Space News Update: Feb 2017

Previously, the most distant blazars detected by Fermi emitted their light when the universe was about 2.1 billion years old. Earlier observations showed that the most distant blazars produce most of their light at energies right in between the range detected by the LAT and current X-ray satellites, which made finding them extremely difficult. Then, in 2015, the Fermi team did a great deal of tinkering and reprogramming, that ushered in so many improvements astronomers said it was like having a brand new instrument. The LAT’s boosted sensitivity at lower energies increased the chances of discovering more far-off blazars.

The research team was led by Vaidehi Paliya and Marco Ajello at Clemson University in South Carolina and included Dario Gasparrini at the Italian Space Agency’s Science Data Center in Rome as well as Ojha. They began by searching for the most distant sources in a catalog of 1.4 million quasars, a galaxy class closely related to blazars and just as weird. As only the brightest sources can be detected at great cosmic distances, they then eliminated all but the brightest objects at radio wavelengths from the list. With a final sample of about 1,100 objects, the scientists then examined LAT data for all of them, resulting in the detection of five new gamma-ray blazars.

Expressed in terms of redshift, the new blazars range from redshift 3.3 to 4.31, which means the light we now detect from them started on its way when the universe was between 1.9 and 1.4 billion years old, respectively.

“Once we found these sources, we collected all the available multiwavelength data on them and derived properties like the black hole mass, the accretion disk luminosity, and the jet power,” said Paliya.

Two of the blazars boast black holes of a billion solar masses or more. All of the objects possess extremely luminous accretion disks that emit more than two trillion times the energy output of our sun. This means matter is continuously falling inward, corralled into a disk and heated before making the final plunge to the black hole.

“The main question now is how these huge black holes could have formed in such a young universe,” said Gasparrini. “We don’t know what mechanisms triggered their rapid development.”

In the meantime, the team plans to continue a deep search for additional examples.

“We think Fermi has detected just the tip of the iceberg, the first examples of a galaxy population that previously has not been detected in gamma rays,” said Ajello.

ANCIENT EARTH TO GIVE CLUES ON EXOPLANET HABITIBILITY

As many of you may know, this is a subject close to my heart! Personally I wouldn’t call this news as such as it’s what I do all day. It’s also why we study our closest neighbours so minutely. The Earth aged around a billion years was a very different place to now. We call it the Archean Age, where our planet took on a decidedly orange hue.

Earth’s atmosphere seems to have been quite different then, probably with little available oxygen but high levels of methane, ammonia and other organic chemicals. Our planet did not get its oxygenated atmosphere until life emerged, which caused its own problems including a mass extinction and ‘snowball Earth’. Geological evidence suggests that haze might have come and gone sporadically from the Archean atmosphere – and researchers aren’t quite sure why. The team reasoned that a better understanding of haze formation during the Archean era might help inform studies of hazy earthlike exoplanets.

“We like to say that Archean Earth is the most alien planet we have geochemical data for,” said Giada Arney of NASA’s Goddard Spaceflight Center in Greenbelt, Maryland, and a member of the NASA Astrobiology Institute’s Virtual Planetary Laboratory based at the University of Washington, Seattle. Arney is the lead author of two related papers published by the team.

 

In the best case, haze in a planet’s atmosphere could serve up a smorgasbord of carbon-rich, or organic, molecules that could be transformed by chemical reactions into precursor molecules for life. Haze also might screen out much of the harmful UV radiation that can break down DNA. In the worst case, haze could become so thick that very little light gets through. In this situation, the surface might get so cold it freezes completely. If a very thick haze occurred on Archean Earth, it might have had a profound effect, because when the era began roughly four billion years ago, the sun was fainter, emitting perhaps 80 percent of the light that it does now. Arney and her colleagues put together sophisticated computer modeling to look at how haze affected the surface temperature of Archean Earth and, in turn, how the temperature influenced the chemistry in the atmosphere. The Earth did in fact have liquid oceans as soon as 100 million years after its formation which being such an excellent solvent, would have enabled all sorts of chemical mixing. This would also have been aided by the Moon being a lot closer than it is now, giving us much bigger tides.

The ‘faint young Sun‘ paradox has bothered scientists for years. How exactly did the Earth keep warm enough? Carbon dioxide is indeed a greenhouse gas, but insufficient on its own to have given the planet an atmospheric duvet. Methane too, is an even more powerful greenhouse gas, but due to the conditions at the time, it can’t be the whole story. At the present time, most of our atmosphere is nitrogen. In itself, insufficient, but the young Sun was a lively creature back in the day, sending out far more Solar flares than now. This may have enabled the production of nitrous oxide, which is a VERY powerful greenhouse gas indeed and may have been produced in sufficient quantities to have warmed the Earth. The jury is still currently out, but it does make sense.

