does anyone know who the first European explorer was to travel to the Pacific Ocean?

Look up Captain Cook.

Ferdinand Magellan

That would be the Portugese explorer Vasco De Gama who was commissioned by King Manuel I to find a sea route to India left Lisbon on July 8, 1497 and rounded the Cape of Good Horn on November 22 the same year. After numerous stops along the east african coast of Africa he arrived in what is now present day Calcutta, India on May 20, 1498.

Here is a link for info on all explorers.

http://www.enchantedlearning.com/explorers/index.shtml

Hope this info helps.