Since its discovery in 2016, the exoplanet Proxima b has been one of our most promising candidates for extraterrestrial life. Recent news that a powerful solar flare blasted the planet with radiation in March 2017 may have dashed those hopes of habitability.

In 2016, when scientists confirmed the discovery of Proxima b, a potentially habitable, Earth-sized planet orbiting the star Proxima Centauri, it was cause for astrobiological celebration. Proxima Centauri is the nearest star to our solar system — just 4.24 light-years away — so, in the search for extraterrestrial life, we’d found a promising candidate in our cosmic backyard.

Now, new information casts doubt on the exoplanet’s life-hosting potential, not to mention our plans to investigate it.

An artist’s impression of a flare from Proxima Centauri, modeled after the loops of glowing hot gas seen in the largest solar flares, with the exoplanet Proxima b in the foreground. Image Credit: Roberto Molar Candanosa / Carnegie Institution for Science, NASA/SDO, NASA/JPL

Based on observations from the Atacama Large Millimeter/submillimeter Array (ALMA), scientists recently found that Proxima Centauri emitted an exceptionally powerful solar flare in March 2017. If life ever did exist on Proxima b, this violent flare, which was 10 times brighter than our Sun’s largest flares, may have wiped it out.

“March 24, 2017, was no ordinary day for Proxima Cen,” said Meredith MacGregor, an astronomer from the Carnegie Institution for Science, in a National Radio Astronomy Observatory press release.

MacGregor’s team found that the flare made Proxima Centauri 1,000 times brighter over the course of just 10 seconds. Though the entire event (including a smaller preceding flare) lasted less than two minutes, it bathed little Proxima b with an estimated 4,000 times more radiation than Earth receives from the Sun’s usual flares.

That’s not great news for anything that might have been alive on the exoplanet’s surface.

We already have powerful telescopes in development that promise to give us a closer look at Proxima b, and missions designed to help us determine if it hosts life. Even if we find out the exoplanet it uninhabitable, that knowledge could inform our search for life on planets beyond the Centauri system.

Small dwarf stars like Proxima Centauri are the most common type in our galaxy, and we’ve already found planets in the habitable zones around several. But given that dwarf stars are prone to violent fits, like Proxima Centauri’s most recent episode, any life on the surfaces of these planets would need to be esheltered from — or hardened against — some intense solar radiation.

References: Axios, National Radio Astronomy Observatory

Space weather emitted by Proxima Centauri, the star closest to our stars (Sun), may make that system rather inhospitable to life after all. Using data from the Atacama Large Millimeter/submillimeter Array (ALMA), a team of astronomers discovered that a powerful stellar flare erupted from Proxima Centauri last March. 

This finding, published in the Astrophysical Journal Letters, raises questions about the habitability of our solar system’s nearest exoplanetary neighbor, Proxima b, which orbits Proxima Centauri.

At its peak, the newly recognized flare was 10 times brighter than our sun’s largest flares, when observed at similar wavelengths. Stellar flares have not been well studied at the millimeter and submillimeter wavelengths detected by ALMA, especially around stars of Proxima Centauri’s type, called M dwarfs, which are the most common in our galaxy.

“March 24, 2017, was no ordinary day for Proxima Cen,” said Meredith MacGregor, an astronomer at the Carnegie Institution for Science, Department of Terrestrial Magnetism in Washington, D.C., who led the research with fellow Carnegie astronomer Alycia Weinberger. Along with colleagues from the Harvard-Smithsonian Center for Astrophysics, David Wilner and Adam Kowalski, and Steven Cranmer of the University of Colorado Boulder — they discovered the enormous flare when they reanalyzed ALMA observations taken last year.

The flare increased Proxima Centauri’s brightness by 1,000 times over 10 seconds. This was preceded by a smaller flare; taken together, the whole event lasted fewer than two minutes of the 10 hours that ALMA observed the star between January and March of last year.

ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 meters

Stellar flares happen when a shift in the star’s magnetic field accelerates electrons to speeds approaching that of light. The accelerated electrons interact with the highly charged plasma that makes up most of the star, causing an eruption that produces emission across the entire electromagnetic spectrum.

“It’s likely that Proxima b was blasted by high energy radiation during this flare,” MacGregor explained, adding that it was already known that Proxima Centauri experienced regular, although smaller, X-ray flares. “Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilized the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”

An earlier paper that also used the same ALMA data interpreted its average brightness, which included the light output of both the star and the flare together, as being caused by multiple disks of dust encircling Proxima Centauri, not unlike our own solar system’s asteroid and Kuiper belts.

But when MacGregor, Weinberger, and their team looked at the ALMA data as a function of observing time, instead of averaging it all together, they were able to see the transient explosion of radiation emitted from Proxima Centauri for what it truly was.

“There is now no reason to think that there is a substantial amount of dust around Proxima Cen,” Weinberger said. “Nor is there any information yet that indicates the star has a rich planetary system like ours.”

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Credit: nrao.edu

The new planet dubbed Proxima C orbits Proxima Centauri, a star system located some 4 light years from Earth. You may remember the Proxima Centauri system from 2016 when astronomers discovered a planet they nicknamed the SECOND Earth.

In August of 2016, astronomers announced the discovery of Proxima b, a potentially habitable orbiting Proxima Centauri, the star closest to the Solar System—located a mere four light years from Earth.

Proxima Centauri is about one-seventh the actual diameter of the Sun. It has a mass about an eighth of the Sun’s mass (M☉), and its average density is about 40 times that of the Sun

The discovery of Proxima B got astronomers very excited, they believed they discovered an alien world extremely similar to Earth, capable of sustaining life as we know it. Some even called Proxima B the SECOND Earth or Earth’s twin.

Now, a new data analysis has shown the presence of another alien world orbiting Proxima Centauri: Proxima C.

Using the  High Accuracy Radial velocity Planet Searcher (HARPS), a high-precision spectrograph installed on ESO’s 3.6-meter telescope at the La Silla Observatory in Chile, astronomers involved in the Red Dots project have found what they believe could be the signature of another exoplanet orbiting Proxima Centauri.

The ongoing Red Dots campaign, is a search for planets around our nearest three red dwarf stars: Proxima Centauri, Barnard’s Star, and Ross 154.

Just as a star influences the planets by means of gravity, the planets also do the same with their star, causing the star to “totter” and change the wavelength of its brightness in a very small but measurable amount. By analyzing these repetitive and predictable changes, astronomers are able to infer the presence of a planet.

This is awesome, mostly because experts still believe Proxima B—the alien world discovered in 2016—could sustaining life as we know it.

The discovery of Proxima C raises hopes of finding another potentially habitable world outside our solar system.

The following chart shows the 2016 data that confirmed the existence of Proxima b (top left), where you can see the curve representing the star’s wobble, with a regular pattern of radial velocity change that repeats every 11, 2 days. In the new measurements of HARPS (top right), astronomers detected another, very similar signal that infers the existence of Proxima C, another alien world orbiting the Proxima Centauri system.

As noted by Astrobiology, the new data once again confirms Proxima B’s signal (in yellow), but also includes additional data patterns — visible here as a downward slope in both the 2016 and 2017 data points — hinting that there may be more to be discovered. To make a firmer statement on what is causing these patterns, astronomers need to use quantitative mathematical tools.

To ascertain whether it is a planet, astronomers made use of quantitative mathematical tools, such as a periodogram (shown at the bottom of the image above), which looks for repetitive signals in the data – graphed as prominent peaks – which indicate the presence of a planet.

The first signal (white) corresponds to Proxima b. The second set of possible periods (in red), of about 200 days, would be the hypothetical planet Proxima c.

The Red Dots exoplanetary search campaign will continue until the end of September, so the next few weeks will be critical to confirm or discard this data.

Sources and References: 

Space.com

National Geographic