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The Sun’s surface temperature is around six thousand degrees kelvin, but the solar atmosphere—the corona and the solar wind—can reach a million degrees kelvin, a long-standing mystery in solar physics. Now, with data from the Parker Solar Probe, researchers have found evidence supporting a partial explanation for this mystery: magnetic waves driven by subsurface turbulence can impart energy to ions in these regions.

The exact mechanism of heating has been debated for decades, but the story appears to start with turbulent flow in the Sun’s convection zone, the outermost layer below the surface. In fluid dynamics, turbulence causes heating through a process known as turbulent energy cascade, where large eddies are converted into progressively smaller eddies. The energy in the smallest eddies is converted into heat through collisions between molecules.

Solar physicists think that a similar turbulent cascade happens in the Sun. Heat-driven turbulence below the surface disturbs the solar magnetic-field lines that extend into the corona, causing waves to propagate like the vibrations of a plucked guitar string. These long-wavelength, low-frequency magnetic waves travel into the corona and the solar wind, generating disordered waves at progressively shorter wavelengths. But the plasma of charged particles that constitutes the solar corona is not dense enough for collisions between particles to generate enough heat to explain the coronal temperature. Instead, something more exotic must be occurring.

One idea, called cyclotron resonant heating, is that the turbulent cascade generates waves that are short enough to be in resonance with the motion of ions in the corona. This resonance allows these waves to pump energy into the ions’ cyclotron motion—helical trajectories that spiral around magnetic-field lines. This energy boost heats the corona and the solar wind, which consists of particles that follow magnetic-field lines extending outward from the corona. There are several other proposed heating mechanisms, and it’s likely that more than one of them is in effect.

NASA will on Monday attempt a feat humanity has never before accomplished: deliberately smacking a spacecraft into an asteroid to slightly deflect its orbit, in a key test of our ability to stop cosmic objects from devastating life on Earth.

Click on Graphic Above for Live NASA feed

If all goes to plan, impact between the car-sized spacecraft, and the 530-foot (160 meters, or two Statues of Liberty) asteroid should take place at 7:14 pm Eastern Time (2314 GMT), viewable on a NASA livestream.

 

A 6.5-magnitude earthquake struck the remote Maluku Islands in eastern Indonesia on Thursday morning, killing at least 20 people.

Indonesian officials said the quake, which was detected at 8:46 a.m. local time, did not present the threat of a tsunami. But it was classified as a “strong” earthquake in Ambon, a city of more than 300,000 people and the capital of Maluku Province. The United States Geological Survey said the epicenter was about 23 miles northeast of Ambon.

At least 20 people were killed in the quake, the authorities said, including a man who was killed when a building partially collapsed at an Islamic university in Ambon, according to Reuters. More than 100 people were reported injured in the quake, and the authorities said about 2,000 had been displaced from their homes.

It was not immediately known how many people were injured or how extensive the damage was across the islands, but the nation’s disaster management agency posted several photos and videos on Twitter showing cracked roads and damaged buildings. The nation’s meteorology, climate and geophysics agency reported at least 69 aftershocks, including one of magnitude 5.6.

Deadly earthquakes are common for Indonesia and its roughly 260 million people. In 2004, a tsunami generated by an earthquake largely destroyed the city of Banda Aceh, killing about 225,000 people in more than a dozen countries.

In 2018 alone, six quakes had at least a 6.0 magnitude. More than 4,300 people were killed in an earthquake and subsequent tsunami in Sulawesi in September 2018, and the previous month, a magnitude 7.0 earthquake killed more than 550 people when it struck the island of Lombok, near Bali.

For 400 years people have tracked sunspots, the dark patches that appear for weeks at a time on the Sun’s surface. They have observed but been unable to explain why the number of spots peaks every 11 years.

A University of Washington study published this month in the journal Physics of Plasmas proposes a model of plasma motion that would explain the 11-year sunspot cycle and several other previously mysterious properties of the Sun.

“Our model is completely different from a normal picture of the Sun,” said first author Thomas Jarboe, a UW professor of aeronautics and astronautics. “I really think we’re the first people that are telling you the nature and source of solar magnetic phenomena — how the Sun works.”

The authors created a model based on their previous work with fusion energy research. The model shows that a thin layer beneath the Sun’s surface is key to many of the features we see from Earth, like sunspots, magnetic reversals and solar flow, and is backed up by comparisons with observations of the Sun.

“The observational data are key to confirming our picture of how the Sun functions,” Jarboe said.

In the new model, a thin layer of magnetic flux and plasma, or free-floating electrons, moves at different speeds on different parts of the Sun. The difference in speed between the flows creates twists of magnetism, known as magnetic helicity, that are similar to what happens in some fusion reactor concepts.

“Every 11 years, the Sun grows this layer until it’s too big to be stable, and then it sloughs off,” Jarboe said. Its departure exposes the lower layer of plasma moving in the opposite direction with a flipped magnetic field.

When the circuits in both hemispheres are moving at the same speed, more sunspots appear. When the circuits are different speeds, there is less sunspot activity. That mismatch, Jarboe says, may have happened during the decades of little sunspot activity known as the “Maunder Minimum.”

“If the two hemispheres rotate at different speeds, then the sunspots near the equator won’t match up, and the whole thing will die,” Jarboe said.

“Scientists had thought that a sunspot was generated down at 30 percent of the depth of the Sun, and then came up in a twisted rope of plasma that pops out,” Jarboe said. Instead, his model shows that the sunspots are in the “supergranules” that form within the thin, subsurface layer of plasma that the study calculates to be roughly 100 to 300 miles (150 to 450 kilometers) thick, or a fraction of the sun’s 430,000-mile radius.

