The first Australian NASA astronaut to go in to space has questioned whether the entrepreneurial Mars One project is "morally defensible".
Andy Thomas, in Brisbane for the World Science Festival, said he was "very unimpressed with Mars One", which plans a corporate-funded one-way mission to the red planet.
"They claim they can launch a crew to Mars in the mid to late 2020s and do it for less than $9 billion," Mr Thomas said.
"It (the cost estimate) is so low as to be laughable. We don't know how to build a habitat that can sustain a crew for an outbound mission and on Mars indefinitely.
"I don't think it's morally defensible to send crews one way to Mars.
"We can bring them home. We don't know what the long-term health impacts of living on Mars are and I suspect they are quite serious."
Despite his outlook on that project, Mr Thomas believed travel to Mars was essential for the human race and would most likely happen in this century.
"I think Mars is the Holy Grail of human exploration," he said.
"I think in the next century people will look back on this century the way we look back on the time of Magellan and Columbus."
Physicist, engineer, comedian and Mars One hopeful Josh Richards was preselected to be among the 24 earth-dwellers selected for the Mars One mission.
"I see myself as a communicator, I have a background in physics, engineering, diverse in sciences generally - a jack of all trades. They want people who can do a little bit of everything," said Mr Richards, also in Brisbane.
"The biggest gift I can give is to make what we're doing relatable.
"It's about going exploring somewhere we've never been before."
A previous version of this story incorrectly stated Andy Thomas was the first Australian in space. It's been corrected to note that he was the first Australian NASA astronaut in space.