By Robert Hazen, Ph.D., George Mason University
Samples collected from space help to understand the properties of the solar system. The solar system is littered with planets, moons, comets, asteroids, and much more. Scientists gather samples to learn about the composition of these objects, their distribution, and their dynamics. Those data provide hints about the origin of the planetary system.
Samples from Mars and Moon
Meteorites are rocks that fall to Earth from space. While the vast majority of meteorites appear to be fragments of asteroids that have collided and broken up and sent their fragments flying off, a small number of these meteorites appear to come from the surface of Mars.
The way we know this is because Mars has a very distinctive atmosphere; a CO2 atmosphere. If you look at these supposed Martian meteorites, there are tiny air bubbles that have been trapped, and the air is exactly matching the composition of Mars. How does this happen? How can you get a meteorite from the surface of Mars?
The idea is that you have a large asteroid or comet coming in, smashing into the Martian surface. That impact is so energetic that some of the Martian material is ejected into space, in a violent event, and become objects that are floating around the Sun. Some of those things that blasted off the Martian surface eventually may come to Earth as a meteorite, a rock from space.
One of the greatest sets of samples we have are the samples returned from the Moon, primarily the hundreds of kilograms of samples, of rocks and soils, collected by the Apollo astronauts. There were six Apollo missions that landed on the Moon, and each of those missions brought back samples.
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Interplanetary Dust Particles
There are other samples as well. There are things called the interplanetary dust particles, or IDPs. These can be collected in high-altitude aircraft. They’re dust particles that come from collisions, and other sorts of things in space, and they form literally a fine dust. NASA collects them using an old U-2 spy plane that can fly at high altitude and has collectors, and just sweeps up these dust particles.
Most of them are debris from our solar system, but occasionally, maybe one in 1,000 particles is actually a piece that came from before the solar system. It’s a piece of supernova that’s exploded; it’s a piece of a red giant wind, the great solar flares, the winds that came off red giant stars. Amazing particles that tell us about the earliest history of our universe, not just our solar system.
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Distinctive Properties of the Solar System
Our solar system has many objects, and their systematic behavior tells us something about its origin.
First, consider the very non-uniform distribution of mass. The Sun is roughly 1,000 times more massive than everything else in the solar system put together. 99.9 percent of all the mass in the solar system is concentrated right at its center. Of the remaining mass, Jupiter is more than twice as massive as everything else.
So we have one huge mass in the center, one pretty large mass in Jupiter outside, and everything else is basically trivial, in the context of the total mass of the solar system.
Also, think about the orbits of planets in the solar system. Even though the Sun is by far the most massive object, all the angular momentum—that is, the rotational energy of the solar system—is held in the planets.
Indeed, Jupiter and Saturn, the largest planets, contain more than 99 percent of all the angular momentum of the solar system. That’s another curious fact. The mass is concentrated in the middle; the angular momentum is concentrated out in the Jovian planets, the giant planets.
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Age of the Solar System
We also learn about the solar system’s history from the age of its matter. We can use radiometric dating, using things like uranium-lead dating, to determine the age of various objects. For example, Moon rocks display a variety of ages, from about 4.5 billion years to as young as 3.2 billion years.
Many meteorites also display an age of about 4.5 billion years. These ages suggest that the solid material in the solar system may have first crystallized roughly 4.5 or 4.6 billion years ago. From this then, we date the age of the solar system; the solar system is now said to be 4.5 or 4.6 billion years old.
Common Questions about the Distinctive Properties of the Solar System
Samples are used to understand the properties of the solar system. The solar system is full of planets, moons, asteroids, comets, and more. Sampling helps scientists gain information about the composition of objects, how they are distributed, and their dynamics.
One of the largest sets of samples currently available to understand the properties of the solar system is the returned samples from the Moon. Hundreds of kilograms of rock and soil samples were collected and brought to Earth by Apollo astronauts. Six Apollo missions landed on the moon, each carrying a large amount of samples from the Moon when it returned.
Interplanetary dust particles, or IDPs, are dust particles that come from collisions, and other sorts of things in space, and they form literally a fine dust. These can be collected in high-altitude aircraft.