System The observed and deduced parameters of the star and its entourage of seven planets are given here. We will attempt to keep those values updated. Currently displayed are the parameters from Delrez et al. 2018, from Van Grootel et al. 2018, and from Grimm et al. 2018. Some graphs display the planets' parameters plotted against each other, at the bottom of the page. TRAPPIST-1A - the star Name 2MASS J23062928-0502285 Alternate name TRAPPIST-1 Right ascension α = 23h 06m 29.28s Declination δ = -05º 02' 28.5'' Constellation Aquarius Apparent magnitudes V = 18.80 ± 0.08, R = 16.47 ± 0.07, I=14.0 ± 0.1, J = 11.35 ± 0.02, K = 10.30 ± 0.02 Parallax 82.4 ± 0.8 mas Distance 12.14 ± 0.12 pc Mass 0.089 ± 0.006 M ☉ Radius 0.121 ± 0.003 R ☉ Density 51.1 -2.4 +1.2 ρ ☉ Effective temperature 2511 ± 37 K Luminosity 0.000522 ± 0.000019 L ☉ Metallicity [Fe/H] +0.04 ± 0.08 Age 7.6 ± 2.2 Gyr TRAPPIST-1b Orbital period 1.51087637 ± 0.00000039 days Mid-transit time 2 457 322.51654 ± 0.00010 (Julian Date) Transit depth 0.7277 ± 0.0075 Scale parameter (a/R ★ ) 20.56 -0.31 +0.16 Impact parameter 0.157 ± 0.075 R ☉ Transit duration 36.19 ± 0.12 minutes Orbital inclination 89.56 ± 0.23º Orbital eccentricity < 0.081 Semi-major axis 0.01150 -0.00025 +0.00028 AU Radius 1.127 ± 0.028 R ⊕ Mass 1.02 ± 0.15 M ⊕ Density 0.726 ± 0.92 ρ ⊕ Surface gravity 0.81 ± 0.10 g Irradiation 3.88 ± 0.22 S ⊕ Equilibrium temperature (A=0) 391.8 ± 5.5 K TRAPPIST-1c Orbital period 2.42180746 ± 0.00000091 days Mid-transit time 2 457 282.80879 ± 0.00018 (Julian Date) Transit depth 0.6940 ± 0.0068 Scale parameter (a/R ★ ) 28.16 -0.44 +0.22 Impact parameter 0.148 ± 0.088 R ☉ Transit duration 42.31 ± 0.14 minutes Orbital inclination 89.70 ± 0.18º Orbital eccentricity < 0.083 Semi-major axis 0.01576 -0.00034 +0.00038 AU Radius 1.100 ± 0.028 R ⊕ Mass 1.16 ± 0.14 M ⊕ Density 0.883 ± 0.081 ρ ⊕ Surface gravity 0.966 ± 0.090 M ⊕ Irradiation 2.07 ± 0.12 S ⊕ Equilibrium temperature (A=0) 334.8 ± 4.7 K TRAPPIST-1d Orbital period 4.049959 ± 0.000078 days Mid-transit time 2 457 670.14227 ± 0.00026 (Julian Date) Transit depth 0.3566 ± 0.0070 Scale parameter (a/R ★ ) 39.68 -0.62 +0.32 Impact parameter 0.08 -0.06 +0.10 R ☉ Transit duration 49.33 -0.32 +0.43 minutes Orbital inclination 89.89º -0.15 +0.08 Orbital eccentricity < 0.070 Semi-major axis 0.02219 -0.00048 +0.00053 AU Radius 0.788 ± 0.020 R ⊕ Mass 0.297 ± 0.037 M ⊕ Density 0.616 ± 0.065 ρ ⊕ Surface gravity 0.483 ± 0.50 g Irradiation 1.043 ± 0.060 S ⊕ Equilibrium temperature (A=0) 282.1 ± 4.0 K TRAPPIST-1e Orbital period 6.099043 ± 0.000015 days Mid-transit time 2 457 660.37910 ± 0.00040 (Julian Date) Transit depth 0.4802 ± 0.0094 Scale parameter (a/R ★ ) 52.13 -0.82 +0.41 Impact parameter 0.240 -0.047 +0.056 R ☉ Transit duration 55.92 ± 0.39 minutes Orbital inclination 89.73º -0.066 +0.053 Orbital eccentricity < 0.085 Semi-major axis 0.02916 -0.00063 +0.00070 AU Radius 0.915 ± 0.025 R ⊕ Mass 0.772 ± 0.077 M ⊕ Density 1.024 ± 0.073 ρ ⊕ Surface gravity 0.930 ± 0.066 g Irradiation 0.604 ± 0.034 S ⊕ Equilibrium temperature (A=0) 246.1 ± 3.5 K TRAPPIST-1f Orbital period 9.205585 ± 0.000016 days Mid-transit time 2 457 671.39470 ± 0.00022 (Julian Date) Transit depth 0.634 ± 0.010 Scale parameter (a/R ★ ) 68.6 -1.1 +0.6 Impact parameter 0.382 -0.029 +0.040 R ☉ Transit duration 63.14 ± 0.36 minutes Orbital inclination 89.719º -0.039 +0.026 Orbital eccentricity < 0.063 Semi-major axis 0.03836 -0.00084 +0.00092 AU Radius 1.052 ± 0.026 R ⊕ Mass 0.934 ± 0.79 M ⊕ Density 0.816 ± 0.037 ρ ⊕ Surface gravity 0.853 ± 0.040 g Irradiation 0.349 ± 0.020 S ⊕ Equilibrium temperature (A=0) 214.5 ± 3.0 K TRAPPIST-1g Orbital period 12.354473 ± 0.000018 days Mid-transit time 2 457 665.35084 ± 0.00020 (Julian Date) Transit depth 0.764 ± 0.011 Scale parameter (a/R ★ ) 83.5 -1.3 +0.7 Impact parameter 0.406 -0.025 +0.031 R ☉ Transit duration 68.53 ± 0.37 minutes Orbital inclination 89.721º -0.026 +0.019 Orbital eccentricity < 0.061 Semi-major axis 0.0467 ± 0.0011 AU Radius 1.154 ± 0.029 R ⊕ Mass 1.148 ± 0.097 M ⊕ Density 0.759 ± 0.034 ρ ⊕ Surface gravity 0.871 ± 0.040 g Irradiation 0.236 ± 0.014 S ⊕ Equilibrium temperature (A=0) 194.5 ± 2.7 K TRAPPIST-1h Orbital period 18.767953 ± 0.000080 Mid-transit time 2 457 662.55467 ± 0.00054 (Julian Date) Transit depth 0.346 ± 0.014 Scale parameter (a/R ★ ) 110.3 -1.7 +0.9 Impact parameter 0.392 -0.043 +0.039 R ☉ Transit duration 76.92 ± 0.96 minutes Orbital inclination 89.796 ± 0.023º Orbital eccentricity unknown Semi-major axis 0.0617 -0.0013 +0.0015 AU Radius 0.777 ± 0.025 R ⊕ Mass 0.331 ± 0.053 M ⊕ Density 0.72 ± 0.11 ρ ⊕ Surface gravity 0.555 ± 0.080 g Irradiation 0.135 ± 0.076 Equilibrium temperature (A=0) 169.2 ± 2.4 K TRAPPIST-1x It is possible that other planets exist around TRAPPIST-1. Further observations may tell us about their presence, notably from transit timing variations. Lengthy observations with Spitzer and with K2 have shown no additional transit signal. Plots video of the system:

Timeline Most discoveries take time to make. Even though time seemed to have flown by very rapidly when it came to TRAPPIST-1, the path leading to the discovery of the system took many efforts over nearly a decade. 2018 Feb 22nd A year after the big announcement, what have we learned. See here. Feb 5th New series of scientific papers finally published. They refine the properties of the star, and its seven planets, as well as start their atmospheric investigations. Several of the planets appear under-dense compared to Earth, maybe indicating vast amount of water. TRAPPIST-1e is the closest of the seven to Earth. 2017 Aug 31st Scientific paper reporting Ultraviolet observations, suggesting the outer planets might still host water. May 22nd Scientific paper on the orbital period of TRAPPIST-1h is published. Apr 4th Scientific paper on the orbital period of TRAPPIST-1h is accepted by Nature Astronomy. Mar 20th Europa, the first of the four SPECULOOS telescopes has its first light! Mar 11th Scientific paper on the orbital period of TRAPPIST-1h is sent to Nature Astronomy. Mar 9th Planet 1h is recovered from the K2 data, at the expected orbital period! Mar 8th K2 data is made public, start of analysis. Mar 4th K2 finishes its observations. Feb 23rd Publication of the discovery in Nature. Feb 22nd Press conference at NASA's headquarters in Washington DC. Feb 2nd Prediction made that TRAPPIST-1h will likely have an orbital period of 18.765 days. Request sent to Spitzer to observe the March 28th transit opportunity (which was successful). Jan 3rd The scientific paper is accepted by Nature. 