NASA’s Sun-touching Parker Solar Probe spacecraft will mark St. Patrick’s Day (March 17) by once again approaching our star. While people all over Earth are enjoying cold beer, the spacecraft will endure incredibly hot temperatures of up to 2,500 degrees Fahrenheit (1,400 degrees Celsius) when it makes its 15th approach to the Sun, or perihelion.
According to the NASA Parker Solar Probe website, (will open in a new tab) the exact close approach time will be 4:30 pm EDT (2030 GMT), when the spacecraft will come within about 5.3 million miles (8.5 million km) of the Sun’s surface, the photosphere.
This is closer than the innermost planet to the Sun, Mercury, which orbits the planet more than 6 times as far away, about 34 million miles (54 million kilometers) from the Sun. This close approach means that Parker will get closer to the Sun’s outer atmosphere, known as the corona.
Related: Parker Solar Probe: First Spacecraft to ‘Touch’ the Sun
One of the main missions of the Parker Solar Probe, launched on August 12, 2018, is to find out why the corona is hundreds of times hotter than the photosphere below it.
The corona reaches over 1.8 million degrees Fahrenheit (1 million degrees Celsius) compared to the photosphere’s average temperature of about 10,000 degrees Fahrenheit (5800 degrees Celsius). Because most of the sun’s heat comes from the fusion processes at its heart, stellar models say the interior must be hotter. Also, the photosphere’s plasma is 10 million times denser than the corona’s plasma, which means the pressure inside the star must also be greater, so it’s kind of a mystery why the corona is so incredibly hot.
The corona is difficult to study from Earth because the light it produces is “washed out” by light from the aptly named photosphere, which is only truly visible when the Moon obscures the Sun’s surface during an eclipse. At this time, the crown looks like a blazing ring of white light.
To solve this long-standing solar mystery, the Parker solar probe must touch the corona and race through this thin and hazy plasma at up to 365,000 miles per hour (587,000 kilometers per hour). This makes the spacecraft the fastest human-built object, capable of flying about 250 times faster than the top speed of the Lockheed Martin F-16 jet.
(Image credit: NASA/Johns Hopkins APL/Steve Gribben)
However, beating the corona heat doesn’t depend on Irish luck, instead the Parker Solar Probe depends on groundbreaking engineering to beat the heat. Specifically, the spacecraft is equipped with a 4.5-inch (11.4-centimeter) thick carbon-composite screen that retains its scientific payload at room temperature, even at perihelion.
The spacecraft last reached perihelion during its 14th close pass on December 11, 2022, when it approached the surface of the Sun by about the same distance as on St. Patrick’s Day 2023. However, the Parker Solar Probe has already reached the Sun. On November 21, 2021, the spacecraft passed the Sun just a fraction of a second closer.
Later this year, Parker will fly past Venus and adjust its trajectory to bring it closer to the Sun. The probe’s planned mission includes 24 approaches to the Sun before it ends in 2025, and it will eventually come within 3.8 million miles (6.1 million km) of the photosphere. This is closer than any other spacecraft that has approached our star, and is only one-tenth the distance between our star and its innermost planet, Mercury.
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