Another study has cast doubt on the habitability of an Earth-like exoplanet in the "habitable zone" of a red dwarf, in this case Proxima Centauri specifically:
At only four light-years away, Proxima b is our closest known extra-solar neighbor. However, due to the fact that it hasn't been seen crossing in front of its host star, the exoplanet eludes the usual method for learning about its atmosphere. Instead, scientists must rely on models to understand whether the exoplanet is habitable.
One such computer model considered what would happen if Earth orbited Proxima Centauri, our nearest stellar neighbor and Proxima b's host star, at the same orbit as Proxima b. The NASA study, published on July 24, 2017, in The Astrophysical Journal Letters [DOI: 10.3847/2041-8213/aa7eca], suggests Earth's atmosphere wouldn't survive in close proximity to the violent red dwarf.
[...] In Proxima Centauri's habitable zone, Proxima b encounters bouts of extreme ultraviolet radiation hundreds of times greater than Earth does from the sun. That radiation generates enough energy to strip away not just the lightest molecules — hydrogen — but also, over time, heavier elements such as oxygen and nitrogen.
The model shows Proxima Centauri's powerful radiation drains the Earth-like atmosphere as much as 10,000 times faster than what happens at Earth.
Previously: "Earth-Like" Exoplanet Found in Habitable Zone of Proxima Centauri
Proxima b May Have Oceans
Researchers Suffocate Hopes of Life Support in Red Dwarf "Habitable Zones"
Proxima B Habitability Study Adds Climate Model
Related: MAVEN Results Find Solar Wind and Radiation Responsible for Stripping the Martian Atmosphere
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Astronomers have reportedly discovered an Earth-like exoplanet in the habitable zone of Proxima Centauri, one of the closest stars to our Sun. However, the claim is based on an anonymous source who is said to have leaked the news ahead of an announcement by the European Southern Observatory:
[In] what may prove to be the most exciting find to date, the German weekly Der Spiegel [translation] announced recently that astronomers have discovered an Earth-like planet orbiting Proxima Centauri, just 4.25 light-years away. Yes, in what is an apparent trifecta, this newly-discovered exoplanet is Earth-like, orbits within it's sun's habitable zone, and is within our reach. But is this too good to be true? [...] Citing anonymous sources, the magazine stated:
The still nameless planet is believed to be Earth-like and orbits at a distance to Proxima Centauri that could allow it to have liquid water on its surface — an important requirement for the emergence of life. Never before have scientists discovered a second Earth that is so close by.
In addition, they claim that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory's reflecting telescope. Coincidentally, it was this same observatory that announced the discovery of Alpha Centauri Bb back in 2012, which was also declared to be "the closest exoplanet to Earth". Unfortunately, subsequent analysis cast doubt on its existence, claiming it was a spurious artifact of the data analysis.
However, according to Der Spiegel's unnamed source – whom they claim was involved with the La Silla team that made the find – this latest discovery is the real deal, and was the result of intensive work. "Finding small celestial bodies is a lot of hard work," the source was quoted as saying. "We were moving at the technically feasible limit of measurement." The article goes on to state that the European Southern Observatory (ESO) will be announcing the finding at the end of August. But according to numerous sources, in response to a request for comment by AFP, ESO spokesman Richard Hook refused to confirm or deny the discovery of an exoplanet around Proxima Centauri.
[Continues...]
Researchers have calculated that Proxima b may have liquid water oceans on its surface, or even be an "ocean planet" based on larger estimates of its radius:
A rocky planet discovered in the "habitable" zone of the star nearest our Sun may be covered with oceans, researchers at France's CNRS research institute said Thursday. A team including CNRS astrophysicists have calculated the size and surface properties of the planet dubbed Proxima b, and concluded it may be an "ocean planet" similar to Earth.
[...] They calculated the radius was between 0.94 and 1.4 times that of Earth, which is 6,371 kilometres on average. Assuming a minimum radius of 5,990 km, the planet would be very dense, with a metallic core making up two-thirds of the entire planet's mass, surrounded by a rocky mantle. If there is surface water, it would not contribute more than 0.05 percent to the planet's total mass, the team said—similar to Earth, where it is about 0.02 percent.
