At a press conference yesterday afternoon, NASA announced what is unequivocally its biggest discovery outside of our solar system: Not aliens (sorry), but seven Earth-sized planets orbiting Trappist-1, an ultracool dwarf star only 40 light years away.
"The discovery gives us a hint that finding a second Earth is not just a matter of if, but when." —Thomas Zurbuchen
Of these seven, three orbit inside what's called a habitable zone, where liquid water has the potential to pool on the planets' surfaces. Thomas Zurbuchen, the associate administrator of the Science Mission Directorate at NASA's Washington headquarters said in the press conference, "The discovery gives us a hint that finding a second Earth is not just a matter of if, but when."
The first exoplanet—that is, a planet that orbits a star other than our sun—was discovered in 1995, but the planets orbiting Trappist-1 make up the largest find of exoplanets to date. Trappist-1 is much cooler and much smaller than our sun, noted Michael Gillon, an astronomer at the University of Liege in Belgium, and its planets are generally much smaller and orbit far closer to their star than the planets in our solar system. The innermost planet has an orbit of only one and a half days, with the outermost planet's orbit still only about 20 days long.
The planets are in such close proximity that if you were standing on one, you would see the other planets not as tiny blips in the sky as you do Venus or Mars on Earth, but as worlds as tantalizingly close as the moon seems to us at night. Indeed, said Zurbuchen, the planets orbiting Trappist-1 are "only a few times as far apart as the Earth is from the moon." NASA has released a travel poster that imagines just how spectacular a view this would be, with the slogan "Voted Best 'Hab Zone' Vacation."
See what major scientific possibilities this discovery holds.
Speaking of the planets with the most potential for future human habitation: Trappist-1E is close in size to Earth, and receives about the same amount of starlight as Earth does in our own solar system. This means its surface temperatures could be incredibly similar to our own. Trappist-1F, astronomer Nikole Lewis said in the press conference, is a "potentially water-rich world" with a nine-day orbit, receiving about the same amount of light as Mars. Lastly, the largest planet in the Trappist-1 system, Trappist-1G, has a radius about 13% larger than Earth's, and receives the same amount of starlight as somewhere between Mars and the asteroid belt.
Like our moon, all the planets in the Trappist-1 system are tidally locked. One side of the planets always faces the star, thus experiencing possibly scorching, unbroken daylight, with the other side cast forever in night.
The seven planets of the Trappist-1 system were discovered by the Spitzer Space Telescope. In 2018, NASA will launch the James Webb Telescope, which will be able to send back more data about the Trappist-1 planets. The astronomers making yesterday's announcement estimate that more information about the atmosphere of the Trappist-1 planets in the habitable zone should be available by the early 2020s.
Any chance that life already exists on Trappist-1E, Trappist-1F, or Trappist-1G? One social media user asked at the press conference, "Is it possible to listen to these planets?" Zurbuchen replied, "To my knowledge, [they were] already listened to by SETI, and they found no artificial signal." So, even if life is found in the future, sadly, it's probably not intelligent. Still, a second Earth just became more of a reality.
To find out more about these new worlds, visit nasa.gov.