LTT 1445 is a

triple Triple is used in several contexts to mean "threefold" or a " treble": Sports * Triple (baseball), a three-base hit * A basketball three-point field goal * A figure skating jump with three rotations * In bowling terms, three strikes in a row * I ...

M-dwarf system distant in the constellation Eridanus. The primary LTT 1445 A hosts two

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

s—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 Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...

. As of October 2022 it is the second closest transiting exoplanet system discovered, with the closest being

HD 219134 b HD 219134 b (or HR 8832 b) is one of at least five exoplanets orbiting HD 219134, a main-sequence star in the constellation of Cassiopeia. HD 219134 b has a size of about , and a density of 6.4 g/cm3 and orbits at 21.25 light-years away. The exo ...

Stellar system

All three stars in the system are M-dwarfs, with masses between 0.16 and 0.26 . LTT 1445 A and LTT 1445 BC are separated by about 34

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s 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 In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless quantity, dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circu ...

(e= ~0.5). The alignment of the three stars and the edge-on orbit of the BC pair suggests

co-planarity In geometry, a set of points in space are coplanar if there exists a geometric plane that contains them all. For example, three points are always coplanar, and if the points are distinct and non-collinear, the plane they determine is unique. How ...

of the system. The existence of transiting planets suggests that the entire system is co-planar, with orbits in one plane. The TESS light curve showed

stellar flare The asterisk ( ), from Late Latin , from Ancient Greek , , "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star. Computer scientists and mathematicians often vocalize it as st ...

s and rotational modulation due to

starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...

s, likely on either the B or C component. Observations with

Chandra Chandra (), also known as Soma (), is the Hindu god of the Moon, and is associated with the night, plants and vegetation. He is one of the Navagraha (nine planets of Hinduism) and Dikpala (guardians of the directions). Etymology and other ...

showed that component C is the dominat

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

source, with some contributions by component B. Flares are detected for component A in

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

with Hubble and in x-rays with Chandra. Hubble observations also revealed an ultraviolet flare for component C, which was invisible at optical wavelengths.

Planetary system

LTT 1445 Ab

LTT 1445 Ab is an

located approximately 22 light years away from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. Astrophysicists of the Harvard Center for Astrophysics discovered it in June 2019 with data from the

Transiting Exoplanet Survey Satellite Transiting Exoplanet Survey Satellite (TESS) is a space telescope for NASA's Explorer program, designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the Kepler mission. It was launched on ...

. The team obtained follow-up observations, including

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision Echelle grating, echelle planet-finding spectrograph installed in 2002 on the ESO 3.6 m Telescope, ESO's 3.6m telescope at La Silla Observatory in Chile. The First l ...

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

measurements to constrain the mass of the planet. LTT 1445 Ab takes 5 days to orbit its star, which in turn orbits two sibling stars, making a total of three stars in the system. In July 2021, the mass of the planet was measured as Earth masses, confirming an Earth-like composition. LTT 1445 Ab likely has a rocky composition, and because it orbits close to the M-dwarf, it has an

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, th ...

of (). In 2022, a planetary transmission spectrum showed no evidence for an atmosphere, although an atmosphere with high altitude hazes cannot be ruled out yet. 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 Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the chemical formula, formula HCN and structural formula . It is a highly toxic and flammable liquid that boiling, boils slightly above room temperature, at . HCN is ...

. Some retrievals weakly favour an atmosphere, but these could be stellar contamination. A thermal emission spectrum of LTT 1445 Ab was detected with

JWST The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, di ...

MIRI Miri () is a coastal city in north-eastern Sarawak, Malaysia, located near the border of Brunei, on the island of Borneo. The city covers an area of , located northeast of Kuching and southwest of Kota Kinabalu. Miri is the second largest ...

low resultion spectroscopy (LRS). The observation observed the planet during the secondary

eclipse An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ...

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 (). 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 Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

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 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 In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

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 planet's existence was independently confirmed in 2022. In 2023, observations with the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

allowed a more precise determination of the planet's size, supporting a rocky composition for both planets. Its equilibrium temperature is ().

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 A super-Earth is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to t ...

orbiting within the

habitable zone In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressu ...

References

{{DEFAULTSORT:LTT 1445 14101 Triple star systems M-type main-sequence stars

455 __NOTOC__ Year 455 ( CDLV) was a common year starting on Saturday of the Julian calendar. At the time, it was known as the Year of the Consulship of Valentinianus and Anthemius (or, less frequently, year 1208 ''Ab urbe condita''). The denomin ...