Read this and answer the question. If the question is unanswerable, say "unanswerable".

The islands were first sighted in 1506 by Portuguese explorer Tristão da Cunha; rough seas prevented a landing. He named the main island after himself, Ilha de Tristão da Cunha, which was anglicised from its earliest mention on British Admiralty charts to Tristan da Cunha Island. Some sources state that the Portuguese made the first landing in 1520, when the Lás Rafael captained by Ruy Vaz Pereira called at Tristan for water. The first undisputed landing was made in 1643 by the crew of the Heemstede, captained by Claes Gerritsz Bierenbroodspot.

Who first sighted the Islands in 1643?
unanswerable