TRAPPIST-1 TRAPPIST-1 Star

The TRAPPIST-1 star is an ultra-cool red dwarf of spectral class M8. It is approximately 8% of the mass of our sun, and 11% of its diameter, making it slightly larger, but 84 times more massive than Jupiter. Red dwarf stars age far more slowly than hotter, larger stars. TRAPPIST-1 has an estimated surface temperature of 2,550 K, and is about 500 million years into a 12 trillion year life-span. By comparison, our Sun’s surface is 5778 K, and is about halfway through a 10 billion year life-span.

Long-lasting stars intrigue exobiologists because they allow so much time for life to arise and evolve. But at only 500 million years old, the TRAPPIST-1 star may be too young for life to have arisen already.

The TRAPPIST-1 star shines with only 0.000373% of the visible light that the Sun emits. It emits proportionately more infrared radiation than our sun. Viewed from the surfaces of orbiting planets, the star would glow a dull red. The habitable zone for TRAPPIST-1 extends 4 to 7 million km from the star, enough for three of the planets to occupy it.

A comparison of the TRAPPIST-1 system to our solar system. The close orbits of the TRAPPIST-1 planets are reminiscent of Jupiter and its system of orbiting moons. Image credit: NASA/JPL-Caltech

The size of the Trappist-1 Solar System is one of the remarkable features of it. Not only is the star Jupiter-sized, but the bounty of planets around it fit within a volume of space roughly three times larger than the orbits of Jupiter’s four Galilean moons. The outermost star, TRAPPIST-1h, orbits only one-sixth as far from its star than Mercury does from our Sun!

Did You Know?
The Nearest Exoplanet

The nearest known exoplanet is located just 4.2 light-years from Earth and circles the closest star to our Sun - Proxima Centauri - a small red dwarf star that is part of a triple star system known as Alpha Centauri. The exoplanet, known as Proxima Centauri b, has a mass 1.3 times the Earth (indicating it might be rocky) and orbits within the habitable zone of its star every 11.5 days at a distance of about one-tenth the space between Mercury and the Sun.
Try This!
The TRAPPIST-1 Stellar Neighborhood

The TRAPPIST-1 system is 39 light-years from our Sun. Let's explore the local group of stars within 50 light-years of our Sun.

  • Click here to view the stars within 50 light-years of the Sun.

The view in the main window now displays a 3-dimensional set of reference axes and a reference plane for the ecliptic coordinate system. The Trappist-1 star has been selected and has its position highlighted on the 3D grid. Notice that the Trappist-1 star is slightly above the ecliptic plane. As seen from Earth, TRAPPIST-1 will be 'north' of the ecliptic.

  • Click here to view the names of the stars within 50 light-years of the Sun. You can point and click on any star to plot it on the reference grid.
Every star is moving rapidly through space, in a unique direction. However, from the Earth, stars appear to remain in the same place in the sky because they are so far away. Only over thousands of years can we see the stars shift position with respect to each other. This slow movement of the stars is called proper motion. Starry Night lets you display proper motion vectors, lines that represent the speed and direction of each star’s motion. The length of a star’s proper motion vector indicates its relative speed.
  • Click here to view the proper motion vectors of the stars within 50 light-years of the Sun.
You should see that many of the stars have vectors pointing in the same direction, indicating that they are moving together through space and might be part of the same group. However, many other stars are moving in very different directions.
  • Click here to view the stars moving relative to each other over a time span of thousands of years.