50 km) scar left by a recent impact. NASA/JPL/DLR

HEAT AND MATERIALS from Europa’s interior might be released through hydrothermal vents
on the moon’s ocean floors. Warm water rising toward the base of the icy shell could cause cracks and other
features, such as diapirs, while large chunks of the surface — ice rafts — may detach and float to new
locations. Plumes could spout the ocean’s contents high above the moon, while radiation, impacts, and
sunlight can all cause changes on the ice from above. ASTRONOMY: ROEN KELLY

A PEEK INSIDE EUROPA