For one NASA mission, flying too close to the sun isn’t a concern. It’s the whole point.
On Wednesday, the space agency announced some details about its planned mission to send a robotic spacecraft into the sun’s upper atmosphere, a first for humanity. NASA said it would rename the Solar Probe Plus mission after Eugene Parker, an American astrophysicist who first wrote about the dynamics of solar wind in the 1950s. The Parker Probe Plus is scheduled to launch in summer 2018 to study the sun’s scorching corona, which is hotter than the core itself.
NASA has taken some poetic license by describing it as a mission to “touch the sun,” but it’s certainly close enough. At its closest approach, the spacecraft will fly within 3.9 million miles of the sun’s surface, coasting at about 450,000 miles per hour as it circles the star’s atmosphere.
“The sun doesn’t have a sharp edge, but we’ll be getting into a part of the sun where ‘real action’ takes place,” said Jeff Kuhn, an astronomer at the University of Hawaii who has worked on NASA’s solar observatories for almost 20 years.
The instruments on Parker Probe Plus will investigate the sun’s corona, its outer layer of hot plasma that produces streams of charged particles known as the solar wind. The corona, a white-hot halo around the star, can be imaged by sun-tracking satellites or seen by the naked eye during total eclipses. Temperatures in the corona can exceed 1.8 million degrees Fahrenheit (1 million degrees Celsius), while the photosphere—the visible surface of the sun we can see from Earth—stays comparatively cooler, at 10,000 degrees Fahrenheit (6,000 degrees Celsius). Scientists don’t know why the corona is so hot or how it can eject solar wind at supersonic speed, and they’re hoping Parker Probe Plus will provide some answers.
The probe will also study the sun’s magnetic field, another mystery for scientists. “I’m excited about directly measuring its magnetism, something we aspire to do in a coarser way with the instruments we’re building on Earth,” Kuhn wrote over email. “Knowing the solar-corona magnetism is like knowing about dark energy in the universe—it’s the magnetism that controls and powers the dynamics of the corona but that we otherwise can't measure directly.”
The probe’s findings could also help humans better predict space weather, NASA says, like clouds of gas ejected from the sun’s corona that can knock out disrupt satellite operations and knock out whole power grids. In 1989, the entire province of Quebec lost power after an explosion on the sun sent a stream of particles traveling at a million miles per hour toward Earth. Studies have suggested sun-induced blackouts could cost the U.S. economy tens of billions of dollars.
Parker Probe Plus will wearing more than a little sunscreen for this journey. The probe’s payload will be shrouded in a 4.5-inch thick carbon-composite shield capable of withstanding temperatures of nearly 2,500 degrees Fahrenheit (1,377 degrees Celsius). As the probe coasts through the blistering heat of the sun, its instruments and operating systems will be working at room temperature.
The probe will launch in a 20-day window starting in late July next year. It will loop around Venus seven times, trimming its orbit each time as it moves closer and closer to the sun. During its final three orbits, the probe will fly more than seven times closer than the Helios 2 spacecraft, which came within 27 million miles (43 million kilometers) of the star in 1976. NASA has not publicly said what will happen to the probe after its mission ends in 2025, but it will most likely remain in its orbit around the sun after its final ping back to Earth. The pair of Helios probes stopped transmitting data in 1985, but continue to circle the sun.
While data from this mission is still years away from reaching scientists, the sheer existence of the probe is significant. Humans have spent decades sending robotic missions to other planets, leaving orbiters and dropping landers along the way. They’ve even sent a spacecraft beyond the edges of the solar system, into interstellar space. There are several NASA satellite missions out there actively observing the sun’s dynamics, but no one has ever sent anything right to the sun.
Humanity also has never been this close to a star, period. For years, one of the rallying cries for space exploration, ad astra, Latin for “to the stars,” has been directed outward, to the universe at large. But before we send probes to Alpha Centauri, and the many twinkling lights beyond, humans would do well to inspect the star that lives right next door.
