Short answers, pulled from the story.
Sputnik 2 was the second spacecraft launched into Earth orbit, launched by the Soviet Union on the 3rd of November 1957. It was a 4 m cone-shaped capsule weighing around 500 kg and was the first spacecraft to carry a living animal into orbit.
Laika, a part-Samoyed terrier formerly called Kudryavka, flew on Sputnik 2. She was chosen primarily for her even temperament and was selected from ten candidates supplied by the Air Force Institute of Aviation Medicine.
Laika died from overheating by the fourth circuit of flight. In October 2002, scientist Dimitri Malashenkov revealed this at the World Space Congress in Houston, Texas, explaining that it was practically impossible to create a reliable temperature control system in the limited time available.
Sputnik 2 was built in approximately three weeks because Soviet leader Nikita Khrushchev asked Sergei Korolev to have a satellite ready for the 40th anniversary of the Bolshevik revolution in early November 1957. Korolev adapted a payload container from the existing sounding rocket program rather than designing a new spacecraft.
Sputnik 2 carried two spectrophotometers for measuring solar ultraviolet rays and X-rays, provided by Professor Sergei Mandelstam of the Lebedev Institute of Physics, and a cosmic ray detector built by Sergei Vernov's team at Moscow University. The photometers were oversaturated and returned no usable data; the cosmic ray detector transmitted for one week before its battery failed on the 9th of November.
Sputnik 2's cosmic ray detector recorded particle counts jumping from 18 pulses per second to 72 pulses per second at the highest latitudes of its orbit, likely detecting the lower edges of the Van Allen Belt. However, Soviet secrecy over data sharing and the satellite's limited telemetry coverage meant the discovery was never properly documented, and credit went to James Van Allen of the State University of Iowa, whose experiments on Explorer 1 and Explorer 3 first mapped the belts.