NASA craft to head for the sun

Why the corona?

Unlike a campfire, which feels hottest at the source, the heat from the sun gets more intense further away from its surface.

"As we go from the surface of the sun, which is 10,000 degrees Fahrenheit (5,538 C), and move up into the corona, we find ourselves quickly at millions of degrees," he said.

NASA calls this mismatch "the coronal heating problem", and hopes the Parker Solar Probe will solve the mystery of why the corona reaches temperatures of up to 5.6 million C.

Fox said scientists have already studied the corona "every way imaginable", and a closer look is now needed.

"We need to get into this action region, where all of these mysteries are actually occurring."

Heat shield

The probe is protected by a 11.5-centimeter carbon-composite shield, built to withstand 500 times the sun's radiation on Earth.

A series of instruments on board the spacecraft will measure the magnetic and electric fields, plasma waves and high energy particles.

There is also a white light imager, taking pictures of what the spacecraft is about to "plow through", Fox said.

"The goal is to have the instruments on all the time but the prime science gathering for us is about 11 days," she told reporters ahead of the launch.

A 45-minute launch window opens on Saturday at 3:48 am local time.

Awaiting liftoff, the car-sized probe is already packed on to the Delta IV-Heavy rocket at Cape Canaveral Air Force Station in Florida.

AFP