Proxima Centauri Unleashes ‘Doomsday’ Flare

Proxima b just got roasted.

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Proxima b weather report: Sunny with the chance of a flare of doom (NASA)

Having a bad day? Well, spare a thought for any hypothetical aliens living on Proxima b.

Proxima Centauri is a small, dim M dwarf—commonly known as a red dwarf—located approximately 4.2 light-years away. Over the last couple of years, this diminutive star has spent a lot of time in the headlines after the discovery of a small rocky world, called Proxima b, inside the star’s habitable zone.

With the knowledge that there’s a potentially temperate world on our cosmic doorstep, speculation started to fly that this exoplanet could become a future interstellar destination for humanity or that it’s not just a “habitable” world, perhaps it’s inhabited, too.

Putting aside the fact that we have no idea whether this interesting exoplanet possesses water of any kind, let alone if it even has an atmosphere (two pretty important ingredients for life as we know it), it is certainly an incredible find. But there are some caveats to Proxima b’s habitability and the main one is the unpredictability of its star.

The problem with red dwarfs is that they are angry little stars. In fact, they have long been known as “flare stars” as, well, they produce flares. What they lack in energy output they certainly make up for in explosions. Really, really big explosions.

Last March, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile detected a cataclysmic stellar flare erupting from Proxima Centauri, and this thing put anything our Sun can produce to shame.

“March 24, 2017, was no ordinary day for Proxima Cen,” said astronomer Meredith MacGregor, of the Carnegie Institution for Science in Washington D.C., in a statement.

Over just ten seconds on that special day, a powerful flare boosted Proxima Centauri’s brightness by over 1,000 times greater than normal. This mega-flare event was preceded by a smaller flare event and both flares occurred over a two minute period.

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The brightness of Proxima Centauri as observed by ALMA over the two minutes of the event on March 24, 2017 (Meredith MacGregor, Carnegie)

Although astronomers have little idea where Proxima b was in relation to the flaring site, it would have undoubtedly received one hell of a radiation dose from the eruption.

“It’s likely that Proxima b was blasted by high energy radiation during this flare,” said MacGregor. “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.”

The habitable zone around any star is the distance at which a world must orbit to receive just the right amount of energy to maintain water in a liquid state. Liquid water, as we all know, is necessary for life (as we know it) to evolve. Whereas the Earth orbits the Sun at an average distance of nearly 100 million miles (a distance that unsurprisingly puts us inside our star’s habitable zone), for a star as cool as Proxima Centauri, its habitable zone is closer. Much, much closer. This means Proxima b, with an orbital distance of approximately 4.6 million miles, is nearly 22 times closer to its star than the Earth is to the Sun. Orbiting so close to a star pumping out a flare ten times more powerful than the largest flare our Sun can generate is the space weather equivalent of sitting inside the blast zone of a nuclear weapon.

As MacGregor argues, Proxima Centauri is known to generate these kinds of flares, and Proxima b has been bathed in its radiation for eons. It doesn’t seem likely that the exoplanet would be able to form an atmosphere, let alone hold onto one.

So, what of Proxima b’s hypothetical aliens? Well, unless they’ve found a niche deep under layers of ice and/or rock, it seems that this “habitable” world is anything but.

For more on why Proxima b would be a bad place to take your honeymoon, read
Sorry, Proxima Centauri Is Probably a Hellhole, Too.

Exocomets Seen Transiting Kepler’s Stars

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ESO/L. Calçada

If you thought detecting small planets orbiting stars dozens of light-years distant was impressive, imagine trying to “see” individual comets zoom around their star. Well, astronomers have done just that after poring over 201,250 targets in the Kepler dataset.

NASA’s Kepler mission has been taking observational data since 2009, staring unblinkingly at a small area of sky in the direction of the constellation Cygnus until it transitioned into the K2 mission in 2013. In total, the space telescope has discovered over 2,500 confirmed exoplanets (and over 5,000 candidate exoplanets), transforming our understanding of the incredible menagerie of alien worlds in our galaxy. After including discoveries by other observatories, we know of over 3,500 exoplanets that are out there.

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Kepler looks for very slight dips in light as exoplanets pass in front of their stars to detect alien worlds (NASA/JPL-Caltech)

Kepler detects exoplanets by watching out for periodic dips in the brightness of stars in its field of view. Should a slight dip in brightness be detected, it could mean that there’s an exoplanet orbiting in front of its host star—an event known as a “transit.” While these transits can help astronomers learn about the physical size of exoplanets and the period of their orbits, for example, there’s much more information in the transit data than initially meets the eye.

