Moving On from Planet Earth

Where do you want to live? Only two weeks into another New York winter, let's just say I'm ready for Florida. Or at least Florida weather, even if the humidity seems to drive people insane. But why confine your habitation choice to a country, hemisphere or even planet?

After all, a Mars colony seems to be a forgone, inevitable conclusion. Mars One plans to send four people every two years to the red planet beginning in 2024. Even if the planned advertising revenues and reality TV show make the program seem like a publicity stunt and an MIT engineering report concludes that participants will die less than 70 days into their Mars odyssey. As long as you have one billionaire ready to throw gobs of money at a technology deficiency, it will be overcome. Mars exploration has been so overplayed, NASA is now looking at opportunities to send humans to Venus (in the blimp-like crafts at right) instead.

These missions are mighty ambitious for a race that has, to greatly oversimplify, essentially driven some high-tech RC cars around from 225 million km away. And there are many other planets that would better serve as humanity's first space outpost.

Planet habitability is evaluated by several criteria. The Earth similarity index (ESI) rates a planet's size, density, gravity and temperature, with Earth having a default value of 1. Other parameters consider suitability for vegetation; how far from a star the planet is; what the planet is composed of, as well as its atmosphere; common climates; and how adaptable resources are for human use.

In consideration of these variables, there are an estimated 8.8 billion habitable, Earth-like planets orbiting Sun-like stars in our galaxy alone. So, let's hypothetically fulfill any doomsday prophecy you wish, and see what new planets might serve as the first extrasolar incarnation of human life.

KOI-4878.01

This unconfirmed planet has an ESI rating of .98, making it the most Earth-esque replica yet discovered. Despite being unconfirmed, the Kepler telescope has recorded three transits to date, and another one is expected in July 2015. It has an orbit time equivalent to 449 Earth days. Its mass, radius and mean temperatures are also incredibly similar to Earth's, and 4878.01 is almost a sure bet to be an ocean planet. All of these factors mean an incredibly high likelihood of life on the planet. Its star, KOI-4878, is 1075.2 light years away, meaning that we'll never get there in our lifetimes. But a future race with the right technology could make it Earth 2. The only questions are: does anything live there? And if it does, are we willing to become the planetary invaders if it means saving our species and threatening others?

Gliese 667 Cc (artist rendering on left)

Several other planets are more suitable for human life than this one, which has an ESI of .85, but this is the highest-rated confirmed planet to date. It's also much, much closer to home than 4878.01, at [only] 22.7 light years away. Gliese 667 Cc has an orbit that is 28.155 days long (enjoy figuring out that leap year). Gliese 667 Cc exists in a triple-star solar system and receives 90% of the light that Earth does. However, the majority of the light is infrared; in fact Gliese 667 Cc would be 80% dimmer than the Earth. Despite this, it would also be quite hot, so hot that it borders on uninhabitable. If you picked climate change as your preferred Earth doomsday scenario, Gliese 667 Cc is an unlikely pick as home number two. Several other planets might also exist in the Gliese system that can sustain humanity, but are also unconfirmed.

Tau Ceti e and Tau Ceti f

Tau Ceti e is included as it is the closest potential extrasolar real estate. At 11.9 light years away, it will likely be one of the first planets investigated for life once we initiate the search. It has an ESI of .77 and a year of 168 days. Also notable about Tau Ceti e is its size: as it has 4.3 times more mass than the Earth, and is almost twice as big overall. This makes it a 'super-Earth.' Tau Ceti e is very hot though, as it orbits its star Tau Ceti at a distance closer than Venus orbits our Sun. Surface temperatures average around 70°C, so it's unlikely to be a permanent home. Its neighbor, Tau Ceti f, is worth mentioning only because it's much colder (about -40° C) than Tau Ceti e, but a gaseous atmosphere may warm the planet enough to sustain complex life.

For reference, Venus and Mars grade a .78 and .64 on the ESI scale, respectively. ESI isn't a perfect grade for habitability--many variables, perhaps ones not even quantified, effect the suitability of a planet for colonization.

Perhaps this is putting the cart in front of the ox. Until lightsails or warp drives are invented, we're stuck on this ball of mud. But one very distant day retirees may live out their golden years in the oven of Venus, instead of the stickiness of Sarasota.