Halley’s Comet: a new mission is being planned

Halley’s Comet is heading back towards the Sun; the year of its rendez-vous is 2061. As always, it will be visible and will capture the public’s attention. It returns, then, and records of its frequent appearances have been found in chronicles spanning the last two millennia; indeed, it is believed to be the comet depicted by Giotto in the stunning ‘Nativity’ fresco in the Scrovegni Chapel in Padua. It is only since the early 18th century, thanks to Sir Edmund Halley, that we have known it to be a periodic comet, with an orbital period very close to that of a human lifetime – approximately 76 years. This is why it is also ‘the comet’ par excellence and, above all, the first whose solid nucleus we have observed and photographed, thanks to a splendid European mission: Giotto.

A somewhat blurred image, as the comet had already begun to emit its coma – consisting of gas and solid particles surrounding the nucleus – but a historic one: it was the first time we had seen what the heart of a comet really looked like. Admittedly, it was a fly-by; the comet was essentially ‘crossed’ by the satellite at extremely high speed and viewed from just one side. That landmark image was captured thanks to a highly sophisticated camera developed by the University of Padua, which also suggested the name for the European mission. Today, Cesare Barbieri, professor emeritus at that university, who led the team that built the camera, is calling for a new mission to be planned for a date that is certain, even if it is still a long way off.

This is one of the lesser-known aspects of scientific research in physics: many phenomena occur in extremely brief intervals of time – often unimaginably short – whilst others take years and years to unfold, and one must give them due consideration well in advance, regardless of whether one will ultimately be able to observe the result.

If we are to return to Halley’s Comet – and this time accompany it for a good stretch so we can study it properly – there isn’t much time to waste. A major feasibility study for this new mission, carried out by Khalifa University in Abu Dhabi – with many Italians among the researchers – concludes that there isn’t much time left to catch up with Halley. The calculations show that there are only two possible dates between 2030 and 2040 to reach it whilst it is between Mars and Jupiter, so that we can slow down and then travel alongside the nucleus for a significant part of its journey, in order to study it in depth. We can do it, say the astrodynamics researchers, even with the technology we have today, but planning must begin soon: there are only two possible departure dates – 2036 and 2037.

Despite the success of the first mission in 1986, many important questions remain unanswered: is Halley’s Comet made up of two bodies fused together? How are the regions from which gas and dust are emitted distributed? How much material does the nucleus lose, what is its internal structure, and what story do the features on its surface tell?