In a new study to be published in the journal Monthly Notices of the Royal Astronomical Society on Feb. 21, a team of researchers are reporting that they have found evidence for individual comets transiting in front of two stars. They detected six individual transits at the star KIC 3542116, which is located approximately 800 light-years from Earth, and one transit at KIC 11084727. Both stars of a similar type (F2V) and are quite bright.

Though other observations have revealed dusty evidence of cometary activity in other star systems before, this is the first time individual comets have been found leaving their own transit signal in Kepler data. And it turns out that their transit fingerprint is a little bit special:

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One comet’s three transits around its host star, KIC 3542116. Credit: Rappaport et al. MNRAS 474, 1453, 2018.

“The transits have a distinct asymmetric shape with a steeper ingress and slower egress that can be ascribed to objects with a trailing dust tail passing over the stellar disk,” the astronomers write in their paper (arXiv preprint). “There are three deeper transits with depths of ≃ 0.1 percent that last for about a day, and three that are several times more shallow and of shorter duration.”

In other words, when compared with the transit of an exoplanet, comet transits appear wonky (or asymmetric). This is because comets possess tails of gas and dust that trail the nucleus; as the comet passes in front of its star, starlight is quickly blocked, but as it drifts by in its orbit, the dusty tail will act as a starlight dimmer, gradually allowing more starlight to be seen by Kepler. An exoplanet—or, indeed, any spherical object without a dusty tail—will create a symmetrical dip in the transit signal. Other possible causes of this unique transit signal (such as starspots and instrumental error) were systematically ruled out. (Interestingly, in a 1999 Astronomy & Astrophysics paper, this asymmetric comet transit signal was predicted by another team of researchers, giving this current work some extra certainty.)

But just because there was evidence of six comet transits at KIC 3542116, it doesn’t mean there were six comets. Some of those transits could have been caused by the same comet, so the researchers have hedged their bets, writing: “We have tentatively postulated that these are due to between 2 and 6 distinct comet-like bodies in the system.”

Using these transit data, the study also takes a stab at how big these comets are and even estimates their orbital velocities. The researchers calculate that these comets have masses that are comparable to Halley’s Comet, the famous short-period comet that orbits the sun every 74-79 years and was last visible from Earth in 1986. For the deeper transits (for KIC 3542116 and the single transit at KIC 11084727), they estimate that the comets causing those transits are travelling at speeds of between 35 to 50 kilometers per second (22 to 31 miles per second). For the shallow, narrow transits at KIC 3542116, the inferred speeds are between 75 to 90 kilometers per second (47 to 56 miles per second).

“From these speeds we can surmise that the corresponding orbital periods are ⪆ 90 days (and most probably, much longer) for the deeper transits, and ⪆ 50 days for the shorter events,” they write.

But the fact that comets were detected at two similar F2V-type stars gives the researchers pause. Is there something special about these stars that means there’s more likelihood of possessing comets? Or is it just chance? Also, the fact that these comet transits were identified by visually analyzing the Kepler datasets suggests that there are likely many more transits hiding in the archived Kepler observations.

One thing’s for sure: this is a mind-blowing discovery that underscores just how valuable exoplanet-hunting missions are for probing the environment around other stars and not just for discovering strange new worlds. I’m excited for what other discoveries are waiting in Kepler transit data and for future exoplanet-hunting missions such as NASA’s Transiting Exoplanet Survey Satellite (TESS) that is scheduled for launch this year.

It’s a Trap: Extraterrestrial Ozone May be Hidden at Exoplanets’ Equators

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ESO/M. KORNMESSER

Fortunately for life on Earth, our planet has an ozone layer. This high-altitude gas performs an invaluable service to biology, acting as a kind of global “sunscreen” that blocks the most damaging forms of ultraviolet radiation. Early in the evolution of terrestrial life, if there were no ozone layer, life would have found it difficult to gain a foothold.

So, in our effort to seek out exoplanets that are suitable for life, future telescopes will seek out so-called “biosignatures” in the atmospheres of alien worlds. Astrobiologists would be excited to find ozone in particular — not only for its biology-friendly, UV-blocking abilities, but also because the molecule’s building blocks (three oxygen atoms) can originate from biological activity on the planet’s surface.

