Geotail Mission Celebrates 20th Anniversary
July 28, 2012

20 Years Later, Geotail Still Working Like Champ

Lee Rannals for - Your Universe Online

Twenty years ago, the United States relationship with Japan showed just how restored it was since the second world war, as the two countries' space agencies launched a joint mission together.

The Geotail mission launched into space aboard a Delta II launch vehicle 20 years ago from this week, kick-starting a set of coordinated missions known as the International Solar Terrestrial Physics (ISTP) project.

ISTP studied the magnetic environs on Earth, and Geotail flew up to space to help provide information about the way the magnetic envelope surrounding our blue sphere responds to incoming material and energy from the sun.

Proving a point that they just don't quite make things like they use to, Geotail's instruments still continue to function, giving scientists valuable information about how aurora form, how energy from the sun funnels through near-Earth space, and the ways magnetic field lines move around to create bursts that rearrange the shape of the Earth's magnetic environment.

"Before Geotail was launched, previous missions had provided discoveries about what existed around Earth," said Don Fairfield, who was NASA's first project scientist for Geotail. "So we knew basic things about what was in the magnetosphere, but we didn't completely understand them. Geotail and ISTP provided additional details on the physics of how the aurora was created and how the steady stream of particles from the sun called the solar wind interacted with Earth."

Geotail's orbit originally extended into the night side of the magnetosphere, stretching over 800,000 miles away from Earth at apogee, giving it a tremendous view of the magnetotail.

"Other spacecraft had traveled through the distant tail," said Guan Le, a Goddard scientist who took over as NASA's project scientist for Geotail when Fairfield retired in 2008. "But Geotail was the first with a comprehensive suite of instruments that could provide unprecedented measurements of electric fields, magnetic fields, the kinds of particles, and the waves traveling through the region."

After a couple of years, the spacecraft moved into a new orbit that carries Geotail as close as 40,000 miles on one side of Earth, and out to about 120,000 miles on the other side.

By passing through these diverse areas, Geotail has provided scientists with a slew of information about the location of certain events. The spacecraft helped scientists determine where in Earth's environment explosive energetic bursts, or magnetic reconnection, take place.

These bursts result from fast changes in shape of magnetic field lines, and are responsible for sending particles towards the poles that cause aurora. They also connect incoming soar wind from the sun to our magnetosphere.

By determining the locations for where to expect magnetic reconnection, Geotail has helped guide decisions about orbits for future missions, such as the Magnetospheric Multiscale (MMS) mission, which is expected to launch in 2014. This mission will provide even more details on the physics behind magnetic reconnection.

The JAXA and NASA spacecraft helped confirm the location and mechanisms of how aurora form as well. It observed initial magnetic reconnection in the magnetotail that corresponded to the appearance of aurora over the poles. The spacecraft's observations also showed bubbles of plasma shooting away from these magnetic reconnection sites down the magnetotail away from Earth.

After being in orbit for 20 years, Geotail is still able to be of use to even newer spacecraft.  It provides a complementary set of data at a remote location for missions like THEMIS, Cluster and Wind, which currently study the magnetosphere.

"It's always useful to have another satellite to provide observations," Fairfield said. "Geotail can be used in many different ways. When you see something happening in one part of the magnetosphere, you always want to know what's happening somewhere else, and Geotail offers that crucial information."