premise: Swift crater is a crater on Mars's moon Deimos. It is about 3 km in diameter. Swift crater is named after Jonathan Swift, whose 1726 book "Gulliver's Travels" predicted the existence of two moons of Mars. Swift crater is one of two named features on Deimos, the other being Voltaire crater. On 10 July 2006, Mars Global Surveyor took an image of Deimos from 22985 km away showing Swift crater.
hypothesis: Voltaire crater is 3 km in diameter.
reason: We do not know the size of the Voltaire crater.