A team of Australian scientists has found the closest potentially habitable planet orbiting a star just 14 light years away.
At 130 trillion kilometres it might sound impossibly distant, but Wolf 1061 in the constellation Ophiucus is the 35th closest star to Earth. And 14 light years is just peanuts when it comes to space.
The University of NSW team, led by Duncan Wright, said three planets are orbiting Wolf 1061, a red dwarf “M-type” star.
All three are thought to be rocky like the Earth or Venus, rather than gaseous like Neptune, due to their estimated mass and radius.
“It is a particularly exciting find because all three planets are of low enough mass to be potentially rocky and have a solid surface. The middle planet, Wolf 1061c, sits within the ‘Goldilocks’ zone where it might be possible for liquid water – and maybe even life – to exist,” Dr Wright said.
Of the three planets, one is too close to the star and hence too hot for life, and the other is too far out, and hence too cold. The middle planet could be just right.
That planet, Wolf 1061c, orbits the star every 18 days at a distance about 10 per cent of Earth’s orbit of the sun. However, the red dwarf star is substantially cooler than the sun, about 3300 Kelvin compared with the sun’s surface temperature of about 5800 Kelvin.
“Given how close the planet is to the star it is likely to be ‘tidally locked’,” Dr Wright told Fairfax Media. This means that one hemisphere of the planet will always face towards the star, much like one side of the moon always faces Earth.
“This changes the circumstances on the surface of the planet substantially. You have one very hot side and one very cool side.”
However, Dr Wright said that atmospheric modelling shows that heat can circulate around such a planet, albeit producing very high winds across the permanent twilight zone between the two sides.
The three newly detected planets orbit the small, relatively cool and stable star about every five, 18 and 67 days. Their masses are at minimum 1.4, 4.3 and 5.2 times that of Earth, respectively.
Dr Wright’s team used the “doppler wobble method” to detect the planets. As smaller objects (planets) orbit a larger object (the star) it causes the central mass to “wobble”, or rotate around the centre of their combined masses. These small movements create a doppler shift in the light reaching Earth depending on whether the star is moving towards or away from us. This is similar to how we can tell whether an ambulance is moving towards us or away depending on the pitch of its siren: the doppler effect.
By measuring the nature of this wobble from the star’s light, scientists are able to get a very accurate picture of what is causing this movement. They are able to tell the number of objects, their distance from the star, as well as their estimated mass and orbital period.
“With our current measurements we are able to get precision of the motion of the star down to a ‘walking speed’,” Dr Wright said. “The motion of the star is detected at about a one metre per second precision.”
Dr Wright and his team used observations of Wolf 1061 collected by the HARPS spectrograph at the European Southern Observatory’s 3.6 metre telescope in La Silla, Chile.
The next step will be for telescopes to look at Wolf 1061 and search for “transits” of the planets in front of the star. The small dip in light caused by the planets passing in front of the star will allow scientists to find out more about this planetary system.
“The close proximity of the planets around Wolf 1061 means there is a good chance these planets may pass across the face of the star. If they do, then it may be possible to study the atmospheres of these planets in future to see whether they would be conducive to life,” said team member Rob Wittenmyer.
Dr Wright is keen for this discovery to have some galactic perspective.
“There is somewhere in the vicinity of 100 billion stars in our galaxy,” he said. “We know that half of those stars are red dwarf stars, like Wolf 1061. From observations made by the Kepler space telescope, we also know that half of those stars are expected to have multiple rocky planets orbiting them.
“So if you consider our find in that context we are talking about billions and billions of rocky planets in our galaxy alone. And of course we know of more than 100 billion galaxies in the universe.”
That’s a lot of planets to explore.