ESA - NASA on Solar Science Mission

On October 4, 2011, the European Space Agency announced it's two next science missions, including Solar Orbiter, a spacecraft geared to study the powerful influence of the sun. Solar Orbiter will be an ESA-led mission, with strong NASA contributions managed from Goddard Space Flight Center in Greenbelt, Md.

The mission's launch is planned for 2017 from Cape Canaveral, Florida aboard a NASA-provided launch vehicle. Solar Orbiter will be placed into an elliptical orbit around the sun. Its closest approach will be near the orbit of Mercury, 75% of the distance between Earth and the sun – some 21,000,000 miles away from the sun's surface.

Solar Orbiter will venture closer to the Sun than any previous mission. The spacecraft will also carry advanced instrumentation that will help untangle how activity on the sun sends out radiation, particles and magnetic fields that can affect Earth's magnetic environment, causing aurora, or potentially damaging satellites, interfering with GPS communications or even Earth's electrical power grids.

Being so close to the sun also means that the Solar Orbiter will stay over a given area of the solar surface for a longer time, allowing the instruments to track the evolution of sunspots, active regions, coronal holes and other solar activity far longer than has been done before.

Solar Orbiter is also designed to make major breakthroughs in our understanding of how the sun generates and propels the flow of particles in which the planets are bathed, known as the solar wind. Solar activity and solar eruptions create strong perturbations in this wind, triggering spectacular auroral displays on Earth and other planets. Solar Orbiter will be close enough to the sun to both observe the details of how the solar wind is accelerated off the sun and to sample the wind shortly after it leaves the surface.

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Holes in the Sun's Corona

This Solar Dynamics Observatory image of the Sun taken on January 10 in extreme ultraviolet light captures a dark coronal hole just about at sun center. Coronal holes are areas of the Sun's surface that are the source of open magnetic field lines that head way out into space. They are also the source regions of the fast solar wind, which is characterized by a relatively steady speed of approximately 800 km/s (about 1.8 million mph). As the sun continues to rotate, the high speed solar wind particles blowing from this hole will likely reach Earth in a few days and may spark some auroral activity.

The High Temperature of the Corona

The most remarkable aspect of the corona is its high temperature, deduced by the Swedish astronomer Bengt Edlen in 1942 after a study of the corona's light. Much of that is sunlight scattered by coronal dust, but some light is also produced by the corona itself, in narrowly defined colors ("spectral lines") characteristic of its emitting atoms. In the 19th century, some of the spectral lines of sunlight did not match the lines of any substance on Earth, and it was proposed that they came from a new unknown chemical element, named helium (from the Greek helios--Sun). Later, in 1895, William Ramsey actually discovered helium on Earth.

    Unknown spectral lines emitted by the corona were similarly credited to a new element "coronium" until Edlen showed that they came from the familiar atoms of iron, nickel and calcium, after they had lost an appreciable number of electrons (e.g. 13 or 14 for iron). Such high levels of ionization require the atoms to be buffeted around by extremely 

high temperatures, around 1,000,000 C (1,800,000 F).

    The source of the corona's heat remains a puzzle. It is almost certain that its energy comes from the Sun's internal furnace, which also supplies the rest of the Sun's heat. However, as a rule, temperatures are expected to drop the further one gets from the furnace, whereas the million-degree corona lies outside the surface layer where sunlight originates, whose temperature is less that 6000 C.

The Corona in X-ray Light 

All hot objects emit electromagnetic waves--for example, visible light is emitted by the hot filament inside a lightbulb. The hotter the object, the shorter the wavelength, which is why the corona emits "soft x rays," whose waves are much shorter than those of visible or ultra-violet light.

The corona has been observed in these wavelengths by, among others, the space station Skylab in 1973-4 and more recently by the Japanese spacecraft Yohkoh, which provided the picture shown below. The corona in such pictures appears quite uneven. It is brightest near sunspots, whose arched field lines apparently hamper the outflow of solar wind which carries away energy and helps cool the corona. It is darker in "coronal holes" in between, where field lines apparently extend out to distant space, making it easier for the solar wind to escape.

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Ultraviolet Radiation

The sun radiates energy in a wide range of wavelengths, most of which are invisible to human eyes. The shorter the wavelength, the more energetic the radiation, and the greater the potential for harm. Ultraviolet (UV) radiation that reaches the Earth’s surface is in wavelengths between 290 and 400 nm (nanometers, or billionths of a meter). This is shorter than wavelengths of visible light, which are 400 to 700 nm.

UV radiation from the sun has always played important roles in our environment, and affects nearly all living organisms. Biological actions of many kinds have evolved to deal with it. Yet UV radiation at different wavelengths differs in its effects, and we have to live with the harmful effects as well as the helpful ones. Radiation at the longer UV wavelengths of 320-400 nm, called UV-A, plays a helpful and essential role in formation of Vitamin D by the skin, and plays a harmful role in that it causes sunburn on human skin and cataracts in our eyes. The incoming radiation at shorter wavelengths, 290-320 nm, falls within the UV-B part of the electromagnetic spectrum. (UV-B includes light with wavelengths down to 280 nm, but little to no radiation below 290 nm reaches the Earth’s surface). UV-B causes damage at the molecular level to the fundamental building block of life— deoxyribonucleic acid (DNA).

