On Proxima b
August 2016 saw the announcement of the discovery of an Earth-like planet orbiting our nearest neighbourhood star – the red dwarf Proxima Centauri. The official press release was preceded by a leak to the German media from within the team of astronomers. Here, I tell the story of the rumours of the announcement, and the wider implications of the discovery itself:
Rumours of an Earth-like Planet Orbiting Proxima Centauri
The German magazine Der Spiegel has reported that a major announcement is imminent: there is an Earth-like planet orbiting the red dwarf star Proxima Centauri; the Sun’s closest stellar neighbour at 4.24 light years distance.
The magazine claims that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory’s reflecting telescope in Chile, based upon a leak from an astrophysicist who has been working with the La Silla team (1). This alleged discovery is in keeping with the current work being carried out at La Silla, as described in January earlier this year:
“What good news that the Pale Red Dot project is now planning a two-month observing campaign to search for potential Earth-analogs around Proxima Centauri using HARPS, the High Accuracy Radial velocity Planet Searcher spectrograph at the ESO La Silla 3.6m telescope. Nightly monitoring began on January 18th.” (2)
‘Pale Red Dot’ is a campaign to examine Proxima Centauri for exoplanets using the radial velocity method, seeking the signature of an orbiting planet tugging on its host star. The search by the (HARPS) detector in Chile is not the only close examination of Proxima Centauri to take place this year:
““It seems that suddenly, Proxima has fallen in the spotlight,” says [Guillem] Anglada [of Queen Mary University, London]. “We are talking about three top techniques scheduled in the same year: high-precision Doppler, transit photometry, and microlensing.” The Hubble Space Telescope will take advantage of Proxima Centauri’s passage in front of a background star to hunt for possible microlensing events, small spikes in brightness that an Earth-size planet orbiting the red dwarf star could produce as it magnifies the background star’s light.” (3)
Since details of the Der Spiegel leak were published, speculation has been rife that this Earth-like world might harbour life (4). After all, the red dwarf star is a little older than our Sun. This kind of dwarf star is commonplace through the Milky Way, and are known to harbour their own planetary systems. Their habitable zones are much closer to the star, as the light and heat they give off are clearly less bright than Sun-like yellow dwarf stars, but that environment could be a positive factor for life, too (5). SETI have recently started to focus attention on red dwarfs, seeking out artificial signals from 20,000 of these small stars (6). This recent focus on red dwarfs is a far cry from the time – not so long ago – when life was predominantly considered to be restricted to systems around Sun-like stars. However, it should be borne in mind that Proxima Centauri is capable of producing some strong flare activity (2), like most M-dwarfs, which might be a problem for the emergence of life. Nevertheless, an Earth-like planet orbiting this dwarf star might prove to be the best chance yet of detecting and subsequently investigating life outside the solar system.
But first, I suspect, the most urgent investigation will be about who leaked this story…
Written by Andy Lloyd, 17th August 2016
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The Discovery of Proxima b
As discussed above, the ‘leak’ from a member of the La Silla team proved to be correct. An announcement duly followed describing a 1.3 MEarth planet orbiting in the habitable zone of the red dwarf Proxima Centauri (7), with an accompanying paper published in Nature (8). Naturally, questions of whether life might be possible on such a world arise. The system’s age is old enough to have allowed for life to emerge and consequent evolution to complex forms, but are conditions on the planet itself Earth-like enough?
Image Credit: ESO/M. Kornmesser
The habitability or otherwise of Proxima b depends upon many factors, a lot of which are essentially still educated guesses. Red dwarfs produce powerful flares which may, over time, strip atmospheres from rocky planets in their immediate vicinity. Proxima Centauri is thought to emit flares every 20 minutes or so, most of which are relatively insignificant. But extrapolations from the data available so far about the red dwarf indicates that it is capable of dealing out about 10 flares each year powerful enough to erode the atmosphere of a nearby orbiting planet (9, 10).
Which then leads to another important factor – whether Proxima b has a magnetic field capable of withstanding this kind of steady assault? This is very much an open question.
Life might arise in an ocean which, like some of the Galilean moons of Jupiter, is encased within a protective global ice sheet. It’s likely to be cold enough for a significant distribution of ice, whether the planet is tidally locked or not.
“The research (8) reveals that if the planet’s temperature were down to its sun alone, its surface would be, on average, a chilly -40C. “It seems cold, but then if you look at the same numbers for Earth you would get minus 20, minus 30C,” says [Guillem] Anglada-Escudé [from Queen Mary, University of London]. “What keeps Earth warm is basically that it has an atmosphere and an ocean,” he adds, pointing out that should the newly discovered world also boast an atmosphere, its temperature would likewise be higher.” (7)
Astronomers will now be wanting to get a closer look at this new planet, particularly if it transits across the face of Proxima Centauri, thus allowing any possible atmosphere it may have to be glimpsed. That’s a big ask, but not impossible with up-coming technology.
Image Credit: OAR/National Undersea Research Program (NURP); NOAA
Very much ahead of the game, some theoretical work has already been carried out by Cuban astrobiologists addressing the potential for life to emerge on a planet in the Proxima Centauri system (11). Under the conditions imagined for such a world, the need for a photosynthesis process driven by infrared light seems to be an important requirement. Such a process is certainly possible, as has been discovered around hydrothermal vents at the bottom of our world’s oceans (12). Ironically, the very same flares emitted by the red dwarf star that might cause long-term cause erosion to Proxima b’s atmosphere could also be the life-givers of oceanic biological processes. Red dwarf flares might be problematic for atmospheres, but would surely aid oceanic photosynthesis.
