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Live video of the announcement will be available here beginning at 2 p.m. EST.
NASA's Messenger, which is an acronym of Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft, launched in 2004. It made three flybys of Mercury before arriving to orbit the planet in 2011.
Messenger's scientific goals, among others, include gathering data about the planet's geologic history, core and magnetic field.
Messenger is the first spacecraft to orbit Mercury.
UPDATE: Thursday, 2:20 p.m. -- NASA announced Thursday afternoon that Messenger has found new evidence that ice made from water "and other frozen volatile materials" exist on Mercury.
For more details about water on Mercury and the Messenger mission, read this report from HuffPost's Andres Jauregui.