NASA SDO: Sun Monitoring Satellite captures 100 millionth image

The Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory captured its 100 millionth image of the sun on Jan. 19, 2015. 

The dark areas at the bottom and the top of the image are coronal holes, areas of less dense gas, where solar material has flowed away from the sun. 

Credit: NASA/SDO/AIA/LMSAL

On Jan. 19, 2015, at 12:49 p.m. EST, an instrument on NASA's Solar Dynamics Observatory captured its 100 millionth image of the sun.

The instrument is the Atmospheric Imaging Assembly (AIA), which uses four telescopes working parallel to gather eight images of the sun, cycling through 10 different wavelengths -- every 12 seconds.

The Atmospheric Imaging Assembly (AIA) images the solar atmosphere in multiple wavelengths to link changes in the surface to interior changes. 

Data includes images of the Sun in 10 wavelengths every 10 seconds. 

Credit: NASA SDO, Lockheed Martin Solar Astrophysics Laboratory

The Helioseismic and Magnetic Imager extends the capabilities of the SOHO/MDI instrument with continual full-disk coverage at higher spatial resolution and new vector magnetogram capabilities.

Credit: NASA SDO, Lockheed Martin Solar Astrophysics Laboratory

Between the AIA and two other instruments on board, the Helioseismic Magnetic Imager (HMI) and the Extreme Ultraviolet Variability Experiment (EVE), SDO sends down a whopping 1.5 terabytes of data a day.

The Extreme Ultraviolet Variability Experiment measures the solar extreme-ultraviolet (EUV) irradiance with unprecedented spectral resolution, temporal cadence, and precision. 

EVE measures the solar extreme ultraviolet (EUV) spectral irradiance to understand variations on the timescales which influence Earth's climate and near-Earth space.

Credit: NASA SDO, Lockheed Martin Solar Astrophysics Laboratory

AIA is responsible for about half of that. Every day it provides 57,600 detailed images of the sun that show the dance of how solar material sways and sometimes erupts in the solar atmosphere, the corona.

In the almost five years since its launch on Feb. 11, 2010, SDO has provided images of the sun to help scientists better understand how the roiling corona gets to temperatures some 1000 times hotter than the sun's surface, what causes giant eruptions such as solar flares, and why the sun's magnetic fields are constantly on the move.

NASA MAVEN: How magnetic crustal fields affect planets - Video

Radiation environments on Earth and Mars. Credit: NASA JPL

If you are ever lost on the surface of Mars, don't count on a compass to help you get home.

On Mars, compasses don't work.

They don't work because there is not one magnetic field on Mars, rather there are dozens.

These small fields are powerful, concentrated in the crust, and scattered over the surface of the planet.

In their absence, compass needles would lie still; in their presence, they spin, pointing first at one bar magnet, then another.

How well these crustal fields protect the planet is a mystery, and one that may be solved soon by the MAVEN satellite, which is on its way to Mars right now.

What we do know is that if a compass ever worked well on Mars, it was over 3.5 billion years ago.

Before that time, Mars had a molten core, whose contents constantly churned upward towards the surface.

This process of convection permitted cooling of the interior, as well as active volcanism in the highlands and plains. Volcanoes brought iron to the surface, giving Mars its signature colour.

Iron in the core also moved electrons, which created a planetary dynamo: a device that converts mechanical energy into electric energy.

Electric fields generate magnetic fields. Large magnetic fields can provide protection from solar wind for any planet as long its interior maintains a steadfast supply of molten metal.

Large magnetic fields also decay unless maintained. After the first billion years or so, the Martian interior cooled to the point where convection halted. When the iron ceased to flow, the dynamo died. Volcanism declined.

The last iron deposits from the interior left their marks as pockets of magnetism, called crustal anomalies, largely sequestered in the southern hemisphere.


"Mars is on the interesting borderline of the magnetized and the unmagnetized objects," said Janet Luhmann, MAVEN's deputy principal investigator.

"We think that the weak magnetic field has been in place since it was about a billion years old."

We first learned about Mars' strange magnetic fields from the way they interacted with the solar wind.

In 1965 Mariner 4, one of America's first interplanetary probes, passed within 8,000 kilometers (4,971 miles) of Mars' surface.