Travel to Proxima b
Is it feasible to send a probe to Proxima b, once it has been established that there’s a reasonable chance of life there? Many articles considering this possibility tend to extrapolate the time needed to get there from the distance involved (4.24 light years) and the speed of our current rocket or ion drive technology. Figures of 70-80,000 years get banded about based upon existing spacecraft velocities:
“If Voyager 1 was traveling in the direction of the red dwarf Proxima Centauri at a constant velocity of 60,000 km/hr, it would take 76,000 years (or over 2,500 generations) to travel that distance. But if it could attain the record-breaking speed of Helios 2‘s close approach of the Sun – a constant speed of 240,000 km/hr – it would take 19,000 years (or over 600 generations) to travel 4.243 light years. Significantly better, but still not in the ream of practicality.” (13)
Although true, these times assume that a craft is initially accelerated up to then settle into a cruising speed for almost the entirety of the journey. A spacecraft exhibiting the capability to constantly accelerate during its journey quickly picks up a real head of steam, and potentially could attain velocities that are in the order of a fraction of the speed of light.
Artist’s impression of a thermo-nuclear rocket decelerating towards Mars. Image Credit: NASA
That spacecraft would, however, also need to decelerate during the second half of the journey so that it doesn’t rush through the target star system like an express train through a sleepy rural station. That limits a spacecraft designed using current nuclear technologies to a 1000 year flight time – still a considerable saving (13)!
The best bet seems to be the long-awaited advent of nuclear fusion technology, which could, potentially, reduce the flight time to Proxima Centauri to between 36 and 40 years (13,14). Other possibilities have been theoretically explored, of course, but would require huge research investments, beyond even the wildest dreams of our modern scientific communities. The best bet seems to be to continue to improve our imaging technologies, and take a closer peak at this wonderfully exciting new world.
Written by Andy Lloyd, 28th August 2016
1) Olaf Stampf “Faraway, So Close! Earth-Like Planet Discovered Orbiting Proxima Centauri” 16th August 2016, http://www.spiegel.de/international/zeitgeist/scientists-find-earthlike-planet-orbiting-proxima-centauri-a-1107983.html
2) Pale Red Dot “Intensifying the Proxima Centauri Planet Hunt” 24th January 2016, https://palereddot.org/intensifying-the-proxima-centauri-planet-hunt/
3) David Dickinson “Hunting for Planets Around Proxima Centauri” 25th January 2016, http://www.skyandtelescope.com/astronomy-news/hunting-for-planets-around-proxima-centauri-0126201667/
4) Eric Mack “What life would be like on an Earth-like planet around Proxima Centauri” 16th August 2016 http://www.cnet.com/news/why-an-earth-like-planet-around-proxima-centauri-might-not-be-so-earth-like/
5) Andy Lloyd “Search for Alien Life” 28th January 2016 http://www.andylloyd.org/darkstarblog37.htm
6) Alan Boyle “SETI Institute launches radio search for alien life amid 20,000 red dwarf stars” 30th March 2016 http://www.geekwire.com/2016/seti-institute-launches-search-alien-life-amid-20000-red-dwarf-stars/
7) Nicola Davis “Discovery of potentially Earth-like planet Proxima b raises hopes for life” 24th August 2016 https://www.theguardian.com/science/2016/aug/24/earth-like-planet-found-orbiting-our-suns-nearest-star-raises-hopes-for-life-proxima-b
8) Guillem Anglada-Escudé et al “A terrestrial planet candidate in a temperate orbit around Proxima Centauri” Nature 536, 437–440 (25 August 2016) doi:10.1038/nature19106 http://www.nature.com/nature/journal/v536/n7617/full/nature19106.html
9) Jacob Aron “Proxima b’s star could be blasting away the planet’s atmosphere” 26th August 2016, https://www.newscientist.com/article/2102892-proxima-bs-star-could-be-blasting-away-the-planets-atmosphere/
10) James R. A. Davenport et al “MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri” 24th August 2016, Submitted to ApJ Letters, http://arxiv.org/abs/1608.06672
11) Madeleine Lopez et al “On the habitability of exoplanets orbiting Proxima Centauri” 11th January 2014 https://arxiv.org/abs/1401.3267 Revista Cubana Fisica (Cuban Journal of Physics), 30, 77 (2013) with thanks to Eitan
12) Adam Hadhazy “Infrared Photosynthesis: A potential power source for alien life in Sunless Places” 6th Jun 2013 http://www.astrobio.net/news-exclusive/infrared-photosynthesis-a-potential-power-source-for-alien-life-in-sunless-places/
13) Matt Williams “How long would it take to Travel to the Nearest Star?” 9th August 2016, http://www.universetoday.com/15403/how-long-would-it-take-to-travel-to-the-nearest-star/
14) Kip Thorne “The Futuristic Technology That Could Enable Interstellar Travel” 14th November 2014 http://gizmodo.com/the-futuristic-technology-that-could-enable-interstella-1658145398