Kepler-444

Kepler-444 (or KOI-3158, KIC 6278762, 2MASS J19190052+4138043, BD+41°3306)[8] is a triple star system, estimated to be 11.2 billion years old (more than 80% of the age of the universe),[10] approximately 119 light-years (36 pc) away from Earth in the constellation Lyra. On 27 January 2015, the Kepler spacecraft is reported to have confirmed the detection of five sub-Earth-sized rocky exoplanets orbiting the main star. The star is a K type star.[11][12][13][10][14] 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.[11]

Kepler-444
Observation data
Epoch J2000      Equinox 2000
Constellation Lyra
Right ascension 19h 19m 00.5488s[1]
Declination +41° 38′ 04.5816″[1]
Apparent magnitude (V) 8.86[2]
Characteristics
Spectral type K0V[3]
Astrometry
Radial velocity (Rv)−123.05±0.17[4] km/s
Proper motion (μ) RA: 94.682±0.055[1] mas/yr
Dec.: −632.202±0.051[1] mas/yr
Parallax (π)27.4137 ± 0.0295[1] mas
Distance119.0 ± 0.1 ly
(36.48 ± 0.04 pc)
Orbit[4]
PrimaryA
CompanionBC
Period (P)198+8
−9 yr
Semi-major axis (a)36.7+0.7
−0.9 AU
Eccentricity (e)0.864±0.023
Inclination (i)90.4+3.4
−3.6°
Longitude of the node (Ω)73.1±0.9°
Periastron epoch (T)2488500±900
Argument of periastron (ω)
(secondary)		342.8+3.2
−2.6°
Details
A
Mass0.754±0.030[5] M☉
Radius0.753±0.010[5] R☉
Surface gravity (log g)4.595±0.060[6] cgs
Temperature5046±74.0[6] K
Metallicity [Fe/H]−0.55±0.07[6] dex
Rotation49.40±6.04 d[7]
Age11.00±0.8[5] Gyr
B
Mass0.29±0.03[4] M☉
Surface gravity (log g)5.0±0.2[6] cgs
Temperature3,464±200[6] K
C
Mass0.25±0.03[4] M☉
Surface gravity (log g)~5[6] cgs
Temperature3,500 - 4,000[6] K
Other designations
BD+41°3306, WDS J19190+4138, KOI-3158, KIC 6278762, 2MASS J19190052+4138043
Kepler-444A: Gaia DR2 2101486923385239808, HIP 94931, LHS 3450, TYC 3129-00329-1, 2MASS J19190052+4138043[8]
Kepler-444BC: Gaia DR2 2101486923382009472[9]
Database references
SIMBADdata
B/C

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.[15]

Characteristics

The star, Kepler-444, is approximately 11.2 billion years old, whereas the Sun is only 4.6 billion years old. The age is that of Kepler-444 A, an orange main sequence star of spectral type K0.[16]

The original research on Kepler-444 was published in The Astrophysical Journal on 27 January 2015 under the title "An ancient extrasolar system with five sub-Earth-size planets" by a team of 40 authors, the abstract reads as follows:[6]

The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations. We use asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that Kepler-444 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, leaving open the possibility for the existence of ancient life in the Galaxy. The age of Kepler-444 not only suggests that thick-disk stars were among the hosts to the first Galactic planets, but may also help to pinpoint the beginning of the era of planet formation." The star is believed to have 2 M dwarfs in orbit around it with the fainter companion 1.8 arc-seconds from the main star.

Stellar system

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 198 year orbit. The pair comes within 5 AU of the primary potentially severely truncating the protoplanetary disk from which the planets formed at 1–2 AU. This would have depleted the availability of solid material to form the observed planets.[4]

Planetary system

All five rocky exoplanets (Kepler-444b; Kepler-444c; Kepler-444d; Kepler-444e; Kepler-444f) are confirmed,[14] smaller than the size of Venus (but bigger than Mercury) and each of the exoplanets completes an orbit around the host star in less than 10 days.[11][10] The system is also very compact and Kepler-444b is the smallest at 0.403 earth diameters, and even the furthest planet, Kepler-444f, still orbits closer to the star than Mercury is to the Sun.[16] 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.[11] To keep known planetary system stable, no additional giant planets can be located within 5.5 AU from the parent star.[17]

