Trappist-1: 7 exoplanets, 3 in the Goldilocks Zone

After a bit of a wind up and several hints, NASA finally dropped their big news: 7 earth-sized exoplanets were discovered circling a ultracool dwarf star called Trappist-I, 40 light years from Earth. Of these, 3 planets (e, f, and g) are considered to be in the so-called Goldilocks Zone, which is where it is not too close or too far from the sun, in a range where water could be found – and with water, the potential for alien life.

Let’s break down this discovery.

An ultracool dwarf star is a star that is less than 2,700 Kelvin and in this case is much smaller than our sun – it’s just barely the size of Jupiter. It’s also roughly 2,000x dimmer. It’s found in the constellation of Aquarius (The Water Carrier).

Trappist is the name of the telescope that discovered the star and its planets, the TRansiting Planets and PlanestIsimals Small Telescope. By studying the light from the star, they could determine that it was being orbited by planets, by measuring when and how the light would dim periodically, based on the orbiting bodies blocking the light from reaching the telescope.

The discovery was confirmed by the Himalayan Chandra 2-metre Telescope (HCT) in India, and with the Very Large Telescope (VLT) in Chile and the UK Infrared Telescope (UKIRT) in Hawaii.

Emmanuël Jehin, a co-author of the new study, is excited: “This really is a paradigm shift with regards to the planet population and the path towards finding life in the Universe. So far, the existence of such ‘red worlds’ orbiting ultra-cool dwarf stars was purely theoretical, but now we have not just one lonely planet around such a faint red star but a complete system of three planets!”

Michaël Gillon, lead author of the paper presenting the discovery, explains the significance of the new findings: “Why are we trying to detect Earth-like planets around the smallest and coolest stars in the solar neighbourhood? The reason is simple: systems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology. So if we want to find life elsewhere in the Universe, this is where we should start to look.”*


Artist’s illustration of the surface of a planet in the TRAPPIST-1 system, which hosts seven roughly Earth-size worlds.

Credit: NASA/JPL-Caltech

The planets are very close together – so close that they would be visible in each other’s skys if you were to stand on one at look out at the horizon; some would even appear larger than our moon is to us. Their tight orbits also mean that they travel close to their sun, lying closer to TRAPPIST-1 than Mercury does to our sun. The tight orbit also means they are probably tidally locked – so unlike our world, these planets always show the same face towards their sun, acting more like our moon. What else would you see? Due to the dimness of the star, it would be a sunset world, never getting any brighter than dawn or dusk on ours; due to the infrared light, the air would be warm with a rosy glow.


Characteristics of the seven TRAPPIST-1 worlds, compared to the rocky planets in our solar system.

Credit: NASA/JPL-Caltech

Data suggests that all six inner planets are rocky, like the Earth; not enough is known about planet h to determine its composition. Powerful gravitational tugs, both from TRAPPIST-1 and neighboring planets, could heat up the worlds’ insides, leading to volcanism, especially on the innermost two worlds.

The TRAPPIST-1 system is at least 500 million years old, but its age cannot be constrained more precisely than that, Gillon said. Ultracool dwarfs such as TRAPPIST-1 generally live for 4 to 5 trillion years — about 1,000 times longer than sun-like stars.#

Due to the distance of these planets it will be hard to find more information without better equipment. However “NASA’s $8.8 billion James Webb Space Telescope is slated to launch in late 2018, and huge, capable ground-based scopes such as the European Extremely Large Telescope and the Giant Magellan Telescope are scheduled to come online in the early to mid-2020s.”

Sources: *ESO Science Release;; ESO Public Archives