2016 Dec 15th K2 starts observing its campaign 12. TRAPPIST-1 is right on the edge of the telescope's field of view. Nov 21st The paper describing the existence, and providing the radii and masses of seven planets in the TRAPPIST-1 system, is submitted to Nature. They also communicate their enthusiasm at the idea of pairing our scientific paper with a sci-fi short story. (read it here). Oct 7th End of observations with Spitzer. By eye, it is clear that many planets transit the star at the centre of the TRAPPIST-1 system. Excitement is at its peak! Oct 6th TRAPPIST-North is inaugurated in Oukaïmeden Observatory, Morocco. Oct 1st First recorded transit of TRAPPIST-1h. Sep 19th Beginning of observations with the Spitzer Space Telescope. TRAPPIST (North & South), the Liverpool Telescope and UKIRT are in support from the ground to fill in gaps in the Spitzer coverage (caused by a need to upload data back to Earth). Aug 5th Announce that the Spitzer Space Telescope will observe TRAPPIST-1 for nearly continuous 20 days. By this date our collected ground-based data made clear that more that the original period for TRAPPIST-1d was incorrect that more than 3 planets orbited the star. Jun 6th First recorded transit of TRAPPIST-1d (using the nomenclature of the most recent paper). Jun 3rd First spectrum for the planets TRAPPIST-1b & 1c is publicly announced. May 4th TRAPPIST-1b & TRAPPIST-1c transit at the exact same time.

The Hubble Space telescope is recording the event. May 2nd Public announcement that three Earth-sized planets orbit a nearby ultracool dwarf. May 1st TRAPPIST resumes observations of the system (visible >1h from La Silla Observatory). It is soon joined by the Liverpool Telescope and the William Herschel in La Palma, the VLT in Chile, the 1 metre telescope at the South-African Astronomical Observatory, and UKIRT in Hawai'i. Mar-Apr Many requests sent to observatories around the globe to monitor for TRAPPIST-1, to confirm the orbital period of planet d, and search for additional planets. Feb 18th Scientific article is accepted by Nature. Jan 11th Submission of the discovery of TRAPPIST-1b & 1c, and proposing a solution of a planet 1d to Nature. 2015 December 15th TRAPPIST stops observations of the system (visible <1h from La Silla Observatory) December 11th The VLT captures a triple transit on TRAPPIST-1, puzzling but amazing the team, later known to be a combination of TRAPPIST-1c, 1e & 1f. October 27th First recorded transit of TRAPPIST-1b. October 26th First recorded transit of TRAPPIST-1f, but not recognised right away as such. October 17th First recorded transit of TRAPPIST-1e, but not recognised right away as such. September 29th First recorded transit of TRAPPIST-1g, but mistaken as TRAPPIST-1d and announced as such in the first scientific paper on the system. September 17th First recorded transit of TRAPPIST-1c. Intense photometric monitoring of the star begins. 2013 October 3rd First datapoints collected on TRAPPIST-1. June 10th The initial funding for SPECULOOS is accepted. April 1st First publication of TRAPPIST photometry on an ultra-cool dwarf, the nearby brown dwarf pair Luhman-16, is submitted to the Astronomy & Astrophysics journal. These observations demonstrated it was possible to discover Earth-sized planets from the ground, using small telescopes. 2011 January 9th First observation of an ultra-cool dwarf by TRAPPIST, in preparation for SPECULOOS. 2010 June 8th First light of the telescope at La Silla Observatory. Operations are starting. The main focus is to participate in the search for hot Jupiters with WASP (www.wasp-planets.net) and to study small bodies of the Solar system. 2008 The funding for the construction of TRAPPIST is accepted.