The new modeling indicates that as the haze got thicker, less sunlight would have gotten through, inhibiting the types of sunlight-driven chemical reactions needed to form more haze. This would lead to the shutdown of haze-formation chemistry, preventing the planet from undergoing runaway glaciation due to a very thick haze. The team calls this self-limiting haze, and their work is the first to make the case that this is what occurred on Archean Earth – a finding published in the November 2016 issue of the journal Astrobiology. The researchers concluded that self-limiting haze could have cooled Archean Earth to about 2.2 C – enough to make a difference but not to freeze the surface completely.

“Our modeling suggests that a planet like hazy Archean Earth orbiting a star like the young sun would be cold,” said Shawn Domagal-Goldman, a Goddard scientist and a member of the Virtual Planetary Laboratory. “But we’re saying it would be cold like the Yukon in winter, not cold like modern-day Mars.”

Such a planet might be considered habitable, even if the mean global temperature is below freezing, as long as there is some liquid water on the surface. In subsequent modeling, Arney and her colleagues looked at the effects of haze on planets that are like Archean Earth but orbiting several kinds of stars.

“The parent star controls whether a haze is more likely to form, and that haze can have multiple impacts on a planet’s habitability,” said co-author Victoria Meadows, the principal investigator for the Virtual Planetary Laboratory and an astronomy professor at the University of Washington.

It looks as if the Archean Earth hit a sweet spot where the haze served as a sunscreen layer for the planet. If the sun had been a bit warmer, as it is today, the modeling suggests the haze particles would have been larger – a result of temperature feedbacks influencing the chemistry – and would have formed more efficiently, but still would have offered some sun protection. The same wasn’t true in all cases. The modeling showed that some stars produce so much UV radiation that haze cannot form. Haze did not cool planets orbiting all types of stars equally, either, according to the team’s results. Dim stars, such as red dwarfs, emit most of their energy at wavelengths that pass right through atmospheric haze; in the simulations, these planets experience little cooling from haze, so they benefit from haze’s UV shielding without a major drop in temperature.

For the right kind of star, though, the presence of haze in a planet’s atmosphere could help flag that world as a good candidate for closer study. The team’s simulations indicated that, for some instruments planned for future space telescopes, the spectral signature of haze would appear stronger than the signatures for some atmospheric gases, such as methane.

“Haze may turn out to be very helpful as we try to narrow down which exoplanets are the most promising for habitability,” said Arney.

Interesting as this study is, the early Earth would be unrecognisable to us and frankly hostile as you’d not be able to breathe, so habitable? Yes, but pleasant…no.

THE PROBLEM WITH RED DWARFS

The search for life beyond Earth starts in habitable zones, the regions around stars where conditions could potentially allow liquid water, which is essential for life as we know it, to pool on a planet’s surface. New NASA research suggests some of these zones might not actually be able to support life due to frequent stellar eruptions, which spew huge amounts of stellar material and radiation out into space, from young red dwarf stars. I’ve talked about flare stars before in relation to our nearest neighbour Proxima Centauri who’s planet Proxima Centauri b was thought to be habitable, but the star’s activity may have erased its chances.

Now, an interdisciplinary team of NASA scientists wants to expand how habitable zones are defined, taking into account the impact of stellar activity, which can threaten an exoplanet’s atmosphere with oxygen loss. This research was published in The Astrophysical Journal Letters on Feb. 6, 2017.

“If we want to find an exoplanet that can develop and sustain life, we must figure out which stars make the best parents,” said Vladimir Airapetian, lead author of the paper and a solar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re coming closer to understanding what kind of parent stars we need.”

To determine a star’s habitable zone, scientists have traditionally considered how much heat and light the star emits. Stars more massive than our sun produce more heat and light, so the habitable zone must be farther out. Smaller, cooler stars yield close-in habitable zones. But along with heat and visible light, stars emit X-ray and ultraviolet radiation, and produce stellar eruptions such as flares and coronal mass ejections – collectively called space weather. One possible effect of this radiation is atmospheric erosion, in which high-energy particles drag atmospheric molecules – such as hydrogen and oxygen, the two ingredients for water – out into space. Airapetian and his team’s new model for habitable zones now takes this effect into account.

