TRAPPIST-1c is the second closest planet to the star, orbiting in a near-circular orbit at a distance of only 2.27 million km (0.015 AU). It is approximately 1.38 times the mass of the Earth, but only 6% larger in radius, suggesting it has a silicate rocky composition similar to Earth, but with a slightly larger iron core. It receives 2.27 times more solar irradiance than Earth (similar to Venus), giving it a mean surface temperature of 342 K (69°C) – considered too hot for surface water or Earth-like life to be present.

Artist concept showing what TRAPPIST-1c may look like. Image credit: NASA/JPL-Caltech

The star’s size as viewed from the surface of TRAPPIST-1c would be 4.1 degrees across, more than 8 times larger than we see our own Sun. The planet is tidally locked to its star, keeping the same face towards it at all times. For a visitor to the sunward side of the planet, the dull red sun would hang in place, neither rising nor setting. The inner planet TRAPPIST-1b, appearing nearly three times larger than our moon does from Earth, would regularly cross the sky, probably transiting (but not eclipsing) the sun’s disk each time. On the opposite side of the planet, it would be perpetually dark, broken only by the other five planets racing across the sky, regularly passing near or in front of one another. Unlike our Solar System, the other TRAPPIST-1 planets are close enough to show as small disks, even with naked eyes. At closest approach, the next planet out, TRAPPIST-1d would cover 0.69 degrees, a bit larger than the moon does from Earth. Meanwhile, the distant stars would rise in the east and cross the sky to set in the west a little slower than they do on Earth. With a year only 2.42 Earth-days long, the entire celestial sphere would be observable every 58 hours!