In the larger planet scenario, with a radius of 8,920 km, Proxima b's mass would be split 50-50 between a rocky centre and surrounding water. "In this case, Proxima b would be covered by a single, liquid ocean 200 km deep," said the CNRS. "In both cases, a thin, gassy atmosphere could surround the planet, like on Earth, rendering Proxima b potentially habitable," it concluded.
The exoplanet has not been seen transiting Proxima Centauri, so further data about its size and composition will require the James Webb Space Telescope or other observatories to directly observe it.
Previously: "Earth-Like" Exoplanet Found in Habitable Zone of Proxima Centauri
ESO Confirms Reports of Proxima Centauri Exoplanet
Astrophysicists have modeled the effects of red dwarf star flare activity on the atmospheres of orbiting exoplanets, and found that heavy gases including oxygen would be lost quickly, even in the so-called "habitable zone":
[When] the scientists accounted for superflares, their new model indicates the violent storms of young red dwarfs generate enough high-energy radiation to enable the escape of even oxygen and nitrogen – building blocks for life's essential molecules.
"The more X-ray and extreme ultraviolet energy there is, the more electrons are generated and the stronger the ion escape effect becomes," Glocer said. "This effect is very sensitive to the amount of energy the star emits, which means it must play a strong role in determining what is and is not a habitable planet."
Considering oxygen escape alone, the model estimates a young red dwarf could render a close-in exoplanet uninhabitable within a few tens to a hundred million years. The loss of both atmospheric hydrogen and oxygen would reduce and eliminate the planet's water supply before life would have a chance to develop.
"The results of this work could have profound implications for the atmospheric chemistry of these worlds," said Shawn Domagal-Goldman, a Goddard space scientist not involved with the study. "The team's conclusions will impact our ongoing studies of missions that would search for signs of life in the chemical composition of those atmospheres."
The research has obvious implications for exoplanets like Proxima Centauri b.
YouTube video (20 seconds).
How Hospitable Are Space Weather Affected Habitable Zones? The Role of Ion Escape (DOI: 10.3847/2041-8213/836/1/L3) (DX)
NASA's MAVEN spacecraft has found that solar wind and radiation are responsible for stripping away most of the Martian atmosphere, and that the rate of atmosphere loss was higher earlier in the history of the solar system:
Solar wind and radiation are responsible for stripping the Martian atmosphere, transforming Mars from a planet that could have supported life billions of years ago into a frigid desert world, according to new results from NASA's MAVEN spacecraft. "We've determined that most of the gas ever present in the Mars atmosphere has been lost to space," said Bruce Jakosky, principal investigator for the Mars Atmosphere and Volatile Evolution Mission (MAVEN), University of Colorado in Boulder. The team made this determination from the latest results, which reveal that about 65 percent of the argon that was ever in the atmosphere has been lost to space. Jakosky is lead author of a paper on this research to be published in Science on Friday, March 31.
In 2015, MAVEN team members previously announced results that showed atmospheric gas is being lost to space today and described how atmosphere is stripped away. The present analysis uses measurements of today's atmosphere for the first estimate of how much gas was lost through time. Liquid water, essential for life, is not stable on Mars' surface today because the atmosphere is too cold and thin to support it. However, evidence such as features resembling dry riverbeds and minerals that only form in the presence of liquid water indicates the ancient Martian climate was much different – warm enough for water to flow on the surface for extended periods.
It's time to stop it.
YouTube video attached to the article, and infographic. Also at University of Colorado Boulder.
Mars' atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar (DOI: 10.1126/science.aai7721) (DX)
[N]ew models increasingly suggest that the closest Earth-like planet to our solar system could be habitable. Researchers first started playing a bit of "fantasy exoplanet" with the rocky world—dubbed Proxima b—last year after scientists discovered it orbiting our nearest neighbor star, Proxima Centauri. With knowledge only of the luminosity of the star (1/600 that of the sun), the mass of the planet (1.3 times that of Earth), and the length of its orbit (11.2 days), the team was able to predict that, with a variety of possible atmospheres, it would be possible for Proxima b to harbor liquid water on its surface.
