Tag Archives: space weather

An artist's conception of HD 209458 b, an exoplanet whose atmosphere is being torn off at more than 35,000 km/hour by the radiation of its close-by parent star. This hot Jupiter was the first alien world discovered via the transit method, and the first planet to have its atmosphere studied. [NASA/European Space Agency/Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS)]

Stellar flares can strip away the atmosphere of planets, make them less habitable

As humanity continues to explore planets beyond the solar system — exoplanets — investigations into conditions on these worlds become increasingly complex. This includes the question of whether these exoplanets can support life. 

New research has identified which stars would be most likely to host planets with the necessary conditions for habitability, based upon that star’s stellar activity and crucially the rate at which such activity strips away a planet’s atmosphere. 

“We wanted to figure out how planets lose their atmospheres from extreme ultraviolet radiation and estimate their impact on their potential to host life,” Dimitra Atri, a researcher from the Space Science at NYU Abu Dhabi (NYUAD), tells ZME Science. “We focused on a channel of escape called hydrodynamic escape where stellar radiation heats up the planet’s atmosphere and a part of it escapes into space.”

An artist's conception of HD 209458 b, an exoplanet whose atmosphere is being torn off at more than 35,000 km/hour by the radiation of its close-by parent star. This hot Jupiter was the first alien world discovered via the transit method, and the first planet to have its atmosphere studied. [NASA/European Space Agency/Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS)]
An artist’s conception of HD 209458 b, an exoplanet whose atmosphere is being torn off at more than 35,000 km/hour by the radiation of its close-by parent star. This hot Jupiter was the first alien world discovered via the transit method, and the first planet to have its atmosphere studied. [NASA/European Space Agency/Alfred Vidal-Madjar (Institut d’Astrophysique de Paris, CNRS)]

Atri is the author of a paper published in the journal Monthly Notices of Royal Astronomical Society: Letters, which analyzes flare emissions using data collected by NASA’s Transiting Exoplanet Survey Satellite (TESS) observatory ultimately helping to determine where else in the Universe life is most likely to prosper.

Harbouring Life: A Question of Water Retention

Planet habitability is closely associated with that world’s ability to hold liquid water. That means that factors which can boil away that water or cause it to be lost to space reduce that habitability. The habitable zone of a star’s environment is defined as the range at which a planet can orbit and still possess liquid water. This means not too hot or too cold — criteria that led to the alternative name for such regions, the Goldilocks zone.

Yet, distance and a star’s luminosity are not the only factors which can affect a planet’s ability to hold liquid water. Space weather — including solar flares — is another determining element, one that as of yet is not well understood. “Flares erode planetary atmospheres,” Atri says. “A substantial atmosphere is needed to sustain liquid water on a planet’s surface. Flares reduce those chances and make planets less habitable.”

Betelgeuse a type H 1-2 star similar to those Atri found jettison frequent XUV flares which can strip an exoplanet’s atmosphere reducing conditions for habitability (NASA/SDO)

What Atri, alongside coauthor and graduate student Shane Carberry Mogan, discovered was that whilst luminosity from a star was still the primary driving factor in atmosphere stripping, flares were a more important factor for some stars than others. In particular, they discovered that flares from M0-M4 stars — cool, red stars like Betelgeuse — were more likely to strip an orbiting planet’s atmosphere. 

The duo determined that more frequent, lower energy flares in the extreme ultraviolet region (XUV) of the electromagnetic spectrum were more effective at stripping a planet’s atmosphere and thus reducing its habitability than less frequent, higher energy outbursts. XUV radiation strikes a planet’s atmosphere heating it. This causes hydrodynamic escape, pushing out light atoms first, which through collision and other drag effects also pull out heavier molecules. 

“We find that for most stars, luminosity-induced escape is the main loss mechanism, with a minor contribution from flares,” Atri explains. “However, flares dominate the loss mechanism of around 20 per cent of M4–M10 stars.

“M0–M4 stars are most likely to completely erode both their proto- and secondary atmospheres, whilst M4–M10 stars are least likely to erode secondary atmospheres.”

The study also highlights the fact that better modelling of the factors that affect an exoplanet’s atmosphere is needed. Determining the systems and planets most likely to harbour life will play an important factor in selecting targets for the upcoming James Webb Space Telescope — set to launch on October 31st 2021 — and the ESO’s Extremely Large Telescope (ELT) currently under construction in the Acatma desert, Chile. 

“The next research step would be to expand our data set to analyze stellar flares from a larger variety of stars to see the long-term effects of stellar activity, and to identify more potentially habitable exoplanets,” adds Atri.

The researcher also points out that the continued investigation of how planets lose their atmosphere could also focus on a target closer to home, our nearest neighbour, Mars. “Since it is extremely difficult to observe the escape process in exoplanets, we are planning to study this phenomenon in great detail on Mars with the UAE’s Hope mission,” the researcher says, explaining how observations from Mars missions can be used to better understand atmospheric escape and how this knowledge can be applied to exoplanets.“We will then apply our understanding of atmospheric escape to exoplanets and estimate the impact of extreme UV radiation on planetary habitability.”

