Kepler-42
 Artist's impression of the Kepler-42 (KOI-961) system Credit: NASA |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Cygnus |
| Right ascension | 19h 28m 52.56s |
| Declination | 44° 37′ 0.96″ |
| Apparent magnitude (V) | 16.12 |
| Characteristics | |
| Spectral type | M5V |
| Astrometry | |
| Radial velocity (Rv) | −84.48±0.2 km/s |
| Proper motion (μ) |
RA: 84 mas/yr Dec.: −423 mas/yr |
| Distance | 126±20.5ly (38.7±6.3 pc) |
| Details | |
| Mass | 0.13±0.05 M☉ |
| Radius | 0.17±0.04 R☉ |
| Luminosity | 2.40x10−3.0±0.3 L☉ |
| Temperature | 3068±174 K |
| Metallicity | [Fe/H] =−0.48±0.17 |
| Rotational velocity (v sin i) | 2.9±0.4 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
| KIC | data |
Kepler-42, formerly known as KOI-961, is a red dwarf located in the constellation Cygnus and approximately 126 light years from the Sun. It has three known extrasolar planets, all of which are smaller than Earth in radius, and likely also in mass.
Kepler-42's mass is estimated to be 0.13 times that of the Sun, and to have a radius 0.17 times that of the Sun, that is, just 1.7 times that of the gas giant Jupiter. Due to its small radius and hence surface area, the luminosity of Kepler-42 is only 0.24% of that of the Sun. Its metallicity is one third of the Sun. Kepler-42 has an appreciable proper motion of up to 431±8 mas/yr. Due to its small size and low temperature, the star's habitable zone is much closer to the star than Earth is to the Sun.
On 10 January 2012, using the Kepler Space Telescope three transiting planets were discovered in orbit around Kepler-42. These planets' radii range from approximately those of Mars to Venus. The Kepler-42 system is only the second known system containing planets of Earth's radius or smaller (the first was the Kepler-20 system pictured at left). These planets' orbits are also compact, making the system (whose host star itself has a radius comparable to those of some hot Jupiters) resemble the moon systems of giant planets such as Jupiter or Saturn more than it does the Solar System. Despite these planets' small size and the star's being one of the faintest stars in Kepler field with confirmed planets, the detection of these planets was possible due to small size of the star, causing these planets to block a larger proportion of starlight during their transits.
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