Solar Superflares Set Stage for Life on Earth
Earth could have grown warm enough for liquid water as far back as 4 billion years ago thanks to massive and frequent solar flares.
Scientists may have cracked a 40-year-old mystery about how early Earth grew warm enough for water to pool on its surface - a condition believed to be necessary for life – despite meager warming from a young sun.
The key, says a team of NASA astronomers, is a phenomena known as superflares, which are massive and frequent solar flares that blasted high-energy particles toward baby Earth and its sibling planets.
Computer models show that near-daily deluges of energetic particles streaming from the sun would have compressed Earth's magnetic bubble and caused gaps to open over the polar regions.
The particles could then penetrate into the atmosphere, setting off a cascade of chemical reactions that created the extremely potent greenhouse gas nitrous oxide, as well as hydrogen cyanide, an essential compound for life, a study published in this week's Nature Geoscience shows.
Earth would have grown warm enough for liquid water as far back as 4 billion years ago, the study shows.
The first signs of microbial life appear as fossilized rock dating back to about the same time.
Scientists have tried for decades to solve the so-called "faint young sun" paradox, an issue raised by astronomers Carl Sagan and George Mullen in 1972.
"It's perplexing because it is unclear why Earth was not permanently glaciated under the less luminous sun," Cornell University's Ramses Ramirez writes in a related commentary in Nature Geoscience.
The new theory extrapolates data collected by the Kepler space telescope, whose primary mission was to look for planets orbiting sun-like stars.
Temporary dips in the amount of light coming from target stars could be caused by planets flying across the face of their parent stars, relative to Kepler's line of sight. But the changes also could be caused by other events, including, it turns out, superflares.
"Kepler observed the superflares of young stars, resembling our sun at the time when life started on Earth ... We used these as proxies," astrophysicist Vladimir Airapetian, with NASA's Goddard Space Flight Center in Greenbelt, Maryland, told Discovery News.
The superflares turn out to be three times more powerful than the biggest flare in recent history, the so-called Carrington event in 1859, which caused Northern Lights auroras as far south as Miami.
"A very, very conservative number is that one of these events occurred every single day, and each event lasts for two or three days, so that suggests the Earth was under constant attack from these powerful coronal mass ejections," Airapetian said.
Coronal mass ejections, or CMS, release massive amounts of solar particles and electromagnetic radiation into space.
Ramirez, for one, already is putting Airapetian's theory to test by using the atmospheric chemistry data in another computer model.
"My goal is to compute the resultant greenhouse warming from the predicted gas concentrations and determine if they are enough to solve the faint young sun problem," Ramirez told Discovery News.
The study not only has implications for how Earth evolved for life, but also how neighbor planet Mars managed to support liquid surface water.
"Our concept implies that the activity of the early sun provided a window of opportunity for prebiotic life on Earth. The proposed model also redefines the conditions of habitability, not just in terms of a ‘liquid water zone,' but as a biogenic zone, within which the stellar energy fluxes are high enough to ignite reactive chemistry that produces complex molecules crucial for life," Airapetian writes.
Artist rendering of magnetic cloud from superflare colliding with young Earth, squeezing the planet's magnetic field to 1,000 miles above the ground.
The sun may be an average star when compared to the menagerie of stars that exist in our galaxy, but to Earth and all life on our planet, the sun is the most important object in the Universe. However, regardless of its importance and close proximity, our nearest star holds many mysteries that continue to fox solar physicists after decades of modern studies with cutting-edge observatories. One of the biggest mysteries surrounding the sun is the underlying mechanisms that drive solar flares and coronal mass ejections (CMEs). Monday evening (EST), the sun reminded us that it hasn't quite finished with the current solar maximum (of solar cycle 24), unleashing a powerful X4.9 solar flare -- the biggest of 2014. An armada of space telescopes witnessed the event, including NASA's Solar Dynamics Observatory that can spy the sun's temper tantrums in astounding high definition. Shown here, 5 of the 10 filters from the SDO's Atmospheric Imaging Assembly (AIA) instrument are featured, showing the sun's lower corona (the solar multimillion degree atmosphere) through 5 wavelengths; each wavelength of extreme ultraviolet light representing a different plasma temperature and key coronal features -- such as coronal loops (highlighted here in the 'yellow' 171A filter) and ejected plasma that formed a CME.
At 7:13 p.m. EST (00:13 UT, Feb. 25) -- pictured here on the far left -- the active region (AR) 1990 was crackling with activity. Then, as magnetic field lines from the sun's interior forced together and through the solar photosphere, large-scale reconnection events occurred. Reconnection is a magnetic phenomena where field lines "snap" and reconnect, releasing huge quantities of energy in the process. At 7:44 p.m. EST (00:44 UT) -- second frame from the right -- a kinked coronal loop can be seen rising into the corona. At 7:59 p.m. EST (00:59 UT) -- far right -- solar plasma contained within the magnetic flux is accelerated to high energy, generating powerful x-rays and extreme ultraviolet radiation, creating the X-class flare.
The X4.9 flare was caught through the range of SDO fliters, including this dramatic view as seen through the 131A filter. The flare was so bright that photons from the flare overloaded the SDO's CCD inside the AIA instrument, causing the signal to "bleed" across the pixels. This bleeding effect is common for any optical instrument observing powerful solar flares.
Intense coronal activity is often associated with active regions -- the active lower corona is pictured here, left. In this case, the flare erupted from AR1990, at the limb of the sun. Also associated with active regions are sunspots, dark patches observed in the sun's photosphere (colloquially known as the sun's "surface") -- pictured right. The sun's cooler photosphere has been imaged by a different SDO instrument called Helioseismic and Magnetic Imager (HMI), which detects the intensity of magnetic fields threading though the sun's lower corona and photosphere.
In the case of AR1990, a large sunspot can be seen at the base of the coronal loops that erupted to generate the powerful flare. This is a prime example of how sunspots can be used to gauge solar activity and how they are often found at the base of intense coronal activity and flares.
The HMI monitors magnetic activity across the disk of the sun and can also generate a picture on the direction of the magnetic field polarity. In this observation of the sun's magnetic field around the time of the recent X-class flare, other active regions can be easily seen -- intense white and black regions highlighting where magnetic field lines emerge and sink back into the sun's interior in active regions.
The joint NASA/ESA Solar and Heliospheric Observatory (SOHO), which has been watching the sun since 1996, also spotted the flare, tracking a CME that was generated shortly after. Seen here by SOHO's LASCO C2 instrument, that monitors the interplanetary environment surrounding the sun for CMEs and comets, a growing bubble of solar plasma races away from the sun.
Approximately an hour after the flare, the CME grew and continued to barrel into interplanetary space. Space weather forecasters don't expect that this CME will interact with the Earth's atmosphere as it is not Earth-directed. This observation was captured by SOHO's LASCO C3 instrument -- an occulting disk covers the sun to block out any glaring effect. By combining observations by the SDO, SOHO and other solar observatories, the connection between the sun's internal magnetic "dynamo", the solar cycle, flares and CMEs, solar physicists are slowly piecing together what makes our nearest star tick, hopefully solving some of the most persistent mysteries along the way.