Comets are solid bodies that are believed to originate in the outer solar system.  They move around the sun and are eventually caught in an elliptical orbit. Comets aren’t only influenced by the sun; they can also be influenced by other planets.  They are slow-moving bodies and often move only about a degrees a night which is too slow for the human eye to notice.   They consist of several things including ice, carbon-containing materials and dust. 

Comets consist of five parts.

• The first part is the nucleus.  This is the solid center of the comet.  It is sometimes rocky and usually ranges from one to ten kilometers in diameter but it can be as big as one hundred kilometers.  The nucleus is a fragile rock that contains ices of compounds like water, carbon dioxide and ammonia.
• The next part of the comet is the coma.  This is the part of the comet that surrounds the nucleus and evaporated gas and dust.  It grows as the comet grows hotter and hotter and can reach sizes as big as Saturn or Jupiter.  It can reach sizes as big as a million kilometers in diameter, making it bigger than the sun. 
• The next part is the hydrogen envelope which is a layer of hydrogen that surrounds the coma.  As the comet gets closer to the sun, the hydrogen envelope begins to grow.
• Another part is the dust tail*.  This part is made of dust particles that were blown off from the nucleus from the pressure of the sun.   These dust particles are usually vaporizing ices from the nucleus.  Once these dust tails leave the nucleus, they follow their own orbit which make them look curved.
• The last part is called the ion tail*.  It’s made of ionized gas particles that were pushed away from the nucleus.  This tail of the comet can disappear and also be reattached. 

*These tails are usually pointed away from the sun, but their directions is decided by the flow of solar wind and the orbital motion of the nucleus.

Past Voyages to Comets:

In the past, there have been quite a few voyages to try and get a closer glimpse at comets.  It's difficult to do because comets can be very dangerous and destructive.  

• One of the voyages was by the Internation Cometary Explorer, also known as ICE.   On this voyage, ICE went through the plasma tail of a comet, about 27,000 kilometers away from the nucleus of the comet.  On September 11, 1985, the same spacecraft got within 7,800 kilometers of the nucleus.  No pictures were captured on this voyage, but the spacecraft was able to measure fields and particles around the comet.
• The next voyage was a very important one to the world of astronomy.  Two russian spacecrafts (Vega 1 and 2) also known as "Halley's Armada" went up into space.  They were accompanied by ICE, two Japanese spacecrafts and the European Space Agency's Giotto.  ICE remained the furthest from the comet with Giotto being the closest to Halley's Comet (within 600 kilometers).  Giotto was able to get the first pictures of a comet's nucleus.  As it began to get closer, Giotto was hit by dust impacts and the camera was destroyed.  Before it was destroyed, it captured over 2000 images.  Below is one of the images of Halley's Comet that was captured on this voyage by Giotto.

• Giotto was later sent up in 1990 to get information on Comet Grigg-Skjellerup.  By 1992, it got information that confirmed that it wasn't as dusty as Halley's Comet.  No pictures were taken due to the camera being destroyed in the previous voyage.
• On September 22, 2001, Deep Space 1, another spacecraft, was sent into space to Comet Borrelly.  The spacecraft got 1,350 miles close to the nucleus.  It captured pictures of the nucleus. Below is one of the photos captured on this journey.

• In 1999, a spacecraft was sent to collect dust from comets and returned in a capsule in 2006.
• At the current moment, a European spacecraft, Rosetta, is on a ten year journey to Comet 67P/Churyumov-Gerasimenko.  It started in 2004 and is expected to end by November 2014.  Rosetta is different from previous voyages because it has an orbiter that makes it able to do long term mapping of the comet.

Experiments: 

One of the things that scientists are still trying to find out about comets is what is inside the nucleus.  Such an experiment will help scientists find the answer to more that one question.  It has been proposed that a probe be sent up to crash into a comet's nucleus, making an impact big enough to gather information on what's inside.  To carry out this plan, we propose to make a probe that is made of the strongest metal in the world, titanium.  This probe will be launched at a comet at a very high speed.  The speed will be enough to make an impact on the comet's nucleus but not enough to destroy the probe or the comet.  In case the probe is destroyed, we will have a back-up probe that will follow the first one out.  Once the impact is made, the probe will take photos of the inside of the nucleus and gather samples to return back to Earth with.

In order to follow through with this experiment, we will need: 

• 2 titanium probes equipped with a camera and multiple capsules to collect samples

Another thing that we want to figure out is if any type of life has ever existed on a comet.  To carry out this experiment, we plan to use information found in the last experiment, such as what is inside the nucleus.  We plan to send a probe up to a comet to collect samples to bring back to Earth.  With these samples, we plan to create an environment that will be similar to what a comet would be like.  In this environment, we are going to plant some type of vegetation.  We will try to genetically modify this plant to live in the given environment.

In order to follow through with this experiment, we will need:

• A rover to collect samples from the comet
• Samples from a comet
• An enclosed space to create an environment similar to that of a comet's
• A plant to modify

If the previous experiment was a success, we plan to take the plant that was altered and place it on a comet. To do this, we will send a probe up to a comet, carrying the plant.  When the plant is released into the environment of the comet, a rover will track whether the plant is able to survive on the comet or not by sending pictures and data.

• a spacecraft equipped with a camera and the right equiptment to send data to Earth
• genetically modified plant

Works Cited:

1. http://www.astronomy.com/asy/default.aspx?c=a&id=2295
2. http://www.space.com/scienceastronomy/071224-mm-comet-mysteries.html
3. http://www.space.com/php/multimedia/comets/
4. http://science.howstuffworks.com/comet.htm
5. http://videos.howstuffworks.com/hsw/20407-the-outer-solar-system-comets-video.htm
6. http://www.nasa.gov/directorates/esmd/home/whyweexplore/Why_We_17.html

Pictures from:

1. http://www.nasa.gov/directorates/esmd/home/whyweexplore/Why_We_17.html
2. http://cometography.com/pcomets/019p.html