Another planet earth?
An artist’s impression of the newly discovered planet, Proxima Centauri b. (photo from ESO/M. Kornmesser)
An international team announced recently that a planet with a mass similar to that of earth has been observed orbiting the star Proxima Centauri – the closest star to our sun, just over four light years (about 40 trillion kilometres) away.
The collaboration of scientists from nine countries, known as the “Pale Red Dot” and led by Dr. Guillem Anglada-Escudé of Queen Mary University of London, included Weizmann Institute of Science’s Dr. Aviv Ofir, who is in the group of Prof. Oded Aharonson of the earth and planetary sciences department.
Proxima Centauri is a red dwarf – a star with a diameter about one seventh that of our sun and far dimmer: it gives off only 1/600 the light of our sun. The team’s calculations show that the planet, known as Proxima Centauri b, has a mass of at least 1.3 times that of earth and its year – the time it takes to orbit its sun – is a little over 11 days. It orbits quite close to its sun – only five percent of the distance from earth to our sun; but, since its sun is so dim, the temperature on Proxima Centauri b may be relatively balmy and liquid water could theoretically exist on its surface.
The range of distances where the planet’s temperature permits liquid water is often referred to as “the habitable zone.” Although conditions on the planet’s surface are as yet unclear, the scientific team hopes to learn more about this planet in further research. Ofir said it is not at all clear whether life as we know it could have evolved on the planet, and the subject is already the focus of intense debate.
The planet was discovered through measurements of the radial velocity of the star. Such measurements rely on the Doppler effect, the shift in wavelength as an object moves closer to or away from the viewer. The star, according to the team’s highly accurate measurements, is moving at a speed of about a metre a second (or 3.6 kilometres an hour) towards and away from us.
Ofir explained that, when we speak of a planet orbiting a star, in reality they are both orbiting a shared centre of gravity. Since the mass of the star is naturally much greater than that of its planets, that centre of gravity is usually close to the centre of the star, and planets make the star’s motion appear as a “wobble.” And that wobble can be detected by today’s instruments: in the case of Proxima Centauri, the scientists observed periodic changes in the star’s velocity, the result of another body tugging at it. That body, according to the measurements, is a planet with a relatively small mass, just over that of earth.
Ofir pointed out that Proxima Centauri has been studied for the past century, but only now have observations – designed for this very purpose – become sensitive enough to decisively detect the presence of this small planet. He is continuing to work on this and other projects to identify and study planets around Proxima Centauri.
“We discovered the planet with an observatory in Chile. We can’t see Proxima Centauri from our observatories in Israel,” he explained. “It is well below the southern horizon, so it is unobservable from Israel all year round.”
For more information about Weizmann Institute research, visit wis-wander.weizmann.ac.il.