The headlines are breathless and shouted. “NASA’s Kepler Mission Announces a Planet Bonanza, 715 New Worlds.”
Big deal? Maybe it is. Likely it isn’t.
The Kepler mission points an orbiting telescope at a small slice of the sky. Day-after-day it watches the light from the stars in that slice, looking for variations in intensity.
When a planet crosses in front of its star as viewed by an observer, the event is called a transit. Transits by terrestrial planets produce a small change in a star’s brightness of about 1/10,000 (100 parts per million, ppm), lasting for 1 to 16 hours. This change must be periodic if it is caused by a planet. In addition, all transits produced by the same planet must be of the same change in brightness and last the same amount of time, thus providing a highly repeatable signal and robust detection method. – NASA
The planets aren’t actually being seen. That’s why the image at the top of this entry is an artist’s conception, not a photo. Kepler is instead looking for a predictable dimming as planets pass between the stars and Earth.
The rest is speculation! We have no idea what the planets are made of or conditions on their surface.
NASA looks for planets in the ‘habitable zone.’ That doesn’t mean they’re habitable! These objects are incredibly far away. Our data is thin.
NASA readily admits what is doesn’t know, but since that’s not the glamorous part of the release we seldom hear it.
One of these new habitable zone planets, called Kepler-296f, orbits a star half the size and 5 percent as bright as our sun. Kepler-296f is twice the size of Earth, but scientists do not know whether the planet is a gaseous world, with a thick hydrogen-helium envelope, or it is a water world surrounded by a deep ocean.
Even the Earth, the benchmark for habitable planets, is only ‘habitable’ over a small portion of its surface. We can’t live in the ocean, or tall mountaintops, or where it’s too hot or cold, or too dry or wet. We’re picky eaters in the world of habitation!
So, what does the Kepler mission and these discoveries mean to us? From a practical standpoint, little. Maybe nothing!
These planets are too far to ever consider visiting. Our lives won’t change. We’ll learn enough to solidify some theories, no more.
Kepler is an amazing engineering accomplishment. That’s indisputable. It has taken complex planetary theories and made them observable. No small trick. Just don’t expect an exoplanet photo or financial payoff soon… or ever.