Future The study of the TRAPPIST-1 system is only starting. In the short term, photometric follow-up using the repurposed Kepler satellite (named K2) along with with newer observations using Spitzer ought to reveal the period of planet 1h. We will also search for additional planets. Theses lightcurves, combined with ground-based measurements will increase the number of transit timing measurements for each of the planets. This will give us more accurate masses and orbital eccentricities. This will confirm whether the planets are mostly rocky or whether they contain a certain amount of volatiles, like water. In the medium term, we can expect the first attempts at detecting the atmospheres of the TRAPPIST-1 planets, using Hubble, followed by deeper investigations thanks to the James Webb. The James Webb could in principle measure the temperature of the planets, and detect the chemical composition of their atmospheres. It will do so by collecting dozens of eclipses of the TRAPPIST-1 planets. The advantage of having seven planets in one system is that we will be able to compare them to one another. TRAPPIST monitored a few dozen ultra-cool dwarfs photometrically. This is a prototype for a more important and ambitious survey called the Search for Planets EClipsing ULtra-COOl Stars (SPECULOOS), which is currently under construction at Cerro Paranal. With SPECULOOS, we will observe more than ten times more stars than TRAPPIST did, at a greater precision. Before the survey is over we expect to have discovered a dozen of planetary systems akin to TRAPPIST-1. All will be amenable for in-depth atmospheric investigations with the James Webb.

Stories Music, visual art, literature and graphic novels freely inspired by the TRAPPIST-1 system. As scientists, we thought that one way to communicate how excited we are about this new system, is to allow artist to imagine what it would like there. Please enjoy these works keeping in mind that those are mostly works of fiction, written with artistic licence! The Terminator, a short-story by Laurence Suhner TRAPPIST-1 (A Space Anthem), a single by In Isolation Portals to Wonderland 2, a novel by Jean Young Trappist-1, an album by Lucius Fox Trappist-1, can you hear me?, a song by Majungas La Oportunidad, a short-story by Adam Burgasser Trappist-1, a musical and visual saga by Adam Łukawski & Julia Borzucka TRAPPIST-1, what is it?, a graphic novel by Lepithec An Ode to 7 Orbs, a poem by Sean Raymond The Terminator by Laurence Suhner © 2017 translated from French by Sheryl Curtis. The full text can be publicly accessed on Nature's website. This short-story is currently a finlist to the Bob Morane prize, and eligible for the Hugo awards. Laurence also wrote a piece describing the source of her inspiration, which can be read here. published in Nature, 542, p512 html French version available here. Version franÇaise ici. TRAPPIST-1 (A Space Anthem) a single, by In Isolation © 2017 This is Earth and I forsake it Will the Earth cry when I’m gone? Here on Earth, we war in isolation Planet Earth has left me numb I’m in love with TRAPPIST-1, though I’ll never see your sunrise You tore imagination a new hole I’m in love with TRAPPIST-1, but your children have a dark side Got a Hippocratic conscience to uphold Caught in calm, perpetual twilight Forty light years seems so far Do you feel the same? Because I cannot breathe Distant loving breaks my heart I’m in love with TRAPPIST-1, though I’ll never see your sunrise You tore imagination a new hole I’m in love with TRAPPIST-1, but your children have a dark side Got a Hippocratic conscience to uphold Aquarian sun, give me TRAPPIST-1 As the feeling burns and the dreaming yearns Portals to Wonderland 2 a novel, by Jean Young - 2017 Julia and Benjamin are back on another adventure through the Portal. This time, they travel to the TRAPPIST-1 star system (located 235 trillion miles from Earth) to save the astronauts from crashing into the forcefield around the star’s planets. Who put up the force field around the planets in