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The Solar Orbiter (SolO) is a
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
-observing probe developed by the
European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...
(ESA) with a
National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the United States's civil space program, aeronautics research and space research. Established in 1958, it su ...
(NASA) contribution. Solar Orbiter, designed to obtain detailed measurements of the inner
heliosphere The heliosphere is the magnetosphere, astrosphere, and outermost atmospheric layer of the Sun. It takes the shape of a vast, tailed bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding ...
and the nascent
solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...
, will also perform close observations of the polar regions of the Sun which is difficult to do from Earth. These observations are important in investigating how the Sun creates and controls its heliosphere. SolO makes observations of the Sun from an eccentric orbit moving as close as ≈60 solar radii (RS), or 0.284
astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
s (au), placing it inside Mercury's
perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...
of 0.3075 au. During the mission the orbital inclination will be raised to about 24°. The total mission cost is US$1.5 billion, counting both ESA and NASA contributions. SolO was launched on 10 February 2020 from Cape Canaveral, Florida (USA). The nominal mission is planned until the end of 2026, with a potential extension until 2030.


Spacecraft

The Solar Orbiter spacecraft is a Sun-pointed, three-axis stabilised platform with a dedicated heat shield to provide protection from the high levels of solar flux near perihelion. The spacecraft provides a stable platform to accommodate the combination of remote-sensing and in situ instrumentation in an electromagnetically clean environment. The 21 sensors were configured on the spacecraft to allow each to conduct its in situ or remote-sensing experiments with both access to and protection from the solar environment. Solar Orbiter has inherited technology from previous missions, such as the solar arrays from the BepiColombo Mercury Planetary Orbiter (MPO). The solar arrays can be rotated about their longitudinal axis to avoid overheating when close to the Sun. A battery pack provides supplementary power at other points in the mission such as eclipse periods encountered during planetary flybys. The Telemetry, Tracking and Command Subsystem provides the communication link capability with the Earth in X-band. The subsystem supports telemetry, telecommand and ranging. Low-Gain Antennas are used for Launch and Early Orbit Phase (LEOP) and now function as a back-up during the mission phase when steerable Medium- and High-Gain Antennas are in use. The High-Temperature High-Gain Antenna needs to point to a wide range of positions to achieve a link with the ground station and to be able to downlink sufficient volumes of data. Its design was adapted from the BepiColombo mission. The antenna can be folded in to gain protection from Solar Orbiter's heat shield if necessary. Most data will therefore initially be stored in on-board memory and sent back to Earth at the earliest possible opportunity. The ground station at
Malargüe Malargüe () is a city in the southwest part of the province of Mendoza, Argentina, about 370 km south of the provincial capital Mendoza. It is the head town of the Malargüe Department, and it has about 27,000 inhabitants as per the . Et ...
(Argentina), with a antenna, is used for 4 to 8 hours/day (effective). ESA's Malargüe ground station will be used for all operations throughout the mission with the ground stations in
New Norcia New or NEW may refer to: Music * New, singer of K-pop group The Boyz * ''New'' (album), by Paul McCartney, 2013 ** "New" (Paul McCartney song), 2013 * ''New'' (EP), by Regurgitator, 1995 * "New" (Daya song), 2017 * "New" (No Doubt song), 1 ...
, Australia, and Cebreros, Spain, acting as backup when necessary.


