SOHO

Solar and Heliospheric Observatory

active Mission
A spacecraft appears in the foreground on the right, while the Sun appears in orange in the background on the left.

Launched in December 1995, the joint NASA-ESA Solar and Heliospheric Observatory mission (SOHO), was designed to study the Sun inside out. Though its mission was scheduled to run until only 1998, it has continued collecting data, adding to scientists' understanding of our closest star, and making many new discoveries, including more than 5,000 comets.

Type

Orbiter

Launch

Dec. 2, 1995

Target

Sun

Objective

Study the Sun from its deep core to the outer corona and the solar wind
Spacecraft in space.
An artist's concept of the ESA-NASA SOHO spacecraft.
NASA

What is SOHO?

SOHO is the longest-lived Sun-watching satellite to date. Numerous mission extensions have enabled the spacecraft to observe two 11-year solar cycles and to discover thousands of comets.

  • SOHO is a cooperative international project between ESA and NASA. NASA contributed three instruments and launch services. ESA leads the mission.
  • During its pioneering career, SOHO has returned a wealth of new information about the Sun—from its core to its outer atmosphere and the solar wind.
  • SOHO monitors the effects of space weather on our planet, and it plays a vital role in forecasting potentially dangerous solar storms.
  • SOHO is the most prolific discoverer of comets in astronomical history, with more than 5,000 tracked during their encounters with the Sun.
Nation
European Space Agency (ESA) and United States of America (USA)
Objective(s)
Sun–Earth L1 Lagrange Point
Spacecraft
SOHO
Spacecraft Mass
4,109 pounds (1,864 kilograms)
Mission Design and Management
ESA / NASA
Launch Vehicle
Atlas Centaur IIAS (AC-121 / Atlas IIAS no. 8206 / Centaur II)
Launch Date and Time
Dec. 2, 1995 / 08:08:01 UT
Launch Site
Cape Canaveral, Fla. / Launch Complex 36B
Scientific Instruments
1. Solar-Ultraviolet Measurements of Emitted Radiation Experiment (SUMER)
2. Coronal Diagnostic Spectrometer (CDS)
3. Extreme Ultraviolet Imaging Telescope (EIT)
4. Ultraviolet Coronograph Spectrometer (UVCS)
5. Large Angle and Spectrometric Coronograph (LASCO)
6. Solar Wind Anisotropies Experiment (SWAN)
7. Charge, Element, and Isotope Analysis Experiment (CELIAS)
8. Comprehensive Suprathermal and Energetic Particle Analyzer (COSTEP)
9. Energetic and Relativistic Nuclei and Electron Experiment (ERNE)
10. Global Oscillations at Low Frequencies Experiment (GOLF)
11. Variability of Solar Irradiance and Gravity Oscillations Experiment (VIRGO)
12. Michelson Doppler Imager/Solar Oscillations Investigation (MDI/SOI)

Key Dates

Dec. 2, 1995: Launch

Feb. 14, 1996: Sun-Earth L1 orbit insertion

March 25, 2024: 5,000 comets discovered

In Depth: SOHO

The ESA-sponsored Solar and Heliospheric Observatory (SOHO) carries 12 scientific instruments to study the solar atmosphere, helioseismology, and the solar wind. Information from the mission has allowed scientists to learn more about the Sun’s internal structure and dynamics, the chromosphere, the corona, and solar particles.

The SOHO and Cluster missions, part of ESA’s Solar Terrestrial Science Programme (STSP), are ESA’s contributions to the International Solar Terrestrial Physics (ISTP) program, which has involved the work of other spacecraft such as Wind and ACE, which, like SOHO, operate in the vicinity of the Sun-Earth L1 point.

NASA contributed three instruments to SOHO as well as launch and flight operations support.

About two months after launch, on Feb. 14, 1996, SOHO was placed at a distance of 932,000 miles (1.5 million kilometers) from Earth in an elliptical Lissajous orbit around the L1 libration point where it takes approximately six months to orbit L1 (while the L1 itself orbits the Sun every 12 months).

