All About Space - UK (2020-02)

Mercury

risky low-altitude observations in the last few

months of the MESSENGER mission.”

The measurements indicated that not only is

Mercury’s magnetism very old – going back at

least 3.8 billion years – but it was much stronger

in the past, “comparable to the strength of Earth’s

magnetic field today,” according to Johnson.

When all its propellant was used up,

MESSENGER was deliberately crashed into

Mercury’s surface – the first Earth-made artefact on

the planet – on 30 April 2015. From NASA’s point

of view the mission was a huge success, repeatedly

surprising researchers with its discoveries. “In the

end, most of what we considered to be gospel

about Mercury turned out to be a little different

than we thought,” as mission scientist William

McClintock said at the time.

“ We’d never have been

able to measure them

if not for these really

risky low-altitude

observations” Catherine Johnson

A protective

magneticfield

LikeEarth,Mercuryhas

a globalmagneticfield

whichhelpstoshieldit

fromthesolarwind.The

dashedredlineshows

MESSENGER’sorbit

throughthisfield.

Mercury’s

ancient

magnetism

MESSENGERmade

severallowpasses

tomeasure‘fossil

magnetism’insurface

rocks,withresults

indicatingthatMercury

hada muchstronger

magneticfieldbillionsof

yearsinthepast.

North

cusp

Planetary ions

South

cusp

© NASA