Now, another team has upped the level of detail by taking a climate model designed for Earth—the Unified Model developed by the United Kingdom's Met Office—and pasted it onto Proxima b.
[...] As the team reports today in Astronomy & Astrophysics, it found an even wider range of circumstances in which Proxima b could have liquid water than the earlier study. The fact that the two very different models agree so closely is "somewhat remarkable," the team writes.
Source: Daniel Clery at sciencemag.org
The Atacama Large Millimeter Array (ALMA) has reported the detection of a dust belt around 1-4 astronomical units (AU) from Proxima Centauri, as well as a possible outer belt 30 AU away and an "unknown source" (possible exoplanet) about 1.6 AU away from the star. The data also show "a hint of warmer dust closer to the star".
Proxima b is 0.05 AU from Proxima Centauri, and is considered to be in the star's "habitable zone". The 1-4 AU belt on the other hand has a characteristic temperature of about 40 K, while the 30 AU outer belt would have a temperature of about 10 K. Neptune's moon Triton is roughly 30 AU from the Sun with a temperature of 38 K.
The 1-4 AU belt is estimated to contain 0.01 Earth masses of asteroids (primarily?) up to 50 km in diameter. By comparison, our main asteroid belt (including Ceres) is estimated to contain 4% of the Moon's mass, or about 0.000492 Earth masses (Ceres is about 0.00015 Earth masses, roughly a third of the main asteroid belt). A minimum estimate for the Kuiper belt's mass is 20x that of the main asteroid belt, or the equivalent of this newly detected dust belt around Proxima Centauri.
Astronomy Magazine has an interview with one of the co-authors, who noted another possible exoplanet at 0.5 AU:
Alien Life Could Thrive On Four Earth-Like Planets Close To The Solar System, Says Study
Alien life could be evolving right now on some of the nearest exoplanets to our solar system, claim scientists at Cornell University in Ithaca, New York. Their proof is you.
It's been presumed that the high levels of radiation known to be bombarding many of the rocky Earth-like exoplanets discovered so far by astronomers precludes life, but that theory is turned on its head by new research published [open, DOI: 10.1093/mnras/stz724] [DX] in Monthly Notices of the Royal Astronomical Society.
In "Lessons from Early Earth: UV Surface Radiation Should Not Limit the Habitability of Active M Star System", the authors say that all of life on Earth today evolved from creatures that thrived during an era of much higher levels of UV radiation assault. So why not life on alien worlds? It also poses another question: does the evolution of life actually require high levels of radiation?
The exoplanets studied are Proxima b, TRAPPIST-1e, Ross 128 b, and LHS 1140 b.
Related: ESO Confirms Reports of Proxima Centauri Exoplanet
Proxima b May Have Oceans
Seven Earth-Sized Exoplanets, Including Three Potentially Habitable, Identified Around TRAPPIST-1
Possible Habitable Planet, LHS 1140b, Only 40 Light Years Away
An Earth-Like Atmosphere May Not Survive the Radiation in Proxima b's Orbit
Hubble Observations Suggest TRAPPIST-1 Exoplanets Could Have Water
Ross 128b: A Newly Discovered "Earth-Like" Exoplanet Orbiting a Less Active Red Dwarf
Another TRAPPIST-1 Habitability Study
(Score: 0) by Anonymous Coward on Friday August 04 2017, @05:28PM
Fuggetaboot it. It's Spaceballs.
I can assure both of your readers that there's absolutely no air shortage whatsoever on Proxima b.
(Score: 0) by Anonymous Coward on Friday August 04 2017, @06:07PM
With apologies to El Reg - surely we already knew this about the Red Dwarf near Proxima B? If you went there you'd find that it's cold outside, there's no kind of atmosphere. You'd be all alone, more or less...