on-board magnetometers
... that Luna 2 was the first of several spacecraft to use on-board magnetometers to discover that the Moon has almost no magnetic field?
... that <a href="./Luna_2" id="mwCv0" rel="mw:WikiLink" title="Luna 2">Luna 2</a> was the first of several spacecraft to use <b id="mwCv4"><a class="mw-redirect" href="./Spacecraft_magnetometers" id="mwCv8" rel="mw:WikiLink" title="Spacecraft magnetometers">on-board magnetometers</a></b> to discover that the Moon has <a href="./Magnetic_field_of_the_Moon" id="mwCwA" rel="mw:WikiLink" title="Magnetic field of the Moon">almost no magnetic field</a>?