NASA's newest Martian explorer is on the launch pad in Florida, ready to soar.
The Maven spacecraft is scheduled to blast off aboard an unmanned rocket Monday afternoon from Cape Canaveral.
NASA is sending Maven to Mars to study its upper atmosphere. Scientists want to know why Mars went from being warm and wet during its first billion years, to the cold and dry place it is today.
The early Martian atmosphere was thick enough to hold water and possibly support microbial life. But much of that atmosphere may have been lost to space, eroded by the sun.
Maven will take nearly a year to reach Mars, entering into its orbit next September.
The mission costs $671 million.
It's NASA's 21st shot at Mars. Nearly three-quarters have succeeded.