Credit: Digitized Sky Survey 2; Davide De Martin/Mahdi Zamani
The Kepler space telescope has uncovered a bounty of planets orbiting other stars, but many of those worlds are too distant for in-depth study. Now astronomers have discovered an exoplanet far closer to home—4.22 light-years, to be exact—and it’s potentially habitable to boot. Proxima b, reported 24 August in Nature, sits in the liquid-water-friendly habitable zone of the red dwarf Proxima Centauri, the smallest of the three-star Alpha Centauri system and the star nearest to the Sun. From telescope data collected between 2000 and 2008, researchers picked out hints of a signal indicating that the star was wobbling with a velocity of about 1.38 m/s, potentially due to the gravitational tug of an orbiting planet. A dedicated observing run earlier this year by the European Southern Observatory’s 3.6 m telescope at La Silla Observatory, Chile, confirmed the planet’s presence. The radial velocity measurements reveal that the planet circles the star every 11.2 days, an orbit that puts the planet within Proxima Centauri’s habitable zone, and has a mass at least 1.1 times that of Earth’s. Although those parameters seem to suggest that Proxima b is both rocky and suitable for life, it’s important to note that the planet’s diameter, density, and precise mass are unknown. And astronomers are unsure whether life could thrive on red dwarf planets, since they are probably tidally locked and frequently doused in UV and x-ray radiation from stellar flares.
Still, the fact that Earth’s nearest stellar neighbor hosts a potentially habitable planet is a discovery worth celebrating. It’s a moment astronomers had hoped for ever since the 2012 claimof a planet circling another star in the Alpha Centauri system was thrown in doubt after follow-up observations and analyses. The discovery should also provide a boost for the ambitious interstellar mission Breakthrough Starshot, which aims to launch high-speed miniature probes to the Alpha Centauri system. Although there are many obstacles to overcome for launching such a mission, Proxima b certainly represents an enticing target.
Here are the best places to learn more about the discovery:
The Washington Post has a nice roundup that emphasizes the limitations in our knowledge of whether Proxima b qualifies as “Earth-like.”
At Scientific American, Lee Billings, author of a book on exoplanets, details the discovery and adds helpful context.
A New York Times visualization illustrates the location and orbit of Proxima b along with the radial velocity signal that led to the planet’s discovery.
Astronomer Abel Méndez at the University of Puerto Rico at Arecibo’s Planetary Habitability Laboratory writes that by one measure Proxima b is the most similar exoplanet to Earth that we know, but that doesn’t mean it’s the most suitable for life.