Short answers, pulled from the story.
Deep Impact was a NASA spacecraft designed to fire a copper-cored probe into comet Tempel 1 to expose and study the comet's interior composition. It launched on the 12th of January 2005, from Cape Canaveral Air Force Station and was the first mission to deliberately eject material from a comet's nucleus.
Deep Impact found that Tempel 1 was far dustier and less icy than expected, with excavated material resembling talcum powder rather than sand. The comet was approximately 75% empty space, and spectroscopic analysis of the ejecta revealed clays, carbonates, sodium, and crystalline silicates. Based on the presence of ethane, astronomers hypothesized the comet formed in the Oort cloud region near Uranus and Neptune.
The Deep Impact impactor used a 113 kg block of copper because the element is not found naturally on comets, allowing scientists to discard its spectral signature when analyzing the ejected material. At a closing speed of 10.2 km/s, the kinetic energy equaled 4.8 tonnes of TNT, making explosives unnecessary.
The crater was approximately 150 m in diameter, as confirmed by the Stardust spacecraft, which passed within about 200 km of Tempel 1 on the 15th of February, 2011. Initial photographs taken moments after the impact were obscured by a large dust cloud. The crater contained a bright central mound where ejected material had settled back in.
EPOXI stood for Extrasolar Planet Observation and Deep Impact Extended Investigation, the extended mission assigned to Deep Impact after completing its primary objective at Tempel 1. It included a flyby of comet Hartley 2 on the 4th of November 2010, passing within 700 km and returning photographs of its peanut-shaped nucleus and bright jets.
Contact was lost between August 11 and 14, 2013, with the last confirmed signal on August 8. Chief scientist A'Hearn traced the cause to a software overflow: the spacecraft tracked time as an unsigned 32-bit integer counting tenth-second intervals from the 1st of January 2000, and that counter overflowed on the 11th of August 2013. NASA abandoned recovery efforts on the 20th of September 2013.