APL craft returns stunning 3-D images of the Sun

By: STEPHEN BERGER

Posted: 4/26/07

A pair of satellites designed by the Applied Physics Laboratory at Hopkins has just produced their first images of the Sun. The mission, launched late last year, is tasked with taking high-quality three-dimensional images of the Sun.

The satellites comprise the Solar Terrestrial Relations Observatory (STEREO) mission, part of efforts by NASA and APL to improve our understanding of the dynamic processes of the solar surface.

The STEREO mission is unique because it provides three-dimensional pictures, a first for space-bound observatories.

To achieve depth perception, the two satellites orbit the Sun and Earth at a slight offset from each other. As a result, a large portion of their respective "visual fields" overlap, a situation analogous to the human visual system.

Just like in the human eye, the use of two overlapping sensors allows for the detection of depth. Cameras on the two spacecraft take simultaneous images, which are then overlaid by scientists to produce the three-dimensional images. This is called binocular or stereoscopic vision.

The first 3-D images can be accessed at http://stereo.jhuapl.edu and on the NASA main page at http://www.nasa.gov.

The pictures appear to be three-dimensional when viewed through easily obtainable 3-D glasses, which polarize the light coming from the image and allow the brain to process it as if it were an actual object. (Two-dimensional images are also available for viewing online.)

Even these early images are a windfall for scientists at NASA, APL, and elsewhere. The various phenomena on the solar surface - events such as sunspots and solar flares - are characterized poorly and understood even less.

These few early images from the mission capture several distinct eruptions of material from the Sun.

One of the primary goals of the STEREO mission is to understand the solar phenomenon termed coronal mass ejections (CMEs), the most powerful and potentially deadly type of solar eruption.

The Sun has a layered atmosphere, similar in many ways to the Earth's. The corona is the outermost layer of the solar atmosphere.

In a CME, tremendous quantities of highly energetic charged particles are released from the corona. These include free protons and electrons, as well as some comparatively heavier elements such as helium.

All of the particles travel very quickly at high energy, reaching the vicinity of the Earth in 24 to 48 hours. The ionizing radiation of a CME is one of the main contributors to weather patterns in the solar system.

It can also exert extreme effects on the magnetic field of the Earth's atmosphere, and it can damage artificial satellites and spacecraft, including manned vessels such as the International Space Station.

It is hoped that improved understanding of CMEs will allow their timing and properties to be predicted.

There is only a one or two day warning before a CME reaches the vicinity of the Earth; this represents the time lag between visual detection of the CME and the arrival of the particles.

Each STEREO satellite carries several cameras that can observe the solar surface at different wavelengths on the electromagnetic spectrum.

Different wavelengths correspond to different types or temperatures of solar radiation.

The two satellites orbit the Sun in a highly elliptical path that takes them close to the Earth's own orbit.

After swinging around the Moon in January, one of the satellites was shot ahead of the Earth's orbit, while the other lags slightly behind.

As the expected two-year mission continues, the orbits of the two satellites will continue to diverge, until they are on opposite sites of the Sun.

The Applied Physics Laboratory designed, built and manages the two STEREO satellites in collaboration with NASA scientists at the Jet Propulsion Laboratory in Pasadena, Calif., and the Goddard Space Flight Center in Greenbelt, Md.