Super solar flares may have kicked off life on Earth

Tuesday, May 24, 2016, 7:13 PM - How did life on Earth develop, and how did the planet warm enough to sustain that life under the glow of a cooler, younger Sun? New NASA research sheds light on this fascinating paradox.

Today, the Sun is more than adequate for providing Earth with the right conditions to support life. Billions of years ago, however, this wasn't necessarily the case.

When the Sun was still developing through its 'adolescent' years, some 4 billion years ago, it was far more active, blasting out flares and solar storms (coronal mass ejections or CMEs) much more frequently than it does now. At the same time, though, it was around 30 per cent dimmer than it is today, and thus provided less light (and thus heat) to the Earth.

"That means Earth should have been an icy ball. Instead, geological evidence says it was a warm globe with liquid water. We call this the Faint Young Sun Paradox," Vladimir Airapetian, a NASA solar scientist that led a research team to investigate this paradox and attempt to unravel it, said in a NASA statement.

So, how did Earth develop an environment warm enough to allow life to develop and flourish? The answer, it seems, was found in the extreme "space weather" that would have been generated by the activity of the young Sun.

By looking through data gathered by NASA's exoplanet hunter, the Kepler Space Telescope, the researchers were able to see the activity of young stars that are very similar to the Sun. This gave them insights into how our Sun behaved when it was only a few million years old, and the Kepler data showed that the Sun would have been far more active than it is today. The young sun wouldn't just have flares, it would have super-flares.

The young Sun, only around 500 million years old, blasts out a super-flare. Credit: NASA/GSFC/CIL

In the past 150 years or so, two events have been recorded that could be ranked as super-flares. Based on what Kepler has shown, though, roughly 4 billion years ago, the Sun was so active that it was capable of producing super-flares on a daily basis, and sometimes multiple times each day.

According to Airapetian and his team, when the extreme solar storms from these super-flares reached Earth, they would have been funneled down into Earth's atmosphere by the planet's developing geomagnetic field. Since the weaker field would have left larger gaps at the poles than it does now, this would have allowed more particles to interact with the abundant nitrogen in the early atmosphere. In addition to widespread auroras, this would have produced molecules of nitrous oxide, which is a greenhouse gas nearly 300 times stronger, on a molecule-by-molecule basis, than carbon dioxide.

"Our calculations show that you would have regularly seen auroras all the way down in South Carolina," Airapetian told NASA. "And as the particles from the space weather traveled down the magnetic field lines, they would have slammed into abundant nitrogen molecules in the atmosphere. Changing the atmosphere's chemistry turns out to have made all the difference for life on Earth."

Nitrous oxide is present in very small concentrations today, less than 1/1000 of the concentration of carbon dioxide. Back on the young Earth, though, according to Airapetian, an increase in the amount of nitrous oxide in the atmosphere, up to around 1/100 of the concentration of carbon dioxide, would have trapped enough of the younger, cooler Sun's heat to keep the environment warm enough to make it suitable for the development of life.

Super-flares sparking life?

Sparking the chemical changes that build up simple molecules into complex ones, such as the RNA and DNA that form the basis of life here on Earth, takes plenty of energy.

Scientists have pointed to other potential energy sources for this in the past, such as lightning strikes and meteorite impacts. This latest research adds super-flares and their associated extreme solar storms to the list, as well, and the researchers are hoping that their study will help in the search for life elsewhere in the galaxy.

If the extreme activity of the young Sun contributed to life here on Earth, could activity on young, active stars elsewhere have caused life to form on planets there too? Credit: NASA/GSFC/CIL

The effects of solar storms would be a balancing act, however, as recent evidence has shown what extreme solar storms have done to Mars. While the fourth planet from the Sun may have started out far more Earth-like, billions of years ago, over time, its lack of a strong planetary magnetic field left it vulnerable, allowing subsequent solar storms to tear away much of its atmosphere.

Two "modern" super-flares

Super-flares are solar flares so extreme that they're well off the standard scale (B, C, M and X-class, shown to the right). Each class has an internal scale from 1 to 9, and moving from one class to the next represents a tenfold increase in flare strength. Thus, an X1-class flare is ten times stronger than an M1-class flare, and 100 times stronger than a C1-class flare.

Since the X-class is open-ended, though, the strongest flares we've seen have reached up to X20 or higher, and two notable cases come up when the term "super-flare" is used.

The first was the very rare "white light" flare, spotted by amateur astronomer Richard Carrington, during the so-called Carrington Event of September 1859. This just happened to be the first solar flare ever observed. 

Although there was no scale to rank solar flares on at the time, researchers have more recently estimated it as the strongest in history, ranking it at around X45-class. The immense coronal mass ejection it launched into space is also very likely the largest one that has ever interacted with Earth. It produced bright auroras stretching far from the poles, with some reports that they could be seen from regions close to the equator.

The second was on November 4, 2003, and was observed from space by the NASA/ESA Solar and Heliospheric Observatory (SOHO) and NOAA's Geostationary Orbiting Environmental Satellite (GOES) and Advanced Composition Explorer (ACE) satellites. This flare was so powerful that it actually overwhelmed the GOES X-ray detector, preventing an accurate record of the its total strength.

Conservative estimates of its strength put it as an X28-class flare - the strongest in the satellite record - but it may have been much higher, possibly rivaling the Carrington super-flare. This flare was part of a series of flares and CMEs over about a week, which caused aurorae that were visible as far south as Texas, and the fluctuations in Earth's geomagnetic field caused an hour-long blackout in Sweden.

The November 4, 2003 superflare, as seen by SOHO. Credit: NASA

Another extreme event, in 2012, was considered to be a "super solar storm." Rather than one powerful flare and one massive CME, though, it was caused by three different moderate-strength solar flares, and the combined effects of their associated CMEs. The immense, fast-moving CME produced by this combination of events swept out into space well ahead of Earth's position in its orbit at the time, which was lucky for us. If the flares had erupted just a little over a week before, when the active region they originated from was pointed directly at Earth, we would have taken a direct hit.

While it would not have directly harmed anyone on the surface, due to the protection we enjoy from the atmosphere, it would have resulted in something similar to the Carrington Event. In addition to the vivid auroras, however, it would have been bad for our technology in orbit and our power grids on the ground. In 1859, the geomagnetic storm only affected telegraph services. With today's more advanced technology, a comparable event would damage orbiting satellites and spacecraft, and likely cause widespread blackouts. 

Regardless of the potential impacts, this would not have qualified as a "super-flare" event. It was, however, an excellent example of how even moderate space weather can still pose a risk to our way of life.

Source: NASA | Science@NASA