'Monster' planet discovery challenges formation theory

Scientists have discovered a 'monster' planet orbiting a small, distant star, a finding that defies theories which state that such a massive planetary body cannot form around a small stellar host.

According to these theories, small stars can readily form rocky planets but do not gather enough material together to form Jupiter-sized planets.

The newly discovered planet 'NGTS-1b' however, is a 'gas giant'. Due to its size and temperature, the planet is known as a 'hot Jupiter', a class of planets that are at least as large as our solar system's very own Jupiter, but with around 20 percent less mass.

Unlike Jupiter, NGTS-1b is very close to its star - just three percent of the distance between Earth and the Sun, and completes an orbit every 2.6 days, meaning a year on NGTS-1b lasts two and a half Earth-days.

In contrast, the host star is small, with a radius and mass half that of our Sun.

"Despite being a monster of a planet, NGTS-1b was difficult to find because its parent star is so small and faint," said Peter Wheatley from the University of Warwick in the UK.

The significance of the discovery given the challenging circumstances "small stars like this red M-dwarf are actually the most common in the universe, so it is possible that there are many of these giant planets waiting to be found," Wheatley said.

NGTS-1b is the first planet to be spotted by The Next-Generation Transit Survey (or 'NGTS') which employs an array of 12 telescopes to scour the sky.

The researchers made their discovery by continually monitoring patches of the night sky over many months, and detecting red light from the star with innovative red- sensitive cameras.

They noticed dips in the light from the star every 2.6 days, implying that a planet was orbiting and periodically blocking the starlight.

Using these data, they then tracked the planet's orbit and calculated the size, position and mass of NGTS-1b by measuring the radial velocity of the star.

In fact, this method, measuring how much the star 'wobbles' due to the gravitational tug from the planet, was the best way of measuring NGTS-1b's size, researchers said.