Observation data Epoch J2000 Equinox 2000 | |
---|---|
Constellation | Lyra [2] |
Kepler-444 A | |
Right ascension | 19h 19m 00.5489s [3] |
Declination | +41° 38′ 04.582″ [3] |
Apparent magnitude (V) | 8.86 [4] |
Kepler-444 B/C | |
Right ascension | 19h 19m 00.3922s [5] |
Declination | +41° 38′ 04.013″ [5] |
Characteristics | |
Spectral type | K0V [6] |
Astrometry | |
Kepler-444 A | |
Radial velocity (Rv) | −123.05±0.17 [7] km/s |
Proper motion (μ) |
RA: 94.639(13)
mas/
yr
[3] Dec.: −632.269(14) mas/ yr [3] |
Parallax (π) | 27.3578 ± 0.0125 mas [3] |
Distance | 119.22 ± 0.05
ly (36.55 ± 0.02 pc) |
Kepler-444 B/C | |
Proper motion (μ) |
RA: 94.508(55)
mas/
yr
[5] Dec.: −630.781(78) mas/ yr [5] |
Parallax (π) | 27.6079 ± 0.0545 mas [5] |
Distance | 118.1 ± 0.2
ly (36.22 ± 0.07 pc) |
Orbit [1] | |
Primary | A |
Companion | BC |
Period (P) | 324+31 −25 yr |
Semi-major axis (a) | 52.2+3.3 −2.7 AU |
Eccentricity (e) | 0.55+0.05 −0.05 |
Inclination (i) | 85.4+0.3 −0.4° |
Longitude of the node (Ω) | 250.7+0.2 −0.2° |
Periastron epoch (T) | JD 2537060+10881 −8533 |
Argument of periastron (ω) (secondary) | 227.3+6.5 −5.2° |
Details | |
A | |
Mass | 0.754±0.030 [8] M☉ |
Radius | 0.753±0.010 [8] R☉ |
Surface gravity (log g) | 4.595±0.060 [2] cgs |
Temperature | 5046±74.0 [2] K |
Metallicity [Fe/H] | −0.55±0.07 [2] dex |
Rotation | 49.40±6.04 d [9] |
Age | 11.00±0.8 [8] Gyr |
B | |
Mass | 0.307+0.009 −0.008 [1] M☉ |
Surface gravity (log g) | 5.0±0.2 [2] cgs |
Temperature | 3,464±200 [2] K |
C | |
Mass | 0.296±0.008 [1] M☉ |
Surface gravity (log g) | ~5 [2] cgs |
Temperature | 3,500 - 4,000 [2] K |
Other designations | |
Kepler-444A: Gaia DR2 2101486923385239808, HIP 94931, LHS 3450, TYC 3129-00329-1, 2MASS J19190052+4138043 [10] | |
Kepler-444BC: Gaia DR2 2101486923382009472 [11] | |
Database references | |
SIMBAD | data |
B/C |
Kepler-444 (or KOI-3158, KIC 6278762, 2MASS J19190052+4138043, BD+41°3306) [10] is a triple star system, estimated to be 11.2 billion years old (more than 80% of the age of the universe), [12] 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 main sequence star. [13] [14] [15] [12] [16] All of the planets are far too close to their star to harbour life forms. [13]
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. [17]
Characterization of the host star with asteroseismology was supported in part by the Nonprofit Adopt a Star program operated by White Dwarf Research Corporation, a crowd funded non-profit organization. [15]
On 28 January 2015, astronomers using data from NASA's Kepler Mission 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 Earth.
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. [18] 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 on 27 January 2015 under the title "An ancient extrasolar system with five sub-Earth-size planets" by a team of 40 authors. [2]
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 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. [1]
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. [7]
All five rocky exoplanets (Kepler-444b; Kepler-444c; Kepler-444d; Kepler-444e; Kepler-444f) are confirmed, [16] 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. [13] [12] 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 Sun. [18] 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. [13] To keep the known planetary system stable, no additional giant planets can be located within 5.5 AU of the parent star. [20]
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.
Companion (in order from star) |
Mass |
Semimajor axis ( AU) |
Orbital period ( days) |
Eccentricity | Inclination | Radius |
---|---|---|---|---|---|---|
b | — | 0.04178 | 3.600105+0.000031 −0.000037 |
0.16 | 88 ° | 0.406±0.013 R🜨 |
c | — | 0.04881 | 4.545876±0.000031 | 0.31 | 88.2 ° | 0.521±0.017 R🜨 |
d | 0.036+0.065 −0.020 M🜨 |
0.06 | 6.189437+0.000053 −0.000037 |
0.18 | 88.16 ° | 0.54±0.017 R🜨 |
e | 0.034+0.059 −0.019 M🜨 |
0.0696 | 7.743467+0.00006 −0.0001 |
0.1 | 89.13 ° | 0.555+0.018 −0.016 R🜨 |
f | — | 0.0811 | 9.740501+0.000078 −0.000026 |
0.29 | 87.96 ° | 0.767±0.025 R🜨 |