That's one small disappointment for man, a giant trip for women

A new study by experts in the United States has claimed that women may make better and fitter astronauts for long trips into space. Men are simply biologically inferior and less able to withstand the rigours of space flight.

Professor William Rowe, of the Medical College of Ohio, said that men in their 30s and 40s, regarded as the prime age for astronauts, are more likely to develop the first signs of heart disease - an illness which is exacerbated by space voyages.

However, women under 30 are more likely to be healthier because of their physical and hormonal make-up, which protects them from cardiovascular disease. Heart rates on space walks can reach very high levels of 170 beats per minute.

So when Nasa and the European Space Agency begin their manned missions to Mars in 2020 or so, the trips to the Red Planet "should be fact be 'womanned'", he said in the Journal of Men's Health and Gender.

Using drugs to counter- act the condition is unhelpful, he added, because the medicines used are poorly absorbed in weightless conditions, the liver and kidneys work less well, and because drugs deteriorate more quickly in the higher levels of radiation found in space.

Men have another problem, he contends. They retain higher levels of iron in the body than women, particularly in space, and this iron can reach toxic levels. Women's reduced mass, requiring fewer calories and producing less waste, makes them yet more suitable as long-term astronauts.

However, there is one major biological hurdle of younger women. Menstruation, he warns, presents particular problems during space-walks because it increases the dangers of decompression sickness from decreased total blood volume.

But overall, women would be much better placed than men to take a trip to Mars - a mission which is expected to last around two years.