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In late October, the rather modestly named Parker Solar Probe (PSP) dropped within 42 million kilometers (26 million miles) of the surface of the Sun–becoming the closest to the center of the solar system that a human-made object has ever reached.
Radiation, caused by the solar wind of various particles ejected by the Sun, is so intense there that no present technology can stay there for long without being utterly brutalised. Therefore, PSP is rounding the Sun in an eccentric loop that sweeps out as far as the orbit of Venus, whose gravity it will use multiple times to edge ever closer to the Sun. In fact, at its closest, in 2025, PSP is scheduled to reach within 6 million kilometers (3.7 million miles), less than fifteen times the distance from the Earth to the Moon.
At first glance, the very inner solar system is hardly its most glamourous region. There is virtually nothing mysterious waiting to be found, no planets to be visited. Centuries ago, it was hypothesised that there lay a scorched planet named “Vulcan” (unrelated to any other planet Vulcan) that lay even closer than Mercury; this has long since been disproven. It’s also been proposed that there are asteroids, “Vulcanoids,” tightly orbiting inside Mercury. These have never been found, and also seem very unlikely.
All that leaves is the overbearing Sun.
PSP’s approach is so close to the Sun’s surface that it will dip into the corona: the extremely hot aura of plasma and magnetic activity that shrouds the Sun. The corona is the white-coloured halo visible during total solar eclipses, when the Moon wholly blocks the otherwise dominating light of the Sun itself. It is an extremely active region, and one that is difficult to observe precisely because it usually is domineered by the rest of the Sun. That’s part of why PSP is still interesting; it is entering unknown space.
Even if the Sun is not the most exciting destination, it is an important one. It is, after all, the lamp of the solar system, and the reason any of us are here in the first place. The Sun also unleashes a storm of radiation that bombards the rest of the solar system. Earth is protected, but the same cannot be said for what lies outside Earth’s magnetic field. Coronal mass ejections, events when large amounts of solar radiation are unleashed at once, can disrupt human communications and electronics.
The Sun does have a long history of space exploration. Pioneer 5, an unseemly-looking sphere with solar panels awkwardly slapped on that resembles a robot from Fallout more than it does a spacecraft, was the first, in 1960, only three years after the beginning of the Space Age. Pioneer 5 was positioned between Earth and Venus, and amongst other things observed the solar wind–the potpourri of radiation and particles continuously streaming from the corona.
Other Sun-facing satellites followed: more Pioneers in the 1960s and 1970s; operating as late as 1983, the Solar Maximum Mission in 1980; Ulysses in 1990; Yohkoh in 1991; the extremely successful SOHO in 1995; STEREO in 2006; SDO in 2010. What all these had in common, however, was that they operated from a distance. Most solar observatories are positioned in Earth orbit, or very near Earth–or even further away. Ulysses, in an attempt to shift its orbit out of the plane of the solar system so that it could observe the Sun’s polar regions, flew all the way past Jupiter. The two Helios probes of the 1970s were the exceptions: they flew inwards of Mercury, and Helios 1 held the record for nearing the Sun until the far more daring PSP came along.
PSP was first proposed well back in the 1990s, but Bush administration funding changes meant it only took off in 2018. PSP may not be going outwards, but it still is pushing new boundaries.
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