Investing.com - Some investment opportunities are, well, out of this world!And investors are lining up for them.Almost $4 billion was invested in commercial space companies in 2017-- a record amount. according to the investment firm Space Angels.With the U.S. government cutting spending in recent years, private companies have picked up the slack, launching more rockets.Private companies conducted 37 of the 88 launches in 2017The space industry is now worth about $350 billion. It is expected grow to more than $1 trillion by 2020.It's hard to invest directly in space, though.Leading companies are not publicly traded. That's the case with those founded by Elon Musk of Tesla (NASDAQ:TSLA) and Jeff Bezos of Amazon (NASDAQ:AMZN).Investors can get exposure through major aerospace and defense companies, such as Boeing (NYSE:BA), Lockheed Martin (NYSE:LMT) and Northrup Grumman. There are also half a dozen ETFs representing those two sectors.Tech giants like Apple (NASDAQ:AAPL), Microsoft (NASDAQ:MSFT) and Alphabet (NASDAQ:GOOGL) have even invested in the space business..