An artist’s illustration of UAE’s Tess probe approaching the surface of Mars. Atri believes this investigation could yeild important data about exoplanet habitability.
(Mohammed bin Rashid Space Centre)

Further to the question of habitability, the study begins to address the wider question of the dynamics of stars and their planetary systems and the evolution of such arrangements. “Given the close proximity of exoplanets to host stars, it is vital to understand how space weather events tied to those stars can affect the habitability of the exoplanet,” Atri concludes. “Stars and planets are very tightly coupled in a number of ways and an improved understanding of this coupling are absolutely necessary to find habitable planets in our Galaxy and beyond.”

Atri. D., Carberry Morgan. S. R., [2020], ‘Stellar flares versus luminosity: XUV-induced atmospheric escape and planetary habitability,’ Monthly Notices of Royal Astronomical Society: Letters.

Astronomers get the first glimpse of solar wind as it forms

Using images of the Sun and strong processing algorithms, scientists have observed solar winds emerging from the corona.

It’s a beautiful sight. An extreme ultraviolet light image of the Sun and its corona from NASA’s Solar Terrestrial Relations Observatory (STEREO). Credit: NASA/STEREO

Solar wind is a stream of charged particles released from the upper atmosphere of the Sun. First described as a phenomenon in 1859, it has been observed only in the 1960s. But scientists wanted to know how the solar wind looks like when it first forms, inside our star’s corona.

“This is part of the last major connection we need to make to understand how [the Sun] influences the environment around the Earth,” Craig DeForest, an astrophysicist at the Southwest Research Institute in Boulder, Colo., told Eos. DeForest is the lead author on a new paper describing the novel technique, published last week in the Astrophysical Journal.

Visualizing and understanding solar wind is not just an academic task – it can be extremely important for our modern society. The solar wind is responsible for the overall shape of Earth’s magnetosphere, interacting with it very strongly. The magnetosphere is the magnetic analog of the atmosphere. When there are changes in the wind’s speed, density, direction, and entrained magnetic field, our own planet’s magnetic field can be greatly affected. For instance, GPS satellites can be very vulnerable to this. Space weather can also knock out telecommunications, short out satellite circuitry, and damage electrical transmission lines which could cause immeasurable damage on Earth. So much of our modern technology on which we are so reliant can be threatened by solar wind.

But studying the formation of solar wind is no easy feat. The corona is very bright, and the solar wind is very faint, imposed on a background of stars and interplanetary dust. Whenever they tried to look at it before, they couldn’t realize exactly when it was forming.

So they applied an image processing algorithm, removing objects of fixed brightness (such as the stars on the background), exposing emerging features like the wind. The approach turned out to be successful, and the formation of the wind was visualized.

The new analysis already revealed some interesting things, showing that when the material travels a third of the distance to the Earth, the magnetic fields start to weaken enough for the particles to dissipate. This will help scientists to better predict the arrival and strength of the Sun’s outbursts, which, as mentioned above, can make a big difference.

Solar flare

The sun goes through quasi-seasonal changes, a find that could help protect power grids back on Earth

Just like our own planet, the sun goes through seasonal changes in its activity, waxing and waning over the course of nearly two years driven by changes in newly discovered bands of strong magnetic fields. This variability helps shape the sun’s long-term 11 year cycle, yet again part of a longer cycle that lasts 22 days. Largely unpredictable, the sun constantly spews highly charged particles known as coronal mass ejections which can severely affect power grids, satellites and even airplane passengers. During its seasonal peaks, however, the sun is much more prone to solar storms, so understanding how this cyclic variability happens is key to averting a potential disaster.

Solar flare

Image: NASA

The researchers at the National Center for Atmospheric Research (NCAR) carefully studied data from NASA satellites, as well as  ground-based observatories. They found that magnetic bands (fluctuations in density of magnetic fields)  rise from the sun’s interior to the surface through a transition region known as the tachocline.

Scott McIntosh, lead author of the new study and director of NCAR’s High Altitude Observatory, likens magnetic bands in the sun’s atmosphere to the Earth’s jet stream, a river of air that encircles the planet.

“Much like Earth’s jet stream, whose warps and waves have had severe impact on our regional weather patterns in the past couple of winters, the bands on the Sun have very slow-moving waves that can expand and warp it too,” said co-author Robert Leamon, a scientist at Montana State University. “Sometimes this results in magnetic fields leaking from one band to the other. In other cases, the warp drags magnetic fields from deep in the solar interior, near the tachocline, and pushes them toward the surface.”

“These surges or ‘whomps’ as we have dubbed them, are responsible for over 95 percent of the large flares and CMEs–the ones that are really devastating,” McIntosh said.

First, the bands start off at the high latitudes and carry opposite magnetic polarity. When they’re far apart, sunspots  – and hence solar storms – are at their peak. When the bands migrate towards the equator, the instability terminates and new bands are born at the poles restarting the cycle.

Knowledge like this is fundamental to predicting space weather and taking preemptive measures against a potential solar onslaught. In 1979, solar flares knocked-out  long-distance telephone service across Illinois and, in 1989, another flare caused a nine-hour power outage in Quebec, leaving about 6 million people without electricity. New observations on models made on supercomputers will definitely render more insight, but if we’re really serious about studying the capricious sun then we might need to put in place a swarm of satellites. According to McIntosh, just like the current fleet hovering beyond Earth, such satellites could vastly advance solar weather models.

“If you understand what the patterns of solar activity are telling you, you’ll know whether we’re in the stormy phase or the quiet phase in each hemisphere,” McIntosh said. “If we can combine these pieces of information, forecast skill goes through the roof.”