Nasa officials said at a press conference that the left side of the shuttle started getting hotter and hotter as it got closer to landing.
Lots of people have been mourning at the Johnson Space Center
They added that this could be because of the tiles falling off or becoming uneven, but said they were also investigating lots of other bits of information too.
These include huge amounts of computer data sent back by the shuttle in its final moments and also the debris that fell onto the southern parts of America.
Shock and grief at the disaster has been expressed around the world.
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