First detection of a predicted unseen exoplanet

Dec 17, 2013
Artist impression of the Kepler-88 system. Credit: Alexandre Santerne (CAUP)/ESO/Serge Brunier

A team of European astronomers, including EXOEarths member Alexandre Santerne (CAUP), used the SOPHIE spectrograph at the Observatoire de Haute-Provence (France), to confirm the presence of Kepler-88 c, an unseen planet that was previously predicted thanks to the gravitational perturbation it caused on its transiting brother planet, Kepler-88 b.

Searching for periodic transits in hundreds of thousands of stars was the primary goal of the Kepler space telescope. More than 3,500 of such periodic transits were found during the 4 years of the mission. However, not all the planets located in the Kepler field-of-view are transiting their host star. Indeed, if their orbital plane is slightly misaligned (only a few degrees is enough) with the line of sight from the Earth, the planet is not transiting and, thus, is "unseen" from the Kepler spacecraft.

Planets that share the same host star gravitationally interact with each other. This interaction between planets can cause perturbations in the predicted times of transit of planets in multi-planetary systems. "This is called transit timing variations (TTV)" explains the leading author of the paper, Susana Barros, a researcher at the Laboratoire d'Astrophysique de Marseille (LAM).

The TTV technique is sensitive to planets in multiple systems down to the mass of the Earth, and can therefore be used to unveil the existence of non-transiting planets, that cause perturbations in the orbital motion of transiting planets.

This is the case of the Kepler-88 system, which hosts a transiting planet (Kepler-88 b), discovered by the Kepler space telescope (NASA) , that is strongly perturbed by a non-transiting planet (Kepler-88 c). "This system presents such strong interactions that it has earned the nickname of the king of transit variations" adds Rodrigo Diaz, a researcher working at the Geneva Observatory (OAUG).

Picture of the dome of the 1.93-m telescope of Haute-Provence Observatory (France) which hosts the SOPHIE spectrograph, with the Kepler field-of-view. Credit: Alexandre Santerne (CAUP)

A careful analysis of the dynamical interaction between planets, previously performed by a team led by David Nesvorny (Southwest Research Institute), predicted that this system had two planets near a two-to-one resonance (the orbital period of the unseen outer planet is exactly two times longer than the transiting inner planet). This configuration is similar to the Earth and Mars in the solar system, with Mars orbiting the Sun in nearly 2 years.

Using the SOPHIE velocimeter, the team independently measured the mass of Kepler-88 c. "SOPHIE is a French instrument capable of measuring the velocity of stars with a precision equivalent to the speed of a bicycle. It has been used to characterize nearly 20 Kepler planets so far" adds Alexandre Santerne a researcher at Centro de Astrofísica da Universidade do Porto (CAUP) and responsible of the observations of Kepler targets with SOPHIE.

The inferred mass for the unseen planet is in perfect agreement with the value that was predicted from TTV. "This is the first time that the mass of an unseen exoplanet inferred based on transit timing variation is independently confirmed by another technique," comments Susana Barros. This result therefore confirms TTV as a valid technique to detect unseen planets and explore multiplanet systems. TTV has already been used to determine the mass of more than 120 exoplanets detected by Kepler, around 47 planetary systems, down to a few Earth-mass .

"This independent confirmation is a very important contribution to the statistical analyzes of the Kepler multiple planet systems. It helps to better understand the dynamical interactions and the formation of planetary systems. This also permits to anticipate the future exploration of exoplanetary systems from space as would do the PLATO mission" concludes Magali Deleuil, professor at Aix-Marseille University and leader of LAM's exoplanet research.

Neptune was the first planet detected based on the gravitational influence it had on another planet (Uranus). The French mathematician Urbain Le Verrier calculated that the anomalies in Uranus orbit were due to a two-to-one resonance from a previously unseen planet. His calculation led Johann Gottfried Galle to find Neptune on September 23, 1846.

The article "SOPHIE Velocimetry of Kepler Transit Candidates X KOI-142c: First Radial Velocity Confirmation of a Non-Transiting Exoplanet Discovered by Transit Timing," is published 17 December 2013 in Astronomy & Astrophysics:

Explore further: The latest Kepler Orrery video

add to favorites email to friend print save as pdf

Related Stories

41 new transiting planets in Kepler field of view

Aug 27, 2012

(—Two newly submitted studies verify 41 new transiting planets in 20 star systems. These results may increase the number of Kepler's confirmed planets by more than 50 percent: to 116 planets hosted ...

Keele astronomers push worldwide exoplanet tally over 1000

Oct 24, 2013

As reported by BBC News, the total number of extra-solar planets known through the efforts of worldwide astronomers has just passed 1000. Keele astronomers pushed it over that number by announcing 12 new planets from the ...

Researchers reveal unseen planet by its gravity

May 10, 2012

More than a 150 years ago, before Neptune was ever sighted in the night sky, French mathematician Urbain Le Verrier predicted the planet's existence based on small deviations in the motion of Uranus. In a ...

Tilted suns

Nov 04, 2013

( —The Earth's axis of rotation is tilted 23.4 degrees to its orbital motion around the Sun (more precisely, its spin axis has a tilt of 23.4 degrees with respect to the axis of its orbit). This ...

Recommended for you

Quest for extraterrestrial life not over, experts say

Apr 18, 2014

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

( —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 0

More news stories

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Cosmologists weigh cosmic filaments and voids

( —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.