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TRAPPIST-1

Coordinates: Sky map 23h 06m 29.383s, −05° 02′ 28.59″
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TRAPPIST-1[1]

An artist's impression of TRAPPIST-1 and its seven planets
Observation data
Epoch       Equinox
Constellation Aquarius
Right ascension 23h 06m 29.283s[2]
Declination –05° 02′ 28.59″[2]
Apparent magnitude (V) 18.80
Characteristics
Spectral type M8V[3]
M8.2V[note 1]
V−R color index 2.33
R−I color index 2.47
Astrometry
Radial velocity (Rv)−56.3 km/s
Parallax (π)82.58 mas
Distance39.5 ± 1.3 ly
(12.1 ± 0.4 pc)
Absolute magnitude (MV)18.4 ± 0.1
Details
Mass0.08 ± 0.009 M☉
Radius0.114 ± 0.006 R☉
Luminosity (bolometric)0.000525±0.000036[4] L☉
Luminosity (visual, LV)0.00000373[note 2] L☉
Surface gravity (log g)~ 5.227[note 3][5] cgs
Temperature2550 ± 55 K
Metallicity0.04 ± 0.08
Rotation1.40 ± 0.05 days
Rotational velocity (v sin i)6 ± 2 km/s
Age> 1 Gyr
Other designations
2MASS J23062928-0502285, 2MASSI J2306292-050227, 2MASSW J2306292-050227, 2MUDC 12171
Database references
SIMBADdata

TRAPPIST-1, also designated as 2MASS J23062928-0502285,[6] is an ultra-cool dwarf star,[4][7] slightly larger than the planet Jupiter, located 39.5 ly (12.1 pc; 3.74×1014 km; 2.32×1014 mi), from the Sun in the constellation Aquarius.[8][9] As of February 2017, the dwarf star has been shown to host seven terrestrial planets, a larger number than detected in any other planetary system.[10][11]

Astronomers first discovered three Earth-sized planets orbiting the dwarf star in 2015. A team led by Michaël Gillon at the University of Liège in Belgium detected the planets using transit photometry with the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at the La Silla Observatory in Chile.[12][7][13] On 22 February 2017, astronomers announced four additional exoplanets around TRAPPIST-1.[14] This work used the NASA Spitzer Space Telescope and the Very Large Telescope at Paranal, among others, and brought the total number of planets to seven, of which three are considered to be within its habitable zone; conceivably, the others also could be habitable so far as they may possess liquid water somewhere on their surface.[15][16] If any of the habitable zone planets have an atmosphere similar to that of the Earth, they are expected to possess oceans. However, this is unlikely as these planets are near enough to their star to be exposed to intense x-ray and extreme UV radiation, sufficient to have potentially stripped these planets dry in a short time.

Discovery and nomenclature

The star at the center of the system was discovered in 1999 during the Two Micron All-Sky Survey (2MASS).[17] It was entered in the subsequent catalog with the designation "2MASS J23062928-0502285". The numbers refer to the right ascension and declination of the star's position in the sky and the "J" refers to the Julian Epoch.

The system was later studied by a team at the University of Liège, who made their initial observations using the Transiting Planets and Planetesimals Small Telescope–South from September to December 2015 and published their findings in the May 2016 issue of the journal Nature.[12][4] The robotic telescope's acronym of TRAPPIST underscores the Belgian origins of the project, denoting as it does the contemplative Roman Catholic religious order of Trappists (the astronomers celebrated their discovery with a round of the contemplatives' Trappist beer,[18] which they hold in high regard).[19] Since the star hosted the first exoplanets discovered by this telescope, the discoverers accordingly designated it as "TRAPPIST-1".

The planets are designated in the order of their discovery, beginning with b for the first planet discovered, c for the second and so on.[20] Three planets around TRAPPIST-1 were first discovered and designated b, c and d in order of increasing orbital periods,[4] and the second batch of discoveries was similarly designated e to h.

On 23 February 2017, the discovery was celebrated with an animated Google Doodle created by Nate Swinehart.[21]

Stellar characteristics

TRAPPIST-1 is an ultra-cool dwarf star, of spectral class M8.0 ± 0.5, that is approximately 8% the mass of and 11% the radius of the Sun and, although slightly larger than Jupiter, about 84 times more massive.[22][4] It has a temperature of 2550 K and is at least 500 million years old (beyond this minimum, indicating the star is past its youthful active phase, the age is poorly constrained due to the very slow evolution of this class of stars).[4] In comparison, the Sun is about 4.6 billion years old[23] and has a temperature of 5778 K.[24]

Owing to its low luminosity, the star has the ability to live for up to 12 trillion years.[25] The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. Its luminosity is 0.05% of that of the Sun (L☉), most of which is emitted in the infrared spectrum.

