Exoplanet Discovery!

Just yesterday, the European Southern Observatory announced the discovery of an exoplanet orbiting our closest star, Proxima Centauri.

Proxima Centauri is located 4.22 light-years away from us and is classed as a red dwarf. So, despite its relative proximity, Proxima Centauri glows very dimly and is quite undersized, at 1.5 times the size of Jupiter. Located in the constellation Centaurus in the southern sky and part of a triple star system, it orbits two other stars, Alpha Centauri A and Alpha Centauri B, with an orbital period of at least 1 million years, suggesting that it might not even be gravitationally locked to them.

Proxima Centauri is hardly visible to the naked eye. Because it 500,000 dimmer than the sun, it is 100 times less faint than could be seen by the naked eye! Indeed, it is one of the faintest stars ever and because of that was only just recently discovered by Scottish astronomer Robert Innes in 1915, notwithstanding its distinction as the nearest star to us. In doing so, Innes had revolutionized a new “blinker” method. Using a device called a blink comparator, he examined plates of photographs of the same region of the sky taken on two different dates, in 1910 and in 1915. The device aimed to align the two plates and present the two stellar fields alternately in rapid sequence so as to detect motion “jumps”. The new star in question would, henceforth, change position against the background of stationary stars as the comparator shows the two plates in succession. The method also works by showing a first plate with a possible object and a second plate without it, resulting in the flashing on and off of the object in question. Indeed, the planet Pluto was discovered using this method.

Proxima Centauri
Proxima Centauri, our closest stellar neighbour

The newfound planet, Proxima b, detected by the ESO Observatory lies in orbit around this star. Located inside the star’s habitable zone, it could conceivably be a life-bearing planet and thus support liquid water on its surface. The less luminous a star is, the closer its habitable zone is to itself. Thus, Proxima b, lies much closer to its star than we do in relation to our own star (closer than Mercury is to the Sun). Its mass, estimated at 1.3 times that of the Earth, suggests that it is quite certainly a rocky planet. It is not known, however, whether it possesses an atmosphere.

Artist’s impression of Proxima b surface. Credit: ESO Observatory

The planet was discovered using the Doppler technique. This technique makes use of radial velocity to detect the wobble of a parent star as it moves around its centre of mass in our line of sight. An orbiting planet would cause its star to periodically move towards or away from us. Accordingly, light from the star moving towards us would be shifted towards the blue end of the electromagnetic spectrum and thus the star would appear bluer. However, light from the star moving away from us would be shifted towards the red end of the electromagnetic spectrum and thus the star would appear redder. Therefore, the star’s spectrum could be analyzed for corresponding blue or red shift effects that would provide evidence of a gravitational pull exerted by a possible planet. The technique is quite sensitive that it detects velocities to within a walking speed of one metre per second.

The Doppler technique for detecting exoplanets. Credit: University of Cincinnati

The spectrum shifts were detected by the HARPS (High-Accuracy Radial Velocity Planet Searcher) spectrometer mounted on the 3.6 meter ESO telescope and operating with the extraordinary precision level of 1 m/s, as earlier described. It is positioned in a temperature-controlled vacuum environment to minimise temperature and pressure disturbances. An observed spectrum is cross-correlated with a thorium-argon reference spectrum. Two optical fibres are employed, one from the star and one from the thorium-argon lamp.

Yesterday’s discovery is very significant indeed. With many repercussive situations threatening our planet, it is not known how far into the conceivable future the human race could survive. But, one could only hope that the miraculous advances in rocket technology  of the projected future would perpetuate that possibility further onto this newly discovered world!


Featured Image: 3.6-metre telescope at La Silla, Chile/ESO



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