But in a new study published Wednesday (Nov. 29) in the journal Monthly Notices of the Royal Astronomical Society, researchers modeling atmospheric dynamics on tidally-locked “habitable zone” exoplanets have concluded that finding ozone in these exo-atmospheres may be a lot more challenging than we thought.

Red Dwarf Hellholes

Recently, two exoplanets have taken the science news cycle by storm. The first, Proxima b, is touted as the closest temperate exoplanet beyond our solar system. Located a mere 4.22 light-years from Earth, this (presumably) rocky world orbits its star, Proxima Centauri, at just the right distance within the habitable zone. Should this world possess an atmosphere, it would receive just the right amount of energy for any water on its surface to exist in a liquid state. As liquid water is essential for life on Earth, logic dictates that life may be possible there too.

Whether or not Proxima b has the right orbit about its star is academic; there are many other factors to consider before calling it “Earth-like.” For starters, habitable zone exoplanets around red dwarfs will be “tidally locked.” Tidal locking occurs because red dwarf habitable zones are very close to the cool star; so to receive the same amount of heating as our (obviously) habitable Earth, habitable exoplanets around red dwarfs need to cuddle up close. And because they are so close, the same hemisphere will always face the star, while the other hemisphere will always face away. These strange worlds are anything but “Earth-like.”

Also, Proxima Centauri is an angry little star, blasting its locale with regular flares, irradiating its interplanetary space with X-rays, UV and high-energy particles — things that will strip atmospheres from planets and drench planetary surfaces with biology-wrecking radiation. As I’ve previously written, Proxima b is likely a hellhole. And things don’t bode well for that other “habitable” exoplanet TRAPPIST-1d, either.

It’s a Trap

But let’s just say, for astrobiology-sake, that a tidally-locked world orbiting a red dwarf does host an atmosphere and an alien biosphere has managed to evolve despite these stellar challenges. This biosphere is also pretty Earth-like in that oxygen-producing lifeforms are there and the planetary atmosphere has its own ozone layer. As previously mentioned, ozone would be a pretty awesome molecule to find (in conjunction with other biosignatures). But what if no ozone is detected? Well, according to Ludmila Carone, of the Max Planck Institute for Astronomy in Germany, and her team, not finding detecting ozone doesn’t necessarily mean it’s not there, it’s just that the atmospheric dynamics of tidally-locked worlds are very different to Earth’s.

“Absence of traces of ozone in future observations does not have to mean there is no oxygen at all,” said Carone in a statement. “It might be found in different places than on Earth, or it might be very well hidden.”

Earth’s ozone is predominantly produced at the equator where sun-driven chemical reactions occur high in the atmosphere. Atmospheric flows then transport chemicals like ozone toward the poles, giving our planet a global distribution. When carrying out simulations of tidally-locked worlds, however, Carone’s team found that atmospheric flows may operate in reverse, where atmospheric flows travel from the poles to the equator. Therefore, any ozone produced at the equator will become trapped there, greatly reducing our ability to detect it.

“In principle, an exoplanet with an ozone layer that covers only the equatorial region may still be habitable,” added Carone. “Proxima b and TRAPPIST-1d orbit red dwarfs, reddish stars that emit very little harmful UV light to begin with. On the other hand, these stars can be very temperamental, and prone to violent outbursts of harmful radiation including UV.”

So the upshot is, until we have observatories powerful enough to study these hypothetical exoplanetary atmospheres — such as NASA’s James Webb Space Telescope (JWST) or the ESO’s Extremely Large Telescope (ELT) — we won’t know. But modelling the hypothetical atmospheres of these very alien worlds will help us understand what we will, or won’t, see in the not-so-distant future.

“We all knew from the beginning that the hunt for alien life will be a challenge,” said Carone. “As it turns out, we are only just scratching the surface of how difficult it really will be.”

TRAPPIST-1: The ‘Habitable’ Star System That’s Probably a Hellhole

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Red dwarfs can be angry little stars (NASA/GSFC/S. Wiessinger)

There are few places that elicit such vivid thoughts of exotic habitable exoplanets than TRAPPIST-1 — a star system located less than 40 light-years from Earth. Alas, according to two recent studies, the planetary system surrounding the tiny red dwarf star may actually be horrible.

For anyone who knows a thing or two about red dwarfs, this may not come as a surprise. Although they are much smaller than our sun, red dwarfs can pack a powerful space weather punch for any world that orbits too close. And, by their nature, any habitable zone surrounding a red dwarf would have to be really compact, a small detail that would bury any “habitable” exoplanet in a terrible onslaught of ultraviolet radiation and a blowtorch of stellar winds. These factors would make the space weather environment around TRAPPIST-1 extreme to say the least.

