Download Questions about Comets: Created by Laura Vican, 2014 Q: What are

Questions about Comets:
Created by Laura Vican, 2014
Q: What are comets made of?
A: Mostly water and dirt. They also have trace amounts of sugar (the corn syrup),
nitrogen (the ammonia; NH4), and dry ice (frozen CO2). We believe that comets brought
these materials to Earth early on in the formation of our solar system (~4.5 billion years
ago). The water is important, since 70% of the Earth’s surface is made of water. So is
~80% of the human body. Sugar is also important for life on Earth; the DNA in our
bodies that determines our genetic make-up is mostly made of sugar! The nitrogen is
important as well, since over 75% of the Earth’s atmosphere is made of nitrogen (not
oxygen, as many people would expect). Finally, we use frozen carbon dioxide (CO2) in
our comet. On Earth, CO2 exists as a gas (if you leave a block of dry ice outside, it will
completely turn to vapor). But comets are formed far from the sun, where it is cold
enough that CO2 can exist as an ice.
Q: Where do comets come from?
A: Comets come from two main places in our solar system. Short period comets (comets
that come by the sun every 200 years or less) come from the Kuiper Belt. This is a ring of
rocks, dust, and ice that is near the orbit of Pluto (4.5 billion miles from the Sun). Long
period comets (comets that come by the Sun every 200 years or more) come from the
Oort Cloud. The Oort Cloud is a cloud filled with hundreds of millions of comets. It is a
spherical cloud of rocks and ice that extends out to 93 trillion miles from the Sun.
Q: When were comets formed?
A: Most comets were formed shortly after our planets formed. Originally, the entire Solar
System was a giant cloud of gas and dust. When that cloud collapsed, most of the
material went into the forming Sun. Some of the rocks and gas accreted (stuck together)
to form planets. The leftover material is what makes up comets and asteroids. This
process of planet formation happened 4.6 billion years ago!
Q: How fast do comets go?
A: The average comet speeds through the solar system at 25,000 MPH (a typical airplane
goes ~500-600 MPH). But comets get faster when they get closer to the Sun. The planets
are on circular orbits, but comets are on elliptical orbits. That means that they get very
close to the Sun and speed up, then swing out far away from the Sun and slow down. At
different times, they are the closest and furthest things from the Sun in our Solar System!
Q: How many comets are there?
A: We believe there are hundreds of millions of comets in our Solar System alone, but no
one has seen them all. In fact, only ~5,000 comets have been observed directly. They
spend much of their time very far away from the Sun, where they are difficult to take a
picture of.
Q: Has a comet ever hit the Earth?
A: Yes! Probably! The problem is that comets are made mostly of water, so they are a bit
delicate. When they smack into our atmosphere, it’s like they are “belly-flopping.”
Usually, they are destroyed as soon as they enter our atmosphere. When that happens, we
see a meteor streak across the sky. This is why comets are sometimes called “shooting
stars.” But bits of comets hit the Earth all the time. When a comet goes around the Sun,
bits of it fall off as the ice melts, and they leave a trail of small rocks behind them. When
the Earth passes through that trail, it’s like driving a car through the rain. The rocks
smash against the Earth’s atmosphere, and we see them burn up. We call this event a
“meteor shower.” **we have seen a comet hit the surface of Jupiter. It left big bruises on
the surface of the atmosphere which were visible for weeks after the impact!**
Q: What is the difference between a comet and an asteroid?
A: A comet is mostly water ice and dirt. An asteroid is more rocky and solid. Asteroids
are found closer to the Sun in the Asteroid Belt, which lies between the orbits of Mars
and Jupiter. Asteroids, unlike comets, can survive the entrance into Earth’s atmosphere,
and often crash into Earth’s surface. If a piece of asteroid lands on Earth, we call it a
meteorite.
Q: Have humans ever been to a comet?
A: No, but we have flown a spacecraft behind a comet as it went around the Sun. The
StarDust spacecraft flew in the tail of a comet, collecting samples of the pieces of comet
that fell off as the comet vaporized. Those samples were sent back to Earth where
scientists analyzed them in a lab. That’s part of why we know what a comet is made out
of!
Q: Are comets on fire?
A: No! They just look like they are on fire because they have a large tail spreading out
behind them. In fact, they have two tails – one made of dust and another made of gas.
These tails are only present when the comet is going around the Sun – at that time, the
comet gets hot enough that the dry ice vaporizes and bits of the comet fall apart and make
the long tail. When comets are far from the sun, they just look like “dirty snowballs” with
no tail.