Mission to study space weather moves into formulation

By Sarah Frazier
NASA’s Goddard Space Flight Center

NASA will begin formulation of a new mission to study Earth’s dynamic interface to space: the upper atmosphere. This is a region that is constantly changing, influenced by Earth’s weather percolating up from below and space weather — in the form of solar energy and space plasma — streaming in from above. This new mission will provide the first systematic study of this region in our atmospheric backyard, providing the data needed to assess, and ultimately forecast, the phenomena that course through Earth’s upper atmosphere.

The new mission, called the Geospace Dynamics Constellation, or GDC, answers a call laid out in the most recent solar and space physics decadal survey for a mission to study how Earth’s atmosphere absorbs and responds to energy inputs. GDC is a mission within NASA’s Living With a Star program, focusing on fundamental heliophysics science and applications of that science to protecting human society and technology. On Sept. 8, 2020, GDC successfully completed the Key Decision Point – A review, or KDP-A, moving the project into Phase A, when the team works on concept and technology development that will support the mission. The GDC project management has been directed to NASA’s Goddard Space Flight Center. The target Launch Readiness Date is late 2027, and GDC mission timeline will be developed during Phase A.

Data visualization showing Earth with two bands of dense plasma near the equator, complex upper atmospheric winds, and Earth's magnetic field like a belt near the middle of the planet.
This data visualization combines models of ions, upper atmospheric winds, and Earth’s magnetic field, a few of the many overlapping conditions that feed into complex processes in Earth’s upper atmosphere. The upcoming Geospace Dynamics Constellation mission will study this region of Earth’s atmosphere and provide the first systematic view of this area. Credit: NASA’s Scientific Visualization Studio

GDC will study Earth’s upper atmosphere, where our planet’s near-space environment overlaps with our atmosphere and space weather effects can manifest — ranging from the scrambling of communications and navigation signals to satellite orbit disruptions and induced currents that can trigger power outages on Earth’s surface.

Using a distributed constellation of spacecraft working together to gather comprehensive observations from multiple vantage points, GDC will explore the fundamental physics of this region of near space, investigating the complex processes that transmit energy and momentum on scales ranging from seasonal to daily to minute by minute. The level of detail and resolution provided by GDC will give us an unprecedented understanding of the space environment surrounding our home planet. Understanding these processes will provide crucial information needed to understand, and ultimately predict, the variable nature of the space environment our satellites, signals, and astronauts must travel through — and give us new insights into the forces that shape our home planet and other worlds.

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Comet NEOWISE Seen in an Aurora-Filled Sky

Comet NEOWISE is visible in a sky filled with purple and green aurora
Image: Copyright Donna Lach, used with permission

Comet NEOWISE is visible in an aurora-filled sky in this photo by Aurorasaurus Ambassador Donna Lach. The photo was taken early on July 14, 2020, in western Manitoba, Canada. The purple ribbon-like structure to the left is STEVE, an aurora-related phenomenon discovered with the help of citizen scientists working with the Aurorasaurus project. The bright streak near the top of the image is a meteor.

Read more on nasa.gov.

NASA’s STEREO Sees Comet NEOWISE

By Sarah Frazier
NASA’s Goddard Space Flight Center

Comet NEOWISE appears as a streak against a starry background

This image of comet NEOWISE was captured by NASA’s Solar and Terrestrial Relations Observatory, or STEREO, on June 24, 2020, as the comet approached the Sun. The comet was visible in the field of view of STEREO’s Heliospheric Imager because of a special observing campaign: STEREO underwent a 180-degree roll on June 24 in order to observe the star Betelgeuse, whose brightness variations over the past several months have intrigued scientists. This image has been processed to increase contrast.

Credit: NASA/STEREO/William Thompson

Download additional imagery from NASA Goddard’s Scientific Visualization Studio.

Dancing the Lunar Transit

By Sarah Frazier
NASA’s Goddard Space Flight Center

On March 6, 2019, our Solar Dynamics Observatory, or SDO, witnessed a lunar transit — where both the Sun and Moon displayed a little odd behavior.

First, there was the transit itself. A lunar transit occurs when the Moon passes between SDO and the Sun, blocking the satellite’s view. But instead of appearing on one side of the frame and disappearing on the other, the Moon seemed to pause and double back partway through crossing the Sun. No, the Moon didn’t suddenly change directions in space: This is an optical illusion, a trick of perspective.

Illustration of the relative motion of the Moon and SDO during the lunar transit
NASA’s Solar Dynamics Observatory spotted a lunar transit just as it began the transition to the dusk phase of its orbit, leading to the Moon’s apparent pause and change of direction during the transit. This animation (with orbits to scale) illustrates the movement of the Moon, its shadow and SDO. Credits: NASA/SDO

Here’s how it happened: SDO is in orbit around Earth. When the transit started, the satellite was moving crosswise between the Sun and Earth, nearly perpendicular to the line between them, faster than the Moon. But during the transit, SDO started the dusk phase of its orbit — when it’s traveling around towards the night side of Earth, moving almost directly away from the Sun — but no longer making any progress horizontally to the Sun. The Moon, however, continued to move perpendicular to the Sun and thus could “overtake” SDO. From SDO’s perspective, the Moon appeared to move in the opposite direction.

The second, subtler part of this celestial dance seemed to come from the Sun itself. If you look closely, you may notice the Sun seems to wiggle a bit, side-to-side and up and down, during the transit. That’s another result of SDO’s perspective, though in a different way.

SDO relies on solar limb sensors to keep its view steady and focused on the Sun. These limb sensors consist of four light sensors arranged in a square. To keep the Sun exactly centered in its telescopes, SDO is trained to move as needed to keep all four sensors measuring the same amount of light.

But when the Moon covers part of the Sun, the amount of light measured by some of the sensors drops. This makes SDO think it’s not pointed directly at the Sun, which would cause SDO to repoint — unless that function gets overridden.

Since SDO’s fine guidance system wouldn’t be much use during a lunar transit regardless, the mission team commands the spacecraft to disregard limb sensor data at the beginning of such transits. This loss of fine guidance accounts for some of the Sun’s apparent movement: SDO is now pointing at a general Sun-ward spot in space, instead of keeping its view steady using the much more accurate limb sensors.

The other factor behind the apparently wiggly Sun is temperature. SDO’s instruments are designed to work in the full glare of the Sun’s light and heat. When the Moon’s shadow passes over the spacecraft, the instruments quickly cool in the vacuum of space and start to bend and flex. The flexing of the front part of the telescope can make it look like the image is moving around in the frame.

SDO’s operators use strategically-placed heaters onboard the spacecraft to minimize this flexing as much as possible and to get back to providing science-quality data — images that are focused, centered and steady — as quickly as possible.

You can see and download SDO’s data — science-quality and otherwise — at sdo.gsfc.nasa.gov/data.