“The concept of a habitable zone is based on planets being in orbits where liquid water could exist,” said Manasvi Lingam, a Harvard University researcher who led a Center for Astrophysics (CfA) study, published in the International Journal of Astrobiology. “This is only one factor, however, in determining whether a planet is hospitable for life.”

The habitable zone around any star is the distance at which a small rocky world can orbit and receive just the right amount of heating to maintain liquid water on its hypothetical surface. Orbit too close and the water vaporizes; too far and it freezes. As life needs liquid water to evolve, seeking out exoplanets in their star’s habitable zone is a good place to start.

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The peaceful surface of a TRAPPIST-1 habitable zone exoplanet as imagined in this artist’s rendering (NASA/JPL-Caltech)

For the sun-Earth system, we live in the middle of the habitable zone, at a distance of one astronomical unit (1 AU). For a world orbiting a red dwarf like TRAPPIST-1, its orbital distance would be a fraction of that — i.e. three worlds orbit TRAPPIST-1 in the star’s habitable zone at between 2.8% and 4.5% the distance the Earth orbits the sun. This is because red dwarfs are very dim and produce meager heating — for a world to receive the same degree of heating that our planet enjoys, a red dwarf world would need to snuggle up really close to its star.

But just because TRAPPIST-1 is dim, it doesn’t mean it holds back on ultraviolet radiation. And, according to this study, the three “habitable” exoplanets in the TRAPPIST-1 system are likely anything but — they would receive disproportionate quantities of damaging ultraviolet radiation.

“Because of the onslaught by the star’s radiation, our results suggest the atmosphere on planets in the TRAPPIST-1 system would largely be destroyed,” said co-author Avi Loeb, who also works at Harvard. “This would hurt the chances of life forming or persisting.”

Life as we know it needs an atmosphere, so the erosion by UV radiation seems like a significant downer for the possible evolution of complex life.

That’s not the only bad news for our extraterrestrial life dreams around TRAPPIST-1, however. Another study carried out by the CfA and the University of Massachusetts in Lowell (and published in The Astrophysical Journal Letters) found more problems. Like the sun, TRAPPIST-1 generates stellar winds that blast energetic particles into space. As these worlds orbit the star so close, they would be sitting right next to the proverbial nozzle of a stellar blowtorch — models suggest they experience 1,000 to 100,000 times stellar wind pressure than the solar wind exerts on Earth.

And, again, that’s not good news if a planet wants to hold onto its atmosphere.

“The Earth’s magnetic field acts like a shield against the potentially damaging effects of the solar wind,” said Cecilia Garraffo of the CfA and study lead. “If Earth were much closer to the sun and subjected to the onslaught of particles like the TRAPPIST-1 star delivers, our planetary shield would fail pretty quickly.”

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The TRAPPIST-1 exoplanet family. TRAPPIST-1 e, f and g are located in the system’s habitable zone (NASA/JPL-Caltech)

So it looks like TRAPPIST-1 e, f and g really take a pounding from their angry little star, but the researchers point out that it doesn’t mean we should forget red dwarfs as potential life-giving places. It’s just that life would have many more challenges to endure than we do on our comparatively peaceful place in the galaxy.

“We’re definitely not saying people should give up searching for life around red dwarf stars,” said co-author Jeremy Drake, also from CfA. “But our work and the work of our colleagues shows we should also target as many stars as possible that are more like the sun.”

The ‘Alien Megastructure’ Star Is Doing Weird Things Again

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NASA (edit by Ian O’Neill)

In our quest to understand what the heck is going on with Tabby’s Star, astronomers have been given a cosmic gift — a dimming event is happening right now and they’re collecting data in real time.

Early Friday morning, the star — officially designated KIC 8462852 — dipped in brightness inextricably and bulletins started to fly around the internet. Astronomers involved in the original discovery took to Twitter to announce the awesomeness and rally the world’s observatories to point their telescopes at the action 1,300 light-years away:

But why all the excitement? Well, this is the same star that, last year, hogged the headlines with speculation that a super advanced alien civilization was building some kind of “megastructure” around the star. (You can read my article on it here.) But why would the world’s media, let alone professional scientists, be okay with even hinting at the “alien” thing?

Well, as part of the Planet Hunters project, Tabby’s Star is wonderfully weird. After analyzing observations from NASA’s exoplanet-hunting Kepler Space Telescope, the citizen scientists noticed something peculiar.

