Earthlike exoplanets
Exoplanets are Earth-like planets with a size comparable to Earth, rotating around other suns in the so-called habitable zone. This zone is defined as an orbit around a star in which water is possible to exist as a liquid on a planetary surface (273.15-373.15K). Influences from the greenhouse effect and other atmospheric properties can make this zone somewhat “fuzzy”. Because life on Earth depends on the ability of water to flow and to behave like it does under certain temperatures and pressures, we might not find exoplanets that host life as we know it. Life might be possible to exist in numerous ways, some of which may be hard for us inhabitants of Earth to imagine.
Research directed towards finding exoplanets started in the early 1990s and up until today there are about 3.500 known planets in around 2.500 different solar systems.
Kepler 452b, as it is named after the Kepler space observatory that discovered it, is a fairly known exoplanet, making headlines in the past. Kepler 452b is around 60% larger than Earth, with a mass three to seven times larger than Earth's. Neither information about the atmosphere is certain nor is it clear if there exist water on the planet. The star, around which Kepler 452b is orbiting, is roughly 1.400 light-years away from Earth and is 20% brighter than our Sun. New methods of observation are expected to provide scientists with more data in the future.
In the following video from FactStream, we are taken through 5 exoplanets. Note that the pictures are merely conceptual artwork. Please note they are ranged on the ESI scale. The ESI scale means "Earth Similarity Scale". It's a proposed characterization of how similar a planetary object is to that of our Earth. However this has no quantitative meaning for habitability and is merely used to compare planets in large databases. This scale is also often changed as astronomers learn more about them.
Research directed towards finding exoplanets started in the early 1990s and up until today there are about 3.500 known planets in around 2.500 different solar systems.
Kepler 452b, as it is named after the Kepler space observatory that discovered it, is a fairly known exoplanet, making headlines in the past. Kepler 452b is around 60% larger than Earth, with a mass three to seven times larger than Earth's. Neither information about the atmosphere is certain nor is it clear if there exist water on the planet. The star, around which Kepler 452b is orbiting, is roughly 1.400 light-years away from Earth and is 20% brighter than our Sun. New methods of observation are expected to provide scientists with more data in the future.
In the following video from FactStream, we are taken through 5 exoplanets. Note that the pictures are merely conceptual artwork. Please note they are ranged on the ESI scale. The ESI scale means "Earth Similarity Scale". It's a proposed characterization of how similar a planetary object is to that of our Earth. However this has no quantitative meaning for habitability and is merely used to compare planets in large databases. This scale is also often changed as astronomers learn more about them.
Taking a look at some known exoplanets
Kepler-438 BThis exoplanet took a lot of headlines when it was first discovered. This is due to it being a near-Earth-sized exoplanet, likely to be of rocky origin and orbiting the inner edge of the before mentioned habitable zone. It's parent star is a red dwarf and showers this exoplanet with somewhat the equivalent of what we recieve from our sun, to a factor of 1.4, meaning it recieves 40 % more sunlight than we do here on Earth.
These things all led astronomers to believe that this exoplanet could be of great interest. However it was later brought to attention that the parent star showers Kepler-438B with large amount of radiation. If the planet had a sufficiently strong enough magneticfield, this could be mitigated. However it does not seem to be the case. Neither do we know much about its atmosphere. This information brought about the consensus that finding an Earth-like planet, is so much more complicated than what was previously thought. This exoplanet was detected by using Transit Photometry method, click the button below to see what exactly astronomers see, when they gaze towards the Kepler-438 system. |
Artistic interpretation of Kepler-438 B
Featured image credit: NASA Source: https://hemtecks.wordpress.com/2015/12/02/ kepler-438b-have-we-found-earths-long-lost-twin/ Facts:
Star: Kepler-438 Distance: 470 light years Mass: 1.3 Earth's Radius: 1.12 Earth's Temperature: 3 degrees celsius Discovery method: Transit photometry Text and facts source:
https://en.wikipedia.org/wiki/Kepler-438b |
Artistic interpretation of Gliese 581 c
Featured image credit: NASA Source: https://www.nasa.gov/topics/ universe/features/Gliese_581.html Facts:
Star: Gliese 581 Distance: 20.37 light years Mass: 5.5 Earth's Radius: Unknown due no direct observation Temperature: Uncertain ~ 40 degrees celsius Discovery method: Radial velocity method Text and facts source:
https://en.wikipedia.org/wiki/Gliese_581_c |
Gliese 581 cThe exoplanet Gliese 581 c orbits the red dwarf Gliese 581. It's the second planet discovered in this system and the third from its parent star. This exoplanet is quite larger than Earth, thwarting it 5.5 times. Therefore it falls into category of a Super-Earth, which usually describes and exoplanet that is 5 to 10 times the size of Earth.
