Tardigrades can survive tremendous heat and cold, radiation and vacuum.
Tardigrades, microscopic invertebrates also known as water bears and moss piglets, are found virtually everywhere where liquid water exists, from droplets on leaves to ponds.
If necessary, they can drain their cells of any liquid and enter suspended animation with no measurable metabolism, a condition called cryptobiosis ("hidden life"). They can survive subzero temperatures, boiling water, zero oxygen, radioactive and cosmic radiation, high pressures, and even the vacuum of space for years in cryptobiosis. When re-hydrated tardigrades will regain their full function in a matter of hours.
In 2019, the Israeli spacecraft "Beresheet" carrying a few thousand tardigrades crash-landed on the Moon, prompting - considering their indestructibility - speculation about terrestrial life surviving on other worlds.
The Moon may not the best place to survive, but planets like Mars, with an atmosphere and at least temporary flow of surface water, might sustain life as we know it.
The idea of Earth seeding other planets in our solar system with life is not new. Panspermia is an idea dating back to the 19th century arguing that simple organisms could survive the journey between planets inside a meteorite. Ejected by an impact on a planet with life into space, bacteria, spores, and small invertebrates could travel in the fragment to another planet, seeding a barren world with life.
Meteorites of Martian origin are found on Earth, and meteorites of terrestrial origin could be found on Mars. An impact the size of the dinosaurs killer Chicxulub asteroid would send material far into space. The debris would take about a hundred years for the first material to get near Mars and the material would continue to arrive for up to 20 million years from that date.
But first the tardigrades need to survive the impact shock during "lift-off" and "landing" on another planet. In a study published in the journal Astrobiology, scientists fired tardigrades out of a special gun to simulate an impact event.
The researchers loaded two or three individuals of Hypsibius dujardini, a species of freshwater tardigrade, each into a number of nylon bullets, which were frozen to induce the creatures' cryptobiosis state. The bullets were fired at sand targets in a vacuum chamber at a range of velocities from 556 to 1,000 meters per second.
The tardigrades survived up to and including an impact velocity of 825 meters per second, equivalent to a shock pressure of 1.14 gigapascals. The surviving animals needed more than 8 to 9 hours to resume activity, suggesting at least some tissue damage.
Beresheet crashed on the Moon with a maximum velocity of 946 meters per second, casting severe doubts on the idea of tardigrades surviving the crash. But if a meteorite had a lower impact speed, survival may be possible.
A larger obstacle for space-traveling tardigrades is shock pressure during the impact needed to send material into space. The pressure depends strongly on the impact angles (higher angles correspond to higher pressure), but a 10-km asteroid (like Chicxulub) would cause a shock pressure ranging from 20 to 30 gigapascals, far beyond the survivability of any known organism.
(h/t Michelle Starr at ScienceAlert)
