Ultra-short period planet
An ultrashort Periodic Planet (Engl. Ultra-short period planet shortly USPP ) is an exoplanet with an orbital period of less than a few days and a surface temperature of more than 1000 Kelvin (about 730 ° C) on the day side . Well-known examples are KIC 12557548b, 55 Cancri e , CoRoT-7b and Kepler-10b .
definition
The definition of the ultra-short period planets takes place in most cases via the period of orbit: while some authors set a strict upper limit of one day, others take a non-specific value of a few days.
If one takes an upper limit of one day, then USPP occur with a probability of 0.5 percent around G dwarfs and 0.8 percent around K dwarfs.
properties
Due to the short distance to its central star, the probability of a transit , which can be detected by a change in the obscuration light , is 40 percent. Also due to the small distance between the ultra-short period planet and its central star , the radial velocities reach values of a few m / s, which makes it possible to determine the mass of the planet even with faint stars, namely spectroscopically .
The shortest known orbital period is 4.25 hours at KOI 1843.03. To avoid destruction by tidal forces , the Super Mercury must be made of almost pure iron. If confirmed, it is the first evidence of an iron planet .
The orbital eccentricity is 0 for all observed USPP, and the planets seem to seduce a bound rotation .
The surface temperature can reach values of a few thousand Kelvin, whereby the planet can be detected directly in the infrared .
In the case of KIC 12557548b, a depression can be observed in the light curve after the transit, which is interpreted as a plume of dust along the orbit of the exoplanet. The surface of the planet has melted, the vaporized material has enough kinetic energy to escape the gravitational field and condense as dust .
development
With a few exceptions, the ultra-short period planets have diameters on the order of the earth. They have a high density , which is characteristic of a composition of rock and iron. They are probably former sub-Neptune who lost their atmosphere due to the strong stellar radiation .
The USPP can just as little as the Hot Jupiter have been incurred in their current location and later to her current position hiked . The causes are likely to be the same for both types of exoplanets:
- Planet-planet scattering due to orbital resonance
- the Darwin instability
- the Kozai effect
- Friction in circumstellar disks .
The further development of the USPP should lead to a slow further sinking of the orbital axis up to an immersion in the stellar atmosphere .
literature
- Roberto Sanchis, Saul Rappaport, Joshuan. Winn, Michael C. Kotson, Alan Levine, Ileyk Mellah: A Study of the Shortest-Period Planets Found with Kepler . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1303.2379v1 .
- M. Brogi, CU Keller, M. de Juan Ovelar, MA Kenworthy, RJ de Kok, M. Min, IAG Snellen: Evidence for the disintegration of KIC 12557548 b . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1208.2988v1 .
- M. Gillon et al .: The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1201.2789v2 .
- Kailash C. Sahu et al .: Planets in the Galactic Bulge: Results from the SWEEPS Project . In: Astrophysics. Solar and Stellar Astrophysics . 2007, arxiv : 0711.4059v1 .