Gliese 581 c quickly became famous as it was the first reported exoplanet to be within the habitable zone. The temperature seemed just right for liquid water to exist on its surface, which we see as favorable for life. However, once again, further investigation showed something wasn't right with this contender. The exoplanet is tidally locked with its parent star, the same way our Moon is tidally locked with Earth. This means the same side of the exoplanet always face its parent star. Permanent day on 1 side, permanent night on the other. Further studies have questioned whether or not it's actually inside the habitable zone at all. Gliese 581 c was detected by the radial velocity method and not by direct observation as with Kepler-438B and its transit photometry. This means we're not certain about its radius or its exact mass. However it can be assumed based on several models. |
Detecting exoplanets
Exoplanets can broaden and develop our understanding of the formation and evolution of planets and the history of other solar systems. Detecting exoplanets is therefore one of the most active studies in modern astronomy. It is far more difficult to detect exoplanets than it is to detect the planets in our own solar system. The light from a star is often more than a billion times brighter than the reflected light from a planet orbiting it, so distinguishing the exoplanet from the star is practically impossible. Very few of the detected exoplanets have therefore been observed directly by astronomers, and instead they have been detected with the use of numerous different indirect methods.
One of the most widespread indirect methods is the radial velocity method. This method uses the fact that a star is not completely stationary when a planet is orbiting it. The star moves in a small circle or ellipse around the pair’s center of mass and these movements affect the light spectrum from the star. This change in emitted light can be observed from Earth with spectrographs, with the spectrum being shifted slightly towards the blue when the star is moving towards the Earth and the spectrum shifted towards the red when the star is moving away. If the shifts repeat themselves periodically, it means that the star is moving in a cycle and this is almost certainly caused by the appearance of a nearby planet orbiting the star.
Another indirect method of detecting exoplanets worth mentioning is the transit photometry. A transit is defined as the passage of an object between its parent star and the observer. During the exoplanet’s transit neither the planet nor the star can be resolved as seen from Earth. They can, however, be distinguished indirectly by the reduction in flux from the star as the planet is blocking its light. The reduction in flux from the star received on Earth can then be used to determine the planet’s relative size to the parent star and the time between transits can reveal its orbital period. However, a big disadvantage to this method is, that, in order to observe a transit, the orbital plane of the exoplanet must be perfectly aligned with the observer’s vantage point, which is highly unlikely.
The following video from MinutePhysics shows a few of the most popular ways of finding an exoplanet, among those are both the radial velocity method and the transit photometry.
One of the most widespread indirect methods is the radial velocity method. This method uses the fact that a star is not completely stationary when a planet is orbiting it. The star moves in a small circle or ellipse around the pair’s center of mass and these movements affect the light spectrum from the star. This change in emitted light can be observed from Earth with spectrographs, with the spectrum being shifted slightly towards the blue when the star is moving towards the Earth and the spectrum shifted towards the red when the star is moving away. If the shifts repeat themselves periodically, it means that the star is moving in a cycle and this is almost certainly caused by the appearance of a nearby planet orbiting the star.
Another indirect method of detecting exoplanets worth mentioning is the transit photometry. A transit is defined as the passage of an object between its parent star and the observer. During the exoplanet’s transit neither the planet nor the star can be resolved as seen from Earth. They can, however, be distinguished indirectly by the reduction in flux from the star as the planet is blocking its light. The reduction in flux from the star received on Earth can then be used to determine the planet’s relative size to the parent star and the time between transits can reveal its orbital period. However, a big disadvantage to this method is, that, in order to observe a transit, the orbital plane of the exoplanet must be perfectly aligned with the observer’s vantage point, which is highly unlikely.
The following video from MinutePhysics shows a few of the most popular ways of finding an exoplanet, among those are both the radial velocity method and the transit photometry.
The 5 ways of detecting an exoplanet
Radial Velocity
Transit Photometry
Direct Imaging
Gravitationel Microlensing
Astrometry
To see a demonstration of these techniques, click the link below to go to NASA interactive tool that takes you through these methods step by step.
Transit Photometry
Direct Imaging
Gravitationel Microlensing
Astrometry
To see a demonstration of these techniques, click the link below to go to NASA interactive tool that takes you through these methods step by step.
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