The Solar Orbiter (SolO)[7] is a Sun-observing probe developed by the European Space Agency (ESA) with a 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.
Solar Orbiter 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] Solar Orbiter 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.[10]
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)The Solar Orbiter structural thermal model shortly before leaving the Airbus Defence and Space facility in Stevenage, UKSolar Orbiter spacecraft is prepared for encapsulation in the United Launch Alliance Atlas V payload fairing.
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.[11][12]
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 was confined to the same orbital 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.[11]
The spacecraft makes a close approach to the Sun every six months.[3] The closest approaches are positioned to allow a repeated study of the same region of the solar atmosphere. Solar Orbiter is able to observe the magnetic activity building up in the atmosphere that can lead to powerful solar flares or eruptions.[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:[17]
How do solar transients drive heliospheric variability?[19]
How do solar eruptions produce energetic particle radiation that fills the heliosphere?[20]
How does the solar dynamo work and drive connections between the Sun and the heliosphere?[21]
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 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 ESA's 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.[22]
Communication
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.[22]
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.[22]
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 communications network, linking the various remotely located centres and stations to support the operational data traffic[23]
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.[23][1]
Instruments
The flight model of the Electrostatic Analyser System (EAS), which is part of the Solar Wind Analyser (SWA) Suite
The science payload is composed of 10 instruments:[24]
Heliospheric in-situ instruments (4)
STIX
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][25]
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 64Hz) 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][26][27]
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[28] – 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][29]
Institutions involved
The following institutions operate each instrument:[30]
The launch of Solar Orbiter from Cape Canaveral at 11.03pm EST on 9 February 2020 (US date)Solar Orbiter—journey around the SunTimeline of X-class flares from active region AR3664 that caused the solar storms of May 2024Why Solar Orbiter is angling towards the Sun's polesSolar Orbiter traces superfast electrons back to Sun
Before launch
The €319 million contract to build orbiter was awarded to Astrium UK in April 2012[34] The spacecraft's solar shield completed 2 week bake test in June 2014[35] In April 2015, the launch was set back from July 2017 to October 2018.[36] In August 2017, Solar Orbiter was considered on track for a launch in February 2019.[37] The spacecraft is shipped to IABG in Germany to begin the environmental test campaign in September 2018.[38]
Launch
The Atlas V 411 (AV-087) lifted off from SLC-41 at Cape Canaveral, Florida, on 10 February 2020 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.[39] 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.[40]
In June 2020, Solar Orbiter came within 77,000,000km (48,000,000mi) of the Sun, and captured the closest pictures of the Sun ever taken.[41]
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.[42][43] In December 2021, it flew through the tail of comet C/2021 A1 Leonard.[44]
In August 2021, the second Venus flyby happened only 33 hours before another interplanetary spacecraft by ESA, BepiColombo, conducted its gravity assist at the same planet. Both spacecraft used their science instruments to study the magnetic, plasma, and particle environment around Venus during their flybys, offering unique multipoint datasets. Solar Orbiter's SoloHI imager observed the nightside of Venus, surrounded by a bright crescent of the dayside, in the days before closest approach. Solar Orbiter's magnetometer observed changes in Venus's magnetic environment along the trajectory, including a sharp drop as the spacecraft crossed the bow shock.[45][46][47]
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][48]
2022
The highest resolution image of the Sun's full disc and outer atmosphere, the corona, so far have been taken on 7 March 2022.[49] In September 2022, scientists suggested a solution to the magnetic switchback mystery based on Solar Orbiter data from March 2022.[50]
Between 18 and 24 October 2022, the first coordinated observations of the Sun by Solar Orbiter and Daniel K. Inouye Solar Telescope were performed to demonstrate how such high-resolution joint observations 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.[16]
In 2022, Solar Orbiter and Parker Solar Probe (PSP) planners collaborated to study why the Sun's atmosphere is 150 times hotter than its surface. Solar Orbiter observed the Sun from 140 million kilometers, while PSP simultaneously observed the Sun's corona from nearly 9 million kilometers.[51][52]
2024
In March 2024, both Solar Orbiter and Parker Solar Probe (PSP) were at their closest approaches to the Sun, PSP at 7.3 million km, and Solar Orbiter at 45 million km. Solar Orbiter observed the Sun, while PSP sampled the plasma of the solar wind, allowing scientists to compare data from both probes.[53]
In mid-May 2024, the active sunspot region AR3664 caused the biggest solar storm to hit Earth in over 20 years. Solar Orbiter was able to observe the active region in late May, when it was facing away from Earth, and documented the strongest solar flare yet of solar cycle 25 on 20 May, followed by a surge of fast ions and electrons detected by the EPD instrument. After that, the spacecraft's Metis coronagraph observed a coronal mass ejection, whose effects on the spacecraft's environment were detected by the MAG magnetometer about one day later. The solar flare of 20 May was also detected by other ESA spacecraft, BepiColombo and Mars Express, as a large increase in the number of memory errors.[33]
2025
In February 2025, Solar Orbiter left the orbital plane of the solar system after successfully completing the 4th Venus flyby,[54] 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.[55]
In November 2025, scientists published first results based on the March 2025 observations of the Sun's south pole. The supergranulation data from the PHI and EUI instruments show that, contrary to expectations and previous ecliptic-plane observations, Sun's magnetic field drifts toward the poles at approximately 10 to 20 meters per second—almost as fast as it does at lower latitudes.[58][59]
Trajectory
Animation of Solar Orbiter's trajectory
Polar view. For more detailed animation, see this video
1 2 "GMS: Solar Orbiter's Orbit". svs.gsfc.nasa.gov. 27 January 2020. Archived from the original on 5 April 2020. Retrieved 14 February 2020. This article incorporates text from this source, which is in the public domain.
↑ Biondo, Ruggero; etal. (December 2022). "Connecting Solar Orbiter remote-sensing observations and Parker Solar Probe in situ measurements with a numerical MHD reconstruction of the Parker spiral". Astronomy & Astrophysics. 668: A144. arXiv:2211.12994. Bibcode:2022A&A...668A.144B. doi:10.1051/0004-6361/202244535.This article incorporates textfrom this source, which is available under the CC BY 4.0 license.
1 2 Barczynski, Krzysztof; Janvier, Miho; Nelson, Chris J.; Schad, T.; Tritschler, A.; Harra, Louise; Müller, Daniel; Parenti, Susanna; Valori, Gherardo; Cauzzi, Gianna; Zhu, Yingjie (2025). "First coordinated observations between Solar Orbiter and the Daniel K. Inouye Solar Telescope". Astronomy and Astrophysics. 701: A77. arXiv:2507.19198. Bibcode:2025A&A...701A..77B. doi:10.1051/0004-6361/202554396.
↑ Müller, D.; Cyr, O. C. St; Zouganelis, I.; Gilbert, H. R.; Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.; Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.; Owen, C. J.; Rochus, P. (1 October 2020). "The Solar Orbiter mission - Science overview". Astronomy & Astrophysics. 642: A1. doi:10.1051/0004-6361/202038467. ISSN0004-6361.
Missions are ordered by launch date. † indicates failure en route or before any data returned. ‡ indicates use of the planet as a gravity assist en route to another destination.
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
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