Planetary system

In February 2017, astronomers announced that the planetary system of this star is composed of seven temperate terrestrial planets, of which five (b, c, e, f and g) are similar in size to Earth, and two (d and h) are intermediate in size between Mars (which has a diameter about half that of Earth) and Earth.[26] Three (e, f and g) orbit in the habitable zone.[26][27][28][29] The total mass of the six inner planets is about 0.02% the mass of TRAPPIST-1, a fraction similar to that for the Galilean satellites of Jupiter, suggesting perhaps a similar formation history.[26]

TRAPPIST-1 planetary system (red) in the constellation Aquarius (the Water Carrier).
TRAPPIST-1 planetary system, based on data about diameters, masses and distances from the host star (artist concept).
TRAPPIST-1 planetary system compared with the Sun, Jupiter and other related solar system bodies.
The TRAPPIST-1 planetary system[4][26]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 0.85±0.72 M🜨 0.01111 (1.66 mln km) 1.51087081 ± 0.00000060 < 0.081 89.65 ± 0.25° 1.086 ± 0.035 R🜨
c 1.38±0.61 M🜨 0.01522 (2.28 mln km) 2.4218233 ± 0.0000017 < 0.083 89.67 ± 0.17° 1.056 ± 0.035 R🜨
d 0.41±0.27 M🜨 0.021 ± 0.006 (3.14 mln km) 4.049610 ± 0.000063 < 0.070 89.75 ± 0.16° 0.772 ± 0.030 R🜨
e 0.62±0.58 M🜨 0.028 (4.19 mln km) 6.099615 ± 0.000011 < 0.085 89.86 ± 0.11° 0.918 ± 0.039 R🜨
f 0.68±0.18 M🜨 0.037 (5.54 mln km) 9.206690 ± 0.000015 < 0.063 89.680 ± 0.034° 1.045 ± 0.038 R🜨
g 1.34±0.88 M🜨 0.045 (6.73 mln km) 12.35294 ± 0.00012 < 0.061 89.710 ± 0.025° 1.127 ± 0.041 R🜨
h unknown (likely <1) M🜨 0.063+0.027
−0.013 (~9.4 mln km) 		20+15
−6 		unknown 89.80 ± 0.07° 0.755 ± 0.034 R🜨

The densities of the planets range from ~0.60 to ~1.17 times that of Earth (ρ⊕, 5.51 g/cm3), indicating predominantly rocky compositions. The error bars are too large to indicate whether a substantial component of volatiles is also included, except in the case of f, where the value (0.60±0.17 ρ⊕) "favors" the presence of a layer of ice and/or an extended atmosphere.[26]

All seven of TRAPPIST-1's planets orbit much closer than Mercury orbits the Sun, albeit much further than the Galilean satellites do around Jupiter.[30] The distance between the orbits of TRAPPIST-1b and TRAPPIST 1c is only 1.6 times the distance between the Earth and the Moon. The planets should appear prominently in each other's skies, and in some cases, appearing several times larger than the Moon appears from Earth.[29] A year on the closest planet passes in only 1.5 Earth days, while the sixth planet's year passes in only 12.3 days. The seventh planet's year is much less certain at 20+15
−6 days, because only a single transit has been observed. Young red dwarf stars are subject to frequent, intense flares that are likely to have stripped away the atmospheres of planets in such close orbits.[31]

Orbital near resonance

The orbits of planets b-g are nearly in resonance, having relative periods of approximately 24/15, 24/9, 24/6, 24/4 and 24/3, respectively, or nearest-neighbor period ratios (proceeding outward) of about 8/5, 5/3, 3/2, 3/2 and 4/3 (1.603, 1.672, 1.506, 1.509 and 1.342). This represents the longest known chain of near-resonant exoplanets, and is thought to have resulted from interactions between the planets as they migrated inward within the residual protoplanetary disk after forming at greater initial distances.[26] Such inward migration increases the odds of substantial amounts of water being present on these worlds. Due to the poorly-known orbital period of h, it is unknown if it is in an orbital resonance with the other six planets.

