NASA's robotic spacecraft allow us to visit comets, asteroids, and dwarf planets up close, and even bring back samples to study. We are just beginning to figure out what these places are like, what they are made of, and how they formed. There are so many places to explore and so much to learn.
While actually going there is perhaps the most exciting and direct way to learn about these small worlds, it's not the only way we can experience what they have to teach us. There are lots of ways in which we learn about the small worlds of our solar system.
What Our Eyes See
For most of human history our best tool for observing the sky has been our eyes. With our natural senses, we witness comets, meteor showers, and shooting stars. In ancient times, before we knew much about them, these phenomena were often sources of awe and fear. Learning about what causes these apparitions has removed our fear of them, but done nothing to lessen our awestruck gaze. We are simply fascinated by these messengers in the heavens.
We see comets when they enter the inner part of the solar system where the Sun's light and heat begins to warm their surfaces, causing them to emit jets of gas and dust. When Earth encounters the trail of small particles left behind in the orbital path of a comet, we witness these particles burning up in Earth's atmosphere as a meteor shower.
Shooting or falling stars are another name for meteors. These are bits of space debris that create lots of friction as they fall through our atmosphere, causing them to glow. Most meteors are no bigger than a pea, but larger ones can create brilliant colorful fireballs that break apart as they fall, dropping meteorites over large areas.
Observing Through Telescopes
From the ground, both scientists and amateur observers use telescopes to search the skies. When an object is discovered, telescopes carefully check its path on multiple nights to determine its orbit. An object that is small and orbits close to the Sun might appear just as bright as an object that is much larger and orbits very far from the Sun. How fast an object moves and the path it takes across the sky helps to determine where an object is in the solar system and what the shape of its path around the Sun looks like.
Scientists also use telescopes to watch for changes in the brightness of comets and asteroids. Comets generally brighten as they get closer to the inner solar system and the Sun begins to evaporate ices on and near their surfaces. This material streams out into space and catches sunlight, causing a comet to brighten substantially. Telescopes can observe comets as they first begin to brighten, sometimes as far out as the orbit of Saturn. Outbursts of dust and gas can also cause comets to temporarily flare in brightness.
Most asteroids appear as mere points of light moving against the background stars, but we can use telescopes to watch them change in the brightness as they rotate. Researchers use this information to learn about the shapes of the space rocks and even their structure and composition. For example, from measuring how fast asteroids rotate, scientists realized that many are probably loose rubble piles. If a pile of rubble in space rotates too quickly it will fly apart, but many asteroids spin slowly enough to keep this from happening.
Also, although it may seem incredible, the light that comes from objects in space contains information about what those things are made of, like a chemical fingerprint. Telescopes can be fitted with special instruments called spectrographs that break apart light like a prism to analyze the composition of comets and asteroids. Comparing this chemical fingerprint, called a spectrum, with the composition of meteorites analyzed in the laboratory is how scientists determined that meteorites are pieces of asteroids.
Still another way we use telescopes to explore small worlds is in the search for space rocks that could hit our planet, causing large-scale damage. Telescopes survey the skies, trying to find any objects big enough to cause global catastrophe or even significant regional damage.