FEATURE: SOLAR ORBITER

Solar Orbiter launch to face the Sun

ESA’s new Sun explorer will be launched from Cape Canaveral on 10 February (European time). Media are invited to Europe’s mission control centre in Darmstadt, Germany, to follow the launch and moment of signal acquisition.



Note: this article was updated on 31 January. NASA, ESA, Airbus and United Launch Alliance are now targeting Sunday 9 February 23:03 EST (04:03 GMT / 05:03 CET Monday 10 February) for the launch of the Solar Orbiter mission on an Atlas V rocket from Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida. The launch has a two-hour window.



Facing the Sun



Solar Orbiter, an ESA-led mission with strong NASA participation, will provide the first views of the Sun’s unchartered polar regions from high-latitudes, giving unprecedented insight into how our parent star works. This important mission will also investigate the Sun-Earth connection, helping us to better understand and predict periods of stormy space weather.

ESA’s Solar Orbiter is launching from NASA’s Kennedy Space Center in February 2020.

The mission will answer some of the biggest questions in solar science. What drives the solar wind and how does space weather impact the Earth? What controls the Sun’s 11-year activity cycle? How is the magnetic field generated inside the Sun?

Solar Orbiter will unlock the secrets of how our star works by combining in situ and remote sensing observations. It will use Venus gravity assists to fly out of the ecliptic plane to study the Sun at high latitudes, and it will provide the first images of the Sun’s poles. Solar Orbiter will bring Europe to within the orbit of Mercury for the first time, to face the Sun and understand how our life-giving star influences the entire Solar System.

Solar Orbiter is an ESA mission with strong NASA participation.



Over the course of its mission, the spacecraft will use the gravity of Venus to slingshot it out of the ecliptic plane of the Solar System, giving us new perspectives on our parent star. It will follow an elliptical orbit around the Sun, passing within the orbit of Mercury at its closest. Cutting-edge heatshield technology will ensure the spacecraft’s scientific instruments are protected as they face up to 13 times the heating of satellites in Earth orbit.

Solar Orbiter will use a combination of ten in situ and remote-sensing instruments to observe the turbulent solar surface, its hot outer atmosphere and changes in the solar wind. The mission will also work with NASA’s Parker Solar Probe, collecting complementary datasets that will allow more science to be distilled from the two missions than either could achieve on their own.

Experts will present the mission, its technical challenges and scientific goals during a dedicated media briefing at the European Space Operations Centre (ESOC).

Solar Orbiter ©ESA/ATG medialab

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Mission Overview



Solar Orbiter is an international cooperative mission between ESA (the European Space Agency) and NASA that addresses a central question of heliophysics: How does the Sun create and control the constantly changing space environment throughout the solar system? Solar Orbiter is slated for an early 2020 launch.

New Mission Will Take 1st Peek at Sun’s Poles

A new spacecraft is journeying to the Sun to snap the first pictures of the Sun’s north and south poles.

Solar Orbiter, a collaboration between the European Space Agency, or ESA, and NASA, will have its first opportunity to launch from Cape Canaveral on Feb. 7, 2020, at 11:15 p.m. EST. Launching on a United Launch Alliance Atlas V rocket, the spacecraft will use Venus’s and Earth’s gravity to swing itself out of the ecliptic plane — the swath of space, roughly aligned with the Sun’s equator, where all planets orbit. From there, Solar Orbiter’s bird’s eye view will give it the first-ever look at the Sun’s poles.

“Up until Solar Orbiter, all solar imaging instruments have been within the ecliptic plane or very close to it,” said Russell Howard, space scientist at the Naval Research Lab in Washington, D.C. and principal investigator for one of Solar Orbiter’s ten instruments. “Now, we’ll be able to look down on the Sun from above.”

“It will be terra incognita,” said Daniel Müller, ESA project scientist for the mission at the European Space Research and Technology Centre in the Netherlands. “This is really exploratory science.”

The Sun plays a central role in shaping space around us. Its massive magnetic field stretches far beyond Pluto, paving a superhighway for charged solar particles known as the solar wind. When bursts of solar wind hit Earth, they can spark space weather storms that interfere with our GPS and communications satellites — at their worst, they can even threaten astronauts.

