Today’s post comes to you direct from the world of space where, thanks to the Kepler space observatory, we have discovered 156 officially confirmed extrasolar planets, with another 3,400 awaiting confirmation. Considering the infinitesimally small region of space within our own galaxy we’ve looked to date, the number of planets climbs to a very high number indeed. Lower estimates are one planet for each star … or between 100-400 billion. As we refine our ability to detect smaller planets, this number will likely go up within the next 10 years or so.
The other day I learned about KOI-1686.01. It’s a planet about 1,000 light years away, roughly 33% larger than Earth, and the closest thing we have to a twin in our neck of the woods with an ESI (Earth Similarity Index) of 0.89. In fact, by the metrics we use to determine habitability, it’s actually a little better in some ways than our own home. The parameters are taken from Wikipedia, and I’ve added Earth and KOI-1686.01 for comparison :
- Standard Primary Habitability (SPH) — Suitability for vegetation on a scale from 0 to 1, with 1 being best-suited for growth. SPH depends on surface temperature (and relative humidity if known).
- Earth: 0.72
- KOI-1686.01: 1.00 (winner … my guess is that it probably doesn’t suffer from ice ages, polar caps, or very large oceans.)
- Habitable Zone Distance (HZD) — Distance from the center of the star’s habitable zone, scaled so that –1 represents the inner edge of the zone, and +1 represents the outer edge. HZD depends on the star’s luminosity and temperature and the size of the planet’s orbit.
- Earth: -0.50 (winner, though both are a little far from the center of the “Goldilocks Zone”)
- KOI-1686.01: -0.60
- Habitable Zone Composition (HZC) — Measure of bulk composition, where values close to zero are likely iron–rock–water mixtures. Values below –1 represent bodies likely composed mainly of iron, and values greater than +1 represent bodies likely composed mainly of gas. HZC depends on the planet’s mass and radius.
- Earth: -0.31
- KOI-1686.01: -0.13 (winner)
- Habitable Zone Atmosphere (HZA) — Potential for the planet to hold a habitable atmosphere, where values below –1 represent bodies likely with little or no atmosphere, and values above +1 represent bodies likely with thick hydrogen atmospheres (e.g. gas giants). Values between –1 and +1 are more likely to have atmospheres suitable for life, though zero is not necessarily ideal. HZA depends on the planet’s mass, radius, orbit size, and the star’s luminosity.
- Earth: -0.52
- KOI-1686.01: -0.14 (winner, sort of … this is probably because of the larger size and higher gravity)
Comparing the two worlds gives us a little bit of a mixed bag. Obviously the ESI index is going to make Earth the winner, since it’s the basis of the comparison. However, when you look at things like the planets’ ability to hold an atmosphere, the range of suitability for vegetation and other life, KOI-1686.01 gives homeworld a run for its money. We obviously need to take into consideration our relatively limited understanding of these worlds at this stage in the process, but discoveries like this give us hope that when we finally go to the stars, we’ll have other places we might someday be able to call home.