Facebook shares fell more than 9 percent today, closing at $28.84 on the first day of options trading, which allows investors to bet on the future of the stock with less money at risk.

Today marks the first time the company’s shares dropped below $30 after its initial public offering earlier this month, which priced shares at $38. Facebook now has a market cap of about $79 billion, down from the $104 billion IPO valuation. The broader market was up today with the Nasdaq, Dow and S&P all gaining over 1 percent.

Facebook’s stock had a low of $28.65 today as the company debuted in the public options market. An option is a contract that gives investors the right to buy or sell shares at a specific price on or before a certain date. It does not give investors any ownership of a company. Options can be used to bet on the direction of a stock’s price through “calls” and “puts.” When investors buy a call option, they can purchase a stock at a set price any time before the option expires. When investors buy a put option, they can sell a stock at the strike price any time before the expiration date.

According to Bloomberg, the volume for puts exceeded calls by 1.2-to-1, indicating that many investors believe Facebook’s share price will continue to decline over the next month. The outlet says June $30 puts were the most common, followed by June $34 calls and June $32 calls.

The Wall Street Journal suggested that options trading contributed to Facebook shares’ overall decline today. Other factors could include the lawsuits and controversy that have resulted from the social network’s IPO, as well as rumors that Facebook could be building a phone or buying a browser.