To prepare for arriving solar storms, scientists monitor the Sun’s magnetic field. But their techniques work best with a straight-on view; the steeper the viewing angle, the noisier the data. The sidelong glimpse we get of the Sun’s poles from within the ecliptic plane leaves major gaps in the data.

“The poles are particularly important for us to be able to model more accurately,” said Holly Gilbert, NASA project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “For forecasting space weather events, we need a pretty accurate model of the global magnetic field of the Sun.”

The Sun’s poles may also explain centuries-old observations. In 1843, German astronomer Samuel Heinrich Schwabe discovered that the number of sunspots — dark blotches on the Sun’s surface marking strong magnetic fields — waxes and wanes in a repeating pattern. Today, we know it as the approximately-11-year solar cycle in which the Sun transitions between solar maximum, when sunspots proliferate and the Sun is active and turbulent, and solar minimum, when they’re fewer and it’s calmer. “But we don’t understand why it’s 11 years, or why some solar maximums are stronger than others,” Gilbert said. Observing the changing magnetic fields of the poles could offer an answer.

The only prior spacecraft to fly over the Sun’s poles was also a joint ESA/NASA venture. Launched in 1990, the Ulysses spacecraft made three passes around our star before it was decommissioned in 2009. But Ulysses never got closer than Earth-distance to the Sun, and only carried what’s known as in situ instruments — like the sense of touch, they measure the space environment immediately around the spacecraft. Solar Orbiter, on the other hand, will pass inside the orbit of Mercury carrying four in situ instruments and six remote-sensing imagers, which see the Sun from afar. “We are going to be able to map what we ‘touch’ with the in situ instruments and what we ‘see’ with remote sensing,” said Teresa Nieves-Chinchilla, NASA deputy project scientist for the mission.

After years of technology development, it will be the closest any Sun-facing cameras have ever gotten to the Sun. “You can’t really get much closer than Solar Orbiter is going and still look at the Sun,” Müller said.

Over the mission’s seven year lifetime, Solar Orbiter will reach an inclination of 24 degrees above the Sun’s equator, increasing to 33 degrees with an additional three years of extended mission operations. At closest approach the spacecraft will pass within 26 million miles of the Sun.

To beat the heat, Solar Orbiter has a custom-designed titanium heat shield with a calcium phosphate coating that withstands temperatures over 900 degrees Fahrenheit — thirteen times the solar heating faced by spacecraft in Earth orbit. Five of the remote-sensing instruments look at the Sun through peepholes in that heat shield; one observes the solar wind out to the side.

Solar Orbiter will be NASA’s second major mission to the inner solar system in recent years, following on August 2018’s launch of Parker Solar Probe. Parker has completed four close solar passes and will fly within four million miles of the Sun at closest approach.

The two spacecraft will work together: As Parker samples solar particles up close, Solar Orbiter will capture imagery from farther away, contextualizing the observations. The two spacecraft will also occasionally align to measure the same magnetic field lines or streams of solar wind at different times.

“We are learning a lot with Parker, and adding Solar Orbiter to the equation will only bring even more knowledge,” said Nieves-Chinchilla.

Solar Orbiter is an international cooperative mission between the European Space Agency and NASA. ESA’s European Space Research and Technology Centre (ESTEC) in The Netherlands manages the development effort. The European Space Operations Center (ESOC) in Germany will operate Solar Orbiter after launch. Solar Orbiter was built by Airbus Defense and Space, and contains 10 instruments: nine provided by ESA member states and ESA. NASA provided one instrument suite, SoloHI and provided detectors and hardware for three other instruments.

In NASA

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Banner An animation of Solar Orbiter peering at the Sun through peepholes in its heat shield. ©ESA/ATG medialab

Solar Orbiter Instruments



Solar Orbiter carries a scientific payload of ten different instruments on its voyage around the Sun. Six instruments are remote sensing, which “see” the Sun and return imagery. The other four are in situ instruments, which work by “touch:” They measure the environment immediately surrounding the spacecraft, including solar wind plasma — the electrified gas streaming from the Sun — and the electric and magnetic fields embedded within it. The ten instruments work together to provide an unprecedented, comprehensive view of our star.



