A frequent idea in sci-fi and apocalyptic films is that of an asteroid striking Earth and causing global devastation. While the probabilities of this kind of mass extinction occurring on our planet are incredibly small, they are not zero.

The results of Nasa's Dart mission to the asteroid Dimorphos have now been published in Nature Astronomy. They contain fascinating details about the composition of this asteroid and whether we can defend Earth against incoming space rocks.

The Double Asteroid Redirection Test (Dart) was a spacecraft mission that launched in November 2021. It was sent to an asteroid called Dimorphos and commanded to collide with it, head on, in September 2022.

Dimorphos posed and poses no threat to Earth in the near future. But the mission was designed to see if deflecting an asteroid away from a collision course with Earth was possible through "kinetic" means—in other words, a direct impact of a human-made object on its surface.

Asteroid missions are never easy.

To quote NASA associate administrator Jim Reuter, sending crewed missions to Mars by 2040 is an "audacious goal." The challenges include the distance involved, which can take up to six months to traverse using conventional propulsion methods. Then there's the hazard posed by radiation, which includes increased exposure to solar particles, flares, and galactic cosmic rays (GCRs). And then there's the time the crews will spend in microgravity during transits, which can take a serious toll on human health, physiology, and psychology.

But what about the challenges of living and working on Mars for several months at a time? While elevated radiation and lower gravity are a concern, so is Martian regolith. Like lunar regolith, dust on Mars will adhere to astronauts' spacesuits and inflict wear on their equipment. However, it also contains harmful particles that must be removed to prevent contaminating habitats.

Just over five years ago, on 22 February 2019, an unmanned space probe was placed in orbit around the moon. Named Beresheet and built by SpaceIL and Israel Aerospace Industries, it was intended to be the first private spacecraft to perform a soft landing. Among the probe's payload were tardigrades, renowed for their ability to survive in even the harshest climates.

The mission ran into trouble from the start, with the failure of "star tracker" cameras intended to determine the spacecraft's orientation and thus properly control its motors. Budgetary limitations had imposed a pared-down design, and while the command center was able to work around some problems, things got even trickier on 11 April, the day of the landing.