A few decades ago, we recognized only the eight planets of our solar system – nine if you count Pluto. At that time, it was legitimate to speculate that planets might be rare in the universe. Since then, thousands of exoplanets have been discovered, and the emerging consensus now is that there are more planets than stars.
Kepler and K2
One of the main drivers of discovery has been NASA’s Kepler mission. In 2009, the Kepler telescope was launched into space to look for exoplanets in our own galaxy. NASA used it to monitor how stars change in luminosity, because a star will dim as a planet passes in front of it. Sort of like a solar eclipse, just much weaker.
For four years, the telescope was directed toward a small patch of the sky, but in 2013, when part of the machinery failed, it was no longer able to keep a fixed direction. It started drifting, and, initially, NASA thought that the mission was over. But talented engineers managed to reprogram the dying telescope to a new mission, K2, which surveyed exoplanets in the parts of the sky where the telescope drifted.
This ingenuity allowed the spacecraft to operate productively for four more years, until it ran out of power in 2018. Kepler and K2 found in total around 2,500 exoplanets, most of which are gas giants the size of Jupiter.
However, even after Kepler’s retirement, researchers still squeeze out new knowledge from the data it collected. René Heller of the Max Planck Institute for Solar System Research and his colleagues found some real gems in the K2 mission data.
Utilizing a new statistical technique, they identified 18 new Earth-sized planets, several of which are in a zone suitable for life. Heller and his team say that they have barely scratched the surface. The 18 planets were found in only a fraction of the K2 dataset, which is small in comparison to the full Kepler data. With the new and improved statistical technique, they expect to find many more Earth-like planets not too far away.
Are We Alone?
An immediate question that arises from these discoveries is whether we are alone in the universe. With so many planets suitable for life, even in our own galaxy neighborhood, what are the odds that Earth should be the only planet with life?
That question often ends in metaphysical speculation. We can, however, turn the problem on its head: If there are planets out there suitable for human life, can we go there?
The short answer is maybe. Our current understanding of the laws of physics, which admittedly is not impressive, implies that it is technologically possible to create spacecraft that can travel at a significant fraction of the speed of light.
The nearest Earth-sized planet in the habitable zone orbits the star Proxima Centauri, which is only four light-years away. If we were able to travel at 10% of the speed of light, it would take us about half a century to get there. That’s perhaps not something that Elon Musk will ever achieve, but his obsession with going to Mars may lay the foundation for visiting the stars and new planets surprisingly soon.
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