Revealed: a monster planet orbits a tiny star

A new discovery challenges received wisdom about planet size. Andrew Masterson reports.

For the first time, a giant planet has been observed orbiting a small star.
For the first time, a giant planet has been observed orbiting a small star.
ESO via Getty Images

A planet the size of Jupiter has been found orbiting a star half the size of the sun, confounding one of the tenets of astronomy.

In a report, currently on the prepress site Arxiv and accepted for publication in the Monthly Notices of the Royal Astronomical Society, a team led by Daniel Bayliss from the University of Warwick in the UK describes a “monster planet” that seems to break all the rules.

Previous modelling found there were physical constraints that governed the relative size of stars and their orbiting planets. Simply put, little stars could not have enormous satellites.

The monster, however, more formally known as NGTS-1b, gives the lie to that idea. The researchers say that the planet is a gas giant, about the same size as Jupiter but with about 20% less mass.

It orbits a star – some 600 light years away from us – that has a mass and radius about half that of the sun.

NGTS-1b, which has a surface temperature estimated at a scorching 530 degrees Celsius, is very close to the star, and completes an orbit every 2.6 days. Relative to the size of the star it is by far the largest planet ever discovered.

It was found by the Next Generation Transit Survey, a fully robotic array of small telescopes operated by the European Southern Observatory in Chile, designed to detect exoplanets.

“The discovery of NGTS-1b was a complete surprise to us,” says Bayliss.

“Such massive planets were not thought to exist around such small stars. This is the first exoplanet we have found with our new NGTS facility and we are already challenging the received wisdom of how planets form.

“Our challenge is to now find out how common these types of planets are in the Galaxy, and with the new NGTS facility we are well-placed to do just that.”

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Andrew Masterson is news editor of Cosmos.
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