Usually, Kepler’s ultra-sensitive optics detect the slight dimming of stars when any planets in orbit drift in front — an event known as a “transit.” These transits are typically very slight, but the signals detected at KIC 8462852 were mind-boggling. Between 2011 and 2013, Tabby’s Star exhibited a series of dips, dimming the brightness of the star by over 20 percent. Tabby’s Star was so-named after astronomer Tabetha Boyajian who led this research. Further studies of the star has also revealed a longer period of dimming.

And on Friday morning, it started happening again.

“At about 4 a.m. this morning, I got a phone call from Tabby [Boyajian] saying that Fairborn [Observatory] in Arizona had confirmed that the star was 3 percent dimmer than it normally is and that is enough that we are absolutely confident that this is no statistical fluke,” said Jason Wright, an associate professor of astronomy at Pennsylvania State University, during a live webcast. “We’ve now got it confirmed at multiple observatories I think.”

Now that astronomers are able to observe the star while the dimming is happening live (rather than studying past observations, which as been the case up until now), spectra of the star can be recorded and compared to previous data. This spectral information might reveal what material is causing the weird transit signals, potentially ruling some hypotheses out. But it might also create new questions.

Many hypotheses have been put forward for these unprecedented events before Friday. The most popular natural explanation has been the possibility that a giant “swarm” of comets drifted between the star and us, blocking the starlight. But this explanation falls short and doesn’t really explain why the brightness dips are so dramatic.

The most popular unnatural explanation is — you guessed italiens and astronomers are having a really hard job disproving this hypothesis. This idea is based around the possibility that a super advanced alien civilization (that’s well on its way to becoming a type II Kardashev civilization) is building a star-spanning solar array, akin to a Dyson swarm. In this scenario, the dimming in brightness would be caused by vast solar arrays blocking the light from view.

Now that the dimming is happening again, it will be interesting to see how the megastructure idea evolves.

Although imagining super-advanced aliens building stuff around a nearby star is fun, this episode so early in our hunt for extrasolar worlds is giving us a glimpse of just how strange our galaxy can be. In all likelihood, it probably isn’t an alien megastructure and more likely something astronomers have completely overlooked. But it could also be that these Kepler data are being caused by a natural stellar phenomenon that we’ve never seen before — a possibility that could be revealed very soon.

Alien Worlds: Extrasolar Planets Imaged for First Time

Two of the three confirmed planets orbiting HR 8799 indicated as
Two of the three confirmed planets orbiting HR 8799 indicated as “b” and “c” on the image above. “b” is the ~7 Jupiter-mass planet orbiting at about 70 AU, “c” is the ~10 Jupiter-mass planet orbiting the star at about 40 AU. Due to the brightness of the central star, it has been blocked and appears blank in this image to increase visibility of the planets (Gemini Observatory)

The day has finally come. We now have direct, infrared and optical observations of planets orbiting other stars. Yesterday, reports from two independent sources surfaced, one from the Gemini and Keck II observatories and the second from the Hubble Space Telescope. Brace yourself for an awe-inspiring display of planets orbiting two stars…

The Gemini/Keck observations were carried out using adaptive optics technology to correct in real-time for atmospheric turbulence. The stunning images of a multiple planetary star system were then constructed from infrared emissions (the image, top, was constructed by Keck II as a follow-up to to the Gemini observations). The system in question is centred around a star called HR 8799, approximately 130 light years from Earth and in the constellation of Pegasus. The entire press release can be found at the Gemini observatory site, where they give the discovery a full run-down.

On the same day, the Hubble Space Telescope team also released images of one extrasolar planet, only this time in optical wavelengths. Although the exoplanet in Hubble’s images is less obvious than the infrared Gemini/Keck II images, incredible detail has been attained, showing a ring of dust around the star Fomalhaut (located in the constellation of Piscis Austrinus). Fomalhaut is 25 light years away and the star’s daughter planet (Fomalhaut b) is only a little under 3 Jupiter masses.

Estimated to be no more than three times Jupiter's mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Austrinus (NASA/ESA)
Estimated to be no more than three times Jupiter’s mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Austrinus (NASA/ESA)

For more news on these discoveries, check out the Gemini/Keck II press release and the Hubble announcement. I’ll leave the ground-breaking announcement to the guys who have spent many years working to achieve this monumental goal.

Wow.

Sources: Gemini, ESA