The spacecraft returned its first image Dec. 19, 1995, and was fully commissioned for operations by April 16, 1996. SOHO finished its planned two-year study of the Sun’s atmosphere, surface, and interior in April 1998.

Communications with the spacecraft were interrupted for four months beginning June 24, 1998, after which the spacecraft was apparently spinning, losing electrical power, and not pointing at the Sun. After intensive search efforts, by Sept. 25, 1998, controllers managed to regain control and return SOHO to “normal mode.” Except for three instruments, the spacecraft was functional and was declared operational once again by mid-October 1998.

Because of the failure of onboard gyros, ESA developed a special method of orientation, using reaction wheels instead of gyros, which was successfully implemented beginning Feb. 1, 1999.

SOHO’s original lifetime was three years (to 1998), but SOHO’s mission at L1 has been extended several times and continues to provide valuable information about the Sun.

One of SOHO’s most important discoveries has been locating the origin of the fast solar wind at the corners of honeycomb-shaped magnetic fields surrounding the edges of large bubbling cells located near the Sun’s poles.

Another has been its discovery, as of March 2024, of over 5,000 comets (more than one-half of all known comets), by over 70 people representing 18 different nations. These discoveries were made possible because of the LASCO instrument that blocks out the Sun’s glare, rendering comets visible.

In December 2015, SOHO marked 20 years of continuous operation, having fundamentally changed our conception of the Sun “from a picture of a static, unchanging object in the sky to the dynamic beast it is,” in the words of Bernhard Fleck, the ESA project scientist for SOHO.

The longevity of the mission has allowed SOHO to cover two full 11-year solar cycles and the beginning of a new one. One of the high points of the mission was SOHO’s observation of a bright comet plunging toward the Sun on Aug. 3-4, 2016, at a velocity of nearly 1.3 million miles per hour (2.1 million kilometers per hour).

Additional Resources

European Space Agency: SOHO

NASA: SOHO Project Site

National Space Science Data Center Master Catalog: SOHO

Key Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

SOHO Stories

Explore All SOHO Stories
Article
5 min read

5 Surprising NASA Heliophysics Discoveries Not Related to the Sun

In this illustration, an exploding star powers jets of material. The star is shown as an almost flower-like shape. The purple �petals� represent clouds of material created in the explosion. The bluish-white and yellow center shows where the newly formed black hole begins driving the jets. The core of the jet pointed toward us is whitish and the broader regions are magenta. In the distance, on the far side of the star, you can see the opposite side of the jet disappearing into space.
Article
2 min read

ESA/NASA’s SOHO Spies Bright Comet Making Debut in Evening Sky

A long, white, overexposed comet tail stretches from the upper left to the lower right against a circular blue background scattered with stars. At the center is a blank blue disk with a white circle representing the Sun. A time stamp at the bottom reads 2024/10/10 18:06.
A gray image showing the Moon in the center, a black circle around it, and white streams of light flowing out.
4 min read

New ‘Eclipse Watch’ Tool Shows Eclipses from Space Any Time

Article8 months ago
An image from the SOHO spacecraft shows the Sun covered by a red disk. A white circle within that disk shows the size of the Sun. Around the disk, white and orange streamers in the solar corona extend away from the Sun. In the upper left, a small white box opens up into a larger white box that has “SOHO-5000” written above a faint dot with one short, vertical white line above it and another below it. At the bottom is written “2024/03/25 03:48” and “ESA/NASA SOHO/LASCO C2.”
4 min read

ESA, NASA Solar Observatory Discovers Its 5,000th Comet

Article8 months ago
An animation shows a white cloud of material billowing away from the Sun (which is covered by a black disk at the center) toward the left side of the image, set against a red background with a couple dozen stars. The top says "STEREO Ahead COR2" and the bottom shows the date 2021-04-17 with the time progressing from 12:23:30 to 23:53:30.
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Multiple Spacecraft Tell the Story of One Giant Solar Storm

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