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do aliens exist?

People have wondered since the beginning of time if we are alone in the universe or if there is life outside of Earth. 

Astrobiology is the study of life on Earth and in space. It tries to answer how life began on Earth, if life can exist on another planet, and how humans can live on  another planet. Astronomers estimate from Kepler data that there could be 40 billion Earth-like planets orbiting a Sun-like star in the habitable zone. 

Astrobiologists have determined that the habitable zone around a star is the range in which a planet where liquid water can exist at the surface under normal atmospheric conditions. 

Regarding the future of human civilization, astrobiology is a vital science. Our neighboring planet, Mars, is carefully studied for signs of past life and to decide if humans could colonize another planet in the solar system. 

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the weird ones

TrES 2b is the darkest planet known. The planet is darker than coal and reflects less than 1% of light. The only color seen is from the heat of the planet making it glow red. 

Kepler-16b is an extrasolar planet. It the first confirmed case of a planet orbiting binary stars. 

Wasp-12b is being consumed by its star.  It orbits very close to its parent star with a temperature of 2,800 degrees Fahrenheit. 

J1407-B has rings 200 times as large as Saturn’s. If this planet replaced Saturn in our system, the rings would be visible from Earth.  

TrES 4 is one of the largest known planets with a diameter of  79,917 miles. It is so large that it theoretically should not exist with current understanding of planets.

Cancri e is tidally locked with its star which means it does not rotate itself. It is believed that the surface of the planet is made of water in a super critical state where it is liquid and gas at the same time. 

CoRoT-7b is also tidally locked to the parent star, rain rocks, and is believed to be the core of a gas giant. The surface is also very hellish with temperatures estimated around 4,000 degrees Fahrenheit. 

Kepler-10b is the smallest known exoplanet that is believed to have an ocean of lava on the surface.

Planet Gliese 436 b also known as the planet of burning ice. The planet is constantly on fire because of the close proximity to its star but the ice doesn’t melt because the planet’s gravity prevents the water from evaporating. 

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It takes a long time for solar systems like ours to come into existence.

It begins with a very large molecular cloud.

Molecular clouds are dense, cold clouds of gas and dust perfect for building a star.  Then a part of this cloud gravitationally collapses, with a majority of the mass becoming a protostar in the center and the rest of the material being flattened out in a protoplanetary disk. As the disk orbits the beginner star, some materials start to stick together and accumulate more mass.

Eventually this becomes a baby planet, or a planetesimal. The planetesimals grow larger over thousands of years by gravitationally attracting more gas and rock to themselves and carve a path of orbit around the young star, often colliding with other rocky debris.

In this disk there is an invisible boundary called the snow line. It marks the temperature separation between the types of planets. Planets inside the snow line can withstand the heat from emitting from the star and are composed of rocks and metals.  These planets are known as terrestrial; they are in solid form and are marked with evidence of collision with debris like asteroids. Planets outside the snow line are ones made of rock, ice, and different gases. The planets in the outer region of the system are called Jovian. They have a core of rock and ice with gases collecting and building around it. The temperatures found inside the snow line prevent any gas giants from forming too close to the star. In our solar system this boundary would be found somewhere in between Mars and Jupiter.

This hypothesis is a model of accretion. It suggests that the planets were created by slowly adding more mass to themselves by traveling through a protoplanetary disk.

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