LTT 1445

LTT 1445 is a triple M-dwarf system 22.4 light-years (6.9 parsecs) distant^[1] 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 October 2022 it is the second closest transiting exoplanet system discovered, with the closest being HD 219134 bc.^[7]

LTT 1445 A,BC

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 51.39367s[1]
Declination	−16° 35′ 36.0312″[1]
Apparent magnitude (V)	11.22±0.02[2]
LTT 1445 BC
Right ascension	03h 01m 51.04s[2]
Declination	−16° 35′ 31.1″[2]
Apparent magnitude (V)	11.37±0.03[2]
Characteristics
Spectral type	M2.5+M3.0+M[3][2]
Variable type	flare star (A & C)[4][5]
Astrometry
LTT 1445 A
Radial velocity (Rv)	−5.74±0.33[1] km/s
Proper motion (μ)	RA: −369.972 mas/yr[1] Dec.: −267.931 mas/yr[1]
Parallax (π)	145.6922±0.0244 mas[1]
Distance	22.387 ± 0.004 ly (6.864 ± 0.001 pc)
Orbit[2]
Primary	LTT 1445 B
Companion	LTT 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) (secondary)	209±13°
Details
A
Mass	0.257±0.014[6] M☉
Radius	0.271+0.019 −0.010[6] R☉
Luminosity (bolometric)	0.00805±0.00035[2] L☉
Surface gravity (log g)	4.967+0.061 −0.075[2] cgs
Temperature	3,337±150[2] K
Metallicity [Fe/H]	−0.34±0.08[2] dex
B
Mass	0.215±0.014[2] M☉
Radius	0.236±0.027[2] R☉
C
Mass	0.161±0.014[2] M☉
Radius	0.197±0.027[2] R☉
Rotation	1.4 d[6]
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
SIMBAD	The system
	A
	BC
Exoplanet Archive	data

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 transiting planets suggests that the entire system is co-planar, with orbits in one plane.^[2]

The TESS light curve showed stellar flares and rotational modulation due to starspots, likely on either the B or C component.^[2][8] Observations with Chandra showed that component C is the dominat X-ray source, with some contributions by component B.^[9] Flares are detected for component A in ultraviolet with Hubble and in x-rays with Chandra.^[4][10] Hubble observations also revealed an ultraviolet flare for component C, which was invisible at optical wavelengths.^[5]

Planetary system

LTT 1445 Ab

LTT 1445 Ab is an exoplanet located approximately 22 light years away from Earth. Astrophysicists of the Harvard Center for Astrophysics discovered it in June 2019 with data from the Transiting Exoplanet Survey Satellite.^[11][2] The team obtained follow-up observations, including HARPS radial velocity measurements to constrain the mass of the planet.

LTT 1445 Ab takes 5 days to orbit its star.^[11][12][2]

In July 2021, the mass of the planet was measured as 2.87±0.25 Earth masses, confirming an Earth-like composition.^[13] LTT 1445 Ab likely has a rocky composition, and because it orbits close to the M-dwarf, it has an equilibrium temperature of 431±23 K (158 °C; 316 °F).^[6]

In 2022, a planetary transmission spectrum showed no evidence for an atmosphere, although an atmosphere with high altitude hazes cannot be ruled out yet.^[14] In 2025 a transmission spectrum with Hubble was published. The spectrum is consistent with a flat line. Only the infrared shows potential features consistent with hydrogen cyanide. Some retrievals weakly favour an atmosphere, but these could be stellar contamination.^[5]

A thermal emission spectrum of LTT 1445 Ab was detected with JWST MIRI low resultion spectroscopy (LRS). The observation observed the planet during the secondary eclipse at the 5-12 μm range. During a secondary eclipse the planet disappears behind the star. This allowed the scientists to determine the dayside brightness temperature of 525 ± 15 K (252 °C; 485 °F). This measurement is consistent with a dark rocky surface. The observations disfavour a very thick CO₂ atmosphere, but it is uncertain if a moderately thin atmosphere is possible (atmospheres like those on Mars, Titan or Earth).^[15]

LTT 1445 Ac

A second planet, LTT 1445 Ac, was also found in 2021 on a 3.12 day orbital period, with a mass of 1.54+0.20
−0.19 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. 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.^[13] The planet's existence was independently confirmed in 2022.^[7]

In 2023, observations with the Hubble Space Telescope allowed a more precise determination of the planet's size, supporting a rocky composition for both planets. Its equilibrium temperature is 516±28 K (243 °C; 469 °F).^[6]

LTT 1445 Ad

A third planetary candidate on a 24.3-day orbit, LTT 1445 Ad, was found in 2022. This is a possibly rocky super-Earth orbiting within the habitable zone.^[7]

The LTT 1445 A planetary system^[7][6]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
c	1.37±0.19 M🜨	0.02659+0.00047 −0.00049	3.1238994	<0.223[13]	87.46+0.13 −0.21°	1.07+0.10 −0.07 R🜨
b	2.73+0.25 −0.23 M🜨	0.03810+0.00067 −0.00070	5.3587635	<0.110[13]	89.53+0.33 −0.40°	1.34+0.11 −0.06 R🜨
d	≥2.72±0.75 M🜨	0.09±0.02	24.30+0.03 −0.08	—	—	—

See also

• List of star systems within 20–25 light-years
• List of nearest exoplanets
• EZ Aquarii nearby M-dwarf triple
• GJ 1245 nearby M-dwarf triple^[2]
• Gliese 667 Cc