In situ instruments

EPD: Energetic Particle Detector



Solar Orbiter’s Energetic Particle Detector suite of instruments measures energetic particles from the Sun over a wide range of energies with high temporal, energetic and mass resolutions. Gathering these measurements close to the Sun, at a point where the particles have experienced minimal effects from traveling through space, scientists can observe them in a more pristine condition than is possible near Earth. These close-up observations will allow scientists to shed new light on one of Solar Orbiter’s primary science questions: how solar eruptions generate energetic particle radiation, which can affect astronauts and technology in space.

EPD measures electrons, which provide a unique tracer of the solar magnetic field because they travel along magnetic field lines as they flow out from the Sun. Electron measurements provide a clearer picture of the solar magnetic field close to the Sun, contributing to additional Solar Orbiter science goals: understanding how the solar wind plasma and magnetic field originate in the corona, and exploring how solar transients drive heliospheric variability.

The EPD principal investigator is Javier Rodríguez-Pacheco at the University of Alcala, Spain.



MAG: Magnetometer



The Sun’s magnetic field extends outwards from our star, filling interplanetary space. Solar Orbiter’s ultra-sensitive magnetic field instruments measure the strength and direction of the magnetic field around the spacecraft. This is a complicated, ever-changing characteristic that affects how charged particles move while simultaneously being influenced by the particles themselves as they zip through space. The magnetometer measurements will help scientists address one of Solar Orbiter’s primary science questions about the origins of the magnetic field and solar wind plasma in the corona. Magnetic fields also act as a highway for charged particles moving away from the Sun, so magnetometer measurements will also be key to exploring how energetic particle radiation travels out into the solar system following solar eruptions.

The MAG principal investigator is Tim Horbury at the Imperial College London, UK.



SWA: Solar Wind Analyzer Suite



The Solar Wind Analyzer instruments on board Solar Orbiter together measure more than 99% of the charged particles that come from the Sun towards the spacecraft — specifically, the electrons, protons and heavier particles that make up the bulk of the solar wind. These measurements help scientists understand what the solar wind is made of, and in particular can help determine where a given solar wind stream came from, by comparing SWA measurements to those taken of the Sun’s corona by Solar Orbiter’s remote-sensing instruments.

The Solar Wind Analyzer measures the lower-energy particle populations in the solar wind. However, these bulk solar wind particles also provide the seed populations for energetic particle events that can harm spacecraft and astronauts in near-Earth space. Finding where and how these particles start will allow scientists to put constraints on theories about how solar eruptions produce energetic particle radiation. The SWA instruments’ measurements also give scientists an unprecedented look at transients in the solar wind, like the shock waves created when solar wind streams of different speeds collide.

The SWA principal investigator is Christopher J. Owen of the Mullard Space Science Laboratory at University College London, UK.

Solar Orbiter Mission Goals ©ESA



RPW: Radio and Plasma Waves



Solar Orbiter’s Radio and Plasma Waves suite measures changes in the electric and magnetic fields around the spacecraft. This includes changes caused by natural plasma waves near the spacecraft as well as those due to radio bursts — brief flashes of long-wavelength light — that come from afar. These measurements will help characterize the role of plasma waves in accelerating and heating the solar wind. Additionally, the suite’s measurements of radio bursts triggered by energetic particles will shed light on how energetic particle radiation is created and travels throughout the heliosphere.

The RPW principal investigator is Milan Maksimovic at the Observatoire de Paris in France.



Remote-sensing Instruments

EUI: Extreme Ultraviolet Imager



The Extreme Ultraviolet Imager, or EUI, looks at the Sun in extreme ultraviolet light, a wavelength of light that is invisible to our eyes but useful for tracking plasma at very high temperatures. EUI’s images capture the layers of the solar atmosphere just above the Sun’s surface — the chromosphere and transition region — and through the corona. The images link observations of the surface to those of the blazing corona, allowing scientists to track the heating that occurs throughout the lower solar atmosphere. This part of the atmosphere is shaped by features on the surface like active regions, filaments and coronal holes. In turn, the lower atmosphere defines much of the larger corona. By training EUI’s eye to the lower atmosphere, scientists can track the structures and heating processes that influence the corona overall.

