Microbial life may have resided within the first four kilometers of Mars’s porous crust.

Four billion years ago, the solar system was still young. Almost fully formed, its planets were starting to experience asteroid strikes a little less frequently. Our own planet could have become habitable as long as 3.9 billion years ago, but its primitive biosphere was much different than it is today. Life had not yet invented photosynthesis, which some 500 million years later would become its main source of energy. The primordial microbes — the common ancestors to all current life forms on Earth — in our planet’s oceans, therefore, had to survive on another source of energy. They consumed chemicals released from inside the planet through its hydrothermal systems and volcanoes, which built up as gas in the atmosphere.

Some of the oldest life forms in our biosphere were microorganisms known as “hydrogenotrophic methanogens” that particularly benefited from the atmospheric composition of the time. Feeding on the CO2 (carbon dioxide) and H2 (dihydrogen) that abounded in the atmosphere (with H2 representing between 0.01 and 0.1% of the atmospheric composition, compared to the current approximate of 0.00005%), they harnessed enough energy to colonize the surface of our planet’s oceans. we explore Mars, it is becoming clearer that similar environmental conditions were developing on its surface at the same time as those that enabled methanogens to flourish in the oceans back on Earth.

Breadcrumbs…

When University of Cambridge astronomer Amy Bonsor and her colleagues studied the spectrum of light from white dwarfs — the burned-out remains of small stars — they noticed flecks of heavier elements on the stars’ surfaces where there should have been only a glowing expanse of helium and hydrogen. The astronomers realized the stars’ surfaces were littered with debris from asteroids and comets that had fallen into the stars, visible on the surface just briefly before sinking into the depths.

The chemical makeup of those planet crumbs — visible in their spectra, the specific wavelengths of light each chemical emits — suggests that the building blocks of planets are as ancient as a star system itself, rather than things that form later from the disk of material orbiting the star.

What’s New — It’s morbid but true: most stars eventually gobble up at least some of the planets and other chunks of space rock in their orbits. Solar systems can be dangerous places, especially in their early stages, with planets’ gravity bumping other planets — or smaller things, like asteroids and comets –—off their courses. Some of those objects get launched out of the solar system to start a new life as rogue planets, but others end up spiraling inward toward the immense gravity of the star at the heart of the system.