MessageToEagle.com - A poorly understood "charge-exchange" phenomenon that occurs when the solar wind collides with Earth's
exosphere and neutral gas in interplanetary space, will be studied intensively with a new wide-field-of-view
soft X-ray camera developed by NASA scientists.
The unique collaboration involved heliophysics, astrophysics and planetary science divisions at NASA's Goddard
Space Flight Center in Greenbelt, Md., and 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.
STORM and another NASA-funded experiment, the Diffuse X-ray emission from the Local galaxy (DXL), flew aboard a
two-stage Black Brant IX sounding rocket from the White Sands Missile Range, Las Cruces, N.M., in December 2012.
The charge exchange process. Credit: D. Bodewits University of Maryland
STORM instrument "is a wonderful example of cooperation across divisions to better
understand a process that is of interest to us all, but for different reasons," said Michael Collier, a planetary
scientist who collaborated with astrophysicist Scott Porter and heliophysicist David Sibeck, all of NASA Goddard.
Earlier, DXL, developed by University of Miami professor Massimillano Galeazzi, also studied the same charge-exchange
phenomenon but from a different perspective using a refurbished instrument developed by the University of Wisconsin,
It produced the first all-sky map of soft X-rays several years ago. (X-rays are called "soft"
when their wavelengths are nearer the ultraviolet portion of the electromagnetic spectrum.)
First discovered in the mid-1990s while observing comet Hyakutake, "charge exchange" phenomenon, brings together
scientists from three of the science divisions at Goddard.
"They got quite a surprise," Collier said. "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."
Scientists soon discovered that the X-ray emission was caused by the solar wind, a constantly flowing stream of
charged particles that sweeps across the solar system at about a million miles per hour.
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 -- an exchange that puts the heavy ions in a short-lived excited state.
As they relax, they emit soft X-rays.
Click on image to enlarge
This Black Brant IX rocket carried two instruments designed to study charge exchange, a physical phenomenon that occurs when the solar wind collides with Earth's exosphere and neutral gas in interplanetary space.
Nearly 20 years ago, scientists observed charge exchange and resulting emission of soft X-rays in comets, interplanetary
wind, possibly supernova remnants, and galactic halos.
NASA scientists Michael Collier, David Sibeck, and Scott Porter teamed to develop and demonstrate the first wide-field X-ray camera for studying a poorly understood phenomenon called "charge exchange."
Credit: NASA/Chris Gunn
Planetary scientists have observed soft X-ray emissions in the atmospheres
of Venus and Mars and heliophysicists have studied soft X-ray emissions in Earth's exosphere, and astrophysicists have observed
them - as unwanted noise in data collected by all X-ray observatories sensitive to soft X-rays.
Ion Density Simulation
This simulation uses what's called the Lyon-Fedder-Mobarry model to display ion density within and
surrounding the Earth's magnetosphere (the area around Earth influenced by the planet's magnetic field).
The gray surface illustrates the magnetopause, where the solar wind meets Earth's magnetic field. The display within
the circle in the bottom right shows modeled auroral emissions. Video courtesy: C. Goodrich
"At first blush, STORM seems to have very little to do with astrophysics," Porter said. 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," he explained.
"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."
It gave scientists a global view. The wide-field-of-view camera imaged processes near Earth's magnetosphere,
which until now 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.
If this process is important to determining space weather in and around Earth, it also affects other planetary bodies, to say
nothing of its deleterious effect on data collected by multi-million-dollar X-ray observatories.