HD219134: Rocky planet similar to Earth found
The celestial body is part of a system of four planets detected recently within the distinctive Cassiopeia constellation, a mere 21 light years away.
The system, named HD219134, hosts one outer giant planet and three inner “super-Earths”, one of which has a density similar to Earth’s and transits its host star.
However, experts believe the planet, dubbed HD 219134b, is too hot and inhospitable to support life. They say it is likely to have a surface of molten lava with no liquid water.
The planet was initially spotted by the Italian Galileo National Telescope in the Canary Islands and confirmed by Nasa’s Spitzer space telescope.
The discovery is important because HD 219134b is the closest exoplanet to Earth known to be crossing in front of its star and will provide valuable information for scientists. Its relative proximity to Earth means HD 219134b will be “one of the most studied for decades to come”, says Nasa’s Michael Werner, who has been researching the system.
“Transiting exoplanets are worth their weight in gold,” he said.
Although 21 light years is a long way off, it is close compared to the 1,400 light years it would take to reach the Earth-like planet Kepler-452b identified on a recent Nasa mission.
Though stargazers cannot view HD 219134b using a conventional telescope, its host star can be spotted in dark skies with the naked eye tucked next to one leg of the W in Cassiopeia, near the North Star Polaris.
The planet is more than 1.5 times the size of Earth and 4.5 times heavier, though its density is similar. This suggests a rocky composition and sees it classed as a super-Earth.
Astronomers from two Scottish universities were involved in the discoveries as part of the HARPS-North project, a survey examining nearby stars for signs of small planets. They say the planet’s close orbit suggested it might cross its star.
Annelies Mortier, of the School of Physics and Astronomy at the University of St Andrews, said: “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.”
Their suspicions were verified when observations using the Spitzer telescope showed the star dimmed slightly at the correct time to correspond with the planet crossing its face.
Measuring the depth of the transit revealed the planet’s size and allowed the team to work out its density and make-up.
“It is really exciting that we are now starting to be able to determine the internal composition of such low-mass planets,” Ken Rice, from the University of Edinburgh, said.
The team detected three additional planets in the system – one giant and two further super-Earths. One orbits the star every 6.8 days and another every 47 days. Much further out, a hefty fourth world 62 times heavier than Earth orbits at a distance of 200 million miles and has 1,190 days in its year.
The St Andrews and Edinburgh contributions were part-funded by the Scottish Funding Council.