Electromagnetic radiation exists in a range of wavelengths, which are delineated into major divisions for our convenience. Ultraviolet B radiation, harmful to living organisms, represents a small portion of the spectrum, from 290 to 320 nanometer wavelengths. (Illustration by Robert Simmon)

DNA readily absorbs UV-B radiation, which commonly changes the shape of the molecule in one of several ways. The illustration below illustrates one such change in shape due to exposure to UV-B radiation. Changes in the DNA molecule often mean that protein-building enzymes cannot “read” the DNA code at that point on the molecule. As a result, distorted proteins can be made, or cells can die.

Ultraviolet (UV) photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent bases bond with each other, instead of across the “ladder.” This makes a bulge, and the distorted DNA molecule does not function properly. (Illustration by David Herring)

But living cells are “smart.” Over millions of years of evolving in the presence of UV-B radiation, cells have developed the ability to repair DNA. A special enzyme arrives at the damage site, removes the damaged section of DNA, and replaces it with the proper components (based on information elsewhere on the DNA molecule). This makes DNA somewhat resilient to damage by UV-B.

In addition to their own resiliency, living things and the cells they are made of are protected from excessive amounts of UV radiation by a chemical called ozone. A layer of ozone in the upper atmosphere absorbs UV radiation and prevents most of it from reaching the Earth. Yet since the mid-1970s, human activities have been changing the chemistry of the atmosphere in a way that reduces the amount of ozone in the stratosphere (the layer of atmosphere ranging from about 11 to 50 km in altitude). This means that more ultraviolet radiation can pass through the atmosphere to the Earth’s surface, particularly at the poles and nearby regions during certain times of the year.

Without the layer of ozone in the stratosphere to protect us from excessive amounts of UV-B radiation, life as we know it would not exist. Scientific concern over ozone depletion in the upper atmosphere has prompted extensive efforts to assess the potential damage to life on Earth due to increased levels of UV-B radiation. Some effects have been studied, but much remains to be learned.

 

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Study the Sun During Solar Week

Want to build a pinhole camera to look at an eclipse? Or learn more about how gigantic telescopes examine the sun? The place to go on the Web is solarweek.org from October 18-22. Twice a year, Solar Week provides a weeklong series of web-based educational activities for classrooms about our magnetic variable star, the sun, and its interactions with Earth and the solar system.

Each day of Solar Week offers a different set of lessons and games for students ranging from the upper elementary to high school level. The site covers everything from solar radiation to pursuing careers in science. For example, on Monday, after learning details about how the sun is a star just like the other ones in the sky, students can play a game to determine just where the sun lies in the Milky Way. Or on Thursday, they measure how fast a coronal mass ejection races from the sun.

Helping to answer the students’ questions on an online bulletin board will be three scientists from NASA’s Goddard Space Flight Center in Greenbelt, Md. who have been involved almost since the project began in 2000. Throughout the week, Heliophysics researchers Terry Kucera, Dawn Myers, and Holly Gilbert will be among some twenty scientists who will share their excitement about the dynamic star at the center of our solar system. “I think it’s great that the kids get direct interaction with the scientists,” says solar physicist Kucera, who is involved with the Solar and Heliospheric Observatory and the Solar Terrestrial Relations Observatory.

Currently run by UC Berkeley, Solar Week was originated by David Alexander in 2000 in coordination with his public outreach work for the Yohkoh solar observatory. He began Solar Week as a means of reaching out to girls and encouraging them in the sciences – incorporating many female solar scientists as role models. The site incorporates only women scientists, but welcomes students of both sexes. The former Sun-Earth Connection Education Forum at UC Berkeley took over Solar Week in 2003 where it is now managed by Karin Hauck and funded through spring of 2011 by NASA’s Sun-Earth Day. Berkeley has continued the tradition of incorporating student interaction with leading scientists at the forefront of Sun-Earth research. “The part of the website I enjoy most is the interactive message board because it’s dynamic,” says Hauck. “You never know what’s going to pop up. Students can be very creative with their questions, and I always learning something new from the scientists’ answers.”

Since one of the goals of Solar Week is to encourage girls to pursue STEM (science, technology, engineering, and math) careers, the Goddard scientists often have to answer questions about their jobs specifically, such as how often they travel or whether their jobs are impacted by the current economy –- and, of course, hobbies like Gilbert’s tournament pool-playing and Myers’s work as a dance teacher come up as well.

“I’m always so grateful,” says Hauck, “that these incredibly busy scientists are willing, year after year, to take time out of their very busy schedules to answer the students’ questions.”

Solar Week is ideal for students studying the solar system, the stars, or astronomy in general. It's also for kids wondering what it's like being a scientist, and pondering possible career choices. For those who miss this week, the activities remain online all year around, but the scientists won’t be available again to answer questions online until next March.

Related Links: http://www.nasa.gov/topics/solarsystem/sunearthsystem/main/SolarWeek2010.html

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