Strong X-ray and extreme UV irradiation of the system

An XMM-Newton X-ray study shows that the Earth-sized planets in the habitable zone of the star are subject to sufficient X-ray and extreme ultraviolet (EUV/XUV) irradiation to significantly alter their primary and perhaps secondary atmospheres.[32]

Spectroscopy of planetary atmospheres

Because of the system's relative proximity, the small size of the primary and the orbital alignments that produce transits, the atmospheres of TRAPPIST-1's planets are favorable targets for transmission spectroscopy investigation.[33]

The combined transmission spectrum of TRAPPIST-1 b and c, obtained by the HST, rules out a cloud-free hydrogen-dominated atmosphere for each planet, so they are unlikely to harbor an extended gas envelope unless it is cloudy out to high altitudes. Other atmospheric structures, from a cloud-free water vapor atmosphere to a Venus-like atmosphere, remain consistent with the featureless spectrum.[34]

Observations by future telescopes, such as the JWST or EELT, will be able to assess the greenhouse gas content of the atmospheres, allowing better estimation of surface conditions. They may also be able to detect biosignatures like ozone or methane[35] in the atmospheres of these planets, if life is present there.[8][36][37]

Water loss

TRAPPIST-1 b and c may have lost as much as 15 Earth oceans of water (although the actual loss would probably be lower) depending on their initial water contents. However, they may have retained enough water to remain habitable.[38]

Tidal locking

All seven planets are likely to be tidally locked (one side of each planet permanently facing the star),[26] making the development of life there "much more challenging".[10] A less likely possibility is that some may be trapped in a higher-order spin-orbit resonance. Tidally locked planets would typically have very large temperature differences between their permanently lit day sides and their permanently dark night sides, which could produce very strong winds circling the planets. The best places for life may be close to the mild twilight regions between the two sides, called the terminator line.

  • TRAPPIST-1 is a smaller (11% the size), fainter and redder star than the Sun.
    TRAPPIST-1 is a smaller (11% the size), fainter and redder star than the Sun.
  • TRAPPIST-1 planetary system (artist concept)[39]
    TRAPPIST-1 planetary system (artist concept)[39]
  • Planets transiting TRAPPIST-1 (artist concept)[40]
    Planets transiting TRAPPIST-1 (artist concept)[40]
  • Three planets orbiting TRAPPIST-1 (artist concept).
    Three planets orbiting TRAPPIST-1 (artist concept).
  • TRAPPIST-1c view (artist concept).
    TRAPPIST-1c view (artist concept).
  • TRAPPIST-1 planetary system (artist concept).
    TRAPPIST-1 planetary system (artist concept).
  • TRAPPIST-1 system compared to the solar system; all seven planets of TRAPPIST-1 could fit inside the orbit of Mercury.
    TRAPPIST-1 system compared to the solar system; all seven planets of TRAPPIST-1 could fit inside the orbit of Mercury.
  • Drops in brightness (astronomical transits) of TRAPPIST-1 over 20 days (September/October, 2016; Spitzer Space Telescope and others) due to the seven planets (noted on the bottom) blocking the star's light.
    Drops in brightness (astronomical transits) of TRAPPIST-1 over 20 days (September/October, 2016; Spitzer Space Telescope and others) due to the seven planets (noted on the bottom) blocking the star's light.
  • Dimming of TRAPPIST-1 due to its seven known planets - large planets, more dimming; distant ones, longer (Spitzer Space Telescope).
    Dimming of TRAPPIST-1 due to its seven known planets - large planets, more dimming; distant ones, longer (Spitzer Space Telescope).

Videos

  • Video (00:44) - view of trip from Earth to TRAPPIST-1 (artist concept).
  • Video (00:22) - view from one of the seven planets orbiting TRAPPIST-1 (artist concept).

See also

  • Active SETI, while interstellar travel to the star system is currently impossible, communication with potential extraterrestrials living on one of its planets within a human's lifespan could, hypothetically, be possible
  • Habitability of red dwarf systems
  • KIC 8462852, another star with notable transit data
  • Kepler-90, another star with 7 known transiting planets

Notes

  1. ^ based on photometric spectral type estimation
  2. ^ Taking the absolute visual magnitude of TRAPPIST-1 and the absolute visual magnitude of the Sun , the visual luminosity can be calculated by
  3. ^ The surface gravity is calculated directly from Newton's law of universal gravitation, which gives the formula where M is the mass of the object, r is its radius, and G is the gravitational constant.

