The bill, called the Space Resource Exploration and Utilization Act of 2015, states that "any asteroid resources obtained in outer space are the property of the entity that obtained such resources, which shall be entitled to all property rights thereto."

The bill is designed to protect the interests of American companies, such as Planetary Resources, that want to mine asteroids. As subjects of the US, Congress is attempting to give them legal cover against competitors, be they foreign countries or foreign companies. Seems reasonable, and seems straightforward, except it's not.

The US wrote, signed, and got 124 other countries to sign the Outer Space Treaty in 1967, which states that the Moon and "other celestial bodies" are "not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means."