The actor who plays the captain on TV's Star Trek has said he thinks resources spent on sending people into space should be used on "getting this place right first".
Stewart said human beings were not ready to live on other planets
Patrick Stewart said Earth should be our focus rather than other planets.
"I'm a bit of a wet blanket when it comes to the whole business of space travel," he said in a BBC interview.
As commander of the USS Enterprise on the show, his character Captain Jean-Luc Picard is an avid space traveller.
In an interview with BBC World Service radio, Stewart said he backed unmanned missions such as Nasa's Mars rover Opportunity and the UK's Beagle 2 mission.
But he said he did not believe the human race was ready to begin thinking about beaming down on other planets.
"As I get older my unease at the time and the money that has to be spent on projects putting human beings back to the moon, and on to another planet, is so enormous," he said.
"And it would take up so many resources, which I personally feel should be directed at our own planet."
Interviewed by the World Update programme, he added: "Humankind has just not simply become sufficiently evolved to now leave this planet, take itself out to space and began establishing more of us out there.
"I would like to see us get this place right first before we have the arrogance to put significantly flawed civilisations out on to other planets - even though they may be utterly uninhabited."