NASA probe sets record with daring Sun dive

We are concerned about climate change on Earth, economic upheavals, and military and social conflicts. However, these are issues we can influence, and they occur relatively close to us. Meanwhile, at an average distance of 93 million miles from Earth, there is a celestial body whose existence not only enabled the formation of our civilization but may also shape its fate on a global scale and in the long term. The Sun is the closest and best-known star, yet remains so enigmatic that we continue to send space missions to study it.

Humans are slowly starting to prepare to leave Earth, their home for millions of years. As we venture into space, protection against the effects of solar radiation and wind, as well as plasma ejected by our star, will become a key challenge in astronautics.

Even on Earth, we must remain vigilant—there are already thousands of satellites in orbit, and Earth's energy and telecommunication infrastructure is susceptible to solar activity. To predict when the Sun will "strike," even mildly, we need the best possible understanding of its operations. That’s why the Parker Solar Probe was developed, achieving its close approach on December 24, 2024.

To grasp the significance of this achievement, consider that sunlight reaches Earth in about eight minutes. Solar wind travels much slower, but the ejected matter still reaches us relatively quickly, within several hours to a few days. The record approach distance of 3.8 million miles is crossed by photons in just under 21 seconds. While the physics of matter and energy propagation from the Sun is complex, the comparison demonstrates the extraordinary opportunity to study the Sun and its activities now provided to heliophysicists for the first time.

Currently, we know that the probe has survived its maximum approach and continues its mission. Telemetry data will be transmitted by New Year's Day (January 1, 2025), but this is merely the beginning. Scientists will analyze the observations over many weeks or even longer before publishing the first conclusions. Previous discoveries suggest that they will once again be groundbreaking for our understanding of the Sun.

Initially, astronomers hoped that the Parker Solar Probe would approach the Sun even closer. Early designs from the 1990s planned to use gravitational assistance from Jupiter to place the vehicle into orbit at about 1.2 million miles from the Sun. However, costs and complexity stood in the way. During the extended mission, beginning in the latter half of 2025, the probe may continue these close flybys as long as we can control it, but it will maintain its current orbit.

A mission almost touching the Sun's surface was envisioned from the start of the space flight era in 1957. In December 1974, the Helios 1 probe was sent toward the Sun, and a little over a year later, in January 1976, Helios 2 followed. They approached to within 28.9 and 26.5 million miles, respectively. While still a large distance, it is slightly less than one-third of the Earth-Sun distance and about 6.2 million miles shorter than Mercury's orbit size. The European Solar Orbiter, like Helios 2, currently studies the Sun from a perspective above its poles.

Parker Solar Probe's record was made possible by technologies developed at the end of the 1990s, including a carbon composite foam resistant to high temperatures. However, it took additional years to use this material to create an 11-centimeter shield protecting the valuable electronics of the probe from intense radiation. Such robust protection is necessary because, at a distance of 3.8 million miles from the Sun's surface, every square meter perpendicular to the Sun-Earth direction is illuminated with a power of 650 kW. On Earth, in ideal conditions with the Sun directly overhead, it would be 500 times less.

The surface of the Sun has a temperature of about 9,932 degrees Fahrenheit, and the surrounding corona is heated to over a million degrees Fahrenheit. Forecasts indicate that the Parker Solar Probe's thermal shield reached 1,796 degrees Fahrenheit. At this temperature, silver melts, and gold and copper melt at slightly higher temperatures. These are not the highest temperatures endured by Earth vehicles; during reentry, the shuttle's ceramic tiles reached 3,002 degrees Fahrenheit (the theoretical limit for the probe’s shield), and the Orion vehicle's shield in the Artemis 1 mission reached even 5,000 degrees Fahrenheit (due to, among other things, a more than 40% higher reentry speed than the shuttle).

Unlike a landing Earth vehicle, which performs few tasks, the Parker Solar Probe must fulfill an observation plan while exposed to extreme conditions. The shield must endure repeated, not just one-time, close approaches to the Sun. Yet, the entire probe at launch weighed only 1,510 pounds, several times less than just the thermal shield of the Orion capsule.

Executing the observation plan requires power, which is supplied by solar panels. These panels, prone to damage from excessive radiation, are designed to dissipate 13 W of unnecessary heat for every 1 W of power obtained during the approach to the Sun, with minimal degradation throughout the mission. We will only know how well they withstood the record flyby in time.

Foldable and tiltable panels were used so that during close proximity to the Sun, radiation would impact the cells at a slight angle. This design allows more efficient energy generation when the probe reaches the farthest point of its orbit. Heat is dissipated from the panels' underside through channels with ultra-pure water to cooling systems.

In the vicinity of the Sun, there are additional challenges: accelerating solar winds, dust from comets disintegrated by the star's massive gravity, moving at hundreds of miles per second. The probe may also encounter coronal mass ejections (CMEs), where plasma reaches speeds of up to 1,864 miles per second. Such an event occurred in September 2022, but the CME, where matter had a speed of 839 miles per second, did not damage the probe.

If a similar stream of matter encountered Earth, we would face a geomagnetic storm reminiscent of the largest recorded one from 1859—the Carrington Event. Nour Raouafi, a scientist involved with the Parker Solar Probe project, believes that the potential destruction from a large and very fast CME would be colossal. This is why the Parker Solar Probe continues its mission—to help humanity learn to interpret the Sun's signals, which we can record from orbit and Earth. These insights can then be integrated into computer models and space weather forecasts for the enhanced safety of our civilization.