Mission operations

During nominal science operations, science data is downlinked for eight hours during each communication period with the ground station. Additional eight-hour downlink passes are scheduled as needed to reach the required total science data return of the mission. The Solar Orbiter ground segment makes maximum reuse of ESA's infrastructure for Deep Space missions: * The ground stations, which belong to ESA's space tracking station network (
ESTRACK The European Space Tracking (ESTRACK) network consists of a number of ground-based space-tracking stations belonging to the European Space Agency (ESA), and operated by the European Space Operations Centre (ESOC) in Darmstadt, Germany. The st ...
) * The Mission Operations Centre (MOC), located at ESOC,
Darmstadt Darmstadt () is a city in the States of Germany, state of Hesse in Germany, located in the southern part of the Frankfurt Rhine Main Area, Rhine-Main-Area (Frankfurt Metropolitan Region). Darmstadt has around 160,000 inhabitants, making it the ...
, Germany * The Science Operations Centre (SOC), located at ESAC, Villanueva de la Cañada, Spain * The communications network, linking the various remotely located centres and stations to support the operational data traffic The Science Operations Centre was responsible for mission planning and the generation of payload operations requests to the MOC, as well as science data archiving. The SOC has been operational for the active science phase of the mission, i.e. from the beginning of the Cruise Phase onwards. The handover of payload operations from the MOC to the SOC is performed at the end of the Near-Earth Commissioning Phase (NECP). ESA's Malargüe Station in Argentina will be used for all operations throughout the mission, with the ground stations of New Norcia Station, Australia, and Cebreros Station, Spain, acting as backup when necessary. During the initial cruise phase, which lasted until November 2021, Solar Orbiter performed two gravity-assist manoeuvres around Venus and one around Earth to alter the spacecraft's trajectory, guiding it towards the innermost regions of the Solar System. At the same time, Solar Orbiter acquired in situ data to characterise and calibrate its remote-sensing instruments. The first close solar pass took place on 26 March 2022 at around a third of Earth's distance from the Sun. The spacecraft's orbit has been chosen to be 'in resonance' with Venus, which means that it will return to the planet's vicinity every few orbits and can again use the planet's gravity to alter or tilt its orbit. Initially, Solar Orbiter will be confined to the same plane as the planets, but each encounter of Venus will increase its orbital inclination. For example, after the 2025 Venus encounter, it will make its first solar pass at 17° inclination, increasing to 33° during a proposed mission extension phase, bringing even more of the polar regions into direct view.


Scientific objectives

The spacecraft makes a close approach to the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
every six months. The closest approach will be positioned to allow a repeated study of the same region of the solar atmosphere. ''Solar Orbiter'' will be able to observe the magnetic activity building up in the atmosphere that can lead to powerful
solar flare A solar flare is a relatively intense, localized emission of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and ot ...
s or eruptions. Researchers also have the chance to coordinate observations with NASA's ''
Parker Solar Probe The Parker Solar Probe (PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+) is a NASA space probe launched in 2018 to make observations of the Stellar corona, Sun's outer corona. It used repeated Gravity assist, gravity assists from ...
'' mission (2018–2025) which is performing measurements of the Sun's extended corona, as well as other ground-based assets such as the Daniel K. Inouye Solar Telescope. The objective of the mission is to perform close-up, high-resolution studies of the Sun and its inner
heliosphere The heliosphere is the magnetosphere, astrosphere, and outermost atmospheric layer of the Sun. It takes the shape of a vast, tailed bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding ...
. The new understanding will help answer these questions: * How and where do the
solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...
plasma and
magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
originate in the corona? * How do solar transients drive heliospheric variability? * How do solar eruptions produce energetic particle radiation that fills the heliosphere? * How does the
solar dynamo The solar dynamo is a physical process that generates the Sun's magnetic field. It is explained with a variant of the dynamo theory. A naturally occurring electric generator in the Sun's interior produces electric currents and a magnetic field, ...
work and drive connections between the Sun and the heliosphere?


Science results

Since the launch of the mission, a series of papers have been released in three special issues of the
Astronomy and Astrophysics ''Astronomy & Astrophysics (A&A)'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. It is operated by an editorial team under the supervision of a board of directors re ...
Journal:
The Solar Orbiter missionSolar Orbiter First Results (Cruise Phase)Solar Orbiter First Results (Nominal Mission Phase)
Meanwhile, regular
science nuggets
are released on th
Solar Orbiter science community website


