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SOHO - 10 years in orbit

06/03/2006 - 18:45

ten years ago, on 2 December 1995, SOHO, the ESA/NASA Solar and Heliospheric Observatory was launched.
The images SOHO sent back to Earth have revealed our Mother Star as ever-changing, surrounded by a hot corona, featuring solar quakes on the surface and violent eruptions of particles into space.
On 2 December 1995 the joint ESA-NASA Solar Heliospheric Observatory (SOHO) was launched by an Atlas II-AS rocket from Cape Canaveral in Florida, US.

SOHO was designed to answer the following three fundamental scientific questions about the Sun:

* What is the structure and dynamics of the solar interior?
* Why does the solar corona exist and how is it heated to the extremely high temperature of about 1 000 000 °C?
* Where is the solar wind produced and how is it accelerated?

Clues on the solar interior come from studying seismic waves that are produced in the turbulent outer shell of the Sun and which appear as ripples on its surface.

To obtain a 24 hours a day, 365 days a year view of the Sun SOHO is placed at a permanent vantage point 1.5 million kilometers sunward of the Earth in a halo orbit around the L1 Lagrangian point. SOHO was initially designed to observe the Sun continuously for at least two years. All previous solar observatories have orbited the Earth, from where their observations were periodically interrupted as our planet eclipsed the Sun. The advantage of SOHO has been its continual monitoring of the Sun throughout the current solar cycle.

SOHO is made up of two modules. The Service Module forms the lower portion of the spacecraft and provides power, thermal control, pointing and telecommunications for the whole spacecraft and support for the solar panels. The Payload Module sits above it and houses all the scientific instruments.Science

SOHO has provided an unprecedented breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, to the solar wind and its interaction with the interstellar medium. These findings have been documented in an impressive, still growing body of scientific and popular literature. Some of the key results include:
* Revealing the first images ever of a star’s convection zone (its turbulent outer shell) and of the structure of sunspots below the surface
* Providing the most detailed and precise measurements of the temperature structure, the interior rotation, and gas flows in the solar interior
* Measuring the acceleration of the slow and fast solar wind
* Identifying the source regions and acceleration mechanism of the fast solar wind in the magnetically "open" regions at the Sun's poles
* Discovering new dynamic solar phenomena such as coronal waves and solar tornadoes
* Revolutionising our ability to forecast space weather, by giving up to three days notice of Earth-directed disturbances, and playing a lead role in the early warning system for space weather
* Monitoring the total solar irradiance (the ‘solar constant’) as well as variations in the extreme ultra violet flux, both of which are important to understand the impact of solar variability on Earth’s climate
* Besides watching the Sun, SOHO has become the most prolific discoverer of comets in astronomical history: as of November 2005, more than 1000 comets had been found by SOHO.


* 140 Ph.D. theses have been written on or about SOHO data
* 289 scientific meetings on subjects related to SOHO appear on our meetings pages
* 944 news stories appear on our newsroom pages (only recorded between 1997 and 2005!)
* 1000 comets have been found
* SOHO is the most prolific comet-finder observatory of all times, and has identified almost half of all comets for which an orbit determination has been made 2300 reviewed papers using SOHO data have been published
* 2300 scientists (approximately) appear in the author lists of those papers (we like to say that every current solar scientist has had the chance to work with SOHO data)
* 3230 science planning meetings have been held
* 2 000 000 command blocks have been sent to the spacecraft by the ground system
* 5 000 000 distinct files have been served by the web server
* 10 000 000 exposures (almost!) have been made by the CDS instrument
* 16 000 000 distinct hosts have been served by the web server
* 50 000 000 exposures have been taken by MDI
* They're probably quite high on the list of "the world's most durable camera shutters" Don't try to beat it with your favourite SLR camera! 266 000 000 web page requests have been served
* 16 000 000 000 000 bytes (16 Terabytes) of data are contained in the SOHO archive
* 85 000 000 000 000 bytes (85 Terabytes) of web pages/data have been served

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