20 years on, SOHO changed the way we look at sun


The Solar and Heliospheric Observatory (SOHO) that revolutionised the field of science known as heliophysics and became the greatest comet hunter of all time — reaching 3,000 comet discoveries in September 2015 — has completed 20 years in space.

After 20 years in space, the observatory launched in 1995 to study the sun and its influence out to the very edges of the solar system from the European Space Agency (ESA) and NASA, is still going strong.

SOHO has provided the basis for more than 5,000 scientific papers till date, the US space agency said in a statement on Wednesday.

When SOHO was launched, the field of heliophysics looked very different than it does today.

Questions about the interior of the sun, the origin of the constant outflow of material from the sun known as the solar wind, and the mysterious heating of the solar atmosphere were still unanswered.

Twenty years later, not only do we have a much better idea about what powers the sun, but our entire understanding of how the sun behaves has changed.

“SOHO changed the popular view of the sun from a picture of a static, unchanging object in the sky to the dynamic beast it is,” said Bernhard Fleck, ESA SOHO project scientist at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland.

Even the concept of space weather was not well-understood when SOHO was launched.

At the time, it was thought that solar flares were the primary Earth-effective solar event, in part because they were the most commonly-observed.

Thanks to SOHO’s camera known as coronagraph, scientists know that giant clouds that burst off the sun called coronal mass ejections or CMEs which are a major piece of the space weather puzzle.

“In light of the SOHO data, we realised that CMEs are much more common – and more variable throughout the solar cycle – than we thought,” said Joe Gurman, US project scientist for SOHO at Goddard.

CMEs, which are huge, fast-moving clouds of electrically-charged solar material that contain embedded magnetic fields, can cause geomagnetic storms when they collide with Earth’s magnetic field, causing it to shimmy and shake.

“Thanks to SOHO, there’s a growing public recognition that we live in the extended atmosphere of a magnetically active star,” said Gurman. “And people realise that solar activity can affect Earth.”

“For the first time ever, we saw waves rippling across the sun at a million miles an hour in extreme ultraviolet light,” said Alex Young, space scientist at Goddard.

In 1998, the spacecraft was lost for four months because of a software error.

A joint ESA-NASA team was finally able to recover the spacecraft in September 1998.

“With SOHO, we found that the sun varies on every timescale we can measure,” Gurman added.

SOHO showed us things we’d never seen before, and then we realised we needed more eyes on the sun, the statement read.