“The sunspot is an amazing thing. There’s nothing there, and then all of a sudden, you see it in a flash,” Jarboe said.

The group’s previous research has focused on fusion power reactors, which use very high temperatures similar to those inside the Sun to separate hydrogen nuclei from their electrons. In both the sun and in fusion reactors the nuclei of two hydrogen atoms fuse together, releasing huge amounts of energy.

The type of reactor Jarboe has focused on, a spheromak, contains the electron plasma within a sphere that causes it to self-organize into certain patterns. When Jarboe began to consider the Sun, he saw similarities, and created a model for what might be happening in the celestial body.

“For 100 years people have been researching this,” Jarboe said. “Many of the features we’re seeing are below the resolution of the models, so we can only find them in calculations.”

Other properties explained by the theory, he said, include flow inside the Sun, the twisting action that leads to sunspots and the total magnetic structure of the sun. The paper is likely to provoke intense discussion, Jarboe said.

“My hope is that scientists will look at their data in a new light, and the researchers who worked their whole lives to gather that data will have a new tool to understand what it all means,” he said.

The research was funded by the U.S. Department of Energy. Co-authors are UW graduate students Thomas Benedett, Christopher Everson, Christopher Hansen, Derek Sutherland, James Penna, UW postdoctoral researchers Aaron Hossack and John Benjamin O’Bryan, UW affiliate faculty member Brian Nelson, and Kyle Morgan, a former UW graduate student now at CTFusion in Seattle.

People have long dreamed of re-shaping the Martian climate to make it livable for humans. Carl Sagan was the first outside of the realm of science fiction to propose terraforming. In a 1971 paper, Sagan suggested that vaporizing the northern polar ice caps would “yield ~10 s g cm-2 of atmosphere over the planet, higher global temperatures through the greenhouse effect, and a greatly increased likelihood of liquid water.”

Sagan’s work inspired other researchers and futurists to take seriously the idea of terraforming. The key question was: are there enough greenhouse gases and water on Mars to increase its atmospheric pressure to Earth-like levels?

In 2018, a pair of NASA-funded researchers from the University of Colorado, Boulder and Northern Arizona University found that processing all the sources available on Mars would only increase atmospheric pressure to about 7 percent that of Earth – far short of what is needed to make the planet habitable.

Terraforming Mars, it seemed, was an unfulfillable dream.

Now, researchers from the Harvard University, NASA’s Jet Propulsion Lab, and the University of Edinburgh, have a new idea. Rather than trying to change the whole planet, what if you took a more regional approach?

The researchers suggest that regions of the Martian surface could be made habitable with a material — silica aerogel — that mimics Earth’s atmospheric greenhouse effect. Through modeling and experiments, the researchers show that a two to three-centimeter-thick shield of silica aerogel could transmit enough visible light for photosynthesis, block hazardous ultraviolet radiation, and raise temperatures underneath permanently above the melting point of water, all without the need for any internal heat source.

The paper is published in Nature Astronomy.

“This regional approach to making Mars habitable is much more achievable than global atmospheric modification,” said Robin Wordsworth, Assistant Professor of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Department of Earth and Planetary Science. “Unlike the previous ideas to make Mars habitable, this is something that can be developed and tested systematically with materials and technology we already have.”

“Mars is the most habitable planet in our Solar System besides Earth,” said Laura Kerber, Research Scientist at NASA’s Jet Propulsion Laboratory. “But it remains a hostile world for many kinds of life. A system for creating small islands of habitability would allow us to transform Mars in a controlled and scalable way.”

The researchers were inspired by a phenomenon that already occurs on Mars.

Unlike Earth’s polar ice caps, which are made of frozen water, polar ice caps on Mars are a combination of water ice and frozen CO2. Like its gaseous form, frozen CO2 allows sunlight to penetrate while trapping heat. In the summer, this solid-state greenhouse effect creates pockets of warming under the ice.

“We started thinking about this solid-state greenhouse effect and how it could be invoked for creating habitable environments on Mars in the future,” said Wordsworth. “We started thinking about what kind of materials could minimize thermal conductivity but still transmit as much light as possible.”

The researchers landed on silica aerogel, one of the most insulating materials ever created.

Silica aerogels are 97 percent porous, meaning light moves through the material but the interconnecting nanolayers of silicon dioxide infrared radiation and greatly slow the conduction of heat. These aerogels are used in several engineering applications today, including NASA’s Mars Exploration Rovers.

“Silica aerogel is a promising material because its effect is passive,” said Kerber. “It wouldn’t require large amounts of energy or maintenance of moving parts to keep an area warm over long periods of time.”

Using modeling and experiments that mimicked the Martian surface, the researchers demonstrated that a thin layer of this material increased average temperatures of mid-latitudes on Mars to Earth-like temperatures.

“Spread across a large enough area, you wouldn’t need any other technology or physics, you would just need a layer of this stuff on the surface and underneath you would have permanent liquid water,” said Wordsworth.

This material could be used to build habitation domes or even self-contained biospheres on Mars.

“There’s a whole host of fascinating engineering questions that emerge from this,” said Wordsworth.

Next, the team aims to test the material in Mars-like climates on Earth, such as the dry valleys of Antarctica or Chile.

Wordsworth points out that any discussion about making Mars habitable for humans and Earth life also raises important philosophical and ethical questions about planetary protection.

“If you’re going to enable life on the Martian surface, are you sure that there’s not life there already? If there is, how do we navigate that,” asked Wordsworth. “The moment we decide to commit to having humans on Mars, these questions are inevitable.”