15 Oct 2017

Sun’s atmosphere is hotter than its surface, NASA confirms

The human being has succeeded in sending probes to Moon, Mars, Venus, and other planets of the solar system. The National Aeronautics and Space Administration (NASA) has made the seccond flight of its FOXI instrument. Like most solar sounding rockets, the FOXSI instrument, short for Focusing Optics X-ray Solar Imager, lasted 15 minutes, with just six minutes of data collection.

The flight have helped in solving the mysteries that were remained unsolved for years. As per the data sent by FOXSI, it has recognized a type of light called hard X-rays with tiny wavelengths, even smaller than that of the light which humans see.
Discovery of high-frequency waves gives hint to an extremely hot solar material, around 18 million degrees Fahrenheit. These kinds of temperatures are generally produced in solar flares, powerful bursts of energy. But in this case, there was no observable solar flare, meaning the hot material was most likely produced by a series of solar flares so small that they were undetectable from Earth: nanoflares. The results were published Oct. 9, 2017, in Nature Astronomy.

“The key to this result is the sensitivity in hard X-ray measurements,” said Shin-nosuke Ishikawa, a solar physicist at the Japan Aerospace Exploration Agency, or JAXA, and lead author on the study. “Past hard X-ray instruments could not detect quiet active regions, and the combination of new technologies enables us to investigate quiet active regions by hard X-rays for the first time.”

These observations are a step toward understanding the coronal heating problem, which is how scientists refer to the extraordinarily – and unexpectedly – high temperatures in the Sun’s outer atmosphere, the corona. The corona is hundreds to thousands of times hotter than the Sun’s visible surface, the photosphere. Because the Sun produces heat at its core, this runs counter to what one would initially expect: normally the layer closest to a source of heat, the Sun’s surface, in this case, would have a higher temperature than the more distant atmosphere.

“If you’ve got a stove and you take your hand farther away, you don’t expect to feel hotter than when you were close,” said Lindsay Glesener, project manager for FOXSI-2 at the University of Minnesota and an author on the study.

The cause of these counterintuitively high temperatures is an outstanding question in solar physics. One possible solution to the coronal heating problem is the constant eruption of tiny solar flares in the solar atmosphere, so small that they can’t be directly detected. In aggregate, these nanoflares could produce enough heat to raise the temperature of the corona to the millions of degrees that we observe.

One of the consequences of nanoflares would be pockets of superheated plasma. Plasma at these temperatures emits light in hard X-rays, which are notoriously difficult to detect. For instance, NASA’s RHESSI satellite – short for Reuven Ramaty High Energy Solar Spectroscopic Imager – launched in 2002, uses an indirect technique to measure hard X-rays, limiting how precisely we can pinpoint the location of superheated plasma. But with the cutting-edge optics available now, FOXSI was able to use a technique called direct focusing that can keep track of where the hard X-rays originate on the Sun.

“It’s really a completely transformative way of making this type of measurement,” said Glesener. “Even just on a sounding rocket experiment looking at the Sun for about six minutes, we had much better sensitivity than a spacecraft with indirect imaging.”

FOXSI’s measurements – along with additional X-ray data from the JAXA and NASA Hinode solar observatory – allow the team to say with certainty that the hard X-rays came from a specific region on the Sun that did not have any detectable larger solar flares, leaving nanoflares as the only likely instigator.

“This is a proof of existence for these kinds of events,” said Steve Christe, the project scientist for FOXSI at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and an author on the study. “There’s basically no other way for these X-rays to be produced, except by plasma at around 10 million degrees Celsius [18 million degrees Fahrenheit]. This points to these small energy release happening all the time, and if they exist, they should be contributing to coronal heating.”

There are still questions to be answered, like: How much heat do nanoflares actually release into the corona?

“This particular observation doesn’t tell us exactly how much it contributes to coronal heating,” said Christe. “To fully solve the coronal heating problem, they would need to be happening everywhere, even outside of the region observed here.”

