Exoplanets

Facts and Information
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planet venus Gliese 581 d was the first exoplanet discovered known to orbit in the habitable zone.
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Maat Mons Exoplanet Corot-7b orbits so close to its parent star that its surface has turned into molten lava.
Exoplanet Facts
  • Exoplanets also known as extrasolar planets, are planets which exist outside our solar system.
  • As of 17th September 2011, 684 exoplanets have been discovered.
  • In 1992 two planets orbiting the pulsar PSR 1257+12 became the first exoplanets to be detected.
  • In 1995 51 Pegasi B was the first exoplanet to be discovered orbiting a sun like star.
  • CD-35 2722 b is the most massive exoplanet to be found, it has 31 times the mass of Jupiter.
  • Gliese 581 e is the least massive exoplanet detected orbiting a normal star, it has only around twice the mass of Earth.
  • The habitable zone, also known as the 'Goldilocks Zone' is an area around a star which is at just the right temperature to allow liquid water to exist on an Earth like planet.
  • Several possible Earth size planets have been detected orbiting in the habitable zone of stars although as yet none have been confirmed.
  • Small Earth like planets could exist around our nearest stellar neighbor Proxima Centauri.
Exoplanets - The Search for Life
Kepler 11 has 6 orbiting planets, the largest exo-planetary system yet discovered.

Are we alone in the Universe? This is a question mankind has pondered for centuries, but only now do we have the technology to begin to answer that age old question. The search is truly on to find another Earth like world but as yet we're still the only known planet in the Universe where life exists.

New evidence being compiled suggests that its highly unlikely that Earth is unique, it is estimated there are habitable planets around 10 to 20% of the stars in our galaxy. When you consider that there are 200 billion stars in the Milky Way then it could possibly contain billions of worlds similar to our own. The problem with Earth like planets is that they're very small, making them extremely difficult to detect, even so scientists are predicting that its only a matter of time before one is discovered somewhere in our galaxy.
Types of Exoplanets


Gas Giants
surface of venus
Gas giants are planets similar to Jupiter and Saturn. Their mass is mostly composed of hydrogen and helium with possibly a dense rocky or metallic core. Exoplanets with a mass of more than 10 times the Earth are classified as gas giants. Due to their size the majority of planets detected outside our solar system are gas giants.

Hot Jupiters
surface of venus
Hot Jupiters are gas giant planets similar in mass to Jupiter but which orbit very close to their parent star. As a result of the close proximity to their star their surface temperatures exceed 700C (1300F). Apart from gas giants Hot Jupiters are the most common type of exoplanet detected.

Super Earths
surface of venus
Super Earths are ‘potentially’ rocky planets with up to 10 times the mass of Earth. The term ‘Super Earth’ simply refers to the mass of the planet and not to any planetary conditions, so some of these may actually be gas dwarfs. The first two exoplanets to be detected were Super Earths orbiting around the pulsar PSR B1257+12.

Free Floating Planets
surface of venus
Free floating planets or orphan planets do not orbit around any star. It is believed that these isolated worlds were somehow ejected from developing systems and now free-float around the galaxy. Although very few have been detected they are believed to very common in our galaxy.




Pulsar Planets
surface of venus
Pulsar planets orbit around Pulsars or Neutron Stars. These super dense, rapidly spinning stars are the core remains of a large star after a supernova explosion. It is highly unlikely that any orbiting planet could survive the blast from a supernova so Pulsar Planets probably formed after the event and now orbit around the dead star.

Ocean Worlds
surface of venus
Ocean Worlds are planets whose surfaces are entirely covered in water. Evidence suggests that these planets originally formed as objects made of ice and rock far from their parent star. As they drifted towards the star they heated up melting the ice and so became covered in oceans. Under the surface the water is so dense its consistency is more like ice.

Chthonian Planets
surface of venus
Chthonian Planets were once gas giants but have migrated far too close to their parent star. As a result their atmospheres have been roasted away, leaving only a rocky or metallic core. It is possible their surface may be covered in molten lava. Due to their similarity to terrestrial planets some Super Earths may actually be Chthonian Planets.

Exo Earths
surface of venus
Exo Earths are the Holy Grail of planet hunting. These are Earth like planets that orbit in the habitable zone of its star. This is an area where the temperature would allow water to flow on the planet’s surface and possibly allow life to flourish. To date there have been no confirmed discoveries of any Exo Earths.




