内容摘要：In 1973 he was convicted of ordering the execution of a rival drug dealer. Authorities allege that he continued to lead his gang from prison.

In 1973 he was convicted of ordering the execution of a rival drug dealer. Authorities allege that he continued to lead his gang from prison.

"Without atom motion you have a hard time having the material be able to deform and return," says Dr Padula.The tyres need to be able to deform as they go over rocks and then ping back to their original shape.

"If we permanently deform a tyre, it doesn't roll efficiently, and we have issues with power loss," says Dr Padula.The new wheels will also carry much bigger loads than the lightweight rovers Apollo astronauts cruised around in.The next space missions will need to drive round "bigger science platforms and mobile habitats that get larger and larger", he says.

And that will be an even heftier problem on Mars, where gravity is double that on the Moon.Apollo's lunar rovers used tyres made from zinc-coated piano wire in a woven mesh, with a range of around 21 miles.

Since extreme temperatures and cosmic rays break down rubber or turn it to a brittle glass, metal alloys and high-performance plastic are chief contenders for airless space tyres.

"In general, metallic or carbon fibre-based materials are used for these wheels," says Pietro Baglion, team leader of the European Space Agency's (ESA) Rosalind Franklin Mission, which aims to send its own rover to Mars by 2028.So one option is to replace the refrigerants with more climate-friendly versions. But the candidates with the lower global warming potential, also have problems.

For instance, propane is highly flammable. Ammonia is toxic. Carbon dioxide works at high pressures, requiring specialised equipment.But as many places phase down HFCs, alternative refrigerants will remain important.

Ms Sachar says that we still need refrigerants because for home cooling, "A/Cs as we know them today will continue to be the solution, at least for the next decade or so".In the longer term, some scientists are looking toward cooling devices that don't need liquid refrigerants at all.