Instruments

The science payload is composed of 10 instruments: ;Heliospheric in-situ instruments (4) * SWA – Solar Wind Plasma Analyser (United Kingdom): Consists of a suite of sensors that measures the ion and electron bulk properties (including density, velocity, and temperature) of the solar wind, thereby characterizing the solar wind between 0.28 and 1.4 au from the Sun. In addition to determining the bulk properties of the wind, SWA provides measurements of solar wind ion composition for key elements (e.g. the C, N, O group and Fe, Si or Mg) * EPD – Energetic Particle Detector (Spain): Measures the composition, timing and distribution functions of suprathermal and energetic particles. Scientific topics to be addressed include the sources, acceleration mechanisms, and transport processes of these particles * MAG –
Magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
(United Kingdom): Provides in situ measurements of the heliospheric magnetic field (up to 64 Hz) with high precision. This will facilitate detailed studies into the way the Sun's magnetic field links into space and evolves over the solar cycle; how particles are accelerated and propagate around the Solar System, including to the Earth; how the corona and solar wind are heated and accelerated * RPW – Radio and Plasma Waves (France): Unique amongst the Solar Orbiter instruments, RPW makes both in situ and remote-sensing measurements. RPW measures magnetic and electric fields at high time resolution using a number of sensors/antennas, to determine the characteristics of electromagnetic and electrostatic waves in the solar wind ;Solar remote-sensing instruments (6) * PHI – Polarimetric and Helioseismic Imager (Germany): Provides high-resolution and full-disk measurements of the photospheric vector magnetic field and line-of-sight (LOS) velocity as well as the continuum intensity in the visible wavelength range. The LOS velocity maps have the accuracy and stability to allow detailed helioseismic investigations of the solar interior, in particular of the solar convection zone high-resolution and full-disk measurements of the photospheric magnetic field * EUI – Extreme Ultraviolet Imager (Belgium): Images the solar atmospheric layers above the photosphere, thereby providing an indispensable link between the solar surface and outer corona that ultimately shapes the characteristics of the interplanetary medium. Also, EUI provides the first-ever UV images of the Sun from an out-of-ecliptic viewpoint (up to 33° of solar latitude during the extended mission phase) * SPICE – Spectral Imaging of the Coronal Environment (France): Performs extreme ultraviolet imaging
spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...
to remotely characterize plasma properties of the Sun's on-disk corona. This will enable matching in situ composition signatures of
solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...
streams to their source regions on the Sun's surface * STIX – Spectrometer Telescope for Imaging X-rays (Switzerland): Provides imaging
spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...
of solar thermal and non-thermal X-ray emission from 4 to 150 keV. STIX provides quantitative information on the timing, location, intensity, and spectra of accelerated electrons as well as of high-temperature thermal plasmas, mostly associated with flares and/or microflares *Metis –
Coronagraph A coronagraph is a telescopic attachment designed to block out the direct light from a star or other bright object so that nearby objects – which otherwise would be hidden in the object's bright glare – can be resolved. Most coronagr ...
(Italy): Simultaneously images the visible and far ultraviolet emissions of the solar corona and diagnoses, with unprecedented temporal coverage and spatial resolution, the structure and dynamics of the full corona in the range from 1.4 to 3.0 (from 1.7 to 4.1) solar radii from Sun centre, at minimum (maximum) perihelion during the nominal mission. This is a region that is crucial in linking the solar atmospheric phenomena to their evolution in the inner heliosphere * SoloHI – Solar Orbiter Heliospheric Imager (United States): Images both the quasi-steady flow and transient disturbances in the solar wind over a wide field of view by observing visible sunlight scattered by solar wind electrons. SoloHI provides unique measurements to pinpoint coronal mass ejections (CMEs). (NRL provided)


