Q7: What's the planet closest to earth's structure and atmosphere that scientists have discovered?

Structurally speaking, the closest planet would be Kepler-62 e.

In 2011, Schulze-Makuch and his team decided to come up with 2 scales which would allow scientists to determine if an exoplanet could sustain life. The first scale is known as the Earth Similarity Index (aka easy scale) which compares the exoplanet with the Earth in terms physical or structural characteristics. The properties that are compared in the ESI are: radius, density, escape velocity,  and surface temperature. The scale goes from 0, which indicates no similarity, to 1, which indicates that the exoplanet is exactly similar to Earth.

Illustrated above is the basic ESI expression wherein x_i represents a planetary property (i.e. surface temperature, radius, etc.) and x_io represents the corresponding planetary property of the Earth.

The second scale proposed in Schulze-Makuch’s paper is called the Planetary Habitability Index or PHI for short. The PHI is basically seeks to determine if the proper ingredients and chemistry are available for life to exist. The PHI is constructed in such a way as to be unbiased in the search for extraterrestrial life. In other words, it takes into account life that might exist under more exotic or extreme conditions. However, the PHI is currently not used due to the extensive amount of knowledge required of the planet. Basically, astronomers lack the planetary data to make use of the scale.

Out of the all the exoplanets that have been discovered so far, Kepler-62 e is the exoplanet that rates the highest on the ESI with a score of 0.82. Below is in image which compares Kepler-62e’s position to the Earth’s position, relative to the star they rotate about.

References:

University of Puerto Rico. (n.d.). Earth Similarity Index (ESI). Retrieved from: http://phl.upr.edu/projects/earth-similarity-index-esi

Schulze-Makuch, D., Méndez, A., Fairén, A. G., von Paris, P., Turse, C., Boyer, G., . . . Irwin, L. N. (2011). A Two-Tiered Approach to Assessing the Habitability of Exoplanets [Abstract]. Astrobiology, 11(10). Retrieved from: http://online.liebertpub.com/doi/abs/10.1089/ast.2010.0592

University of Puerto Rico. (2013). The Habitable Exoplanets Catalog. Retrieved from: http://phl.upr.edu/projects/habitable-exoplanets-catalog

Strenge, R. (2011, November 21). New system would assess odds of life on other worlds. Retrieved from: http://news.wsu.edu/pages/publications.asp?Action=Release&PublicationID=28889

Images from:

University of Puerto Rico. (n.d.). Earth Similarity Index (ESI). Retrieved from: http://phl.upr.edu/projects/earth-similarity-index-esi

University of Puerto Rico. (2013). The Habitable Exoplanets Catalog. Retrieved from: http://phl.upr.edu/projects/habitable-exoplanets-catalog

Prepared by: Manuel Christian Schuldes