TRAPPIST-1 and its 7 Exoplanets

This illustration shows the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Scientists using a battery of telescopes around the world and in space have discovered that there are seven Earth-size planets in the system.
Image Credits: NASA/JPL-Caltech


Are we alone in the Universe? This is an age old question that has been the driving force for our ventures into space exploration. And with the record breaking discovery of 7 exoplanets in the TRAPPIST-1 system, it definitely feels like we could be on the cusp of an answer!

At 6pm BST, I, like many of the humans across the world,  was glued to my computer screen, watching NASA and ESO’s announcements confirming the existence of 7 exoplanets orbiting the ultra-cool dwarf star, TRAPPIST-1, the most ever confirmed orbiting a star outside our solar system, and what an impressive and exciting system we have found!

The TRAPPIST-1 system is named after the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile and it was in May 2016 that the telescope had discovered 3 exoplanets orbiting the ultra-cool dwarf star.  This caused a huge stir with many telescopes across the world, as well as those in space, and they turned their curious eyes to the constellation of Aquarius and the star system hidden within. Finally the Spitzer telescope, together with the European Southern Observatory VLT, confirmed the existence of 2 of these exoplanets, as well as 5 more!


This artist’s concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances.
Image Credits: NASA/JPL-Caltech


From the smaller scale of the system to the Earth like sizes of the planets, we were salivating at the new discovery and all they have discovered. So let’s break down what we know.

We know that the system is much smaller than ours as the TRAPPIST-1 star itself is about 11% the radius of our Sun and only 8% of its mass.  This means the planets in this system are much closer to each other, to the point that they can see much more detail of their neighbouring planets than the Earth would of its neighbours, even sometimes appearing larger than our Moon does to us! They also believe this could mean the planets are tidally locked to their host star which would mean that the same side of each of the planets is always facing the star. So one side is in permanent daylight and the other in perpetual darkness! This would mean the weather system on these planets could be shockingly different from our own, from massive winds to extreme fluctuations in temperature!

With the star being an ultra-cool dwarf star it does mean it is much cooler than our Sun but this is a good thing as it increases the chance of finding liquid water and perhaps life on all 7 of the exoplanets. But the best chance of finding the building blocks for life in the system is with the 3 planets that can be found in the habitable or ‘Goldilocks’ zone. This is the area that the Earth is located in our Solar System where water might be found in liquid form and so provide the best chance for finding life. The 3 planets are TRAPPIST 1E, TRAPPIST 1F and TRAPPIST 1G. These are not the catchiest of monikers as exoplanets are not given fun or exciting names, perhaps this could change in the future!

TRAPPIST 1E is the closet of the 3 ‘habitable zone’ exoplanets to the star. It is close in size to the Earth and receives roughly the same amount of light as the Earth, so therefore could be the closest in temperature to the Earth. Its orbit is a staggeringly short, only 6 days around its star!

TRAPPIST 1F is again similar in size to the Earth, with an orbit of 9 days around its star. It would have similar periods of light exposure to Mars.

TRAPPIST 1G is the largest of the planets with a 13% larger radius of the Earth and an orbit of 12 days around its star.

Obviously with the star being much smaller than our Sun the orbits of these planets would be much shorter, taking less time to make a full trip.  The planetary system is in fact much closer to the Jovian moon system in size than to scale of the orbits of the terrestrial planets in our Solar System.


Over its ten years in space, NASA’s Spitzer Space Telescope has evolved into a premier tool for studying exoplanets. The engineers and scientists behind Spitzer did not have even have this goal in mind when they designed the observatory back in the 1990s. Image Credit: NASA/ JPL- Caltech


Using data from the Spitzer and the VLT and several other telescopes, they have managed to precisely work out the sizes of the 7 planets as well as the masses of 6 of them. Due to their estimated density, we do believe that they are rocky bodies like the inner planets of our solar system. The Hubble space telescope has also been observing some of the planets of TRAPPIST-1, including the 3 in the habitable zone, to try to determine if the atmospheres are puffy, hydrogen dominated atmospheres like those of our gas giants, and it has found no evidence to state the case, strengthening the belief that they are rocky worlds.

Now obviously we are all thinking our next space trip should be to this exciting star system but for the technology we have now, this is not possible. If we could travel at the speed of light we could reach the system within 40 years. But with the technology we have today and the speed we can travel at, it is more like 44 million years! This does not mean we will not find out more about these exciting new worlds as we have only scratched the surface!


A rare view of the James Webb Space Telescope face-on. Due to launch in late 2018. Image Credit: NASA


Telescopes across the world, including the Hubble space telescope and Spitzer are continuing their ‘stellar’ work in uncovering the TRAPPIST-1 system’s secrets. And let’s not forget that 2018 will see the launch of the greatly anticipated James Webb Space Telescope, which will obviously turn its gaze to one of the exciting discoveries that could answer our questions about life outside of our planet. It will be able to detect the chemical make-up of the exoplanet’s atmospheres, temperatures and surface pressures, and in turn the habitability of said exoplanets!

This announcement will truly be one of those moments in history where I will always be able to recall and the excitement it has instilled across the world. To quote Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington, this discovery now means that “finding a second Earth is not if, but when!”

Commentary on the discovery by Michael Burton, Director of Armagh Observatory and Planetarium

Article by Kerry Scullion, Education Support Officer

Kerry Scullion, Education Support Officer