LTT 1445


LTT 1445 A,BC
LTT 1445 HST ACS F330W.png
Hubble ACS/HRC image showing all three stars. Upper left is LTT 1445 A and in the lower right part of the image is the LTT 1445 BC pair.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Eridanus
LTT 1445 A
Right ascension 03h 01m 51.39s[1]
Declination −16° 35′ 36.1″[1]
Apparent magnitude (V) 11.22 ± 0.02[1]
LTT 1445 BC
Right ascension 03h 01m 51.04s[1]
Declination –16° 35′ 31.1″[1]
Apparent magnitude (V) 11.37±0.03[1]
Spectral type M2.5+M3.0+M[2][1]
LTT 1445 A
Proper motion (μ) RA: -369.196 ± 0.140[3] mas/yr
Dec.: -268.510 ± 0.147[3] mas/yr
Parallax (π)145.5466 ± 0.0800[3] mas
Distance22.41 ± 0.01 ly
(6.871 ± 0.004 pc)
PrimaryLTT 1445 B
CompanionLTT 1445 C
Period (P)36.2 ± 5.3 yr
Semi-major axis (a)1.159 ± 0.076″
Eccentricity (e)0.50 ± 0.11
Inclination (i)89.64 ± 0.13°
Longitude of the node (Ω)137.63 ± 0.19°
Periastron epoch (T)2019.2 ± 1.7
Argument of periastron (ω)
209 ± 13°
MassA: 0.256 ± 0.014[1] M
B: 0.215 ± 0.014[1] M
C: 0.161 ± 0.014[1] M
RadiusA: 0.276+0.024
B: 0.236 ± 0.027[1] R
C: 0.197 ± 0.027[1] R
Luminosity (bolometric)A: 0.00805 ± 0.00035[1] L
Surface gravity (log g)A: 4.967+0.061
[1] cgs
TemperatureA: 3337 ± 150[1] K
Metallicity [Fe/H]A: -0.34 ± 0.08[1] dex
Other designations
BD-17 588, HIP 14101, WDS J03019-1633A,BC, IRAS 02595-1647, 2MASS J03015142-1635356, 2MASS J03015107-1635306, TIC 98796344, TOI 455, GJ 3192, GJ 3193
Database references

LTT 1445 is a triple M-dwarf system about 22 light-years distant[4] in the constellation Eridanus. The primary LTT 1445 A hosts two exoplanets- one discovered in 2019 that transits the star every 5.36 days, and another found in 2021 that transits the star every 3.12 days, close to a 12:7 resonance. As of August 2019 it is the second closest transiting exoplanet system discovered, with the closest being HD 219134 bc.[4]

Stellar system

All three stars in the system are M-dwarfs, with masses between 0.16 M and 0.26 M. LTT 1445 A and LTT 1445 BC are separated by about 34 astronomical units and orbit each other with a period of about 250 years. The BC pair orbit each other about every 36 years in an eccentric orbit (e= ~0.5). The alignment of the three stars and the edge-on orbit of the BC pair suggests co-planarity of the system. The existence of a transiting planet LTT 1445Ab suggests that the entire system is co-planar, with orbits in one plane.[1]

The TESS light curve showed stellar flares and rotational modulation due to starspots, likely on either the B or C component.[1][5]

Planetary system

LTT 1445Ab was discovered in June 2019[6] with data from the Transiting Exoplanet Survey Satellite by astrophysicists of the Harvard Center for Astrophysics.[4] The team obtained follow-up observations, including HARPS radial velocity measurements to constrain the mass of the planet. The planet orbits only one host star in a stable orbit. The planet likely has a rocky composition and because it orbits close to the M-dwarf, it has an equilibrium temperature of 433+28
Kelvin (160 °C; 320 °F).[1]

In July 2021, the mass of the planet was measured as 2.87±0.25 Earth masses, confirming an earthlike composition.[7] A second planet, LTT 1445Ac, was also found on a 3.1 day orbital period, with a mass of 1.54+0.20
Earth masses. Although it transits the star too, its smaller size made it difficult to detect before the radial velocity measurements, and still makes it difficult to estimate its exact size.[7] The planets orbit near a 12:7 orbital resonance with one another - Ac orbiting 11.988 times for every 7 orbits Ab makes - oscillating one full orbit away from a 'perfect' resonance every 104 years.

