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 * ...

M-dwarf system about 22

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s 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 possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

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 describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...

. As of August 2019 it is the second closest transiting exoplanet system discovered, with the closest being

HD 219134 HD 219134 (also known as Gliese 892 or HR 8832) is a main-sequence star in the constellation of Cassiopeia. It is smaller and less luminous than the Sun, with a spectral class of K3V, which makes it an orange-hued star. HD 219134 is rel ...

bc.

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 or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

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 parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betw ...

(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. Howe ...

of the system. The existence of a transiting planet LTT 1445Ab 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 , ''asteriskos'', "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 voc ...

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.

Planetary system

LTT 1445Ab was discovered in June 2019 with data from the

Transiting Exoplanet Survey Satellite Transiting Exoplanet Survey Satellite (TESS, Explorer 95 or MIDEX-7) 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' ...

by astrophysicists of the Harvard Center for Astrophysics. The team obtained follow-up observations, including

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision echelle planet-finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. H ...

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

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 The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...

Kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...

(160 °C; 320 °F). In July 2021, the mass of the planet was measured as Earth masses, confirming an earthlike composition. A second planet, LTT 1445Ac, was also found 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 relationsh ...

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 confirmed in 2022, along with a 3rd planetary candidate on the 24.3 days orbit. Also, there is a gap between the orbit of this candidate and neighbouring LTT 1445Ab. If this gap is not empty, a still undiscovered fourth planet in it will be a Venus-twin, probably slightly smaller than Venus. It is worth note that LTT 1445Ad receives approx. 76% of Earth's flux and is possibly rocky, spending its full orbit near the middle of habitable zone. LTT 1445 Ad is the first known potentially habitable planet in a multiple star system and the nearest currently known one orbiting star with at least 0.2% of solar luminosity and earlier than M5V spectral type (though Luyten b is closer, at 1.2 earth insolations and with a significantly more dense atmosphere, its habitability is much less certain).

References

{{DEFAULTSORT:LTT 1445 14101 Triple star systems M-type main-sequence stars 455 Planetary systems with one confirmed planet 3 Eridanus (constellation) Durchmusterung objects

Stellar system

Planetary system

See also

References