Astronomers have discovered a planet, likely to be rocky, close to our own solar system.
The planet, which has a three-day orbit round a central star, is joined by a further three planets also newly discovered in the same system.
The star at the centre of the system can be seen in the sky close to the Cassiopeia the Queen constellation, near the North Star.
It is visible to the naked eye from dark skies.
At a distance of just 21 light years away, the rocky planet is the nearest confirmed outside our solar system.
It is also the closest planet to Earth that has been found to transit across the front of its star which, together with its short orbit, makes it ideal for further study.
The newfound Earth-like planet, designated HD 219134b, was discovered by an international team of astronomers using data from the HARPS-North instrument on the 3.6-metre Telescopio Nazionale Galileo in the Canary Islands.
Scientists found that it weighs 4.5 times the mass of Earth, making it what is termed a super-Earth.
Although this planet is far too hot to be habitable, it is an amazing discovery given how close and bright the star is. Going forward this will provide amazing opportunities to learn about and characterise a rocky planet outside our solar system.
Three additional planets in the system were also found - one planet with a mass at least 2.7 times that of the Earth orbits the star once every 6.8 days.
A Neptune-like planet with nine times the mass of Earth circles in a 47-day orbit.
Much further out from the star, a hefty fourth world with 62 times the mass of Earth orbits at a distance of about 200 million miles, with a year length of 1,190 days.
Astronomers used NASA’s Spitzer Space Telescope to capture the smallest planet crossing in front of the star. The star was seen to dim slightly as the planet crossed its face.
Measuring the depth of the transit gave the planet’s size, enabling the team to calculate the planet’s density, which showed that it is a rocky world.
It is really exciting that we are now starting to be able to determine the internal composition of such low-mass planets.
Any of the other three planets might also pass directly in front of the star, so the team plans to search for additional transits across the star in the months ahead.
The star which the planets orbit is cooler, smaller and less massive than our Sun, and is known as HD 219134.
The HARPS-North project is led by the University of Geneva, and involves the Universities of St Andrews, Edinburgh and Queen’s University Belfast.
Other partners are the Harvard-Smithsonian Center for Astrophysics, and the Italian National Institute for Astrophysics.
The project was supported by the Scottish Funding Council through the Scottish Universities Physics Alliance.
The study will be published in the journal Astronomy & Astrophysics.
The amount that we will learn about this planetary system when we train the world’s largest telescopes on it in the coming years will be phenomenal, and I’m sure there will be yet more surprises.
For a planet like this one, orbiting at a distance ten times the radius of its parent star, the chances of transits occurring are better than one in ten, so it was well worth looking.