NASA Constructs Lobster Eye Imager
February 8, 2013

NASA Builds First “Lobster Eye” Camera To Study Soft X-Rays

April Flowers for - Your Universe Online

To study charge exchange, a poorly understood phenomenon that occurs when the solar wind collides with Earth's exosphere and neutral gas in interplanetary space, three NASA scientists teamed up to develop and demonstrate NASA's first wide-field-of-view soft X-ray camera.

It is rare to have researchers from such diverse disciplines as heliophysics, astrophysics and planetary science teaming up, but that's exactly what happened at NASA's Goddard Space Flight Center in Greenbelt, MD. This unique collaboration resulted in the first successful demonstration of the Sheath Transport Observer for the Redistribution of Mass (STORM) instrument and a never-before-flown X-ray focusing technology called lobster-eye optics.

A two-stage Black Brant IX sounding rocket from the White Sands Missile Range flew STORM and another NASA-funded experiment, the Diffuse X-ray emission from the Local galaxy (DXL) in December 2012. University of Miami physicist Massimillano Galeazzi developed DXL to study the same charge-exchange phenomenon from a different perspective. Using a refurbished instrument developed by the University of Wisconsin, DXL produced the first all-sky map of soft X-rays — X-rays whose wavelengths are nearer the ultraviolet portion of the electromagnetic spectrum — several years ago.

Goddard scientists also participated in the development of DXL, but STORM holds a special place for them. The instrument was developed and assembled at Goddard and represents “a wonderful example of cooperation across divisions to better understand a process that is of interest to us all, but for different reasons," in the words of Michael Collier. Collier is a planetary scientist who collaborated with astrophysicist Scott Porter and heliophysicist David Sibeck, all of NASA´s Goddard to create STORM.

"Charge exchange is one of the few phenomena that brings together scientists from three of the science divisions at Goddard," Porter added.

The charge-exchange effect was first discovered in the mid-1990s while scientists were observing comet Hyakutake. "They got quite a surprise," explains Collier. "They found an intense source of soft X-rays at the comet's head, which was unusual because comets are cold objects and soft X-rays are associated with hot objects. How could balls of ice emit X-rays? No one could figure it out."

As it turned out, a constantly flowing stream of charged particles that sweeps across the solar system at about a million miles per hour known as solar wind caused the X-ray emission. The soft X-rays are emitted as heavy ions relax from an excited state caused when highly charged heavy ions in the solar wind collide with neutral atoms found in space. The heavy ions "steal" an electron from the neutrals, causing the short-lived state of electromagnetic excitement.

And this is hardly a rare phenomenon. Since their discovery nearly 20 years ago, researchers have observed charge exchange and the resulting soft X-ray emissions in comets, interplanetary wind, possibly supernova remnants, and galactic halos. Soft X-ray emissions have been observed by planetary scientists in the atmospheres of Venus and Mars as well. Research has even led some scientists to question whether the charge-exchange that produced the radiation has contributed to atmospheric loss on the Red Planet.

Soft X-ray emissions have also been observed in Earth's exosphere, the uppermost atmospheric layer that encompasses Earth's protective magnetosphere. This region is particularly sensitive to solar storms that can damage spacecraft electronics, affect GPS satellite readings, knock out satellite-based communications and crash terrestrial power grids.

Likewise, astrophysicists have observed the soft X-ray emissions — as unwanted noise in data collected by all X-ray observatories sensitive to them.

"At first blush, STORM seems to have very little to do with astrophysics," Porter explains. But "the emission of soft X-rays provides a very significant temporally, spatially, and spectrally varying foreground to all soft-ray observations from every single X-ray observatory.”

"It's essential that we, as astrophysicists, understand and are able to model this foreground emission in detail. On all recent X-ray observatories, significant observing time has been lost and errors in scientific interpretation have happened due to our lack of understanding of this phenomenon," Porter continued.

The three disciplines all need to understand soft X-ray emissions more thoroughly. Planetary scientists and heliophysicists want to measure and quantify them, while astrophysicists want to remove the "noise" they cause.

The new STORM instrument holds the key for gaining a more complete understanding of the physical process behind soft X-ray emissions. This will provide scientists with critical insights that are currently lacking because of the limitations of existing instruments. During the test flight, DXL studied the X-ray emission, but only those emitted when the solar wind interacted with gas entering our solar system from the Milky Way.

The "view" from STORM was more global in nature, as the wide-field-of-view camera imaged processes near Earth's magnetosphere. Until STORM, this kind of observation was impossible.

"These are extremely important, highly dynamic, and poorly understood regions that channel solar wind energy into the magnetosphere where it drives space weather," Porter said.

This process affects more than just space weather, however. It also affects other planetary bodies and has distorted data collected by several multi-million dollar X-ray observatories.

An emerging technology called lobster-eye optics made the new images possible. The optics behind this technology mimic the structure of a lobster's eyes, which are made of long, narrow cells that each captures a tiny amount of light, but from many different angles. After the light is captured, it is then focused into a single image.

Researchers at the University of Leicester, a partner in STORM's development, pioneered lobster X-ray optics to work the same way. The instrument's "eyes" are a microchannel plate — a thin curved slab of material dotted with tiny tubes across the surface. X-ray light enters these tubes from multiple angles and is focused through grazing-incident reflection, providing the wide-field-of-view necessary for imaging the emission of soft X-rays in Earth's exosphere in a global manner.

"I'm unaware of any instrument that can do this," Collier said.

With the successful launch, the team said they are in good position to propose STORM for a possible mission. "We are happy it turned out so well," Sibeck said. "We all stand to gain from STORM's development."