the first place? Julia and Benjamin must travel four hundred million years back into the past to solve the mystery and help two races of aliens from destroying each other. Will they succeed? What will they imagine from the magic pouch to help them on their quest? Trappist-1 an album, by Lucius Fox - 2018 The album is an exploration of the seven planets orbiting TRAPPIST-1. Its opening and closing tracks are imagined as a flyby of the inner and outer planets respectively, while track 4 (TRAPPIST-1: e) explores the emergence of life on one of the planets within the habitable zone. The remaining four tracks are snapshots of the conditions present on on both the interior planets (Violet Horizon and Unsetting) and exterior planets (Fissures and Tidal Lock), due to the compact nature of the planets’ orbits and the tidal heating and tidal locking acting on each planet. Trappist-1, can you hear me? a song, by Majungas - 2018 La Oportunidad by Adam Burgasser © 2017 “Cuidate mi queridita” mamá whispers, the tangle of her grey hair scratching my chin. She cries, as she has for weeks, since we got word that I would go to university. “Cuidate…” she repeats, quietly; then pushes me back, points up and glares, “Show those espacitos how smart you are.” I smile, knowing she can’t see the star I am going to, can’t see any stars in the airglow. Her fierceness falters. She turns to papá. She knows. The 40 lightyears to T-1f, which I will experience as a single month, is the rest of her life. I won’t see her again, nor papá, who stands proud and angry and hurt. “You were to take care of us, you were to give us nietos” he said that night. “You are leaving us to die alone on a tired world.” He hasn’t spoken to me since. Same with my friends. When I told Ana, she spit on me and deleted me from her net, she calls me “la puta de las estrellas.” It is not jealousy; it is my betrayal. They will stay to harvest the fuelgrass around the Stockton Sea; I will travel to the stars. A knock. A tall white man in a slate uniform, face drawn. It is time to leave. Mateo lands a waist-high hug on me. “I’ll follow you chola, to the stars.” But he can’t. He’ll be a middle-aged man when I reach T-1f. I blink back tears and leave without saying anything. Trappist-1 A collaborative effort Adam Łukawski (composer) & Julia Borzucka (visual artist) © 2017 click the image to access a video recording. Their collaboration was established to convey an artistic greeting from homo-sapiens to the TRAPPIST-1 system and its putative inhabitants. TRAPPIST-1, located in the Earth's vicinity becomes a symbol of a new era in our understanding of the Universe, namely the hope that if there are millions of planets capable to host life, that on some of them life did indeed emerge, and that we are not alone in Space. To illustrate how integrated the Universe can be in its complexity, the sound and the image complement each other and were produced as one integrated piece. The enormous, 12m long graphic (accessible below) is a literal interpretation of the electronic score. It can be followed by the public from left to right, from the beginning to the end, and was elaborated based on the pattern of the music. There are seven short parts in the piece that, like in Egyptian hieroglyphs, present a story about the new system. TRAPPIST-1, what is it? Illustrated by Lepithec © 2017 From a text by Amaury Triaud. Colours by Mara Versions exist in English (below), French, Russian, and Italian. Released under Creative Commons Licence (see the end). An Ode to 7 Orbs by Sean Raymond © 2017 Wake up now people, I’ve got some big news! You won’t want to miss this. You don’t want to snooze. We just found some planets while we were stargazing Gather 'round, listen up. These ones are amazing! And it’s not just one new planet. There are seven! All orbiting one star up there in the heavens. (Like in Spinal Tap this thing goes to eleven…) The thing ‘bout this system that just makes us squeal, All seven are Earth-sized. Now, that’s a big deal! And four of those planets