Earth Similarity Index (ESI)
The Earth Similarity Index (ESI) is a unit of measure used for checking how similar is any planet compared to ours. Scientists compute ESI by checking the planet’s orbit, and whether it is in the “Goldilocks Zone” of its star. For example, the planet Jupiter has an Earth similarity index as only 12% similar to Earth, since the atmosphere has mostly helium, compared to Earth’s nitrogen, and its orbital time is 12 years, compared to Earth’s 365 days. Here are the top three planets, which have the highest ESIs.
- KOI 4878.01 (ESI 98%)
KOI 4878.01 is an exoplanet that is located 1075 light-years away (329 parsecs) away from Earth. It orbits a main sequence star very similar to our sun, just a little bit hotter. Water content, and other features in the planet are not confirmed yet, but it most likely has deposits of water. It has an atmosphere similar to ours, and has an average temperature of approximately 64* Fahrenheit. Its mass is almost the same as Earth’s mass, 0.99 Earth masses, and it completes an orbit every 449 days. Based on this, it is in the habitable zone of the star.
2. TRAPPIST-1e (ESI 95%)
TRAPPIST-1e is an exoplanet approximately 12 parsecs away. It orbits an ultra-cool red dwarf, TRAPPIST-1, and is comfortably nestled in the habitable zone of the star. The Spitzer Space Telescope has taken pictures of the planet, and it is confirmed to be an ocean planet like ours. It has a close mass to Earth, slightly bigger, and has a similar orbit.
3. Gliese 273b aka Luyten b (ESI 92%)
Gliese 273b is a confirmed tidally locked rocky exoplanet, which is a Super-Earth, an exoplanet that is more than 2 times the size of Earth. It orbits a relatively quiet red dwarf, similar to TRAPPIST-1e, called Luyten’s Star. It has an equilibrium temperature only 4 Kelvin over Earth’s and it may have an ocean.
