Earth's Twin

The list of confirmed exoplanets keeps growing.  Growing along with that is the list of exoplanets similar to the earth.  We haven't found our twin ... yet, but we have found a few distant cousins.

• Find the confirmed exoplanet that is, so far, the most similar to our own home world. The list keeps changing so make sure your data is recent (within one year should be OK).
  
  
  Newest candidate:

  UPDATE 11/17/2019:  How about KOI 736.01 with a whooping ESI of .98 !!!! Now that is very close to Earth's twin.  The source is this page.  It also lists KOI 494.01 (ESI = .93), KOI 784.01 (ESI = .93), KOI 784.01 (ESI = .91), KOI 610.01 (ESI = .90), and KOI 947.01 (ESI = .90).
  
  It is very hard to update this page!  The list keeps changing.  Just look at this page for the most current leader.  Because you might have found a slightly older source, I'll accept any with an ESI of .90 or above.  Below is what the list looked like a short time ago.

  
   

  Name	Type	Mass (ME)	Radius (RE)	Flux (SE)	Teq (K)	Period (days)	Distance (ly)	ESI
  001. Teegarden's Star b	M-Warm Terran	≥1.05	—	1.21	267	4.9	12	0.93
  002. K2-72 e	M-Warm Terran	—	1.29	1.11	261	24.2	217	0.90
  003. GJ 3323 b	M-Warm Terran	≥2.02	—	1.23	265	5.4	17	0.90
  004. TRAPPIST-1 d	M-Warm Subterran	0.41	0.77	1.21	267	4.0	41	0.89
  005. GJ 1061 c	M-Warm Terran	≥1.75	—	1.35	275	6.7	12	0.88

  Note:  The exoplanet which is physically closest to us is Proxima Cen b and is only 4 1/3 LY from us.  It just missed the top of the list with an ESI of .85
  
  Since my last update, the former top dogs were:
  
  Kepler 438b (with an initial ESI of .88) is a confirmed planet once thought very similar to the earth.  It goes around Kepler 438 a star 470 light years from us.  The parent star is a red dwarf star ... meaning it is smaller and cooler than our sun (about half the size and mass of our sun).  Therefore, the planet must be closer in to be in the habitable zone.    Kepler 438b is slightly larger than our home planet.  It is much closer to its sun than we are (.17 AU), but again, that parent star is much cooler than our sun.  A year on Kepler 438b lasts only 35 days.  It was discovered by the transit method.  The mass is still yet unknown.  This was just added to Wikipedia "However it has been found that this planet is subjected to powerful radiation activity from its parent star every 100 days, much more violent storms than the stellar flares emitted by the Sun and which would be capable of sterilizing life on Earth." .... which might explain why is now OFF the list altogether.  In other words, this exoplanet is no longer a valid answer!  You need to find current data.
  
  
  Gliese 667 Cc with an ESI of .84 (see below) is a confirmed planet very similar to the earth.  It goes around Gliese 667 C a star 23 light years from us.  This planet is one of 7 planets known to orbit the star.  Gliese 667Cc is slightly larger and more massive than our home planet.  It is much closer to its sun than we are but that parent star is much cooler than our sun.  It was discovered by the radial velocity method (Doppler Shift).
  
  Kepler-62e, with an ESI of .83 (see below) is a confirmed planet very similar to the earth.  It goes around Kepler-62, a star 1,200 light years from us.  This planet is one of 5 planets known to orbit the star.  Kepler-62e is slightly larger and more massive than our home planet.  It was discovered by the transit method.
  
  Kepler 452b WAS demoted from top dog with an ESI of  .9 but lowered to .83 based on new data. (see below).  The planet is bigger and more massive than the earth ... with a surface gravity about twice what we feel.  Taking 385 days to orbit its star, it does so in the "Goldilocks Zone" ... meaning liquid water could exist on this world.  What makes this planet interesting is that it orbits a star almost exactly like our sun but the system is 1.5 billion years older than us.  This would give life a great chance to develop .... and evolve.  Imagine what our system will be like in 1.5 billion years!
  
   

• Find these physical properties of this planet :  (see above)
   

  • How does the mass of the parent star compare to our sun?       

  • How does the mass of the exoplanet compare to our earth?        

  • How does the radius of the exoplanet compare to the radius of the earth?    

  • Is it in the habitable zone?   
     

• Astronomers even have a quantity they use to describe how similar an exoplanet to our planet  What is the name of this quantity?  Hint: it assigns a number from 0 to 1 with the earth = 1   What is the number assigned to the planet you listed above?
  
  The Earth Similarity Index (ESI) is a quantity used to measure how similar an exoplanet is to the earth.  Any ESI with a value .8 to 1.0 can be considered "earth like".  Note: this number does NOT say anything about habitability. 
   

• What are the variables that are taken into account to produce this quantity?   (You do NOT have to give the equation ...only list the variables used in it)
  
  

  Actually there are two formulas used to determine ESI.  One uses the radius (size) and "stellar flux" which is the light output of the parent star measured at the surface of the exoplanet.  Actually the formulas compares these values against the values found on earth but those are not variables but considered constants since they don't change.  This formula is used when very little is known about the exoplanet.

  A better formula is used when more information is known about the exoplanet.

  The variables used to determine the ESI are a planet's:
   

  •  radius (size)

  • density (rocky or gas)

  • escape velocity (gravity)

  • surface temperature (can liquid water exist?)