Besides the mystery of the corona’s intense heat, the existence of the corona itself is puzzling too: how does it replenish its energy and mass when it constantly sends out heat and mass, by way of the solar wind? Scientists think that small, repeated processes in the corona are responsible for keeping the corona going; EUI can discern these fine details.

EUI comprises three imagers. One full-disk imager sees the entire Sun at any given point. The other two are high-resolution imagers with the necessary detail and cadence for studying energetic displays like flares or CMEs. The imagers are housed in an optics box that sits behind Solar Orbiter’s heat shield.

EUI works with other instruments aboard Solar Orbiter, relating in situ measurements of the solar wind back to their origins on the Sun. The full-disk imager has an expansive field of view that overlaps with that of Metis, Solar Orbiter’s coronagraph. Combined, images from EUI and Metis can show a CME’s complete exit from the Sun.

The EUI principal investigator for development is Pierre Rochus at the Liège Space Center at the University of Liège in Belgium. The principal investigator for operations is David Berghmans at the Royal Observatory of Belgium.



Metis



Metis is an instrument known as a coronagraph, which captures images of the Sun’s dim outer atmosphere, the corona, by blocking light from Sun’s bright surface. Metis will image the corona in both visible and extreme ultraviolet light from closer than any previous coronagraph has gotten to the Sun.

The Metis field of view varies throughout different parts of Solar Orbiter’s orbit. At closest approach, Metis will image the corona between approximately 302 thousand and 908 thousand miles from the Sun’s surface, the area where the solar atmosphere is accelerated away from the Sun to form the solar wind. By capturing both visible light as well as an extreme ultraviolet wavelength emitted by hydrogen, Metis can calculate the solar wind’s speed. Studying this boundary where the solar wind starts, Metis can help link what happens on the Sun itself with what happens further out into the heliosphere.

The Metis principal investigator is Marco Romoli at the University of Florence in Italy.



PHI: Polarimetric and Helioseismic Imager

Solar Orbiter Mission Overview ©ESA



The Polarimetric and Helioseismic Imager, or PHI, surveys the Sun’s magnetic field — a key to understanding the Sun’s behavior. The magnetic field is the root of all solar activity: It drives the solar cycle, the constantly streaming solar wind, and occasional eruptions.

PHI is central to Solar Orbiter’s goals of working out the mechanisms of the dynamo, the name for the interior process that generates the solar magnetic field. PHI uses information from the outside of the Sun to help scientists determine what is happening inside. Like the tremors that follow an earthquake, waves on the Sun rumble up from the convection zone, the interior region where solar plasma constantly churns. PHI measures the soundwaves associated with sunquakes as they ripple across the solar surface to better understand the dynamo.

PHI comprises two telescopes. The full-disk telescope views the whole Sun at any given time, while a high-resolution telescope views a smaller portion of the Sun, with the ability to resolve fine structures on the surface. These telescopes produce magnetograms — maps of the magnetic peaks and valleys on the solar surface, which in turn enables estimates of the magnetic field in the corona and heliosphere. PHI complements other instruments aboard Solar Orbiter by linking their observations of solar structures to the underlying magnetic field.

The PHI principal investigator is Sami Solanki at the Max Planck Institute for Solar System Research in Göttingen, Germany.



SoloHi: Solar Orbiter Heliospheric Imager



The Solar Orbiter Heliospheric Imager or SoloHI is a visible light telescope that images sunlight reflected off of solar wind electrons. Covering a 40 degree field of view, at closest approach to the Sun it captures a region from about 2.25 million miles to approximately 18 million miles from the Sun.