could have the conditions For liquid water! (based on their positions). “How did you find these new planets?” you ask Well, let me first say it was no easy task To start off, we made a long list of stars. Then, We measured their brightness again and again. Most of the stars just looked awfully boring They stayed the same brightness. They weren’t worth exploring. The ones we were looking for had little blips Their brightness stayed constant except for small dips Each dip is a planet that, just as it passes In front of the star, blocks some light from our glasses The brightness we measure goes blip every time The planet goes once around. Then it re-aligns. (Another way that you can think of the dips: Each blip is like a single tiny eclipse) Armed with the star’s brightness, we measured and figured How big are the planets and how they’re configured. This new star with planets is called TRAPPIST-1 It’s not a star that is at all like the Sun It’s much much much smaller, and also less hot Two thousand times fainter. (Now that is a lot). An “ultracool dwarf” star they call it. And hey, It’s just about 40-odd light years away. The planets have letters for names. Now, you see, From outside to in it’s h, g, f, e, d, And, yes, as you guessed, after that, c and b (The first one’s called b. There is no planet a. The “a” is reserved for the star, by the way). All seven planets are close to their star. They orbit real fast since they’re not very far Planet b’s year: one and a half Earth days. If you lived there you’d have all sorts of birthdays! Stand on a planet in the TRAPPIST-1 system The planets you’d see in the sky – you can’t miss ‘em! Their orbits are so close that they’d each appear As big as the full Moon! Bigger when they’re near. (Imagine the werewolf problem they must fear!) The Sun in the sky would stay in the same place. The planets’ always show the star the same face The planets would shift and sometimes look like crescents Just a peek of that’s sky’s like an antidepressant! The two inner planets, planets b and c. Are too hot for oceans. Water would be steam. But the next four planets: d, e, f, and g Are all at about the right place for a sea. They could have liquid water, although We don’t know if they even have H2 or O. There’s plenty of planets out there that are dry Just look at that big red dot up in Earth’s sky. That’s Mars, it’s got water but only a trace And Venus, of course, is a hot hot dry place. The planets’ orbits were not set by chance They seem to be following a cool cosmic dance Take for example planets d and e When e completes two orbits, d has done three. They meet up again at the very same place This orbital resonance is common in space. Each pair of planets is in resonance. So, It’s like the whole system is doing a tango! We think that a resonant configuration Is a signpost of the planets’ migration That means that the planets’ orbits shifted While they were forming, inward they drifted. One last cool thing I really want to say-o TRAPPIST-1’s actually linked with Galileo! He discovered Jupiter’s four big old moons That you can see with good binoculars too. The TRAPPIST-1’s planets are much farther out But take about the same time to go around. Now let’s wrap up with a ditty for later It’s written for you if you’re a planet hater “Planets”, you say, “no big deal. There’s a zillion. Eight in our Solar System and a billion In orbit around other stars in the sky Why should I care about this one little guy?” I’d answer your question with a look back at history Discovering new planets may help solve a big mystery. Are we all alone? Is there other smart life? (Do I have an alien doppelganger and wife?) How can we answer this key age-old question? It’s not at all simple. But here’s a suggestion Any life out there will need its own planet Maybe with oceans or ice caps or granite. We now have the telescopes, tools and techniques To find other planets and take a sneak peak To try to find out if the Earth is unique.

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