Today in History—July 23: NASA Discovers an Earthlike Planet
On this day in 2015, NASA announced the discovery of Earth’s “bigger, older cousin,” an exoplanet named Kepler-452b.
An exoplanet is a planet located beyond our solar system. This one is special, because it shares three key similarities with Earth. First, its size is considered close to Earth’s, only about 60 percent larger in diameter. (Yes, that’s what we consider “close.”) Next, its star is like our Sun, with a similar temperature and mass. Finally, Kepler-452b sits in the habitable zone—far enough away from its star that liquid water can exist, an essential ingredient for life as we know it.
When scientists discover Earthlike planets, they get excited. These are our best guesses as to where life might exist elsewhere in the universe.
So could Kepler-452b sustain life? We don’t know. It is uncertain if it has a rocky surface—thought to be another important prerequisite for life, as this allows liquid water to pool and harbors critical nutrients.
With our current technology, the planet is too far away to detect the chemical signs of life, known as biosignatures. It is so distant that its light takes 1,800 years to reach us.
On exoplanet HD 189733b, it rains glass.
But it’s still amazing that we know Kepler-452b exists at all. We owe the discovery to a cosmic coincidence: Its orbit happens to be aligned in a way that periodically blocks Earth’s line of sight to its host star, which thus obscures a tiny amount of the star’s light. The Kepler telescope, which discovered 452b, was designed to detect these small dips in brightness.
To date, NASA has confirmed the discovery of more than 6,000 exoplanets, some 2,600 of which were found via the Kepler telescope. Many more are to come: The Nancy Grace Roman Telescope, scheduled to be launched this August, will deploy new techniques to detect exoplanets and even take direct images of them.
Our planet may have many more relatives out there just waiting to be discovered. A larger census of the planetary population will bring scientists closer to determining just how rare planets like Earth are in the universe.
- 385 days: Time it takes Kepler-452b to complete an orbit around its star
- 49–62 percent: Likelihood of Kepler-452b having a rocky surface
- Billions: Estimated number of exoplanets in our galaxy
- 1872: Elijah McCoy patents a device to lubricate steam engines, giving rise to the “real McCoy”
- 1967: Riots in Detroit begin, helping launch the Black Power movement
- 1999: American Eileen Collins becomes the first woman to command a space shuttle mission
