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Solar Orbiter

European space-based solar observatory From Wikipedia, the free encyclopedia

Solar Orbiter
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This article is about the European Space Agency heliophysics orbiter. For the NASA heliophysics orbiter, see Parker Solar Probe.

The Solar Orbiter (SolO)[7] is a Sun-observing probe developed by the European Space Agency (ESA) with a National Aeronautics and Space Administration (NASA) contribution. Solar Orbiter, designed to obtain detailed measurements of the inner heliosphere and the nascent solar wind, also performs 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.

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SolO makes observations of the Sun from an eccentric orbit moving as close as ≈60 solar radii (RS), or 0.284 astronomical units (au), placing it inside Mercury's perihelion of 0.3075 au.[8] 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.[9] 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.

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A comparison of the size of the Sun as seen from Earth (left, 1 au) and from the Solar Orbiter spacecraft (0.284 au, right)
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The Solar Orbiter structural thermal model shortly before leaving the Airbus Defence and Space facility in Stevenage, UK
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Solar Orbiter spacecraft is prepared for encapsulation in the United Launch Alliance Atlas V payload fairing.
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Mission overview

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.[10][11]

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, following the 2025 Venus encounter it makes solar passes at 17° inclination, increasing to 33° during a proposed mission extension phase, bringing even more of the polar regions into direct view.[10]

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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.[12]

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Communication

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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 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.[citation needed]

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 Mission Operations Centre (MOC), located at ESOC, Darmstadt, 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[citation needed]

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.[13][1]

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Scientific objectives

The spacecraft makes a close approach to the Sun every six months.[3] 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 flares or eruptions.[citation needed]

Researchers also have the chance to coordinate observations with NASA's Parker Solar Probe mission (2018–present) 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.[citation needed]

The objective of the mission is to perform close-up, high-resolution studies of the Sun and its inner heliosphere. The new understanding will help answer these questions:

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Science results

Since the launch of the mission, a series of papers have been released in three special issues of the Astronomy and Astrophysics Journal:

Meanwhile, regular "science nuggets Archived 3 August 2023 at the Wayback Machine" are released on the Solar Orbiter science community website Archived 3 August 2023 at the Wayback Machine.

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Instruments

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The science payload is composed of 10 instruments:[14]

Heliospheric in-situ instruments (4)
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The flight model of the Electrostatic Analyser System (EAS), which is part of the Solar Wind Analyser (SWA) Suite
  • 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)[4][15]
  • 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[4]
  • MAG – Magnetometer (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[4]
  • 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[4]
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[4]
  • 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)[4]
  • SPICE – Spectral Imaging of the Coronal Environment (France): Performs extreme ultraviolet imaging spectroscopy to remotely characterize plasma properties of the Sun's on-disk corona. This will enable matching in situ composition signatures of solar wind streams to their source regions on the Sun's surface[4][16][17]
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STIX
  • STIX – Spectrometer Telescope for Imaging X-rays (Switzerland): Provides imaging spectroscopy 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[4]
  • Metis[18] – Coronagraph (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[4]
  • 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)[4][19]

Institutions involved

The following institutions operate each instrument:[20]

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Mission timeline

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The launch of Solar Orbiter from Cape Canaveral at 11.03pm EST on 9 February 2020 (US date)

Before launch

The €319 million contract to build orbiter was awarded to Astrium UK in April 2012[23] The spacecraft's solar shield completed 2 week bake test in June 2014[24] In April 2015, the launch was set back from July 2017 to October 2018.[25] In August 2017, Solar Orbiter was considered "on track" for a launch in February 2019.[26] The spacecraft is shipped to IABG in Germany to begin the environmental test campaign in September 2018.[27]

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 ESA acquired the first signals from the spacecraft a few minutes later.[9]

Cruise phase

After launch, Solar Orbiter entered the crusie phase, which lasted until late 2021.[28] Using repeated gravity assists from Earth and Venus, the spacecraft reached its operational orbit, an elliptical orbit with perihelion 0.29 AU and aphelion 0.91 AU. The first flyby was of Venus in December 2020.[29]

In June 2020, Solar Orbiter came within 77,000,000 km (48,000,000 mi) of the Sun, and captured the closest pictures of the Sun ever taken.[30]

During its cruise towards 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.[31][32] In December 2021, it flew through tail of comet C/2021 A1 Leonard.[33]

Nominal mission phase

Over the expected mission duration of 7 years, Solar Orbiter 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°.[1][34]

The highest resolution image of the Sun’s full disc and outer atmosphere, the corona, so far have been taken on 7 March 2022.[35] In September 2022, scientists suggested a solution to the magnetic switchback mystery based on Solar Orbiter data from March 2022.[36]

In February 2025, Solar Orbiter left the orbital plane of the solar system after successfully completing the 4th Venus flyby,[37] tilting its orbit to 17°. On 11 June 2025, the mission's 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.[38]

In September 2025, scientists published CoSEE-Cat: A Comprehensive Solar Energetic Electron event Catalogue and identified two distinct types of solar energetic electrons, one associated with intense solar flares and other with coronal mass ejections, using in situ data from Solar Orbiter.[39][40]

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Trajectory

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Solar Orbiter—journey around the Sun
Animation of Solar Orbiter's trajectory
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Polar view. For more detailed animation, see this video
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Equatorial view
   Solar Orbiter  ·   Mercury  ·   Venus ·   Earth ·   Sun
More information Date, Event ...

Source:[46][47]

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The speed of the probe and distance from the Sun
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Collaborations

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Parker Solar Probe

SolO and NASA's Parker Solar Probe (PSP) missions cooperated to trace solar wind and transients from their sources on the Sun to the inner interplanetary space.[48]

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.[49][50]

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.[51]

Daniel K. Inouye Solar Telescope

Solar Orbiter and the Daniel K. Inouye Solar Telescope (DKIST) are two of the facilities available to the solar physics community, providing observations with the highest spatial resolution from space and ground, respectively. The first coordinated observations of the Sun by these two facilities occurred between 18 and 24 October 2022. The aim of these initial coordinated observations was to demonstrate how such high-resolution, joint observations—along with similar campaigns—can help address important scientific questions in the field. Coordinated data were successfully collected at several times throughout the week, enabling studies of coronal loop physics, the formation and evolution of small-scale active region brightenings, and coronal rain dynamics.[52]

Outreach

Solar Orbiter news are regularly updated and listed in the official ESA public pages Archived 29 March 2022 at the Wayback Machine, as well as on the Bluesky Archived 4 March 2025 at the Wayback Machine and Twitter/X account Archived 26 November 2023 at the Wayback Machine. Images taken by the spacecraft with various instruments can be found on the official Flickr account Archived 3 August 2023 at the Wayback Machine.

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Gallery

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    PHI's view of the Sun in visible light
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    EUI's view of the Sun in UV light
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    PHI's map of the Sun's magnetic field
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    PHI's velocity map of the Sun's surface
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    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

References

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