Kepler-1520b (initially published as KIC 12557548 b), is a confirmed

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

orbiting the

K-type main sequence star A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("r ...

Kepler-1520 Kepler-1520 (initially published as KIC 12557548) is a K-type main-sequence star located in the constellation Cygnus. The star is particularly important, as measurements taken by the ''Kepler'' spacecraft indicate that the variations in th ...

. It is located about 2,020

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s (620

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s) away from Earth in the constellation of Cygnus. The exoplanet was found by using the

transit method Methods of detecting exoplanets usually rely on indirect strategies – that is, they do not directly image the planet but deduce its existence from another signal. Any planet is an extremely faint light source compared to its parent star. For e ...

, in which the dimming effect that a planet causes as it crosses in front of its star is measured. The planet was previously proposed in 2012 when reports of its host star recorded drops in its luminosity varying from 0.2% to 1.3%, which indicated a possible planetary companion rapidly disintegrating. In 2015, the planetary nature of the cause of the dips was finally verified. It is expected to disintegrate in about 40–400 million years.

Physical characteristics

Mass, radius, and temperature

The mass of Kepler-1520b is unknown; however, modeling of the mass loss rate of the planet indicates that it cannot be more massive than about 2% of the mass of the Earth (less than double the mass of the Moon). According to calculations, it may have lost 70% of its original mass; we may be currently observing its naked iron core. From attempts to measure the

secondary eclipse A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

, the radius of the planet is constrained to be less than one Earth radius (4600 km) for an

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

of 0.5. It has a surface temperature of , far hotter than the surface of

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

Host star

The planet orbits a ( K-type)

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

named

. The star has a mass of 0.76 and a radius of 0.71 . It has a temperature of 4677 K and is 4.47 billion years old. In comparison, the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

is 4.6 billion years old and has a surface temperature of 5778 K. The star's

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

, or how bright it appears from Earth's perspective, is 16.7. Therefore, it is too dim to be seen with the naked eye.

Orbit

Kepler-1520b orbits its host star with about 14% of the Sun's luminosity with an orbital period of slightly over 12 hours and an orbital radius of about 0.01 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU). This is one of the closest orbital periods detected yet.

Remaining lifetime

Kepler-1520b orbits so close to its host star that it is essentially evaporating into space via sublimation, losing about 0.6 to 15.6 Earth masses per billion years. Based on predictions made by scientists, Kepler-1520b will cease to exist in about 40–400 million years. Calculations of mass loss rates show that the planet probably had a mass slightly smaller than Mercury in size when it first formed, since the calculations show that planets with masses larger than 7% the Earth's barely lose any mass over billion year time-scales. This discovery helps shed light on how the Earth will interact with the Sun when it becomes a red giant, roughly 5–7 billion years from now.

Discovery

2012 detections

The existence of the planet was first evidenced in data collected by the ''Kepler'' spacecraft in 2012. However, the light curve of the star, a graph of its stellar flux versus time, showed that while there were regular drops in stellar flux approximately every 15 hours, the amount of light being blocked covered a wide range, from 0.2% to 1.3% of the starlight being blocked.

Saul Rappaport Saul Rappaport is a professor emeritus of physics at the Massachusetts Institute of Technology. Rappaport became assistant professor in the MIT Department of Physics in 1969 and became a full professor in 1981. From 1993 to 1995, he was head of th ...

and collaborators proposed various possible phenomena which may have caused the anomalies in the light curve, including two planets orbiting each other, and an eclipsing binary orbiting the star in a larger triple-star system. However, the authors found the hypothetical binary planet system to be unstable and the latter scenario to be poorly supported by the data collected by ''Kepler''. Therefore, the authors posited that the most likely cause of the observed light curve was a closely orbiting planet, about twice the mass of Mercury, which was rapidly emitting small particles into independent orbits around the star. Exactly the cause of this phenomenon could be the direct sublimation of the planetary surface and its emission into space, the intense volcanism caused by the tidal effects of orbiting extremely close to the host star, or both processes mutually reinforcing the strength of each other in a

positive feedback loop Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop where the outcome of a process reinforces the inciting process to build momentum. As such, these forces can exacerbate the effects ...

2016 confirmation

Following a campaign of observations using

William Herschel Telescope The William Herschel Telescope (WHT) is a optical and near-infrared reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma in the Canary Islands, Spain. The telescope, which is named after William Hersc ...

, another group of astronomers was able to detect color dependence of the transit depth, providing independent, direct evidence in favor of this object being a disrupting low-mass rocky planet, feeding a transiting dust cloud. In the new database released by ''Kepler'' in May 2016, the planetary nature of then-KIC 12554578 b was confirmed, and was then upgraded to the name Kepler-1520 b.

References

External links

Google News link for "disintegrating planet"
{{Portal bar, Astronomy Exoplanets discovered in 2016 Transiting exoplanets Cygnus (constellation)

1520 Year 1520 ( MDXX) was a leap year starting on Sunday of the Julian calendar. Events January–March *January 19 – King Christian II of Denmark and Norway defeats the Swedes, at Lake Åsunden in Sweden. The Swedish regent St ...

Sub-Earth exoplanets Ultra-short period planets