In this artist’s concept, X-ray and extreme ultraviolet light from a young red dwarf star cause ions to escape from an exoplanet’s atmosphere. Scientists have developed a model that estimates the oxygen ion escape rate on planets around red dwarfs, which plays an important role in determining an exoplanet’s habitability.

Credits: NASA Goddard/Conceptual Image Lab, Michael Lentz, animator/Genna Duberstein, producer.

The search for habitable planets often hones in on red dwarfs, as these are the coolest, smallest and most numerous stars in the universe and therefore which makes planet detection easier.

“On the downside, red dwarfs are also prone to more frequent and powerful stellar eruptions than the sun,” said William Danchi, a Goddard astronomer and co-author of the paper. “To assess the habitability of planets around these stars, we need to understand how these various effects balance out.”

Another important habitability factor is a star’s age, say the scientists, based on observations they’ve gathered from NASA’s Kepler mission. Every day, young stars produce superflares, powerful flares and eruptions at least 10 times more powerful than those observed on the Sun. On their older, matured counterparts resembling our middle-aged sun today, such superflares are thankfully only observed once every 100 years.

“When we look at young red dwarfs in our galaxy, we see they’re much less luminous than our sun today,” Airapetian said. “By the classical definition, the habitable zone around red dwarfs must be 10 to 20 times closer-in than Earth is to the sun. Now we know these red dwarf stars generate a lot of X-ray and extreme ultraviolet emissions at the habitable zones of exoplanets through frequent flares and stellar storms.”

Superflares cause atmospheric erosion when high-energy X-ray and extreme ultraviolet emissions first break molecules into atoms and then ionize atmospheric gases. During ionization, radiation strikes the atoms and knocks off electrons. Electrons are much lighter than the newly formed ions, so they escape gravity’s pull far more readily and race out into space. Opposites attract, so as more and more negatively charged electrons are generated, they create a powerful charge separation that lures positively charged ions out of the atmosphere in a process called ion escape. This process is also thought to be behind the young Mars losing much of its atmosphere as its gravity is insufficent to hold on to more volatile gases such as oxygen.

“We know oxygen ion escape happens on Earth at a smaller scale since the sun exhibits only a fraction of the activity of younger stars,” said Alex Glocer, a Goddard astrophysicist and co-author of the paper. “To see how this effect scales when you get more high-energy input like you’d see from young stars, we developed a model.”

The model estimates the oxygen escape on planets around red dwarfs, assuming they don’t compensate with volcanic activity or comet bombardment. Various earlier atmospheric erosion models indicated hydrogen is most vulnerable to ion escape. As the lightest element, hydrogen easily escapes into space, presumably leaving behind an atmosphere rich with heavier elements such as oxygen and nitrogen. But 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, the 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.”

Modeling the oxygen loss rate is the first step in the team’s efforts to expand the classical definition of habitability into what they call space weather-affected habitable zones. When exoplanets orbit a mature star with a mild space weather environment, the classical definition is sufficient. When the host star exhibits X-ray and extreme ultraviolet levels greater than seven to 10 times the average emissions from our sun, then the new definition applies. The team’s future work will include modeling nitrogen escape, which may be comparable to oxygen escape since nitrogen is just slightly lighter than oxygen.

The new habitability model has implications for the recently discovered planet orbiting the red dwarf Proxima Centauri, our nearest stellar neighbor. Airapetian and his team applied their model to the roughly Earth-sized planet, dubbed Proxima b, which orbits Proxima Centauri 20 times closer than Earth is to the sun.

Considering the host star’s age and the planet’s proximity to its host star, the scientists expect that Proxima b is subjected to torrents of X-ray and extreme ultraviolet radiation from superflares occurring roughly every two hours. They estimate oxygen would escape Proxima b’s atmosphere in 10 million years. Additionally, intense magnetic activity and stellar wind – the continuous flow of charged particles from a star – exacerbate already harsh space weather conditions. The scientists concluded that it’s quite unlikely Proxima b is habitable.

“We have pessimistic results for planets around young red dwarfs in this study, but we also have a better understanding of which stars have good prospects for habitability,” Airapetian said. “As we learn more about what we need from a host star, it seems more and more that our sun is just one of those perfect parent stars, to have supported life on Earth.”

However! Life is tenacious, there are ways it could adapt to withstand these flares. Naturally we will know the truth, ugly or otherwise, probably sooner rather than later! As soon as I know, I’ll tell you! Pinky promise!

Until next time spacefans, fly safe.