Hoping to build up the complete picture of nanoflares and their contribution to coronal heating, Glesener is leading a team to launch a third iteration of the FOXSI instrument on a sounding rocket in summer 2018. This version of FOXSI will use new hardware to eliminate much of the background noise that the instrument sees, allowing for even more precise measurements.

A team led by Christe was also selected to undertake a concept study developing the FOXSI instrument for a possible spaceflight as part of the NASA Small Explorers program.

FOXSI is a collaboration between the United States and JAXA. The second iteration of the FOXSI sounding rocket launched from the White Sands Missile Range in New Mexico on Dec. 11, 2014. FOXSI is supported through NASA’s Sounding Rocket Program at the Goddard Space Flight Center’s Wallops Flight Facility in Virginia. NASA’s Heliophysics Division manages the sounding rocket program.

As a separate mission of NASA, the agency will send the probe to the fierce hub of Solar system – Sun. by the end of the next year. As said by NASA, the spacecraft will be placed within six million kilometres of the burning Sun for exploring its atmosphere. To the date, astronomers have successfully sent spacecraft to the Moon, Mars and even far-flung interstellar objects and exoplanets, but sending a robotic spaceship to Sun in a one-of-its-kind attempt of the US-based space agency.

Titled under ‘Solar Probe Plus’ mission, NASA’s upcoming Solar spacecraft will take an in-depth trip to the Sun which is located nearly 149 million kilometres from the Earth.

According to Eric Christian, a NASA research scientist at Goddard Space Flight Centre, and an associated astronomer at NASA’s new solar mission, “Solar Probe Plus is going to be NASA’s first space operation to explore the blazing Sun. Though we can’t reach to the very surface of the hot star, through the robotic spacecraft, we will try to get close enough to the Sun so that four questions, which astronomers and scientists have been trying hard to decipher, are:
Why is the atmosphere of Sun hotter than the temperature of its surface?
Why the Sun infrequently discharges intense radiations and particles that endangered the defenceless astronauts and spacecraft?
What is the nature of the structure and dynamics of the magnetic fields at the springs of solar wind?
What is the dirty plasma found near the Sun and how it influences the formation of solar wind and an energetic particle?

According to NASA, currently, the surface temperature of the Sun is approximately 5,500 degrees Celsius. But its atmospheric temperature is two million degrees Celsius, which is incredibly burning. Currently, the biggest puzzle for the astronomers is ‘Why the atmosphere of Sun is hotter than the temperature of its surface’, and the spacecraft will focus more exploring this dilemma.

For withstanding the scorching temperature of Sun, NASA has designed an 11.4 centimetres carbon-composite protector, which will be integrated outside the spacecraft and can bear up 1,370 degrees Celsius.

As confirmed by NASA, the first mission to Sun is expected to have an effect on 31stJuly 2018. With a targeted orbital period of 6 years, 321 days, the 610-kg weighted spacecraft will be blasted off from Cape Canaveral SLC-37 launch-pad onboard Delta IV Heavy rocket. Currently, the spaceship is being developed by Applied Physics Laboratory. Measuring 1 meter wide, 3 meters tall, and incorporated with a 2.3-meter heat shield, the spacecraft is capable of withstanding 343 Watts at its closest approach to the sun.

The US space agency NASA has released another breathtaking video of plasma rain on the solar surface. The mid-level solar flare was captured using Interface Region Imaging Spectrograph, or IRIS. According to NASA scientists, a sudden flash of bright light on the solar limb – the horizon of the sun – as seen at the beginning of this video. Solar flares are powerful explosions of radiation.

During flares, a large amount of magnetic energy is released, heating the sun’s atmosphere and releasing energized particles out into space. Observing flares such as this helps the IRIS mission study how solar material and energy move throughout the sun’s lower atmosphere, so we can better understand what drives the constant changes we can see on our sun.

As the video continues, solar material cascades down to the solar surface in great loops, a flare-driven event called post-flare loops or coronal rain. This material is plasma, a gas in which positively and negatively charged particles have separated, forming a superhot mix that follows paths guided by complex magnetic forces in the sun’s atmosphere.
Source - Te Cake

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