Asteroids have been drifting through our solar system since long before the Earth had continents, oceans, or even life itself. The ancient space rocks contain clues about the origins of our solar system, and now scientists have finally acquired some of these space treasures.
NASA’s OSIRIS-REx mission has delivered samples from the asteroid Bennu, and their analysis is reshaping our understanding of ancient space rocks.
Color-changing mystery of asteroids
When viewed through telescopes, some gray asteroids appear red while others look blue – despite being made of the same material. Astronomers have been puzzled by why these space rocks scatter light so differently.
It’s not just about the colors. Knowing how asteroids diffuse light enables scientists to determine what they’re composed of without having to travel to each one and take samples.
The answer lies in a process called space weathering. Just as a penny turns green over time or paint fades in the sun, asteroid surfaces change when bombarded by radiation, micrometeorites, and the solar wind.
But the surprising part is this: it’s not different kinds of weathering that make the difference – it’s timing.
How space objects change over time
Michelle Thompson, an associate professor of Earth, Atmospheric, and Planetary Sciences in Purdue’s College of Science, has been studying these space rocks and their interactions with the harsh environment of space.
Her work focuses on understanding how the surfaces of rocky bodies, from our moon to distant asteroids, change over time.
“Sample return missions are a cornerstone of planetary science,” Thompson said. “They give us snapshots of the chemistry and the composition of the very early solar system. They let us look at the building blocks of the planets and inventory what was there.”
“We can also compare Bennu’s samples to samples from Japan’s Hayabusa missions and get a better understanding of how these asteroids change and evolve, and what we can tell about asteroids from the surface of the Earth compared to when we look at the samples themselves.”
Two asteroids, one story
The breakthrough came when scientists compared Bennu to another asteroid called Ryugu, which was visited by Japanese spacecraft.
Both are what scientists call “rubble pile” asteroids – basically cosmic junk piles held together by weak gravity. They’re both made of dark, carbon-rich materials and formed around the same time, roughly 4.6 billion years ago, when our solar system was just getting started.
Logic would suggest they should look identical through telescopes. But Ryugu appears slightly red while Bennu looks blue.
Scientists thought this meant the asteroids were weathering differently in space. The samples revealed something much more interesting.
A cosmic clock of color changes
The real story is about time. These rubble pile asteroids are constantly shifting and tumbling, which brings fresh material from their interiors to the surface. It’s like having a rock tumbler in space that occasionally spills out new pebbles.
Surface grains from Ryugu have been exposed to space for only a few thousand years – practically brand new in cosmic terms. Meanwhile, Bennu’s surface particles have been getting blasted by space radiation for tens of thousands of years. They’re at different points in the same aging process.
“And so instead of looking at two different trajectories for how this process is operating on these bodies, we’re seeing two different points in one cycle,” Thompson said. “Their ‘colors’ are changing, meaning their spectral properties are changing relative to their surface exposure age.”
This discovery is huge for future space exploration. With 1.45 million known asteroids in our solar system, we can’t visit them all. But now scientists can look at an asteroid’s color through a telescope and get a much better idea of what they’ll find on its surface.
Bennu carries ancient recipes for life
The Bennu samples revealed something else exciting. Hidden within the space rock were salts, including phosphates that are essential for life on Earth. These compounds help power our metabolism and make up the backbone of DNA.
Scientists found evidence of ancient brine – basically salty water that would have created perfect conditions for the chemical reactions that might lead to life. The asteroid essentially carried a recipe card for life’s basic ingredients.
“Looking at the organic molecules from Bennu, we are getting an understanding of what kinds of molecules could have seeded life on early Earth,” Thompson said.
“Information about what compounds, what elements are there and in what proportions. We won’t find life itself, but we’re looking at the building blocks that could have eventually evolved into life.”
Time capsules from the dawn of everything
What makes these asteroid samples so special is their age and pristine condition. Earth has been recycling its materials for billions of years through plate tectonics, erosion, and biological processes. The ingredients for life are still here, but they’ve been mixed and remixed countless times.
Bennu’s samples, on the other hand, have been sitting in the cosmic freezer for 4.6 billion years. They’re like finding a perfectly preserved meal from the very first restaurant in the Universe.
“Asteroids are relics of the early solar system,” Thompson said. “They’re like time capsules. We can use them to examine the origin of our solar system and to open a window to the origin of life on Earth.”
The research shows that Bennu contains materials from across our solar system and possibly beyond, all mixed together and transformed by water and space weathering over billions of years. It’s a cosmic mixtape of the early solar system’s greatest hits.
This research opens doors for future asteroid missions, whether for science or resource extraction. By understanding how asteroid colors relate to their surface exposure and composition, future explorers will have a much better roadmap for choosing which space rocks to visit.
The gray asteroids that shine red and blue aren’t just pretty to look at – they’re guidebooks to our solar system’s past and potential keys to its future exploration.
The full study was published in the journal Nature Communications.
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