A Moon-to-Mars-sized astronomical body once existed in our solar system. It’s gone now—but it left an important call to action.
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In 2019, a meteorite was found in the Sahara Desert named Northwest Africa 12774. In 2025, a team of researchers started analyzing it and realized that this meteorite belongs to a rare class of meteorites called angrites. There are fewer than 100 angrites out of the more than 80,000 meteorites discovered on Earth’s surface.
By analyzing Northwest Africa 12774’s chemical fingerprints, scientists found that the number of neutrons in the atoms of its elements (isotopes), specifically oxygen and chromium, matched the composition of astronomical bodies in the solar system.
By measuring the decay of radioactive elements inside Northwest Africa 12774 (which act as natural clocks), scientists determined that it crystallized from molten rock just 4 million years after the first solids formed in the solar system. This dates it to about 4.56 billion years ago, making it one of the oldest known volcanic rocks of the solar system. Only material that formed alongside the Sun and its surrounding disk of gas and dust could be this old.
In addition, by testing Northwest Africa 12774’s mineralogy, scientists observed that the meteorite contains crystals of a mineral called clinopyroxene that are unusually rich in aluminum. To forge these specific crystals, the rock had to be subjected to immense pressure that could only be generated inside a large, differentiated body, not a small, undifferentiated asteroid. Scientists calculated that the “angrite parent body” must have been at least 1,000 km (620 miles) in radius. If the crystals formed at a shallow depth, the body could have been as large as 3,600 km (2,200 miles)—comparable in size to the Moon or even Mars.
Although Northwest Africa 12774 was not seen falling from the sky and its exact path through space cannot be tracked, its classification as an angrite links it to a specific group of meteorites overwhelmingly associated with the main asteroid belt between Mars and Jupiter.
To contextualize where and what the asteroid belt actually is, it might be useful to recap what the solar system consists of today:
- One star: The Sun.
- Orbiting the Sun in different directions: Comets (because they were formed either entirely outside or on the very outskirts of the solar system).
- Orbiting the Sun in the same direction:
- The terrestrial planets: Mercury, Venus, Earth (with 1 moon), and Mars (with 2 moons).
- The asteroid belt: Between 1 and 2 million asteroids composed of rocky, refractory materials, where Ceres (a dwarf planet) is the largest object.
- The giant planets: The gas giants (the number of moons grew exponentially over the last few years) – Jupiter with 95 moons, Saturn with 146 moons; The ice giants – Uranus with 27 moons, Neptune with 16 moons.
- The Kuiper belt: An icy ring with millions of objects made mostly out of ice and volatile elements, featuring proto-planets and dwarf planets like Pluto (with 5 moons), Eris (with 1 moon), Haumea (with 2 moons), and Makemake (with 1 confirmed moon).
Essentially, scientists are able to know all about the size, chemical composition, and age of all these solar system objects through two main sources of evidence.
First: telescopes. By analyzing their images, scientists can infer the size, speed, and rotation of astronomical bodies. By analyzing the light and spectrum of Solar System objects, astronomers can determine their chemical composition.
Second: meteorites. Minerals that either fall to Earth’s surface from space or are sitting at the Earth’s surface waiting to be found carry the chemical signatures of their parent bodies.
By comparing meteorite compositions with those observed through telescopes, scientists can piece together the solar system’s makeup.
It is important to highlight that understanding how, when, and why the solar system developed the way it did is far more valuable than simply listing and classifying its astronomical bodies. In Science, merely describing something, very often, does not move Science forward. In contrast, understanding something is what propels scientific progress.
To illustrate, consider this timeline:
- 5.103.200.000 years ago — A star cluster that would become the solar system was taking place in the Milky Way
- 4.568.200.000 years ago — The first solar system solids were formed
- 4.518.200.000 years ago — Nuclear fusion ignited the Sun
- 4.510.000.000 years ago — Earth and the Moon formed
Knowing these dates is useful. But they don’t change anything if they are not used to understanding why all those milestones happened the way they did. In this context, we can see the data we have as a starting point rather than as an end in itself.
An effective approach is to look at the Solar System timeline and ask: What are the Solar System milestones that could have happened faster or differently? Are there any shortcuts in terms of planetary system formation that could take place, and does that mean that there might be other planetary systems in the universe, for instance, that could have life for a longer period of time than what happened on Earth?
Anyway, understanding how planets formed—and what their characteristics were at specific points in time—can give a roadmap for what to look for elsewhere in the universe.
Without making a direct association between a planet’s emergence conditions in our own solar system, we are just going to be looking for water out there for a very long time… without ever finding anything.