Pseudo-panspermia, also known as soft panspermia, molecular panspermia, or quasi-panspermia, is a widely supported idea about how life began. This theory suggests that many small organic molecules needed for life formed in space and were part of the solar nebula, the cloud of gas and dust from which planets formed. These molecules were then spread to planetary surfaces, where life eventually developed on Earth and possibly on other planets. Pseudo-panspermia is different from the less widely accepted theory of panspermia, which claims that living organisms, not just molecules, traveled from distant planets to Earth.

Background

Theories about how life began have been recorded since the 5th century BC. At that time, a Greek philosopher named Anaxagoras suggested that life came to Earth from space. Today, most scientists do not support the idea that life fully came from space. However, a different idea called pseudo-panspermia, where molecules are created and moved through space, is supported by many scientists.

Extraterrestrial creation of organic molecules

Interstellar molecules are created through chemical reactions in very thin clouds of dust and gas found in space or around stars. This often happens when a molecule becomes charged, usually because it interacts with cosmic rays. The charged molecule then pulls in a nearby molecule using the electric force between its positive charge and the electrons of the neutral molecule. Molecules can also form when neutral atoms and molecules react, but this process is usually slower. Dust is important because it helps protect molecules from harmful ultraviolet light coming from stars. The Murchison meteorite contains organic molecules called uracil and xanthine, which means these molecules were already present in the early Solar System. They may have played a role in the beginning of life.

Nitriles, which are important building blocks for the RNA World scenario, are among the most common types of molecules in the universe. They have been found in clouds of gas near the center of the Milky Way, around young stars of different sizes, in meteorites and comets, and even in the atmosphere of Titan, Saturn's largest moon.

Evidence that organic molecules are created in space includes finding them in many different places in space and successfully making them in laboratories using conditions similar to those found in space.

Planetary distribution of organic molecules

Organic molecules can be spread to planets like Earth during their formation and at later times. If the materials that formed planets included organic molecules and these molecules were not destroyed by heat or other processes, they could be available for the start of life on those planets.

Later, organic molecules can be carried to planets by objects such as comets and asteroids. These objects may fall to a planet's surface as meteorites, releasing any molecules they carry when they turn into gas during impact or later as they wear away.

Scientists have studied rock and dust from asteroid Bennu, which was sent to Earth by NASA's OSIRIS-REx mission. These samples contain molecules that are important for life on Earth and show evidence of past saltwater.

Findings of organic molecules in meteorites include: