Halley’s Comet. Even the name of this giant ball of dust and gas is enough to make anyone over the age of 40 wistfully recall what happened 35 years ago this week when the oldest and most famous observed comet paid us a predicted visit. If you did see Halley’s Comet in 1986 as a child then you have a fighting chance of seeing it again in your lifetime—and you can’t say that about any other naked-eye comet. On February 9, 1986, Halley’s Comet reached its perihelion—the closest it got to the Sun during its short trip into the inner Solar System and between the orbits of Mercury and Venus—before disappearing into the depths of the outer Solar System. So where is it now? And when it is coming back? Officially called 1P/Halley, it’s an intermediate-period comet that’s been seen every 75 years since at least 240 BC, though only in 1705 did anyone work out that the same bright object that kept returning to the night sky. It’s about 9 miles by 5 miles/15 km by 8 km; Halley’s Comet is a big deal. Halley’s Comet has a highly elliptical orbit of the Sun and will return to the inner Solar System in 40 years, reaching its perihelion on July 28, 2061. It’s set to be much brighter than in 1986 because Earth will be closer to the comet. We know this because it returns to the inner Solar System every 75.3 years on average, though it can change to between 74 to 79 years because Jupiter and Saturn’s gravity can alter its orbit. However, some calculate that its close approaches to Jupiter and Venus in future will mean that Halley’s Comet will eventually be ejected from the Solar System altogether ... perhaps to become an interstellar interloper like ‘Oumuamua. Others think it could evaporate within 25,000 years, or collide with something. Largely because we were able to get a close look. Or, at least, the science community was. Although millions of school projects, hundreds of TV documentaries and miles of press coverage was afforded the return of Halley’s Comet, it wasn’t actually that easy to see. Many people alive at the time think they saw it, but it was only slightly brighter than Polaris, the North Star. Far more significant that any fleeting visual observations in 1986 was the incredible close-ups obtained by the European Space Agency (ESA)’s Giotto spacecraft, one of several to study Halley’s Comet in 1986. On March 13-14, 1986 it got to within 373 miles/600 km of Comet Halley and spotted the comet’s nucleus and jets of gas and dust as its flew through its tail, detecting complex organics in its coma—the gas around its nucleus. For space fans it had been a dramatic few months; on January 24, 1986—just as Halley’s Comet was closest to the Sun—NASA’s Voyager 2 spacecraft conducted a flyby of Uranus for humanity’s first and only glimpse of the “Bull’s Eye” planet. However, that was forgotten just four days later when NASA’s Space Shuttle Challenger exploded just after launch.
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