WASHINGTON, August 24, 2016 – A recently discovered planet, broadly considered to be Earthlike in that it has a mass about a third larger than Earth’s and surface temperatures moderate enough to support ground water, orbits our sun’s nearest stellar companion 24.8 trillion miles away, scientists said today.
The planet, Proxima b, “lies squarely in the center of the classical habitable zone” for Proxima Centauri,” the 31 scientists said in a report of their research that will appear in tomorrow’s issue of the British science journal Nature. A habitable zone is the area around a star in which a planet could support liquid water and, consequently, life similar to that found on Earth.
“The search for life on Proxima b comes next,” Dr. Guillem Anglada-Escudé, the lead scientist in the research said in a European Space Observatory (ESO) news release.
The “habitability of planets like Proxima b — in the sense of sustaining an atmosphere and liquid water on its surface — is a matter of intense debate,” theNature report says, and speculative reports issued before today’s announcement have focused on the possibility of life on the Centaurian planet.
However, “discussion of life on Proxima is premature,” Dr. Paul Butler, staff scientist at the Department of Terrestrial Magnetism with the Carnegie Institution for Science and a coauthor of the report, told CDN by e-mail last night. “All astronomers mean when then say ‘potentially habitable’ is that the planet is the right distance from the star to potentially have liquid water.”
“We do not have any evidence for the presence of water,” Dr. Michael Endl, another of the co-authors of the Nature report told CDN today. Dr. Endl is a research scientist and lecturer at the Donald Observatory at The University of Texas at Austin.
“What we don’t know about Proxima Cen b is more important that what we do know,” said Dr. Butler, who is in Chile observing at the 6.5-m Magellan telescope at Las Campanas Observatory owned and operated by the Carnegie Observatories. “We don’t know anything about its atmosphere. We don’t know if the planet has a magnetic field.”
In addition to Proxima b’s mass and its blistering 11.2 Earth-day year, the planet’s orbital distance from its star is about 4.35 million miles compared to the Earth’s 94-million-mile distance from the sun, the Nature report says. “Although Proxima b orbits much closer to its star than Mercury does to the Sun in the solar system, the star itself is far fainter than the Sun,” the ESO news release says.
Proxima Centauri is an active red dwarf star known for its frequent production of damaging radiation flairs, another potential hazard to life.
“While flares would not be good for large animals like us,” Butler explains, “they would have almost no affect on single cell creatures” like those which “live in Uranium mines on earth. High energy radiation is only dangerous if it stops in your body and releases all of its energy. High energy particles and radiation almost always simply pass through single cell creatures. Most life on earth is comprised of single cell creatures. Most of the history of life on earth consists only of single cell creatures. The vast majority of life in the universe is probably single cell creatures.”
Other factors against habitability, according to the Nature report, include Proxima Centauri’s strong magnetic field and tidal locking, the phenomenon in which, in Earth moon-like fashion, only one half of the planet faces its star.
“The planet is most likely tidally locked,” Dr. Endl said, adding that “3D climate models show that there is sufficient heat transport between the day and night side, but the winds would be enormous.”
However, being tidally locked does not preclude the presence of an atmosphere. “Several studies have shown that planetary magnetic fields in tidally locked planets can be strong enough to prevent atmospheric erosion by stellar magnetic fields and flares,” the Nature report says.
Location in a habitable zone, however, is not the only factor required for sustaining life. A study by Yale University Prof. of Geology and Geophysics Jun Korenaga published Aug. 19 in the journal Science Advances points to the importance of a planet’s internal temperature as a factor in sustaining life. The internal temperature of Jupiter’s watery moon, Europa, has been one source of speculation on the possibility of life there.
Of course, it may be a while before we can have a look-see. Travelling at a speed of 100 million miles per hour would make one-way travel to Proxima b from Earth a journey of more than 28 years. Assisted by gravity, the Juno spacecraft that recently arrived to study Jupiter attained a top speed of about 160,000 miles per hour, according to a Scientific American blog, the barest fraction of any practical speed for such a distance.
“This is just a step in a much longer journey,” said Butler, whom the news releases associated with the planetary discover refer to as an exoplanet search pioneer. “After centuries of speculation, extrasolar planets were finally found 20 years ago. At that time we could only find giant planets, like Jupiter and Saturn. Now we have progressed to the point of finding earth-like potentially habitable planets. The next step may take another 20 years: building telescopes capable of directly imaging the planets and taking spectra of planets to learn about their atmospheres.”
“The first hints of a possible planet were spotted back in 2013,” Dr. Anglada-Escudé said in the ESO news release. However, because the results were indistinct and another three years of refined measurements by a world-wide teams of scientists were needed for a more definitive finding. University of Hertfordshire Prof. Hugh Jones, another of the report’s coauthors, said that initial observations of Proxima b were made more than 15 years ago.
Proxima Centauri, discovered by R.T.A. Innes in 1915, is a very faint star the vicinity of Alpha and Beta Centauri, the third and tenth brightest stars, respectively, and visible in the Southern Hemisphere. Proxima Centauri lies 4.218 light years from the sun. A light year is the distance light travels in one year.
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