NASA Aquarius: a new NASA instrument called Aquarius is set to study salt levels in the Earth's oceans after launching on Friday.
The launch of a rocket carrying an ocean science satellite has been postponed until Friday.
The rocket will put an Argentine-built satellite into orbit 400 miles above the Earth. It will use a NASA instrument called Aquarius to map weekly changes in ocean salt levels.
By learning how salt concentration varies on the ocean surface, scientists hope to better predict future climate change and short-term climate phenomena such as El Nino and La Nina.
NASA says the weather looks good for a Friday launch.