Kepler-452b
Kepler-452b is an exoplanet orbiting the Sun-like star Kepler-452 about from Earth in the constellation Cygnus. It was identified by the Kepler space telescope, and its discovery was announced by NASA on 23 July 2015. However, a study in 2018 by Mullally et al. implied that statistically, Kepler-452b has not been proven to exist and must still be considered a candidate. Moreover, its mass of 5 Earth masses increases the possibility that the planet is a mini-Neptune instead of a super-Earth. It is the first potentially rocky super-Earth planet discovered orbiting within the habitable zone of a star very similar to the Sun. The planet is about 1,400 light-years away from the Solar System. At the speed of the New Horizons spacecraft, about, it would take approximately 26 million years to get there.
Characteristics
Mass, radius and temperature
Kepler-452b has a probable mass five times that of Earth, and its surface gravity is nearly twice as Earth's, though calculations of mass for exoplanets are only rough estimates. If it is a terrestrial planet, it is most likely a super-Earth with many active volcanoes due to its higher mass and density. The clouds on the planet would be thick and misty, covering much of the surface as viewed from space.The planet takes 385 Earth days to orbit its star. Its radius is 50% bigger than Earth's, and lies within the conservative habitable zone of its parent star. It has an equilibrium temperature of, a little warmer than Earth. However, since Kepler-452 is nearly 2 billion years older, at approximately 6.5 billion years, the rocky planet's water and atmosphere most likely evaporated. Its surface temperature is estimated to be at.
Host star
The host star, Kepler-452, is a G-type is about the same mass of the sun, only 3.7% more massive and 11% larger. It has a surface temperature of 5757 K, nearly the same as the Sun, which has a surface temperature of 5778 K. The star's age is estimated to be about 6.5 billion years old, about 1.9 billion years older than the Sun, which is 4.6 billion years old. From the surface of Kepler-452b, its star would look almost identical to the Sun as viewed from the Earth.The star's apparent magnitude, or how bright it appears from Earth's perspective, is 13.426; therefore, it is too dim to be seen with the naked eye.
Orbit
Kepler-452b orbits its host star with an orbital period of 385 days and an orbital radius of about 1.04 AU, nearly the same as Earth's. Kepler-452b is most likely not tidally locked, and has a circular orbit. Its host star, Kepler-452, is about 20% more luminous than the Sun..Potential habitability
It is not known if Kepler-452b is a rocky planet but based on its small radius, Kepler-452b is likely to be rocky. It is not clear if Kepler-452b offers habitable environments. It orbits a G2V-type star, like the Sun, which is 20% more luminous, with nearly the same temperature and mass. However, the star is 6.5 billion years old, making it 1.9 billion years older than the Sun. At this point in its star's evolution, Kepler-452b is receiving 10% more energy from its parent star than Earth is currently receiving from the Sun. If Kepler-452b is a rocky planet, it may be subject to a runaway greenhouse effect similar to that seen on Venus. However, due to the planet being 60% bigger than Earth, it is likely to have an estimated mass of 5, which could allow it to hold on to any oceans it may have for a longer period, preventing Kepler-452b from succumbing to runaway greenhouse effect for another 500 million years. This in turn would be accompanied with the carbonate–silicate cycle being "buffered" extending its lifetime due to increased volcanic activity on Kepler-452b. This could allow any potential life on the surface to inhabit the planet for another 500–900 million years before the habitable zone is pushed out of Kepler-452b's orbit.Discovery and follow-up studies
In 2009, NASA's Kepler spacecraft was observing stars on its photometer, the instrument it uses to detect transit 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 observed stars in the Kepler Input Catalog, including Kepler-452; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up by other telescopes. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. Kepler-452b exhibited a transit which occurred roughly every 385 days, and it was eventually concluded that a planetary body was responsible. The discovery was announced by NASA on 23 July 2015.At a distance of nearly, Kepler-452b is too remote for current telescopes or the next generation of planned telescopes to determine its true mass or whether it has an atmosphere. The Kepler spacecraft focused on a single small region of the sky but next-generation planet-hunting space telescopes, such as TESS and CHEOPS, will examine nearby stars throughout the sky with follow up studies planned for these closer exoplanets by the upcoming James Webb Space Telescope and future large ground-based telescopes to analyze their atmospheres, determine masses and infer compositions.
SETI targeting
Scientists with the SETI have already begun targeting Kepler-452b, the first near-Earth-size world found in the habitable zone of a Sun-like star. SETI Institute researchers are using the Allen Telescope Array, a collection of 6-meter telescopes in the Cascade Mountains of California, to scan for radio transmissions from Kepler-452b. As of July 2015, the array has scanned the exoplanet on over 2 billion frequency bands, with no result. The telescopes will continue to scan over a total of 9 billion channels, searching for alien radio signals.Observation and exploration
Kepler-452b is from Earth. The fastest current spacecraft, the New Horizons unmanned probe that passed Pluto in July 2015, travels at just. At that speed, it would take a spacecraft about 26 million years to reach Kepler-452b from Earth, if it was going in that direction.Ryan Weed from Positron Dynamics suggests that with a spacecraft accelerating at a constant 1 g up to a velocity of 0.99995 c and due to time dilation we could reach Kepler-452b in 12 years, although from Earth perspective more than 1,400 years would have passed.
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