The Parker solar probe, a robotic spacecraft the size of a small auto, launched from Cape Canaveral in Florida on Sunday, embarking on a seven-year mission which will see it flying into the sun's corona - the outermost part of its atmosphere - within 3.8m miles (6.1 m km) of its surface.
The car-sized spacecraft will travel directly into the Sun's atmosphere, about four million miles from its surface - and more than seven times closer than any spacecraft has come before, thanks to its innovative Thermal Protection System.
The mission will last 6 years and 11 months, and in that time the Parker probe will orbit the sun 24 times.
And the mystery is profound.
Unlike many planetary exploration missions, which primarily orbit the planet itself, the Parker probe will be swooping closer and closer to the sun by way of an elliptical orbit that will include seven "gravity-assist" flybys of Venus.
Scientists have two theories about what heats up the corona.
The delicate instrument comes equipped with an array of instruments and tools which will scan the Sun for solar winds and magnetic fields.
Nicky Fox, project scientist at the Johns Hopkins University Applied Physics Lab, said: 'The sun is full of mysteries. That defies the laws of nature. "We know the questions we want to answer".
"The spacecraft will trace how energy and heat move through the Sun's atmosphere and explore what accelerates the solar wind and solar energetic particles". NASA hopes the findings will enable scientists to forecast changes in Earth's space environment.
"So it's of fundamental importance for us to be able to predict this space weather much like we predict weather here on Earth".
Of course, the spacecraft won't actually touch the sun - its temperature is a ludicrously toasty 5,500 degrees Celcius, and would instantly destroy any probe.
A last-minute technical problem delayed the rocket's planned Saturday launch, with the countdown halted with just one minute, 55 seconds remaining.
One of those watching the historic moment was Dr Eugene Parker, the now 91-year-old scientist who first suggested the possibility of solar winds in 1958 and who the craft is named after.
The Parker Solar Probe rocketed away from Cape Canaveral, Florida, early on Sunday.
The Delta 4 Heavy did not disappoint.
"I'm in awe", Zurbuchen said.
He added: "It's a whole new phase and it's gonna be fascinating throughout.and we're just waiting for the data now so the experts can get busy because there's a lot of data will be coming in". "We're in for some learning over the next several years".
Liftoff took place from Space Launch Complex 37 at Cape Canaveral Air Force Station in Tampa, Florida.