References

  1. ^ "TRAPPIST-1b". Open Exoplanet Catalogue. Retrieved 2 May 2016.
  2. ^ a b Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (June 2003). "2MASS All Sky Catalog of point sources". VizieR Online Data Catalog. 2246. European Southern Observatory with data provided by the SAO/NASA Astrophysics Data System. Bibcode:2003yCat.2246....0C.
  3. ^ Costa, E.; Mendez, R.A.; Jao, W.-C.; Henry, T.J.; Subasavage, J.P.; Ianna, P.A. (4 August 2006). "The Solar Neighborhood. XVI. Parallaxes from CTIOPI: Final Results from the 1.5 m Telescope Program". The Astronomical Journal. 132 (3). The American Astronomical Society: 1234. Bibcode:2006AJ....132.1234C. doi:10.1086/505706.
  4. ^ a b c d e f g Gillon, M.; Jehin, E.; Lederer, S. M.; Delrez, L.; De Wit, J.; Burdanov, A.; Van Grootel, V.; Burgasser, A. J.; Triaud, A. H. M. J.; Opitom, C.; Demory, B.-O.; Sahu, D. K.; Bardalez Gagliuffi, D.; Magain, P.; Queloz, D. (2016). "Temperate Earth-sized planets transiting a nearby ultracool dwarf star" (PDF). Nature. 533 (7602): 221–224. Bibcode:2016Natur.533..221G. doi:10.1038/nature17448.
  5. ^ Viti, Serena; Jones, Hugh R. A. (November 1999). "Gravity dependence at the bottom of the main sequence". Astronomy and Astrophysics. 351: 1028–1035. Bibcode:1999A&A...351.1028V. Retrieved 6 May 2016.
  6. ^ *"2MASS J23062928-0502285". SIMBAD. Centre de données astronomiques de Strasbourg.
  7. ^ a b "Three Potentially Habitable Worlds Found Around Nearby Ultracool Dwarf Star – Currently the best place to search for life beyond the Solar System". European Southern Observatory.
  8. ^ a b Chang, Kenneth (22 February 2017). "7 Earth-Size Planets Identified in Orbit Around a Dwarf Star". New York Times. Retrieved 22 February 2017.
  9. ^ Staff (24 February 2017). "Twinkle, Twinkle Little Trappist". New York Times. Retrieved 27 February 2017.
  10. ^ a b Witze, A. (22 February 2017). "These seven alien worlds could help explain how planets form". Nature. doi:10.1038/nature.2017.21512.
  11. ^ Marchis, F. (22 February 2017). "Wonderful potentially habitable worlds around TRAPPIST-1". Planetary Society. Retrieved 25 February 2017.
  12. ^ a b "Could these newly-discovered planets orbiting an ultracool dwarf host life?". The Guardian. 2 May 2016.
  13. ^ "Three New Planets Are the Best Bets for Life". Popular Mechanics. 2 May 2016. Retrieved 2 May 2016.
  14. ^ TRAPPIST-1 System – Discovery of Earth-Like Planets – Check123, Video Encyclopedia, retrieved 23 February 2017
  15. ^ "Temperate Earth-Sized Planets Found in Extraordinarily Rich Planetary System TRAPPIST-1". SpaceRef. 22 February 2017. Retrieved 11 February 2017.
  16. ^ "NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star". Exoplanet Exploration: Planets Beyond our Solar System. NASA. Retrieved 22 February 2017.
  17. ^ Bryant, Tracey (22 February 2017). "Celestial Connection". University of Delaware.
  18. ^ Gramer, Robbie (22 February 2017). "News So Foreign It's Out of This World: Scientists Discover Seven New Potentially Habitable Planets". Foreign Policy.
  19. ^ "New National Telescope at La Silla—TRAPPIST to Scout the Sky and Uncover Exoplanets and Comets (eso1023 — Organisation Release)". www.eso.org. ESO. 8 June 2010. Retrieved 4 January 2015.
  20. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  21. ^ Radowitz, John von (23 February 2017). "Exoplanet discovery celebrated with Google Doodle after three planets found". mirror. Retrieved 23 February 2017.
  22. ^ Koberlein, Brian (22 February 2017). "Here's How Astronomers Found Seven Earth-Sized Planets Around A Dwarf Star". Forbes. Retrieved 26 February 2017.
  23. ^ Williams, Matt (24 September 2016). "What is the Life Cycle Of The Sun?". Universe Today. Retrieved 19 February 2011.