The Kepler-444 planetary system[14][18]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b — 0.04178 3.60001053 0.16 88° 0.4 R⊕
c — 0.04881 4.5458841 0.31 88.2° 0.497 R⊕
d 0.036+0.065
−0.020 M⊕		 0.06 6.189392 0.18 88.16° 0.53 R⊕
e 0.034+0.059
−0.019 M⊕		 0.0696 7.743493 0.1 89.13° 0.546 R⊕
f — 0.0811 9.740486 0.29 87.96° 0.741 R⊕

See also

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "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. Gaia DR2 record for this source at VizieR.
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.</ref
  3. Wilson, O. C. (1962). "Relationship Between Colors and Spectra of Late Main-Sequence Stars". The Astrophysical Journal. 136: 793. Bibcode:1962ApJ...136..793W. doi:10.1086/147437.
  4. Dupuy, Trent J.; et al. (2016). "Orbital Architectures of Planet-Hosting Binaries. I. Forming Five Small Planets in the Truncated Disk of Kepler-444A". The Astrophysical Journal. 817 (1). 80. arXiv:1512.03428. Bibcode:2016ApJ...817...80D. doi:10.3847/0004-637X/817/1/80.
  5. Buldgen, G.; et al. (2019). "Revisiting Kepler-444. I. Seismic modeling and inversions of stellar structure". Astronomy & Astrophysics. 630. A126. arXiv:1907.10315. Bibcode:2019A&A...630A.126B. doi:10.1051/0004-6361/201936126. S2CID 198229778.
  6. Campante, T. L.; et al. (2015). "An Ancient Extrasolar System with Five Sub-Earth-size Planets". The Astrophysical Journal. 799 (2). 170. arXiv:1501.06227. Bibcode:2015ApJ...799..170C. doi:10.1088/0004-637X/799/2/170.
  7. Mazeh, Tsevi; et al. (2015). "Photometric Amplitude Distribution of Stellar Rotation of KOIs—Indication for Spin-Orbit Alignment of Cool Stars and High Obliquity for Hot Stars". The Astrophysical Journal. 801 (1). 3. arXiv:1501.01288. Bibcode:2015ApJ...801....3M. doi:10.1088/0004-637X/801/1/3.
  8. "BD+41 3306". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 August 2020.
  9. "BD+41 3306B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 August 2020.
  10. Wall, Mike (27 January 2015). "Found! 5 Ancient Alien Planets Nearly As Old As the Universe". Space.com. Retrieved 27 January 2015.
  11. Johnson, Michele (28 January 2015). "Astronomers Discover Ancient System with Five Small Planets". NASA. Retrieved 29 January 2015.
  12. Dunn, Marcia (27 January 2015). "Astronomers find solar system more than double ours in age". AP News. Retrieved 27 January 2015.
  13. Atkinson, Nancy (27 January 2015). "Oldest Planetary System Discovered, Improving the Chances for Intelligent Life Everywhere". Universe Today. Retrieved 27 January 2015.
  14. Staff (27 January 2015). "Exoplanet Catalog". Extrasolar Planets Encyclopaedia. Retrieved 27 January 2015.
  15. Staff (8 November 2013). "Second Kepler Science Conference - NASA Ames Research Center, Mountain View, CA - Nov. 4-8, 2013 - Agenda". Caltech. Retrieved 28 January 2014.
  16. Phil, Plait (28 January 2015). "Astronomers Find Ancient Earth-Sized Planets in Our Galactic Backyard". Slate. Retrieved 28 January 2015.
  17. Becker, Juliette C.; Adams, Fred C. (2017), "Effects of Unseen Additional Planetary Perturbers on Compact Extrasolar Planetary Systems", Monthly Notices of the Royal Astronomical Society, 468 (1): 549–563, arXiv:1702.07714, Bibcode:2017MNRAS.468..549B, doi:10.1093/mnras/stx461, S2CID 119325005
  18. Mills, Sean M.; Fabrycky, Daniel C. (2017). "Mass, Density, and Formation Constraints in the Compact, Sub-Earth Kepler-444 System including Two Mars-mass Planets". The Astrophysical Journal Letters. 838 (1). L11. arXiv:1703.03417. Bibcode:2017ApJ...838L..11M. doi:10.3847/2041-8213/aa6543.

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