Planetary Resources Inc., an asteroid-mining venture backed by Google Inc. executives, said it added more billionaire investors and is nearing a partnership agreement with a “top 10” mining company, Bloomberg reported.

Planetary Resources has “new billionaires to add to the list we’ve announced,” co-founder Eric Anderson said in an Aug. 3 telephone interview, declining to identify them. “There are a number of other people you know who’ve decided to come on board as investors. We’ve got a lot of people who are committed to the long-term cause.”

The Seattle-based company intends to launch a telescopic space surveyor into Earth’s low orbit in less than two years to identify potential metal- and water-rich asteroids and begin prospecting within four years.

The venture said in April it has the backing of Ross Perot Jr., Google CEO Larry Page, Chairman Eric Schmidt and former Goldman Sachs Group Inc. Co-Chairman John C. Whitehead.

The company aims to be the first to harness potentially trillions of dollars of minerals, including platinum group metals, by using robotic technology to mine asteroids.

“If their step-by-step road map goes to plan, I think it could be quite promising in the longer term,” Ben Taylor, a research fellow in the planetary environments team at the University of Surrey in Guildford, England, said by phone. “We can identify the minerals on the asteroids from orbital surveying, but it becomes a question of whether it’s still going to be cheaper to extract the very small amount that’s on earth compared to the cost of extraction on an asteroid.”

Though the company has “enough funding for several years of operations,” including its initial prospecting missions, it would consider an initial public offering for future financing needs, Anderson said.