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