🧬 Earth could have seeded life on Europa, Jupiter's moon

Earth could have sent life all the way to Europa, the icy moon of Jupiter. A recent study published in the International Journal of Astrobiology explores this idea, and the numbers give pause. According to Zaza Osmanov of the Free University of Tbilisi, terrestrial dust carrying microorganisms could have traveled to Europa and settled there.

This possibility, known as panspermia, has long been debated. Dust, meteorites or comets could have brought life to Earth, but the reverse idea – that our planet seeds other celestial bodies – is less often considered. Osmanov dubbed it the "inverse panspermia problem" and calculated that, over 5 billion years, dust grains can travel considerable distances.


For a bacterium to survive such a journey, its temperature must not exceed 27°C (80.6°F). Micrometer-sized grains can contain bacteria of similar size. According to calculations, atmospheric turbulence or collisions with cosmic dust could propel these grains to over 14 km/s (8.7 mi/s) at altitude, exceeding Earth's escape velocity of 11.2 km/s (7.0 mi/s). This phenomenon would have been occurring for 3.5 billion years, the duration of life on Earth.

After leaving Earth, three forces act on the grains: solar radiation pressure, Jupiter's gravity (which dominates a significant part of the Solar System), and drag from the interplanetary medium. Osmanov calculates that the grain's speed upon arrival near Jupiter would be 20.1 km/s (12.5 mi/s). To survive the impact on Europa, the grains must arrive at a very shallow angle – 1 degree relative to the surface – which concerns only about 3 grains out of a thousand.

The flux of grains leaving Earth is estimated at about 5 × 10¹⁸ particles per second, emitted in all directions. Among them, about 300 million would reach Europa's surface each second. Although the bacteria that land there are dormant, cracks in the ice, caused by Jupiter's tidal forces, could allow it to melt and transport the microbes to the liquid ocean below. The bacteria would find an environment to awaken and thrive.

In total, over billions of years, the number of terrestrial particles that reached Europa would be on the order of 10²³, or one mole. This strongly suggests that life could be present in its ocean if the biochemical conditions are compatible. The future European landing mission to Europa, planned for 2027, could verify this. Drills tested in Antarctica have already penetrated 30 km (19 mi) of ice in 300 days, paving the way for direct exploration.