Rocky exoplanet milestone in hunt for Earth-like worlds.
Astronomers have discovered the smallest planet outside our solar system, and the first that is undoubtedly rocky like Earth.
Measurements of unprecedented precision have shown that the planet, Kepler 10b,has a diameter 1.4 times that of Earth, and a mass 4.6 times higher.
However, because it orbits its host star so closely, the planet could not harbour life.
The discovery has been hailed as “among the most profound in human history”.
This cosmic dance causes tiny changes in the colour of the starlight that is measured by telescopes.
However, what completed the suite of measurements for the Kepler team was the use of asteroseismology – a study of distant stars that is akin to the study of earthquakes on the Earth.
The oscillations that occur within a star – as within the Earth – affect the frequencies of the light that the star emits in a telltale sign of the star’s size.
With the size of the host star, the details of the planet’s and star’s mutual dance, and the planet’s radius, the density of the planet can be calculated.
“All of our very best capabilities have converged on this one result and they all converge to form a picture of this planet,” said Natalie Batalha, a San Jose State University professor of astrophysics who helps lead the Kepler science mission for Nasa.
She told BBC News that the result is unique in an ever-expanding field of exoplanet discoveries, with smaller and smaller exoplanets discovered as experimental methods improve.
“We’re always pushing down toward smaller and less massive, so it’s natural that we’re arriving there,” she said.
“But perhaps what’s not so natural is that we’ve pinned down the properties of this planet with such fantastic accuracy that we’re able to say without a doubt that this is a rocky world, something that you could actually stand on.”
Alone or not?
One could, if it were not so close to its host star that it’s daytime temperature exceeds 1300C – so Kepler 10b is not a sensible candidate to host life. However, as Professor Batalha explained, it is a significant step in Kepler’s mission.
“We want to know if we’re alone in the galaxy, simply put – and this is one link in the chain toward getting to that objective.
“First we need to know if planets that could potentially harbour life are common, and we don’t know if that’s true – that’s what Kepler is aiming to do.”
Pioneer of the hunt for exoplanets Geoffrey Marcy, from the University of California Berkeley, said that Kepler 10b represented “a planetary missing link, a bridge between the gas giant planets we’ve been finding and the Earth itself, a transition… between what we’ve been finding and what we’re hoping to find”.
“This report… will be marked as among the most profound scientific discoveries in human history,” he said.