NASA announces discovery of Earth-like planet with earth similarity index 0.98

The ESI defines a hyperspherical gradient across several different axes of earth similarity. And since each of those axes are defined by a ratio to an Earth value, zeroes would only be found for objects with the following properties:

  - Infinite mean radius.
  - Zero mean radius.
  - Infinite density.
  - Zero density.
  - Infinite escape velocity.
  - Zero escape velocity.
  - Infinite surface temperature.
  - Zero surface temperature.

As such, the only object I can think of that might qualify would be a theoretical zero-entropy singularity that might have existed existed prior to the Big Bang. Zero radius, infinite density, infinite escape velocity, zero surface temperature.

Given the nature of the calculation, it probably would have been better to define perfectly Earth-like as zero, and assign positive indices to bodies, with higher numbers indicating greater dissimilarity to Earth. It would be a distance calculation along multiple axes of similarity, but adjusted by scale factors to coerce the differences between comparison axes with different units to have an order of magnitude proportional to perceived importance to humans.

If you have a difference function for each axis that yields a number from 0-1 for comfortable, 1-10 for tolerable, 10-100 for survivable, and 100+ for lethal, then you can take the square root of the sums of the difference functions for the overall index.

Anything less than 1 would be a near clone of Earth. Anything less than 10 would definitely be habitable. Anything less than 100 might be explorable. Anything greater than that, and you might just seed it with Earth extremophiles and ignore it for a few million years.

I understand, but that's a synthetic benchmark. We actually have no idea why Earth has life and other planets don't and similarity to Earth may not be a big factor (see theories on life in Europa's seas for example or non-carbon based life).

I just feel everyone gets excited over nothing solely because its extra-solar. Our own solar system is fairly diverse. If life was common, we'd probably be seeing more of it here.

They are relevant, you're just misinterpreting. None of these are meant to imply "X must be like Earth for the planet to be habitable," they mean "X is an important factor for habitability and must be considered in our models if we want them to be meaningful, unlike the ESI which captures a mere handful of variables".

For example, "tidal habitable zone" doesn't mean "we need [ocean] tides to survive," it means "tidal heating effects have an enormous impact on planetary conditions". For example, an Earth analogue in orbit around a tiny red dwarf in a seemingly "habitable zone" would be subject to tidal heating effects which would bake the surface, whereas a similar planet in a similar orbit around a sun-like yellow dwarf would not.

Similarly, "rotation rate habitable zone" doesn't mean "the planet must have a ~24 hour day", it means "all else being equal, a planet's rotation rate can greatly affect habitability," mostly due to weather patterns and air/heat circulation. By including rotation rate in our models, some planets previously thought to be inhabitable may turn out not to be, and vice versa.

For reference, a 195lb human being (who is assumed here to be spherical in shape) has an Earth Similarity Index of approximately 0.001:

https://gist.github.com/anonymous/5351f6185e8473a3c002

Yeah I think so. You'd need a telescope bigger than our earth.