NASAs asteroid sample reveals key chemistry that could lead to life
Scientists have detected amino acids and complex mineral compounds in NASA's asteroid Bennu rocks, some never seen before in space rocks.
Scientists poring over a sample brought back from the asteroid Bennu have detected amino acids and complex mineral compounds, some of which have never been found in space rocks.
A team at the Smithsonian’s National Museum of Natural History discovered a salty residue left over from an ancient brine. Through evaporation, it formed minerals rich in sodium, carbon, sulfur, phosphorus, chlorine, and fluorine. Finding these ingredients shows that the conditions to make them existed earlier and more widely in the solar system than previously thought.
Another study led by NASA scientists identified several different types of amino acids — tiny building blocks that make up proteins essential for life — in the asteroid material. Those findings included 14 of the 20 amino acids that Earth life uses to build proteins. These same amino acids have also been found in meteorites.
The new research helps build the case that space rocks brought chemicals necessary for life to emerge on this planet through collisions in ancient cosmic history. The pair of papers were published separately in Nature and Nature Astronomy on Wednesday.
"If water-rich asteroids were commonly producing these elements, and we know that asteroids bombarded the surfaces of planets and moons early in their history," Tim McCoy, one of the Smithsonian paper's lead authors, told Mashable, "these primitive asteroids almost certainly delivered both water and prebiotic organics to Earth, Mars, and other planets and moons in our solar system."
NASA's $800 million OSIRIS-Rex mission, short for Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer, launched in 2016. The robotic spacecraft completed its 4-billion-mile trip when it dropped the capsule from 63,000 miles above Earth onto a patch of Utah desert seven years later. It's the first U.S. mission to grab a sample of an asteroid.
These are the most precious space souvenirs NASA has obtained since the Apollo moon rocks, gathered between 1969 and 1972. The mission succeeded in bringing home about a half-cup of crushed Bennu rocks and dirt. So far researchers haven't been disappointed with their bounty.
All forms of Earth life have specific chemicals in their makeup, such as amino acids and sugars. Scientists have known that asteroids hold molecules believed to be the precursors to these chemicals. By studying the Bennu samples, they hope to gain more insight into how these ingredients could have evolved.
An important reason NASA selected Bennu for the sample return mission is because of its relatively close proximity, making the endeavor achievable. It also has a very remote chance of hitting Earth in the coming centuries. Learning about the asteroid could be helpful in future efforts to redirect it.
But the team also chose Bennu to investigate the chemical origins of life. Some of its mineral fragments could be older than the 4.6 billion-year-old solar system. These grains of stardust could have come from dying stars or supernovas that eventually led to the formation of the sun and planets.
The museum team was especially surprised to find traces of water-bearing sodium carbonate compounds, commonly known as soda ash, in the Bennu sample. These chemicals have never been found in asteroids or meteorites before. They naturally crust in dried lake beds, such as Searles Lake in the Mojave Desert.
But a key difference between the brine and soda lakes is an abundance of phosphorus in the former, and scientists have been keen to follow the phosphates for more clues on the genesis of life. These compounds are crucial, forming the backbone of DNA, yet they're relatively rare compared to the other five main elements — hydrogen, carbon, nitrogen, oxygen, and sulfur — in biology.
Scientists propose that similar brines probably still exist in other distant worlds, including Saturn’s icy moon Enceladus, where spacecraft have detected sodium carbonate.
"From a biological perspective, phosphate is one of the essential building blocks – along with sugar – of the single and double helix that make up RNA and DNA," McCoy said. "Without a phosphate-rich system, these complex molecules that make up living things simply could have never formed."
In the NASA-led study, scientists detected multiple protein-building amino acids and five nucleobases that make up RNA and DNA.
The researchers think Bennu may have come from a larger icy source, perhaps like the dwarf planet Ceres. This is because Bennu contains chemicals like ammonium and carbonate salts, as well as organic carbon, suggesting liquid water once ran through it, even in the asteroid's extremely cold conditions.
The paper posits that minerals found in the rocks formed in stages as water carried dissolved substances: first calcium and magnesium carbonates, phosphates, then sodium carbonates, followed by salts like table salt and sulfates. High amounts of ammonium salts in Bennu may have kept the water flowing, even at temperatures as low as -143 degrees Fahrenheit. This means important chemical reactions for life could have continued long after the asteroid’s heat faded.
Previously, Dante Lauretta, OSIRIS-Rex's principal investigator, said his dream discovery from the Bennu rocks would be evidence of peptides, signaling protein evolution.
"While the detection of amino acids in the Bennu samples is an important discovery," he told Mashable, "we have not yet detected peptides — amino acids linking together — within the samples."
But scientists say this is only the beginning, with the Bennu rocks likely yielding decades of more discoveries.