  24. ^ Cain, Fraser (23 December 2015). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  25. ^ Adams, Fred C.; Laughlin, Gregory; Graves, Genevieve J. M. "Red Dwarfs and the End of the Main Sequence". Gravitational Collapse: From Massive Stars to Planets. Revista Mexicana de Astronomía y Astrofísica. pp. 46–49. Bibcode:2004RMxAC..22...46A. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)
  26. ^ a b c d e f g Gillon, M.; Triaud, A. H. M. J.; Demory, B.-O.; Jehin, E.; Agol, E.; Deck, K. M.; Lederer, S. M.; De Wit, J.; Burdanov, A.; Ingalls, J. G.; Bolmont, E.; Leconte, J.; Raymond, S. N.; Selsis, F.; Turbet, M.; Barkaoui, K.; Burgasser, A.; Burleigh, M. R.; Carey, S. J.; Chaushev, A.; Copperwheat, C. M.; Delrez, L.; Fernandes, C. S.; Holdsworth, D. L.; Kotze, E. J.; Van Grootel, V.; Almleaky, Y.; Benkhaldoun, Z.; Magain, P.; Queloz, D. (2017). "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1" (PDF). Nature. 542 (7642): 456. doi:10.1038/nature21360.
  27. ^ "NASA Telescope Reveals Largest Batch of Earth-Size, Habitable-Zone Planets Around Single Star" (Press release). NASA.
  28. ^ "TRAPPIST-1 Planet Lineup". jpl.nasa.gov.
  29. ^ a b Wall, Mike (22 February 2017). "Major Discovery! 7 Earth-Size Alien Planets Circle Nearby Star". space.com.
  30. ^ Redd, Nola Taylor (24 February 2017). "TRAPPIST-1: System with 7 Earth-Size Exoplanets". Space.com.
  31. ^ Airapetian, Vladimir S.; Glocer, Alex; Khazanov, George V.; Loyd, R. O. P.; France, Kevin; Sojka, Jan; Danchi, William C.; Liemohn, Michael W. (1 January 2017). "How Hospitable Are Space Weather Affected Habitable Zones? The Role of Ion Escape". The Astrophysical Journal Letters. 836 (1): L3. Bibcode:2017ApJ...836L...3A. doi:10.3847/2041-8213/836/1/L3.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  32. ^ Wheatley, Peter J.; Louden, Tom; Bourrier, Vincent; Ehrenreich, David; Gillon, Michaël (8 October 2016) [14 Dec 2016]. "Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1". Monthly Notices of the Royal Astronomical Society: Letters. 465: L74. arXiv:1605.01564. Bibcode:2017MNRAS.465L..74W. doi:10.1093/mnrasl/slw192.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  33. ^ Gleiser, M. (23 February 2017). "Trappist-1 Planet Discovery Ignites Enthusiasm In Search For Alien Life". NPR. Retrieved 25 February 2017.
  34. ^ de Wit, Julien; Wakeford, Hannah R.; Gillon, Michaël; Lewis, Nikole K.; Valenti, Jeff A.; Demory, Brice-Olivier; Burgasser, Adam J.; Burdanov, Artem; Delrez, Laetitia; Jehin, Emmanuël; Lederer, Susan M.; Queloz, Didier; Triaud, Amaury H. M. J.; Van Grootel, Valérie (1 September 2016). "A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c". Nature. 537 (7618): 69–72. arXiv:1606.01103. Bibcode:2016Natur.537...69D. doi:10.1038/nature18641. PMID 27437572.
  35. ^ Swain, M. (2008). "Probing the Atmospheres of Exoplanets" (PDF). Hubble 2008: Science Year in Review. NASA. Retrieved 25 February 2017.
  36. ^ Osgood, M. (22 February 2017). "Sagan Institute director explains what life could be like near Trappist-1". Cornell University. Retrieved 25 February 2017.
  37. ^ Barstow, J. K.; Irwin, P. G. J. (26 May 2016). "Habitable worlds with JWST: transit spectroscopy of the TRAPPIST-1 system?". Monthly Notices of the Royal Astronomical Society: Letters. 461 (1): L92–L96. arXiv:1605.07352v2. doi:10.1093/mnrasl/slw109.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  38. ^ https://arxiv.org/abs/1605.00616 Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: Implications for the planets of TRAPPIST-1
  39. ^ "Ultracool Dwarf and the Seven Planets – Temperate Earth-sized Worlds Found in Extraordinarily Rich Planetary System". www.eso.org. Retrieved 22 February 2017.
  40. ^ "Artist's view of planets transiting red dwarf star in TRAPPIST-1 system". www.spacetelescope.org. Retrieved 21 July 2016.
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Further reading

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