Trappist-1 Exoplanet system (Photo Credit: NASA-JPL Caltech)

About forty light years, or 235 trillion miles, away in the constellation Aquarius lies a planetary system with seven Earth-sized planets, at least three of which could be habitable. The exciting news was revealed to the public at a NASA press briefing and through the release of a study in the journal Nature on February 22.

The team of international astronomers led by Michaël Gillon, an astrophysicist at Belgium’s University of Liège, have dubbed the exoplanet system (worlds outside our solar system), TRAPPIST-1, in honor of the Transiting Planetesimals Small Telescope in Chile that first discovered three of the seven planets in 2015. Further investigation using ground telescopes, including the European Southern Observatory's Very Large Telescope and NASA’s Spitzer, revealed the system comprises seven planets.

Photo Credit: NASA-JPL Caltech

Their densities, calculated by how each planet is being pushed and pulled around by the others in the system, indicates that the newly-found worlds are probably rocky. The astronomers estimate the planets are between 10% larger to 25% smaller than Earth.

However, this is where the similarities end. Unlike our solar system, the planets, labeled 1b to 1h (with 1a being reserved for the star), are much closer to their sun. According to the researchers, 1b is so close that it orbits its star in a mere day and a half, while the furthest, 1h, does it in just 20 days. In comparison, Mercury, the planet nearest to our sun, takes 87.97 days to make the trip. Even cooler? The planets are so close to one another that residents could potentially see the geological features or clouds of neighboring worlds by simply gazing up at the sky.

Photo Credit: NASA-JPL Caltech

Despite the proximity to their star, astronomers think all seven planets could have liquid water. That’s because the 500 million-year-old sun has been classified as an ultra-cool dwarf star. This means it has an effective temperature of under 2,700K (2,430°C; 4,400°F), which is cool enough for liquid water even if the planets are really close. In contrast, our sun burns at a blazing hot 5770K (5496.85°C; 9926.33°F)! Also, given that the star is just slightly larger than Jupiter, it shines with a feeble light that is about 2,000 times fainter than our sun.

The star’s closeness raises the possibility that some or all of the planets are tidally locked. This means that half the planet experiences perpetual day while the other half is permanently shrouded in darkness. If this is the case, the weather would be very different from that on Earth thanks to the strong winds blowing from the day side and extreme temperature differences between the two sides.

Artist's concept of the view from 1f (Photo Credit: NASA/JPL-Caltech)

But these differences have not deterred scientists from hoping for the possibility of life on these distant worlds. They are particularly intrigued by 1e, 1f, and 1g, which lie in what is referred to as the “Goldilocks” zone. That means they are at the perfect distance from their sun for the water to stay in liquid form. The first three — 1b, 1c, and 1d — may be too close to the star, which means that any water present will rapidly evaporate, while 1h, which lies the furthest away, is probably a frozen world.

The team will now focus on investigating whether the planets have atmospheres. If the Hubble Space Telescope can detect methane and water, it will be the first indication of the presence of life in the TRAPPIST-1 system. The launch of NASA’s James Webb Space Telescope in 2018 will hopefully lead to more clues, as will the ground-based Giant Magellan Telescope that is scheduled to go live in 2023. But while all these powerful instruments may give us strong indications of extraterrestrial life, Gillon says, “We’ll never be 100% sure until we go there.” So watch out aliens, you might soon receive some unexpected visitors!

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