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Two giant exoplanets are caught in a 'gravitational dance' light years from Earth

A pair of intermingling exoplanets 800 light-years away from the Earth have been discovered caught up in a 'gravitational dance' in orbit around a Sun-like star. 

The duo were found by using an Earth-based telescope - the first time such an event has been discovered by equipment not based in orbit around the Earth.

Astronomers that make up an international consortium of universities and groups known as the Wide Area Search for Planets (WASP) found the waltzing worlds.

The planets, named WASP-148b and WASP-148c, orbit a Sun-like star in the constellation of Hercules and are between the mass of Saturn and Jupiter.

According to the scientists, these giant objects are able to 'feel each other's gravity', which causes on to speed up and slowdown as it overtakes the other world. 

The planets, named WASP-148b and WASP-148c, orbit a Sun-like star in the constellation of Hercules and are between the mass of Saturn and Jupiter as seen in this artists impression

It is this close gravitational phenomenon that makes it look like the planets are dancing, according to the astronomers behind the discovery.

Professor Andrew Collier Cameron, of the University of St Andrews said this was the first time a pair of giant planets had been found interacting so closely.

'It's exciting to be able to follow their dance from the ground', he said.

Astronomers from the Open University and University of Warwick were also involved in the discovery - using instruments on Earth rather than with space telescopes.

What makes this discovery particularly exciting is the fact it was seen from ground0-based telescopes rather than orbiting satellites outside the atmosphere. 

WASP-148b was identified by a range of instruments installed at the Roque de los Muchachos Observatory in La Palma, Canary Islands.

The star system was then observed with an instrument known as SOPHIE at the Observatoire de Haute-Provence in France.

They found WASP-148b, which is about the size and mass of Saturn, takes about 8.8 days to circle its host star.

The orbital period for WASP-148c is much longer at 34.5 days, and the team believe the planet has a mass half that of Jupiter. 

Dr Guillaume Hébrard, of Institut d'astrophysique de Paris said this was an important discovery for the WASP consortium.  

'WASP has discovered over a hundred transiting giant planets, but this double discovery has more than double the value because of the extra information the timing variations give us,' he said.

Before this discovery a few dozen planetary systems showed transit timing variations had been detected, but they were all found with space telescopes.

Professor Don Pollacco, of the University of Warwick, said: 'Even in this era of very expensive space telescopes, small telescopes on the ground can make vital contributions'.

The star system was then observed with an instrument known as SOPHIE at the Observatoire de Haute-Provence in France (pictured) 

According to the researchers, this ratio between the orbital periods suggests the WASP-148 system is close to resonance, meaning there is enhanced gravitational interaction between the two planets.

The scientists also observed the planetary transit, which is when a planet crosses in front of its host star, of both WASP-148b and WASP-148c.

The found both WASP-148b and WASP-148c undergo acceleration and deceleration as they pass each other in their orbit of the star.

This is evidence of gravitational interaction between them, the astronomers say.

This gravitational dance works like pushing a child on a swing - where adding force just at the right time produces large variations in timing and movement.

Analysis revealed both WASP-148b and WASP-148c orbit in the same plane, just like the planets in the Solar System. 

The mutual tilt between the orbits of WASP-148b and WASP-148c must be less than 35 degrees and so that their configuration is stable, the team found.

NASA’s TESS space telescope (Transiting Exoplanet Survey Satellite) will observe nine consecutive transits of WASP-148b.

The TESS team will  and perform a sensitive search for transits of WASP-148c during the observations and hunt for any additional smaller planets. 

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