Conversation so far:
Where was explorer Thomas Mitchell's first expedition?
Thomas Mitchell's first expedition was to the junction of Barwon and Gwydir.
Where did explorer Thomas Mitchell and his party go on their first expedition?
Thomas Mitchell and his party went to the junction of Barwon, and Gwydir on their first expedition.
What was explorer Thomas Mitchell's goal for the first expedition?
Charles Sturt believed that the Murray-Darling system formed the main river system of New South Wales and Thomas Mitchell wanted to prove Sturt wrong.

Question: Is there anything important about Thomas Mitchell before he goes on his first expedition?
Self-contained rewrite: Is there anything important about Thomas Mitchell before he goes on his first expedition?