Searching for Exoplanets
Doppler Spectroscopy

Doppler Spectroscopy also known as Radial Velocity is the most successful method of finding exoplanets. This technique measures how much a star wobbles due to the gravitational effects of orbiting planets. It is not strictly true to say that planets orbit around stars, they actually both orbit around their common center of mass. As stars are much more massive than planets the common center of mass is very close to the star and very far from the planet, as a result the star has a very slight, circular or elliptical orbit. You can see this demonstrated in the video to the left.

This wobble can be detected by measuring the light from the star as it moves back and forth from Earth. As the star moves towards Earth its light moves very slightly towards the blue part of the spectrum, known as blue-shifting, and as the star moves away its light moves very slightly towards the red part of the spectrum, known as red-shifting. This is called the Doppler Effect. You can see this demonstrated in the video above, if you imagine Earth is below the video then as the star moves away it turns red and as it gets nearer it turns blue. Of course this is an exaggerated version of what actually happens, the shifts in the spectrum are so small only highly sensitive instruments can pick them up. By observing these shifts over a period of time a regular pattern may emerge signalling that a planet or other object is orbiting the star.
Stellar Nurseries

These dark molecular clouds of gas can become stellar nurseries, providing an environment which allows stars to be born. When pockets of the dark nebula have sufficient density, hydrogen molecules will begin to condense, this is possibly triggered by the shockwaves of a nearby supernova explosion. Clumps of hydrogen will grow large enough to begin collapsing under their own weight, heating up and creating the early stage of a star called a Protostar. Over thousands of years the young star continues to grow and heat up until its core is hot enough to allow nuclear fusion, this is when hydrogen atoms are fused together producing enormous amounts of energy. The star is now in its main sequence and will remain in this state for most of its life.

Around 5 billion years ago this process began at the edge of the Milky Way, eventually producing a yellow dwarf star. Out of the large disk of gas and dust that formed around the new star a small rocky planet was created which was in just the right location to allow water to flow on its surface. This was Planet Earth, these conditions allowed life to flourish ultimately leading to the evolution of mankind.



Selected Exoplanet Stats
Name: TrES-2 b
Mass: 1.28 Jupiters
Distance from star: 3.7 million miles (5.95 million km)
Orbit: 2.5 days
Distance from Earth: 500 light years

Due to the very close orbit of its parent star TrES-2 b is a very hot world, but as a result of reflecting less than 1 percent of the sunlight it receives it is darker than coal. Making it the darkest planet ever discovered.
Name:1RSX-J1609 b
Mass: 8 Jupiters
Distance from star: 30 billion miles (48 billion km)
Orbit: Unknown
Distance from Earth: 471 light years

The small dot on the image below is the first ever direct image of a planet outside of our solar system. Due to the vast distance from its parent star it could take the planet over 1,000 years to make a complete orbit. surface of venus
Name:Kepler-16b
Mass: 1 Jupiters
Distance from star: 65 million miles (105 million km)
Orbit: 226 days
Distance from Earth: 200 light years

Kepler-16b is the first planet to be discovered that orbits around 2 suns. Both the stars are smaller and significantly cooler than our Sun making Kepler-16b a very cold gas giant.
Name: PSR B1620-26 b
Mass: 2.5 Jupiters
Distance from star: 2 billion miles (3.2 billion km)
Orbit: 100 years
Distance from Earth: 12,350 light years

PSR B1620-26 b also known as Methuselah is the oldest planet to be discovered. It is thought to have formed only a billion years after the big bang making it around 12.7 billion years old.
Name: Gliese 876 b
Mass: 1.89 Jupiters
Distance from star: 20 million miles (32 million km)
Orbit: 61 days
Distance from Earth: 15 light years

Gliese 876 b was the first planet discovered orbiting a red dwarf star. More importantly this gas giant orbits in the habitable zone meaning any of its large moons could possibly support life.
Name: HD 85512 b
Mass: 3.6 Earths
Distance from star: 25 million miles (40 million km)
Orbit: 54 days
Distance from Earth: 36 light years

HD 85512 b is the smallest exoplanet discovered that orbits in the habitable zone. The temperature of its atmosphere is thought to be around 25C (77F) and the planet could possibly provide a habitable environment.

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