European scientists said they had selected a shortlist of eight men Monday willing to take part in a 105-day isolation experiment to further knowledge about the stress of a manned trip to Mars.

Six of the eight candidates will be chosen to live, eat, sleep and work inside a sealed laboratory in Moscow that will simulate a Martian mission, the European Space Agency (ESA) said.

Their stay, starting in March, is a precursor to a longer study later in 2009 in which another six-member crew will experience 520 days together.

The extreme experiments are aimed at seeing how long-term confinement acts on mood, morale, hormone regulation and the effectiveness of dietary supplements.

The final eight candidates for the 105-day test are all male, aged between 28 and 39, and hail from Denmark, Sweden, Germany (2), France (3) and Belgium, ESA said in a press release.

They were put through their paces at the Central Clinical Hospital of the Russian Academy of Sciences, where doctors carried out extensive medical tests and had them screened by a neurologist, a dentist, a psychologist and an ophthalmologist.

The project is a joint venture between ESA's Directorate of Human Spaceflight and the Russian Institute for Biomedical Problems (IBMP).

ESA and NASA have separately sketched dates around three decades from now for a historic manned flight to Mars.

The distance between Earth and Mars varies between 55 million kilometres (34 million miles) and more than 400 million kms (250 million miles), which means that a round trip to the Red Planet would take at least 18 months.

The health of the crew -- psychological as well as physical -- is considered as daunting a challenge as mustering the financial resources and technical means for the trip.