Global-Scale Observations of Limb and Disk (GOLD)

Summarized by Laurie Averill, Solar System Ambassador, based on talks by GOLD Mission scientists at the Laboratory for Atmosphere and Space Physics, University of Colorado at Boulder—Dr. Richard Eastes, Primary Investigator who is a physicist studying remote sensing data for space weather and space environment research with expertise in far-ultraviolet and molecular emissions for remote sensing of the Earth’s thermosphere, Dr.  Katelyn Greer, Research Scientist, who studies near-Earth environment and its connection to the lower atmosphere, and Dr. Stan Solomon. Co-Investigator, Geo-Space Frontier Section of the High Altitude Observatory, National Center for Atmospheric Research, who studies the physics and chemistry of the upper atmosphere and ionosphere.

Earth’s aurora borealis have long fascinated me.  Learning about NASA’s GOLD (Global-scale Observations of Limb and Disk) mission has helped me to begin to understand a little about why they occur.

The Spacecraft

Launched from the Guiana Space Centre, Kourou, French Guiana, on January 25, 2018, the GOLD instrument was piggybacked on the Earth-ward side of the much larger 4.5 metric ton SES-14 communications satellite with about an 50 yard wingspan riding on the Arianespace Ariane Five rocket.  High-rate science data (each photon’s location on the sensor is recorded) from the instrument is relayed directly in real time to the ground by a transponder on the satellite. Using solar-powered, electric, ion-stream propulsion, the satellite with the GOLD instrument onboard reached its desired geostationary orbit at 47.5 West Latitude over the equator on September 4, 2018, at 22,236 miles above the Western Hemisphere over the mouth of the Amazon River.  GOLD senses within the thermosphere at about 160 kilometers above Earth.

SES-14 Communications Satellite, 4.5 metric tons with 50 yard wingspan, that hosts GOLD (NASA Visualization)

NASA studies near space as well as exploring the solar system and beyond. Turning the space-based, geo-stationary, the Global-scale Observations of Limb and Disk (GOLD) instrument toward Earth, NASA seeks to understand this dynamic near-Earth environment, the boundary between Earth and space, and how the upper atmosphere is affected by the Sun and space from above and by Earth’s magnetic field and weather from below.

“‘First Light’ image of ultraviolet atomic oxygen emission (135.6 nm wavelength in the extreme ultraviolet) from the Earth’s upper atmosphere captured by NASA’s GOLD instrument. It was taken at about 6 a.m. local time, near sunrise in eastern South America on September 11, 2018.  The colors correspond to emission brightness, with the strongest shown in red and the weakest in blue.

This unsmoothed image is from one of the two identical channels in the GOLD imager, and it was taken in just under 30 minutes, the routine imaging cadence for the imager. The data have been binned, during ground processing, into pixels that correspond to 125 km by 125 km at spacecraft nadir, and the emission near 135.6 nm selected from the range observed (133-163 nm) by the GOLD imager.

This emission is produced at altitudes around 160 km (note how it extends above the Earth’s surface on the horizon), when the Earth’s upper atmosphere absorbs high energy photons and particles.

The aurora, at the top and bottom of the image, and daytime airglow, on the right hand side, are also visible. The aurora is seen best at night in the northern latitudes because its location depends on the Earth’s magnetic dipole field, which is tilted southward over North America, and visible just on the southern horizon where the magnetic field is tilted slightly away from the Americas.

An ultraviolet star, 66 Ophiuchi (HD 164284), is visible above the western horizon of the Earth.

Outlines of the continents and a latitude-longitude grid have been added for reference.”

(Illustration and caption courtesy LASP/GOLD science team)