Star-Hopping Travelers Could Sow Seeds of Life

Rock-riding microbes tossed out of our solar system may have become star-trekking voyagers, by crossing deep space and planting themselves on planets circling other suns. This solar system-to-solar system seeding of life is called interstellar panspermia. It is now commonly thought that meteorite-sized rock fragments can be ejected from one planet to land on another. Meteorite collections include rocks believed heaved our way from the planet Mars and the Moon. These celestial hunks of material reached Earth after those worlds were subjected to large impacts of asteroids or comets eons ago. But Earth isn’t only on the receiving end of chunky-style helpings of its planetary neighbors — it works both ways.