Astronomy – October 2019

10 kilometers

Heat shield

Parachute and

backshell

InSight

InSight

Curiosity

Viking 2

Spirit

ELYS

PL IUM

ANI

TIA

WWW.ASTRONOMY.COM 21

back to haunt — but fortunately not kill

— the mission.

Is Mars alive?

Prior to InSight, planetary scientists had

a rudimentary understanding of what

the interior of Mars was probably like,

and some crude hypotheses about its

level of activity. Based on general simi-

larities among our solar system’s terres-

trial planets, and on basic physical,

compositional, geologic, and other infor-

mation about Mars provided by previous

missions, researchers also deduced that

Mars was differentiated — with an inte-

rior segregated into a core, mantle, and

crust like Earth’s.

NASA’s Mars Global Surveyor orbital

mission in the mid-1990s provided a key

piece of information supporting this

hypothesis. The spacecraft’s magnetom-

eter measured strong magnetic fields in

the rocks on certain parts of the planet’s

surface. Scientists presume these signa-

tures are remnants of what was once a

global magnetic field, perhaps similar in some ways to Earth’s. Our planet’s

magnetic field arises in the core. This

partially melted, spinning ball of highly

conductive iron creates a strong mag-

netic field that extends from the core well

out into space. The field helps shield the

surface from harmful radiation and

allowed life to emerge and thrive here.

Did Mars once have a partially molten

core that gave rise to a similarly benefi-

cial global magnetic field?

Another key piece of evidence sug-

gesting that Mars is differentiated comes

from tracking the radio signals Mars

Pathfinder and subsequent missions sent

from the surface. Landers and rovers

transmit their radio signals from a spin-

ning planet that wobbles slightly. Those

tiny wobbles stem from the fact that Mars

is not a uniform sphere, but instead has

internal variations in mass and density.

By modeling the minuscule changes in

radio signal frequency associated with

those wobbles, planetary geophysicists

can deduce the nature of the interior vari-

ations. Scientists tracking the Pathfinder

radio signals, for example, inferred that

Mars has a denser, and presumably iron-

rich, core that extends from the center of

LEFT: NASA’s InSight

spacecraft landed in

Elysium Planitia, a

relatively flat and

rock-free plain not

far north of Mars’

equator. In this

view from the Mars

Reconnaissance

Orbiter, the lander,

its heat shield, and

its parachute and

backshell spread

across about a half

mile (less than 1 km)

of martian terrain.

NASA/JPL/UNIVERSITY OF

ARIZONA

BELOW: The probe

set down about

375 miles (600 km)

north of the

Curiosity rover.

ASTRONOMY: ROEN KELLY

InSight set down within a landing ellipse that
stretched 81 miles (130 km) wide in a largely east-
west direction and 17 miles (27 km) in a north-south
direction. The red dot marks the spot where the
spacecraft landed. NASA’s 2001 Mars Odyssey
orbiter captured this background image in 2015.
NASA/JPL-CALTECH/ARIZONA STATE UNIVERSITY