You failed to provide any bold-faced words, so all I can do is correct the sentence as it should be written.
His first major find was<em><u> the</u></em> discovery of the planet Uranus in 1781 <em><u>.</u></em>
Add the word 'the' and a period as shown. And, technically, if Uranus is already understood to the listener/reader, then the word 'planet' is redundant.
