Just jump to escape to space

The European Rosetta mission achieved the sensational feat of placing a spacecraft in the orbit of a comet and landing a fridge-sized probe onto its surface. The comet is called Churyumov-Gerasimenko, or short 67P. By orbiting around the comet and measuring the changes in the spacecraft's trajectory, we can calculate the comet's mass, who's gravity slightly pulls the spacecraft away from a straight path. 67P's mass was estimated to be about 10^13 kg (a one with 13 zeros). The largest cruise ship in the world, the Oasis of the Seas, weights about 10^8 kg. So the comet weights as much as 100,000 of such cruise ships. Still, this mass is nothing compared to the mass of the Earth, which weights about 6*10^24 kg, 600,000,000,000 times as much as the comet.
    If we would walk on the comet's surface, how strong would be the gravitational pull? Given the known mass and size of 67P in relation to the Earth, we can compare the gravitational forces. This force is proportional to the mass of the space object (Earth or 67P) divided by the square of the distance to the center of the object. (Strictly speaking this relationship is only correct for spherical objects like the Earth, but 67P is shaped like a rubber duck; still it is a reasonably good approximation.) 67P is much lighter than Earth, but we would walk much closer to its center. How much closer? Earth's radius is about 6,400 km (4,000 miles). 67P is maximally 4km long; let's say, we walk 2 km above its center. Then, the gravitational pull would be 3,200*3,200 divided by 600,000,000,000 = 0.002% of the force on Earth. A small force, which makes landing a probe challenging; it could easily bounce off again.
    Imagine how high you could jump on 67P. For each space object, there is a maximum velocity beyond which a spacecraft would escape the object's gravitational pull and never return (it's different for black holes, but I won't discuss them in this post). This velocity is called the escape velocity. For Earth, this velocity is about 11,000 m/s (25,000 mph), which makes it expensive to launch anything into space. The square of this velocity is proportional to the mass of the space object divided by the distance to the center of the object. So for 67P, the escape velocity is the square root of (3,200 / 600,000,000,000) times 11,000 m/s = 80 cm/s (1.8 mph). Compare this value to the average human jump velocity, which is about 3 m/s (6.7 mph). Standing on 67P, you could easily launch into space just by jumping. But you need to walk carefully on the surface to avoid accidentally drifting into space and never returning.

    A manned mission to a comet would be very different from the moon landing. The Apollo mission required a moon lander capable of launching again from the surface. In contrast, a spacecraft circling the comet could eject an astronaut to land on the surface, who then could jump off the surface again to return to the spacecraft.