Institutions involved

The following institutions operate each instrument: * Solar Wind Plasma Analyser (SWA):
Mullard Space Science Laboratory The UCL Mullard Space Science Laboratory (MSSL) is the United Kingdom's largest university space research group. MSSL is part of the Department of Space and Climate Physics at University College London (UCL), one of the first universities in th ...
* Energetic Particle Detector (EPD): University of Alcala,
University of Kiel Kiel University, officially the Christian Albrecht University of Kiel, (, abbreviated CAU, known informally as Christiana Albertina) is a public research university in the city of Kiel, Germany. It was founded in 1665 as the ''Academia Holsator ...
(CAU) * Magnetometer (MAG):
Imperial College London Imperial College London, also known as Imperial, is a Public university, public research university in London, England. Its history began with Prince Albert of Saxe-Coburg and Gotha, Prince Albert, husband of Queen Victoria, who envisioned a Al ...
* Radio and Plasma Waves (RPW): Observatoire de Paris * Polarimetric and Helioseismic Imager (PHI):
Max Planck Institute for Solar System Research The Max Planck Institute for Solar System Research (abbreviation: MPS; ) is a research institute in astronomy and astrophysics located in Göttingen, Germany, where it relocated in February 2014 from the nearby village of Lindau (Katlenburg-Lindau ...
(MPS), Instituto de Astrofísica de Andalucía (IAA) * Extreme Ultraviolet Imager (EUI):
Royal Observatory of Belgium The Royal Observatory of Belgium (; ; ) has been situated in the Uccle municipality of Brussels since 1890. It is part of the institutions of the Belgian Federal Science Policy Office (BELSPO). The Royal Observatory was first established in S ...
, Centre Spatial de Liège, Institut d'astrophysique spatiale,
Max Planck Institute for Solar System Research The Max Planck Institute for Solar System Research (abbreviation: MPS; ) is a research institute in astronomy and astrophysics located in Göttingen, Germany, where it relocated in February 2014 from the nearby village of Lindau (Katlenburg-Lindau ...
(MPS) * Spectral Imaging of the Coronal Environment (SPICE): Institut d'astrophysique spatiale Rutherford Appleton Laboratory,
Max Planck Institute for Solar System Research The Max Planck Institute for Solar System Research (abbreviation: MPS; ) is a research institute in astronomy and astrophysics located in Göttingen, Germany, where it relocated in February 2014 from the nearby village of Lindau (Katlenburg-Lindau ...
(MPS) * Spectrometer/Telescope for Imaging X-rays (STIX): FHNW, Space Research Centre of Polish Academy of Sciences, Leibniz-Institut für Astrophysik Potsdam (AIP) * Coronagraph (Metis):
University of Florence The University of Florence ( Italian: ''Università degli Studi di Firenze'') (in acronym UNIFI) is an Italian public research university located in Florence, Italy. It comprises 12 schools and has around 50,000 students enrolled. History The f ...
,
INAF The National Institute for Astrophysics (, or INAF) is an Italian research institute in astronomy and astrophysics, founded in 1999. INAF funds and operates twenty separate research facilities, which in turn employ scientists, engineers and tech ...
,
Max Planck Institute for Solar System Research The Max Planck Institute for Solar System Research (abbreviation: MPS; ) is a research institute in astronomy and astrophysics located in Göttingen, Germany, where it relocated in February 2014 from the nearby village of Lindau (Katlenburg-Lindau ...
(MPS) * Heliospheric Imager (SoloHI):
United States Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. Located in Washington, DC, it was founded in 1923 and conducts basic scientific research, appl ...


Launch and flight


Launch delays

In April 2015, the launch was set back from July 2017 to October 2018. In August 2017, Solar Orbiter was considered "on track" for a launch in February 2019. The launch occurred on 10 February 2020 on an
Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas (rocket family), Atlas launch vehicle family. It was developed by Lockheed Martin and has been operated by United Launch Alliance (ULA) since 2006. Primarily used to ...
411.


Launch

The Atlas V 411 (AV-087) lifted off from SLC-41 at Cape Canaveral, Florida, at 04:03 UTC. The Solar Orbiter spacecraft separated from the Centaur upper stage nearly 53 minutes later, and the European Space Agency acquired the first signals from the spacecraft a few minutes later.


