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A Queen’s University Belfast researcher is calling on amateur astronomers to help with a European-wide mission helping to prevent future asteroid impacts.

Professor Alan Fitzsimmons from the Astrophysics Research Centre at Queen's is a senior mission advisor for the European Space Agency’s (ESA) Hera spacecraft.

Hera is part of humanity's first deep space test of planetary defence against asteroids. It will also be humankind’s first probe to rendezvous with a binary asteroid system. This is a little understood class which makes up around 15 per cent of all known near-Earth asteroids.

The spacecraft was presented to ESA’s Space19+ meeting in Seville on Wednesday and Thursday this week as part of the Agency’s Space Safety programme, where  Europe’s space ministers made the decision to fly the mission.

The mission is the European contribution to an international double-spacecraft collaboration. NASA will first hit the moon of the asteroid with its own spacecraft, and Hera will then follow-up with a detailed post-impact survey.

As well as exploring its final destination – the Didymos binary asteroid system – the Hera spacecraft could potentially fly past one or more bodies on the way. But the mission team require additional observations to help select their targets.

Professor Fitzsimmons says: “Asteroid research is one area of astronomy where amateur observers continue to make an essential contribution.

“The flyby candidates we have identified so far are little more than tiny dots of light in the sky, so faint they are invisible to the naked eye. We need as much help as possible to refine their orbits and measure their properties, which could give clues to their characteristics in advance of Hera’s launch in October 2024.”

The flyby opportunity arises because Hera will head out to match Didymos’s 770-day orbit around the Sun, which circles from less than 10 million km from Earth to out beyond Mars, at more than double Earth’s Sunward distance. In the process Hera will pass multiple asteroids and the inner edge of the main Asteroid Belt.

ESA’s European Space Operations Centre (ESOC) has come up with a flyby shortlist. ESA’s Hera project scientist Michael Küppers explains: “For a 2-5 km asteroid employing Hera’s main Asteroid Framing Camera, we would aim for a flyby distance of 500 km – but close approaches without real flybys are still useful, as they allow asteroid observations from angles unachievable from Earth.”

The precise targeting will come right down to the day of launch, how much fuel remains after fine-tuning Hera’s trajectory to Didymos, and how accurately it will be possible to refine the potential flyby targets’ orbits. The amount of fine-tuning will also be dependent on the Ariane 6 launcher which will place Hera onto its interplanetary trajectory.

From ESOC’s full set of flyby possibilities Professor Fitzsimmons and the Hera investigation team have come up with an initial list of seven candidate asteroids they would like amateur astronomers to try to observe.

He comments: “Only three of these bodies have known diameters and albedos, or surface brightness. And none of them have known rotation periods – this is something experienced amateurs could try and measure for us, especially for the brighter objects.”

ESA’s first experience with asteroid flybys came during Europe’s Rosetta mission, when the comet chaser passed two Main Belt asteroids in 2008 and 2010, giving the spacecraft an early opportunity to try out its suite of scientific instruments ahead of reaching comet 67P Churyumov–Gerasimenko in 2014.

But Rosetta was a lorry-sized spacecraft on a 10-year cruise phase with multiple planetary flybys, while Hera will be only the size of a desk, headed on a more straightforward route through deep space for a little over two years.

So any additional asteroid encounter cannot be taken for granted, but would be a scientifically valuable extra. And the amateur astronomer community can help select the flyby targets.

Ashleigh Smith
Article by Ashleigh Smith
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