The Solar Probe Plus will help us predict space weather and guard against potentially hazardous coronal mass ejections.

By Jay Bennett

Every now and then, the sun releases giant eruptions of solar plasma and super-charged particles, and sometimes, these high-energy space outbursts collide with the Earth. Luckily, our planet’s magnetic field shields us from the worst of it, preventing the Earth from becoming a desolate wasteland like Mars, but some of this solar weather still makes it through.

These solar particles are the cause of the Northern and Southern Lights, and occasionally they disrupt our satellites and power grids. In 1989, for example, a coronal mass ejection (CME) from the sun disrupted communications with multiple satellites and caused a power blackout for nine hours in Quebec that affected six million people. A bigger CME in our modern interconnected world could have much more devastating effects. Understandably, NASA wants to get better at predicting these CMEs and other types of volatile solar weather.

So they are going to fly a spacecraft into the sun.

The Solar Probe Plus spacecraft will fly through the outer corona of our host star, which is essentially the sun’s atmosphere. This doesn’t mean the craft will be safe from the sun’s intense heat, though. The corona, an aura of plasma that surrounds the sun, is actually hotter than the star’s surface, which is called the photosphere because it is the part that we see emitting light. The photosphere has a temperature of between 4,500 and 6,000 degrees Kelvin, while the corona’s temperatures are more like 1,000,000 or 2,000,000 K and can blaze as hot as 20,000,000 K in the right conditions.

On the outer edge of this burning plasma around the sun, Solar Probe Plus won’t need to contend with temperatures quite that hellish, but it will be flying through about 1,650 K, or roughly 1 370 degrees Celsius. The craft, slated for launch in July 2018, will be the fastest-moving manmade object in history as it zips around the sun 24 times at speeds approaching 200 km/sec, which is an insane 447,387 mph. Solar Probe Plus will fly within 3.67 million miles of the surface of the sun, which is about 8.5 solar radii—23 million miles closer to the sun than any craft before it.

“Such a mission would require a spacecraft and instrumentation capable of withstanding extremes of radiation, high velocity travel and the harsh solar condition,” said Seamus Tuohy, Director of the Space Systems Program Office at Draper, an engineering and technology firm that is helping develop sensors and equipment for the craft.

Over the course of seven years, the Solar Probe Plus will measure the velocity, force, and abundance of ionized particles and electrons using a Faraday cup, which is a conductive metal cup designed to catch and measure particles in a vacuum. The Faraday cup is one of only two science instruments that will sit outside of the craft’s thick carbon fiber-reinforced carbon solar heat shield. By measuring the properties of the particles in the outer corona, astronomers hope to better understand solar storms and develop a way to predict them in advance. Data from the Solar Probe Plus could also help scientists discover why the corona is so much hotter than the surface of the sun, a question that has perplexed astronomers for decades.

“In addition to answering fundamental science questions, the intent is to better understand the risks space weather poses to the modern communication, aviation, and energy systems we all rely on,” said Justin C. Kasper, principal investigator at the Smithsonian Astrophysical Observatory, which is building the Faraday cup and other components with help from Draper. “Many of the systems we in the modern world rely on—our telecommunications, GPS, satellites and power grids—could be disrupted for an extended period of time if a large solar storm were to happen today. Solar Probe Plus will help us predict and manage the impact of space weather on society.”

The craft itself is currently being built at the Johns Hopkins University Applied Physics Laboratory. In a little more than a year, the 1,345-pound spacecraft will fly faster and closer to the sun than any manmade object before it. Godspeed, Solar Probe Plus.

Source: Harvard-Smithsonian Center for Astrophysics