Solar Orbiter
ESA-NASA probe studying the Sun's poles and inner heliosphere.
Solar Orbiter (SolO) is a Sun-watching probe built by the European Space Agency, with NASA pitching in. It launched from Cape Canaveral, Florida, on February 10, 2020. The spacecraft’s job is to gather close-up data on the inner heliosphere and the young solar wind, while also snapping rare views of the Sun’s poles—regions that are tough to observe from Earth. The whole point is to figure out how the Sun shapes and controls its heliosphere.
The probe swings around the Sun in a highly elliptical orbit, coming as close as about 60 solar radii (0.284 astronomical units), which is even tighter than Mercury’s closest approach (0.3075 AU). Over time, the orbit’s tilt will increase to up to 33° during the nominal mission. The total price tag, covering both ESA and NASA, is approximately €1.5 billion (about US$1.6-1.7 billion at launch), with ESA contributing €1.5 billion and NASA adding roughly US$386 million. The nominal mission runs through the end of 2026, with a possible extension to 2030.
After launch, the cruise phase lasted until November 2021. During that time, Solar Orbiter did two gravity-assist flybys of Venus and one of Earth to steer itself inward. It also collected in situ data to test and calibrate its instruments. Its first close solar pass happened on March 26, 2022, at about one-third of Earth’s distance from the Sun.
The orbit is synced with Venus, so the probe returns near the planet every few orbits and uses its gravity to tweak its path and tilt. Initially stuck in the same plane as the planets, each Venus encounter boosts its inclination. After a 2025 Venus flyby, it will observe the Sun at a 17° tilt; by 2031, the inclination will reach 33°, opening up even more of the polar regions. Solar Orbiter makes a close approach every six months, and these passes are timed to repeatedly study the same patches of the solar atmosphere, tracking magnetic activity that can lead to flares or eruptions.
Researchers can also coordinate with NASA’s Parker Solar Probe (launched 2018) and ground-based observatories like the Daniel K. Inouye Solar Telescope.
The mission’s core questions are: Where and how do the solar wind and magnetic field originate in the corona? How do solar transients drive changes in the heliosphere? How do solar eruptions create energetic particles that fill space?
Quick Facts
- Mission Type
- Heliophysics
- Operator
- ESA / NASA
- Manufacturer
- Airbus Defence and Space
- Launch Mass
- 1800 kg
- Payload Mass
- 209 kg
- Dimensions
- 2.5 xx
- Power
- 180 watts
- Launch Date
- 10 February 2020, 04:03 UTC
- Launch Rocket
- Atlas V 411 (AV-087)
- Launch Site
- Cape Canaveral, SLC41
- Launch Contractor
- United Launch Alliance
- Entered Service
- November 2021 / (start of main mission)
Facts from the source article.
Lore & Background
The science payload comprises 10 instruments: four heliospheric in-situ instruments (SWA, EPD, MAG, RPW) and six solar remote-sensing instruments (PHI, EUI, SPICE, STIX, and others). These instruments measure solar wind plasma, energetic particles, magnetic fields, radio and plasma waves, photospheric magnetic fields, extreme ultraviolet imaging, and X-ray spectroscopy. Researchers can coordinate observations with NASA's Parker Solar Probe mission and ground-based assets such as the Daniel K. Inouye Solar Telescope.
Reader's Guide
Solar Orbiter is significant for its ability to perform close-up, high-resolution studies of the Sun and its inner heliosphere, particularly the polar regions, which are difficult to observe from Earth. Its measurements help answer fundamental questions about the origin of solar wind plasma and magnetic fields in the corona, how solar transients drive heliospheric variability, how solar eruptions produce energetic particle radiation, and how the solar dynamo works. By operating in an eccentric orbit as close as 0.284 au (inside Mercury's perihelion) and raising its orbital inclination to up to 33°, it provides unique out-of-ecliptic views. The mission's coordination with NASA's Parker Solar Probe enhances its scientific return. With a total cost of US$1.5 billion and a nominal mission planned until 2026 (potentially extended to 2030), Solar Orbiter represents a major international collaboration in solar physics.
Did You Know?
- Solar Orbiter's closest approach is about 60 solar radii (0.284 au), placing it inside Mercury's perihelion of 0.3075 au.
- The spacecraft's orbit inclination will increase to up to 33° by 2031 as part of the baseline nominal mission, not just during a proposed extension.
More in Missions to the Sun 1-21
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