This week, scientists at NASA announced the discovery of not 1, or 2, or even 3 but 7 Earth-size planets orbiting another star. And not only that, scientists believe that 3 of those planets can potentially harbor life!
Not surprisingly, the discovery got the internet freaking out with excitement. How does this discovery advance our search for life elsewhere in the universe?
Let’s get back to the news first. The newly discovered planets that got everyone excited this week were found going around the dwarf star TRAPPIST-1. The star got its name from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile.
The system around TRAPPIST-1 is a big deal because this is the most number of Earth-size planets ever found in a single system. It’s even more remarkable because of the 7 planets, 3 are thought to be in the “habitable zone” of their star.
The habitable zone is the region around the star that can have liquid water. If a planet is too close to its star, it can get too hot for water to exist in liquid form. If a planet is too far, it can get too cold and water can only exist as ice.
However, the definition of the habitable zone does not only depend on distance from the star, but also on the composition of the atmosphere. In the case of the Solar System, the planets Venus, Earth, and Mars are in the Sun’s habitable zone, and so is the Moon. But conditions on Venus are infernal. Meanwhile, it is frigid both on Mars and the Moon.
Venus is too hot because its very thick atmosphere traps too much of the Sun’s radiation. In fact, conditions on Venus can serve as a warning to us here on Earth, where we continue to add more heat-trapping gases into our atmosphere.
Mars, on the other hand, has a very thin atmosphere, and the Moon has practically no atmosphere to speak of. Hence, most of the radiation coming from the Sun that reaches them just bounces back to outer space instead of staying to melt the ice and keep water in liquid form. Despite its very thin atmosphere, however, Mars still manages to hold a bit of liquid water, so we’re not ruling out the possibility of life on Mars.
We need to know the atmospheres of the planets going around TRAPPIST-1 before we can confidently say which of them can really have oceans and seas of liquid water.
And we might find out soon! The techniques used in searching for exoplanets (planets going around stars other than the Sun) are becoming more advanced with each passing year. And the longer we look, the more of these exoplanets we will find. We now have found thousands of them, and we’ve only been looking for a little more than two decades. And of the thousands we know are out there, more than three quarters were discovered in the last three years. The rate of discovery is accelerating exponentially.
The TRAPPIST-1 planets were discovered by accurately measuring the brightness of the star. As the planets move around their star, they sometimes pass in front of the star. This causes the star to dim slightly, depending on the size of the planets. By measuring the dimming on TRAPPIST-1, scientists learned than its seven planets are about the same size as the Earth.
More sensitive instruments will soon measure the light from the star even more precisely so that we can figure out what part of that light has bounced off the planet passing in front. This will allow scientists to figure out the composition of the atmosphere of the planet.
Only a few planetary systems are positioned in such a way to allow us to use this technique. Hence, a vast majority of the exoplanets out there will not be discovered this way. The fact that we have already discovered so many using this technique speaks about the vast multitudes of planets out there.
The TRAPPIST-1 planets, in particular, prove to us that the universe is teeming with planets, many of them possibly Earth-like. So perhaps, the universe is also teeming with life. We’re quite probably not alone in the universe.
But even the nearest Earth-like exoplanets will be beyond our reach in the next few thousand years. Our fastest robotic spacecraft will take close to a million years to get to TRAPPIST-1. Spacecraft carrying human passengers will take longer—hundreds of millions of years.
The search for Earth-like exoplanets will help us figure out our place in the universe. And for the foreseeable future, that place is here. Our search for other worlds is not a search for replacements. It should be a search that leads us back to our home and makes us see it with fresh eyes.
Decierdo is resident astronomer and physicist for The Mind Museum.