 Approximate size comparison of Kepler-438b (right) withEarth | |
| Discovery | |
|---|---|
| Discovered by | Kepler spacecraft |
| Discovery date | 2015[4] |
| Transit | |
| Orbital characteristics | |
| 0.16600 AU (24,833,000 km) | |
| Eccentricity | 0.03+0.01 −0.03[3] |
| 35.23319d | |
| Inclination | 89.860 |
| Star | Kepler-438 |
| Physical characteristics | |
| 1.12 (± 0.16)R🜨 | |
| Temperature | 276 K (3 °C; 37 °F) |
Kepler-438b (also known by itsKepler Object of Interest designationKOI-3284.01) is a confirmed near-Earth-sizedexoplanet. It is likelyrocky.[5] It orbits on the inner edge of thehabitable zone of ared dwarf,Kepler-438, about 460.2light-years fromEarth in theconstellationLyra.[1][2] It receives 1.4 times the solar flux of Earth.[6] The planet was discovered byNASA'sKepler spacecraft using thetransit method, in which the dimming effect that aplanet causes as it crosses in front of its star is measured. NASA announced the confirmation of the exoplanet on 6 January 2015.[1]
Kepler-438b is anEarth-sized planet, an exoplanet that has a mass and radius close to that of Earth. It has a radius of 1.12R🜨, and an unknown mass. It has anequilibrium temperature of 276 K (3 °C; 37 °F), close to that of Earth.
The planet orbits a (M-type)red dwarf star namedKepler-438. The star has a mass of 0.54M☉ and a radius of 0.52R☉, both lower than those of theSun by almost half. It has a surface temperature of 3748K and is estimated to be about 4.4 billion years old,[3] only 200 million years younger than the Sun[7] and the Sun has a surface temperature of 5778 K.[8]
The star'sapparent magnitude, or how bright it appears from Earth's perspective, is 14.467. Therefore, it is too dim to be seen with the naked eye.
Kepler-438b orbits its parent star once every 35 days and 5 hrs[1][2] It is likely tidally locked due to its close distance to its star.[9] A search forexomoons by theHunt for Exomoons with Kepler project around Kepler-438b placed a maximum mass of a hypothetical moon at 29% that of the planet.[10]
The planet was announced as orbiting within thehabitable zone of Kepler-438, a region whereliquid water could exist on the surface of theplanet. However it has been found that this planet is subjected to powerful radiation activity from its parent star every 100 days, much more violent storms than thestellar flares emitted by the Sun and which would be capable of sterilizing life on Earth.[11]
Researchers at theUniversity of Warwick say that Kepler-438b is not habitable due to the large amount of radiation it receives.[12] The question of what makes a planet habitable is much more complex than having a planet located at the right distance from its host star so that water can be liquid on its surface: variousgeophysical andgeodynamical aspects, the radiation, and the host star'splasma environment can influence the evolution of planets and life, if itoriginated.[13] The planet is more likely to resemble a larger and cooler version ofVenus.
In 2009,NASA'sKepler spacecraft was completing observing stars on itsphotometer, the instrument it uses to detecttransit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed50000 stars in theKepler Input Catalog, including Kepler-62; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-438b occurred roughly every 35 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 35-day transits. The discovery, along with the planetary systems of the starsKepler-442,Kepler-440 andKepler-443 were announced on January 6, 2015.[1]
At nearly 460 light-years (140 pc) distant, Kepler-438b is too far from Earth for either current telescopes, or even the next generation of planned telescopes, to accurately determine its mass or whether it has an atmosphere. The Kepler spacecraft can only focus on a small, fixed region of the sky, but the next generation of planet-hunting space telescopes, such asTESS andCHEOPS, will have more flexibility. Exoplanetary systems, with stars less distant than Kepler 438, can then be studied in tandem with theJames Webb Space Telescope and ground-based observatories like the futureSquare Kilometer Array.[14]
| Notable Exoplanets –Kepler Space Telescope |
|---|
 Confirmed small exoplanets inhabitable zones. (Kepler-62e,Kepler-62f,Kepler-186f,Kepler-296e,Kepler-296f, Kepler-438b,Kepler-440b,Kepler-442b) (Kepler Space Telescope; 6 January 2015).[1] |
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