Trajectory

After launch, Solar Orbiter took approximately 3.5 years, using repeated
gravity assist A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby (spaceflight), flyby which makes use of the relative movement (e.g. orbit around the Sun) and gra ...
s from Earth and Venus, to reach its operational orbit, an elliptical orbit with perihelion 0.28 AU and aphelion 0.91 AU. The first flyby was of Venus in December 2020. Over the expected mission duration of 7 years, it will use additional gravity assists from Venus to raise its inclination from 0° to 24°, allowing it a better view of the Sun's poles. If an extended mission is approved, the inclination could rise further to 33°. During its cruise phase to Venus, Solar Orbiter passed through the ion tail of Comet C/2019 Y4 (ATLAS) from 31 May to 1 June 2020. It passed through the comet's dust tail on 6 June 2020. In June 2020, Solar Orbiter came within of the Sun, and captured the closest pictures of the Sun ever taken.


Mission timeline

Source:


Mission Events

* April 2012: €319 million contract to build orbiter awarded to Astrium UK * June 2014: Solar shield completes 2 week bake test * September 2018: Spacecraft is shipped to
IABG IABG (Industrieanlagen-Betriebsgesellschaft mbH) is a German analysis and test engineering company based in Taufkirchen near Munich. History The company was founded in 1961 on the initiative of the federal government as a central analysis and ...
in Germany to begin the environmental test campaign * February 2020: Successful launch * May–June 2020: Encounter with the ion and dust tails of C/2019 Y4 (ATLAS) *Jul 2020: First images of the Sun released * December 2021: Flight through tail of Comet C/2021 A1 Leonard *March 2022: highest resolution image of the Sun’s full disc and outer atmosphere, the corona, ever taken *September 2022: Solar Orbiter solves the magnetic switchback mystery *February 2025: Solar Orbiter leaves
orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) a ...
of the
solar system The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
after successfully completing the 4th
Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
flyby *On 11 June 2025, the first images and videos of the Sun’s south pole (taken in March 2025) were released. These are the first images of the Sun’s poles taken from outside the ecliptic plane.


Solar Orbiter and Parker Solar Probe collaboration

SolO and NASA's
Parker Solar Probe The Parker Solar Probe (PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+) is a NASA space probe launched in 2018 to make observations of the Stellar corona, Sun's outer corona. It used repeated Gravity assist, gravity assists from ...
(PSP) missions cooperated to trace solar wind and transients from their sources on the Sun to the inner interplanetary space. In 2022, SolO and PSP planners collaborated to study why the Sun's atmosphere is "150 times hotter" than its surface. SolO observed the Sun from 140 million kilometers, while PSP simultaneously observed the Sun's corona from nearly 9 million kilometers. In March 2024, both space probes were at their closest approaches to the Sun, PSP at 7.3 million km, and SolO at 45 million km. SolO observed the Sun, while PSP sampled the plasma of the solar wind, allowing scientists to compare data from both probes.


Outreach

Solar Orbiter news are regularly updated and listed in th
official ESA public pages
as well as on th
Bluesky
an
Twitter/X account
Images taken by the spacecraft with various instruments can be found on th
official Flickr account


Gallery

PHI's view of the Sun in visible light.jpg, PHI's view of the Sun in visible light EUI s view of the Sun in UV light.jpg, EUI's view of the Sun in UV light PHI's map of the Sun s magnetic field.jpg, PHI's map of the Sun's magnetic field PHI's velocity map of the Sun s surface.jpg, PHI's velocity map of the Sun's surface File:Solar Orbiter s world-first views of the Sun s south pole.png, The collage of SoLO's view of the Sun's south pole on 16–17 March 2025, from a viewing angle of around 15° below the solar equator.


See also

* List of heliophysics missions * List of European Space Agency programmes and missions


References


External links


New ESA Solar Orbiter homepage (from December 2020)

Old ESA Solar Orbiter homepage (to December 2020)

Special issue on "The Solar Orbiter Mission"
in ''
Astronomy & Astrophysics ''Astronomy & Astrophysics (A&A)'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. It is operated by an editorial team under the supervision of a board of directors re ...
''
Solar Orbiter at eoPortal

METIS instrument homepage

Media Kit – overview of mission
{{Portal bar, Spaceflight Missions to the Sun European Space Agency space probes Solar space observatories NASA space probes Solar telescopes Space probes launched in 2020 Living With a Star Cosmic Vision Spacecraft launched by Atlas rockets February 2020 in the United States