It sounds like something from science fiction – capturing an asteroid and attaching a huge umbrella to it to help block out the Sun to prevent catastrophic global warming.

That’s probably because previously it has been. In the 2021 disaster comedy Don’t Look Up, the US tries to halt an asteroid bound for Earth using drones in order to mine its contents, rather than just blowing it up.

And of course The Simpsons, ever a portent of doom, hilarity and everything in between, built a Sun-blocker for Mr Burns, ensuring the people of Springfield had to buy his electricity 24/7.

Now however, a real-life scientist is combining the two. 

István Szapudi, an astronomer at the University of Hawaiʻi Institute for Astronomy, has proposed using a captured, tethered asteroid to serve as a counterweight for a huge solar shield. The shield will reduce solar radiation by 1.7%, estimated to be the amount needed to prevent a catastrophic rise in global temperatures.

The idea of a solar shield has been proposed before, but creating an object large enough faces multiple challenges. Firstly, it can’t simply be a large piece of tinfoil or similar – to balance gravitational forces and prevent solar radiation pressure from blowing it away, any shield will have to be massive. This makes even the lightest materials prohibitively expensive.

Writing in the journal Proceedings of the National Academy of Sciences, Mr Szapudi said: ‘One of the biggest hurdles for proposals aimed at blocking a small fraction of sunlight from space is weight. In space, weight translates into unrealistic costs.

‘The preferred location for a sunshade is beyond the L1 Lagrange point toward the Sun, where the solar radiation pressure and gravity of the Earth and the Sun are in balance.’

What are Lagrange points?

Nasa states: ‘Lagrange points are positions in space where objects sent there tend to stay put.’

‘At Lagrange points, the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. These points in space can be used by spacecraft to reduce fuel consumption needed to remain in position.’

Mr Szapudi found that placing a tethered counterbalance toward the Sun could reduce the weight of the shield and counterweight to approximately 3.5 million tons, about one hundred times lighter than previous estimates for an untethered shield. 

However, today’s largest rockets can only launch about 50 tons to low Earth orbit, which still rules out creating such an object – unless most of it was already in space.

Enter the asteroid. By capturing and tethering an object already in space to serve as the counterweight, only the shield itself – which Mr Szapudi estimates at about 35,000 tons – would need to be launched from Earth.

‘Advances in light materials, such as graphene, could produce extremely light solar shades, similar to solar sails,’ said Mr Szapudi. ‘These could be lifted into space at a relatively modest cost.’

On the inspiration for his groundbreaking idea, he added: ‘In Hawaiʻi, many use an umbrella to block the sunlight as they walk about during the day. I was thinking, could we do the same for Earth and thereby mitigate the impending catastrophe of climate change?’

The research is still very much theoretical, but a statement from the University of Hawai’i’s Institute for Astronomy argues that engineering studies using this approach could start now to create a workable design that could mitigate climate change within decades.

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