The LTT 1445A planetary system[1][7]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
c 1.54+0.20
3.12390 <0.223 87.43+0.18
b 2.87+0.26
5.35877 <0.110 89.68+0.22

See also


  1. ^ a b c d e f g h i j k l m n o p q r s t u v w Winters, Jennifer G.; Medina, Amber A.; Irwin, Jonathan M.; Charbonneau, David; Astudillo-Defru, Nicola; Horch, Elliott P.; Eastman, Jason D.; Vrijmoet, Eliot Halley; Henry, Todd J.; Diamond-Lowe, Hannah; Winston, Elaine (October 2019). "Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pc". The Astronomical Journal. 158 (4): 152. Bibcode:2019AJ....158..152W. doi:10.3847/1538-3881/ab364d. hdl:2144/39814. ISSN 0004-6256. S2CID 195584444.
  2. ^ Henry, Todd J.; Jao, Wei-Chun; Winters, Jennifer G.; Dieterich, Sergio B.; Finch, Charlie T.; Ianna, Philip A.; Riedel, Adric R.; Silverstein, Michele L.; Subasavage, John P.; Vrijmoet, Eliot Halley (June 2018). "The Solar Neighborhood XLIV: RECONS Discoveries within 10 parsecs". The Astronomical Journal. 155 (6): 265. arXiv:1804.07377. Bibcode:2018AJ....155..265H. doi:10.3847/1538-3881/aac262. ISSN 0004-6256. S2CID 53983430.
  3. ^ a b c Gaia Collaboration (2018-08-01). "Gaia Data Release 2 - Summary of the contents and survey properties". Astronomy & Astrophysics. 616: A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. ISSN 0004-6361. S2CID 49211658.
  4. ^ a b c Brennan, Pat. "Discovery Alert: Rocky Planet Swelters Under Three Red Suns". Exoplanet Exploration: Planets Beyond our Solar System. Retrieved 2020-02-13.
  5. ^ Howard, Ward S.; Corbett, Hank; Law, Nicholas M.; Ratzloff, Jeffrey K.; Glazier, Amy; Fors, Octavi; del Ser, Daniel; Haislip, Joshua (August 2019). "EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky". Astrophysical Journal. 881 (1): 9. arXiv:1904.10421. Bibcode:2019ApJ...881....9H. doi:10.3847/1538-4357/ab2767. ISSN 0004-637X. S2CID 128361715.
  6. ^ Winters, Jennifer G.; et al. (2019), "Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pc", The Astronomical Journal, 158 (4): 152, arXiv:1906.10147, doi:10.3847/1538-3881/ab364d, S2CID 195584444
  7. ^ a b c Winters, Jennifer G.; Cloutier, Ryan; Medina, Amber A.; Irwin, Jonathan M.; Charbonneau, David; Astudillo-Defru, Nicola; Bonfils, Xavier; Howard, Andrew W.; Isaacson, Howard; Bean, J. L.; Seifahrt, A.; Teske, J. K.; Eastman, Jason D.; Twicken, Joseph D.; Collins, K. A.; Jensen, E. L. N.; Quinn, S. N.; Payne, M. J.; Kristiansen, M. H.; Spencer, A.; Vanderburg, Andrew; Zechmeister, Mathias; Weiss, L. M.; Wang, S. X.; Wang, G.; Udry, Stéphane; Terentev, I. A.; Sturmer, J.; Stefansson, G.; Shectman, Stephen A.; Sefako, R.; Schwengeler, H. M.; Schwarz, R. P.; Scarsdale, N.; Rubenzahl, R. A.; Roy, A.; Rosenthal, L. J.; Robertson, P.; Petigura, Erik A.; Pepe, Francesco; Omohundro, M.; Murphy, J. M. A.; Murgas, Felipe; Movcnik, T.; Montet, B. T.; Mennickent, R.; Mayo, A. W.; Massey, B.; Lubin, J.; Lovis, Christophe; Lewin, P.; Kasper, D.; Kane, S. R.; Jenkins, J. M.; Huber, D.; Horne, K.; Hill, M. L.; Gorrini, P.; Giacalone, S.; Fulton, Benjamin J.; Forveille, Thierry; Figueira, Pedro; Fetherolf, T.; Dressing, Courtney D.; Díaz, Rodrigo F.; Delfosse, Xavier; Dalba, P. A.; Dai, F.; Cortes, C. C.; Crossfield, Ian J. M.; Crane, Jeffrey D.; Conti, D. M.; Collins, K. I.; Chontos, A.; Butler, R. Paul; Brown, P.; Brady, M.; Bouchy, François; Behmard, A.; Beard, C.; Batalha, Natalie M.; Almenara, José M. (30 July 2021). "A Second Planet Transiting LTT~1445A and a Determination of the Masses of Both Worlds". arXiv:2107.14737 [astro-ph.EP].