The B612 Foundation is a private nonprofit foundation headquartered in Mill Valley, California, United States, dedicated to planetary science and planetary defense against asteroids and other near-Earth object (NEO) impacts. It is led mainly by scientists, former astronauts and engineers from the Institute for Advanced Study, Southwest Research Institute, Stanford University, NASA and the space industry. As a non-governmental organization it has conducted two lines of related research to help detect NEOs that could one day strike the Earth, and find the technological means to divert their path to avoid such collisions. It also assisted the Association of Space Explorers in helping the United Nations establish the International Asteroid Warning Network, as well as a Space Missions Planning Advisory Group to provide oversight on proposed asteroid deflection missions. In 2012, the foundation announced it would design and build a privately financed asteroid-finding space observatory, the Sentinel Space Telescope, to be launched in 2017–2018. Once stationed in a heliocentric orbit around the Sun similar to that of Venus, Sentinel's supercooled infrared detector would have helped identify dangerous asteroids and other NEOs that pose a risk of collision with Earth. In the absence of substantive planetary defense provided by governments worldwide, B612 attempted a fundraising campaign to cover the Sentinel Mission, estimated at $450 million for 10 years of operation. Fundraising was unsuccessful, and the program was cancelled in 2017, with the Foundation pursuing a constellation of smaller satellites instead. The B612 Foundation is named for the asteroid home of the eponymous hero of Antoine de Saint-Exupéry's 1943 book The Little Prince. Background When an asteroid enters the planet's atmosphere it becomes known as a 'meteor'; those that survive and fall to the Earth's surface are then called 'meteorites'. While basketball-sized meteors occur almost daily, and compact car-sized ones about yearly, they usually burn up or explode high above the Earth as bolides, (fireballs), often with little notice. During an average 24-hour period, the Earth sweeps through some 100 million particles of interplanetary dust and pieces of cosmic debris, only a very minor amount of which arrives on the ground as meteorites. The larger in size asteroids or other near-Earth objects (NEOs) are, the less frequently they impact the planet's atmosphere—large meteors seen in the skies are extremely rare, while medium-sized ones are less so, and much smaller ones are more commonplace. Although stony asteroids often explode high in the atmosphere, some