CAPE CANAVERAL, Fla. — A historic and audacious mission to probe some of the sun's deepest secrets is underway.
NASA's Parker Solar Probe lifted off this morning (Aug. 12) at 3:31 a.m. EDT (0731 GMT) from a pad here at Cape Canaveral Air Force Station, its powerful United Launch Alliance Delta IV Heavy rocket carving an arc of orange flame into the predawn sky.
If all goes according to plan, the Parker Solar Probe will end up traveling faster than any craft ever has, and getting unprecedentedly close to the sun; indeed, it will fly through our star's outer atmosphere, known as the corona. And the measurements the probe makes there will reveal key insights about our star's inner workings that have eluded scientists for decades. [NASA's Parker Solar Probe Mission to the Sun in Pictures]
"It's going to be absolutely phenomenal," NASA Chief Scientist Jim Green told Space.com. "We've been wanting to do this for 60 years, ever since Eugene Parker got up and said, 'I believe the sun is outgassing.'"
That prediction was met with much skepticism back in the 1950s, but time proved Parker, a pioneering University of Chicago astrophysicist, right. We now know that outgassing as the solar wind, the stream of charged particles that flows constantly from the sun. And Parker, who turned 91 in June, became the first living person ever to have a NASA mission named after him.
Photos of Parker and a digital copy of his seminal 1958 solar-wind paper are flying on the newly launched spacecraft, aboard a memory card that also bears the names of more than 1.1 million people. These folks — who include "Star Trek" icon William Shatner — responded to a March 2018 NASA invitation to kiss the sun along with the Parker Solar Probe.
This morning's launch was initially supposed to occur on July 31, but several technical issues pushed the attempt back to yesterday (Aug. 11). And that try was scuttled after a Delta IV Heavy gaseous-helium pressure alarm went off less than 2 minutes before the scheduled liftoff.
Our mysterious star
The solar wind is very fast, zooming along at between 900,000 mph and 1.8 million mph (1.45 million and 2.9 million km/h) by the time it reaches Earth's orbit. But the particles start out pretty much motionless at the solar surface, said Parker Solar Probe mission scientist Adam Szabo, who's based at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
"Something happens in the corona where it steps on the accelerator and shoots out at supersonic speeds," Szabo told Space.com.
But scientists aren't sure what that "something" is. The same is broadly true for solar energetic particles (SEPs), even faster-moving flecks that are associated with solar flares and gigantic eruptions of plasma called coronal mass ejections. It's unclear exactly how SEPs — which can pose a threat to astronauts and wreak havoc with spacecraft software — attain such tremendously high energies, Szabo said.
And the corona itself is deeply mysterious. Temperatures there range between 1.8 million and 5.4 million degrees Fahrenheit (1 million to 3 million degrees Celsius) on average — far hotter than the solar surface, which is a pedestrian (by comparison) 10,000 degrees F (5,500 degrees C).
This doesn't make sense, at least not intuitively.
"You would expect that things should cool off" as distance from the nuclear-fusion action increases, Szabo said. "This is one of these big unknowns: What's going on there?"
The sun's incredibly powerful magnetic field and convective motion apparently work together to generate the energy driving these phenomena, said Lika Guhathakurta, the lead program scientist for new initiatives at NASA's Ames Research Center in Silicon Valley and former lead for the space agency's Living With a Star program.
"But how you bring that energy to the surface and propagate it is the challenge," Guhathakurta told Space.com. "And that's why we have to go there and measure it." [The Sun's Wrath: Worst Solar Storms in History]
Kissing the sun
That's just what the Parker Solar Probe will do. Over the next seven years, the $1.5 billion mission will perform 24 close flybys of the sun, getting within just 3.83 million miles (6.16 million km) of the solar surface at its closest approach — far nearer than the previous record-holder, the German-American Helios 2 spacecraft, which got within 27 million miles (43 million km) in 1976.
During such tight passes — the first of which will occur in early November — the sun's powerful gravity will accelerate the Parker Solar Probe to top speeds of around 430,000 mph (690,000 km/h), NASA officials have said. That will obliterate the mark of 165,000 mph (265,000 km/h), which was set by NASA's Juno probe during its arrival at Jupiter in July 2016.
(The encounters will get closer and closer as time goes on; the Parker Solar Probe will gradually shrink its elliptical orbit from about 150 Earth days to 88 Earth days, using seven "gravity-assist" flybys of Venus. The record-breaking numbers cited above are for the final flybys.)
Conditions at and around closest approach will be extreme; the Parker Solar Probe will have to withstand about 500 times the solar radiation load we experience on Earth. And the spacecraft's sun-facing side will be heated to about 2,500 degrees F (1,370 degrees C), according to NASA officials. (Most of this heat will come from sunlight; the toasty plasma in the corona is spread so thinly that it won't play much of a role.)
"It's going to get hammered," Green said.
To deal with heat, the solar-powered probe is equipped with a 7.5-foot-wide (2.3 meters), 4.5-inch-thick (11.4 centimeters) shield made of advanced carbon-composite material, which will keep most of the spacecraft's scientific instruments at a comfortable 85 degrees F (29 degrees C).
These instruments will, among other things, measure the sun's electric and magnetic fields and waves; observe superenergetic particles in the solar atmosphere and beyond; count and characterize solar-wind particles; and photograph the corona and inner regions of the heliosphere (the giant bubble of solar plasma and magnetic fields that extends far beyond Pluto's orbit).
The observations made by this gear could help solve the coronal-heating and particle-acceleration puzzles, mission scientists have said. And it will give us a better idea of how stars tick in general.
"How can we possibly understand stellar systems if we don't understand the star next door?" Szabo said.
There should be considerable practical applications as well, he and others stressed. For example, mission data should yield significant insights into space weather, potentially allowing researchers to better predict and plan for the intense solar storms that can cause big disruptions here on Earth.
Such information could also help humanity push out into the solar system, by giving us the knowledge we need to leave our planet's protective magnetic field behind, Guhathakurta said.
"There's going to be no looking back after this mission," she said.