(CNN) - While Mitt Romney has mostly danced around specific attacks against newly minted front-runner Newt Gingrich, he didn't hesitate to take aim at Gingrich over his past advocacy for private space exploration projects.
"I saw the speaker had a measure that I read about to put a permanent colony on the moon, to mine rare materials from the moon," Romney said Friday in an interview with The Des Moines Register editorial board. "I think we've got other priorities for our spending before we do that."
He added: " (Gingrich) even talked about a series of mirrors that we could put in space that would light our highways. I've got better ideas for our resources."
Over the last few weeks, the former Massachusetts governor has watched Gingrich knock him out of his steady spot at the top of several state and national polls.
Several of Romney's high-profile supporters have taken to phone conferences with reporters to attack Gingrich's record, a tactic the former House speaker has also used in response.
Also in the interview, Romney took issue with his opponent's controversial stance on child labor. Gingrich recently repeated that he thinks children in poor communities should take up part-time jobs–including janitorial jobs–in order to learn a strong work ethic.
"I disagree with the speaker thinking we should eliminate some parts of child labor laws so that kids could clean schools," Romney said. "I don't think that's a great idea."
He further hit Gingrich over other issues, including climate change and immigration policies.
Comparing himself with Gingrich, Romney said, "We're very different people."
The former speaker's campaign has previously responded to attacks from his opponents, saying this is only the beginning.
"This won't be the first, this won't be the last. There's going to be an awful lot of them, and none of them are going to work," said Gingrich press secretary R.C. Hammond in a statement on Thursday.
- CNN's Rachel Streitfeld contributed to this report.