SoloHI’s images capture the interplanetary medium — that is, the solar wind, dust and cosmic rays that fill the space between the Sun and the planets. The interplanetary medium is the material that solar eruptions like CMEs travel through, so understanding it is critical to better predicting how solar eruptive events travel through space, including whether and when they will impact Earth.

Flying on Solar Orbiter places SoloHI above and below the ecliptic plane, where the interplanetary medium is the densest. This position allows researchers to track, for the first time, the longitudinal extent of a CME for much longer than is possible from a vantage point embedded inside the ecliptic. The top-down view of the Sun provides a 360-degree view of the solar equator, giving SoloHi a vantage point suitable for capturing most solar eruptions and observing co-rotating interaction regions, or CIRs. The view will allow SoloHi to track how, due to the Sun’s rotation, the solar material spirals outward, tracing out what’s called the Parker spiral – the spread of solar material that flows out into space in much the same shape as water flying off of a rotating sprinkler.

The SoloHI principal investigator is Russell Howard at the Naval Research Laboratory in Washington, D.C.



SPICE: Spectral Imaging of the Coronal Environment



SPICE — short for Spectral Imaging of the Coronal Environment — maps the Sun’s plasma as it seethes on the solar surface and escapes the atmosphere in the form of solar wind. SPICE is an extreme ultraviolet spectrometer, which means it observes several different wavelengths of ultraviolet light and measures how much of each wavelength is present. Because different gases emit specific wavelengths at specific temperatures, SPICE can provide a big picture understanding of what temperature ranges and gases are present on and around the Sun. In addition to temperature and composition, SPICE gathers information on the density and flow of solar material.

SPICE is designed to help determine the origin and formation of the solar wind — and so it focuses on the transition region and corona, from which the solar wind blows. There are two distinct streams of solar wind: slow streams travelling some 215 miles per second and fast streams that rip through space at twice that speed. Understanding their differing origins can improve our understanding of how the Sun’s magnetic field affects the way it sends out solar material. SPICE seeks to identify the regions that give rise to the slow and fast solar wind.

SPICE works in tandem with many other Solar Orbiter instruments. Measurements of the solar wind from the in situ Solar Wind Analyzer can be directly linked to SPICE’s maps. SPICE observations are also useful for mapping plasma over the poles as it relates to the dynamo, and comparing plasma on the Sun before and after solar eruptions. By providing a picture of solar material itself, scientists can better understand connections between the dynamo and the Sun’s surface, and ultimately, throughout the solar system.

The SPICE principal investigator for operations is Frédéric Auchère at the Institute for Space Astrophysics in Orsay, France.



STIX: X-ray Spectrometer/Telescope



The X-ray Spectrometer/Telescope, or STIX, surveys X-rays that burst from the Sun during solar flares. X-rays are photons — particles of light — that carry lots of energy. Specifically, STIX measures hard X-rays: the highest energy X-rays. Hard X-rays are produced by the hottest, most powerful parts of a solar eruption. Like fingerprints at the scene of a crime, hard X-rays can reveal how each eruption unfolds. By studying where this radiation comes from, scientists can piece together the underlying physics of how flares work.

STIX takes note of the timing, location, and intensity of each X-ray burst from the Sun — all important clues to how the star generates such powerful bursts of energy. Scientists pair this information with images of the Sun, which allows them to map out where energy comes from during an explosion, and what produces that energy. A small box-shaped instrument only as heavy as a bowling ball, STIX has a wide field of view. At any given point in Solar Orbiter’s orbit, STIX can see the entire face of Sun — and any flares that occur.

Flares are known to accelerate particles to speeds approaching that of light. These energetic particles can wreak havoc with our technology and satellites in space, and even endanger astronauts. STIX works with other instruments aboard Solar Orbiter to help scientists track where those powerful particles come from. When the spacecraft’s Energetic Particle Detector catches high-energy particles, STIX can use X-rays to determine where they originated on the Sun, linking remote observations to in situ data.

The STIX principal investigator is Sämuel Krucker at the University of Applied Sciences and Arts Northwestern Switzerland in Windisch, Switzerland.

In NASA

http://www.nasa.gov/content/solar-orbiter-instruments