In 1992 astronomers identified for the first time planetary bodies outside our Solar System. Twenty-one years later that number has grown to 1,010. Of these 1% circle their stars in what we have defined as the Goldilocks Zone, a position in space where water can exist in a liquid state. That means we have in this short period of time identified 10 potential Earth-like environments.
So for those of you who are feeling that we humans have outgrown this planet, there are alternative destinations. But wait, we are not done yet. A new NASA probe, the Transiting Exoplanet Survey Satellite, or TESS, will be launched in 2017. This new probe will replace the failing Kepler exoplanetary probe which has had its problems since the spring of this year. Unlike Kepler which has concentrated on only a segment of the sky, TESS will do all-sky surveys using an array of telescopes that will seek out exoplanets from rocky ones like ours to gas giants like Jupiter and Saturn.
Kepler, launched four years ago has discovered a potential 3,548 exoplanets from an observation field of 150,000 stars, a mere drop in the bucket for our galaxy with its estimated 100 to 400 billion. So we know that the 1,010 confirmed so far will continue to grow even with the crippling of the spacecraft as NASA scientists sort through the accumulated data. Kepler first starting exhibiting stability problems when one of its spinning reaction wheels stopped working. But NASA was able to adjust the spacecraft to compensate. When a second wheel failed, however, the problem of stabilizing the telescope worsened. With two remaining wheels the spacecraft may be repurposed to hunt for Near-Earth Asteroids. Another proposal would have Kepler seek out planets circling black holes. But its effectiveness as an exoplanet hunter, particularly small rocky ones in Goldilocks Zones, has been diminished.
In any event for those of you immediately looking for a new Earth may I recommend three planets circling Gliese 581. A mere 20 light-years from Earth, Gliese 581g (seen in an artist’s rendering below), one of the planets circling its red M-class star, is believed to be a planet containing lots of water. The planet is 5 times Earth’s mass with a diameter between 1.2 and 1.4 larger. It has a very short year circling its star every 37 days.
How long would it take to get there? Gliese 581 is 200 trillion kilometers (120 trillion miles) from our Solar System. If we can develop technology to travel at one-tenth the speed of light, to reach Gliese 581 would take 220 years. But our current technology based on chemical propulsion systems would increase that travel time astronomically. The fastest human-built space object so far was the Helios 2 probe which attained speeds of 241,400 kilometers (150,000 miles) per hour back in 1976. At that speed we would arrive at our destination in 4,470 years.