EARTH-LIKE PLANET CONFIRMED.
Proxima b orbits our nearest star
Ateam of scientists from the University of Geneva has confirmed the existence of an Earth-sized planet orbiting the star closest to the sun. The planet, called Proxima b, is 1.17 times the mass of Earth and is located in the habitable zone of Promixa Centauri, 4.2 light years away.
Because Proxima Centauri is a red dwarf, much smaller and cooler than the sun, its habitable zone or Goldilocks zone — neither too hot nor too cold for liquid water to exist — is very close to the star. Proxima b orbits about 20 times closer to its star than Earth does to the sun, and a year on the planet is just over 11 Earth days long.
Red dwarf stars emit huge quantities of X-rays, and the scientists estimate the planet gets 400 times as much radiation as Earth. But Christophe Lovis, a researcher in the astronomy department of the university, was optimistic that this might not rule out the possibility of life, or at least habitability.
“Is there an atmosphere that protects the planet from these deadly rays?” he asks. “And if this atmosphere exists, does it contain the chemical elements that promote the development of life — oxygen, for example? How long have these favourable conditions existed?”
Such questions will, he hopes, be answered in the next few years by the next generation of spectrometers, which will tease out data from the light of the star and its planet. The recent confirmation of Proxima b came from data from a spectrograph called ESPRESSO (Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) mounted on the Very Large Telescope (yep, that’s its name) in Chile.
Proxima b was first detected by an earlier instrument called HARPS, or High Accuracy Radial Velocity Planet Searcher. “We were already very happy with the performance of HARPS, which has been responsible for discovering hundreds of exoplanets over the last 17 years”, says lead researcher Francesco Pepe. “We’re really pleased that ESPRESSO can produce even better measurements.”
In addition, data from ESPRESSO included a second signal that could indicate yet another planet orbiting even closer to the star. “If the signal was planetary in origin, this potential other planet accompanying Proxima b would have a mass less than one third of the mass of the Earth. It would then be the smallest planet ever measured using the radial velocity method,” says Pepe. Proxima b could have a moon-sized neighbour.
Despite the relative nearness of Proxima Centauri as the sun’s closest stellar neighbour, we will have to rely on spectrographic data for the foreseeable future. Our fastest interplanetary probes, the Voyagers and New Horizons, would take tens of thousands of years to reach Proxima Centauri, even if they were headed in that direction. A plan called Breakthrough Starshot imagines a tiny probe travelling at 20 per cent of light speed, and making the journey in 20 years, but it’s still very much on the drawing board.