What about comets?

Comets are similar to asteroids except that their “belt” is much father out, away from the sun, in between Neptune and Pluto. Being so far out, comets have a nucleus, or center, primarily composed of ice, along with various gases and minerals and dust. They too orbit the sun, but with a much larger orbit. Short-period comets complete one orbit in 300 years or fewer. Long-period comets could take as many as 30 million years before they come back around a second time! And some, called sun-grazers, actually crash right into the sun and evaporate.

As the nucleus of the comet gets closer to the sun during its orbit, it warms up, and the gases create an atmosphere, just like nitrogen and oxygen do on Earth. A comet’s atmosphere is called a coma. And as the comet flies through space, the heat and pressure of the sun along with solar winds blow the gases and dust in a trail behind the nucleus—the same way your hair blows back as you ride your bike or go on a swing really fast or face the right way on a windy day. The sunlight beaming through that windblown coma gives comets their well known glowing tails.

Astronomers have been fascinated by comets for hundreds of years. The ancient Chinese documented them carefully, noting when they came, and when they came back again, and since the 1980s, NASA has been sending space craft out to photograph and collect samples of the dust from different comets. In 2005 they even deliberately crashed a space probe into a comet called Tempel 1, to get really close-up pictures and to dislodge some of the interior so we could learn more about the nucleus (don’t worry, Tempel 1 is still out there orbiting around).

As of today, astronomers know about 3,662 different comets, all of them named for the people or space craft that discovered them. Some famous ones include Halley’s Comet, Shoemaker-Levy 9, and Neowise, which just passed close to Earth last month. (2)

☄️Halley’s Comet is one of the most famous because it has a rather short orbit compared to others, and it passes by the earth every 75 years, so if someone was really lucky, they might even get to see it twice! (8)

☄️Shoemaker-Levy is especially fascinating because it actually orbited Jupiter rather than the sun, most likely because it got caught in Jupiter’s gravity as it was trying to orbit the sun. But in 1994, not long after it had been discovered, it broke up and crashed into Jupiter, leaving visible marks for years. (7)

So that just leaves Meteors.

Meteors actually come from meteoroids. They aren’t meteors until they hit the Earth’s atmosphere and burn up—what we think of as “shooting stars.” Meteoroids could be as small as a grain of dust, or a mini marshmallow from your cocoa, or even much larger. If they burn up in the atmosphere they become meteors, and if they make it through the atmosphere to land on Earth, then they’re called meteorites.

Meteoroids can be composed of rock, metal, or a combination of both. You can think of them as “space rocks.” But the really interesting thing is that they could come from asteroids—bits broken off when two asteroids collide with each other, for example—or they could come from comets—bits of dust and larger particles left behind in the cooling trail of that glowing tail as the comet passes through on its orbit. Space rocks aren’t just on the moon—there’s a lot of them floating around out there, just waiting for the earth to pass by and grab them up in its atmosphere for a meteor shower.

Scientists estimate nearly fifty tons of meteoroids hit the earth every single day, mostly burning up in the atmosphere. That means you really could see a shooting star any time. But several times a year the Earth’s orbit passes through a cloud of meteoroids leftover from a comet’s passing, and then we get a meteor shower, increasing your odds of spotting a shooting star by a lot. These are seasonal, happening 8 times every year:

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☄️January (Quadrantids)    

☄️April (Lyrids)                     

☄️May (Eta Aquarids)          

☄️July (Delta Aquarids)        
☄️August (Perseids)

☄️October (Orionids)

☄️November (Leonids) 

☄️December (Gemenids)

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Aquarids and Orionids come from that famous Halley’s comet, and the Perseids, which end tomorrow (August 24), are tiny pieces of the comet Swift-Tuttle which passes the sun every 135 years. (3) They’re considered the best meteor shower of the whole year, with up to 100 meteors per hour, often especially bright and colorful ones, known as fireballs because they burn longer than most meteor streaks, giving you a better opportunity to spot them. But you have to stay up pretty late or wake up before dawn for the best chance to spot them. (9)

The only time I can remember seeing a shooting star myself was during a camping trip in New Mexico two years ago. It would have been the very beginning of the Orionid shower. I had a telescope, but the sky was so dark that I didn’t really need it to see stars. Every time I looked through the eye piece, though, if I looked long enough, I saw another shooting star. It was magical.

Have you ever seen a shooting star?

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★ Want to learn more? Check out these awesome resources that helped me write this little #Science article:

1. https://spaceplace.nasa.gov/asteroid/en/

2. https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/

3. https://solarsystem.nasa.gov/asteroids-comets-and-meteors/meteors-and-meteorites/

4. https://www.universetoday.com/37425/what-are-asteroids-made-of/

5.  https://spaceplace.nasa.gov/comet-nucleus/en/

6. https://nineplanets.org/questions/what-are-comets-made-of/

7. https://www.space.com/19855-shoemaker-levy-9.html

8. https://www.space.com/19878-halleys-comet.html

9. https://solarsystem.nasa.gov/asteroids-comets-and-meteors/meteors-and-meteorites/perseids/in-depth/

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Jean M. Malone - August 2020