Kepler-444 (or KOI-3158, KIC 6278762, 2MASS J19190052+4138043, BD+41°3306) is a

triple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...

, estimated to be 11.2 billion years old (more than 80% of the age of the

universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

), approximately 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 ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Lyra , from ; pronounced: ) is a small constellation. It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union. Lyra was often represented on star ...

. On 27 January 2015, the ''Kepler'' spacecraft is reported to have confirmed the detection of five sub-Earth-sized

rocky ''Rocky'' is a 1976 American independent film, independent sports drama film directed by John G. Avildsen and written by and starring Sylvester Stallone. It is the first installment in the Rocky (film series), ''Rocky'' franchise and also star ...

exoplanets 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 detec ...

orbiting the main star. The star is a

K-type main sequence star A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("r ...

. All of the planets are far too close to their star to harbour life forms.

Discovery

Preliminary results of the planetary system around Kepler-444 were first announced at the second Kepler Science Conference in 2013. At that conference, the star was known as KOI-3158. Characterization of the host star with asteroseismology was supported in part by the

Nonprofit Adopt a Star Nonprofit Adopt a Star is a charitable fundraising program operated by White Dwarf Research Corporation, a 501c3 nonprofit organization based in Golden, Colorado USA. The program features the targets of NASA space telescopes that are searching ...

program operated by White Dwarf Research Corporation, a crowd funded non-profit organization.

History

On 28 January 2015, astronomers using data from NASA's

Kepler Mission The Kepler space telescope is a defunct space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

discovered an ancient triple star system with five Earth-sized planets in Kepler-444. Evidential speculations in research show Kepler-444 formed 11.2 billion years ago, when the universe was less than 20 percent of its current age, making it two and a half times older than the

Characteristics

The star, Kepler-444, is approximately 11.2 billion years old, whereas the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

is only 4.6 billion years old. The age is that of Kepler-444 A, an orange main sequence star of spectral type K0. Despite this great age, it is in middle of its main-sequence lifespan, much like the Sun. The original research on Kepler-444 was published in ''

The Astrophysical Journal ''The Astrophysical Journal'' (''ApJ'') is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler. The journal discontinued its print edition and ...

'' on 27 January 2015 under the title "An ancient extrasolar system with five sub-Earth-size planets" by a team of 40 authors.

Stellar system

Radial velocity time series of Kepler 444

The Kepler-444 system consists of the planet hosting primary and a pair of M-dwarf stars. The M-dwarfs orbit each other at a distance of less than 0.3 AU while the pair orbits the primary in a highly

eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off- center, in geometry * Eccentricity (graph theory) of a ...

324-year orbit. The pair comes within 23.55 AU of the primary potentially truncating the protoplanetary disk from which the planets formed at 8 AU. This would have depleted the availability of solid material to form the observed planets. Previous stellar orbit solution was ever more extreme, period was shorter (211 years) and eccentricity was much larger (e=0.865), moving periastron to 5 AU, severely reducing the estimated protoplanetary disk size to 1–2 AU and its estimated mass from ~600 to ~4 Earth masses.

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 of Kepler-444 show a linear trend, which aligns well with the orbit outlined by Dupuy et al. (see diagram above)

Planetary system

All five rocky exoplanets (Kepler-444b; Kepler-444c; Kepler-444d; Kepler-444e; Kepler-444f) are confirmed, smaller than the size of

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

(but bigger than Mercury) and each of the exoplanets completes an orbit around the host star in less than 10 days. Thus, the planetary system is very compact, as even the furthest known planet, Kepler-444f, still orbits closer to the star than Mercury is to the

. According to NASA, no life as we know it could exist on these hot exoplanets, due to their close orbital distances to the host star. To keep the known planetary system stable, no additional giant planets can be located within 5.5 AU of the parent star. Moreover, the system is pervaded by high-order resonance chain: period ratios are 4:5, 3:4, 4:5, 4:5. This tight chain is unperturbed and very likely continues farther from Kepler-444A. A marginally significant peak appears at 72 days in the radial velocity data when the linear trend attributed to the stellar companions is subtracted. However, this signal suggests an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

that is unphysically high, leading to orbits that would intersect the known planets. The signal likely stems from complexities within the long-term radial velocity signal of the Kepler-444 ABC system and may also be associated with the orbit of the BC pair.

Notes

References

External links

NASA – Kepler-444/KOI-3158
at The NASA Exoplanet Archive
NASA – Kepler-444bcdef
at

Extrasolar Planets Encyclopaedia The Extrasolar Planets Encyclopaedia (also known as Encyclopaedia of exoplanetary systems and Catalogue of Exoplanets) is an astronomy website, founded in Paris, France at the Meudon Observatory by Jean Schneider in February 1995, which maintains ...

{{Sky, 19, 19, 01.0, +, 41, 38, 05, 117 Lyra Planetary systems with five confirmed planets K-type main-sequence stars 3158 Planetary transit variables J19190052+4138043 94931 Durchmusterung objects M-type main-sequence stars Triple star systems TIC objects