At that distance, it failed to detect any magnetic field. By contrast, Earth's planet-wide field can be sensed by magnetometers within 60,000 kilometers (37,282 miles).

What Mariner did note was that the solar wind was being bent around the planet, widely in some places.

Position of magnetometers on the MAVEN spacecraft. Credit: NASAexplorer

In terms of solar storms, MAVEN will arrive on the downslope of a solar cycle, during the optimum window for observing one of the most powerful forces affecting atmospheric escape: coronal mass ejections.

"More CMEs (and larger CMEs) occur during the declining phase of the solar cycle, rather than at maximum," said Frank Eparvier, science lead on the Extreme Ultraviolet (EUV) Sensors attached to LPW.

"MAVEN will be at Mars during the declining phase of the current solar cycle, so we will actually be there at the right time to see CME impacts."

NASA Maven: Looking for Mars' missing atmosphere - Video

NASA's MAVEN satellite will measure the process affecting the remaining atmosphere on Mars. 

These include incoming Solar Energetic Particles (SEPs), escape on a molecule-by-molecule basis (Jeans Escape), the effect of Coronal Mass Ejections (CMEs) and extreme solar ultraviolent radiation (EUVs). 

Credit: The Lunar and Planetary Institute and LASP

Ninety kilometers over our heads, the sky is glowing. During the day, the Sun turns the top of our sky into a sea of electrons.

They flow over one another without friction, creating plasma. Radio waves that hit these electrons bounce back to Earth, allowing transmissions to literally turns corners and circle the globe.

The free electron layer conducts current and responds to magnetic fields. As a result, during solar storms this part of the atmosphere lights up, creating undulating auroras.

While liberated, the electrons devise visual spectacles and technical challenges, but the atoms they leave behind must content themselves with being ions.

For this reason, this part of our atmosphere is known as the ionosphere. It's the largest part of our atmosphere, and does a commensurately big job.

It absorbs x-rays that would otherwise destroy life on Earth. If it weren't for our atmosphere, Earth might look a good deal more like Mars.


Why Mars doesn't look more like Earth is the subject of ongoing study. The loss of most of the atmosphere is believed to have been a major factor in Mars turning away from the path of water, warmth and habitability.

Uncovering where that atmosphere went, when and why is the mission of the Mars Atmosphere and Volatile Evolution (MAVEN) satellite.

Scheduled to arrive in September, MAVEN carries with it two instruments designed to probe the remaining ionosphere for clues about the past four billion years, and what will happen going forward.

Our first direct glimpse at ions in the upper atmosphere will be courtesy of the Neutral Gas and Ion Mass Spectrometer (NGIMS). Mass spectrometers like NGIMS are ubiquitous in the world of physical science.

They function like the ionosphere itself: by bombarding specimens with electrons and creating ions. This process allows mass spectrometers to divine the contents of a liquid, solid or gas.

Small and durable, as well as extremely useful, mass spectrometers have been placed on dozens of satellites and rovers, including NASA's Mars rover Curiosity.

To find Mars' missing atmosphere, NGIMS will search for certain elements and molecules in the Martian ionosphere: helium, argon, nitrogen, oxygen, carbon monoxide, and carbon dioxide.

It will note how often each occurs in its neutral and ionized states over 170 miles of sky. It will also count the abundance of heavy and light versions of atoms, also known as isotopes.

Counting isotopes may hold the key to atmospheric loss. The Earth, the Sun and Jupiter have balanced amounts of heavy and light argon isotopes.

These bodies have also retained their atmospheres over time. Mars has too much heavy argon and almost no atmosphere. The heavy argon left behind likely represents the original volume of the atmosphere; light argon reflects the lost air.

"The lighter atom in an isotope pair is able to leave the upper atmosphere just a bit faster than the heavier atom," said NGIMS principle investigator Paul Mahaffey.

"Our direct measurement of the vertical distribution of these isotope pairs will let us understand the physics of escape better and ultimately understand how much of the atmosphere has been lost in the past several billions of years."

22kg IUVS instrument. Credit: LASP, Colorado

As NGIMS tries to catch light argon in the act of leaving the planet, it will also watch space weather and dust storms change the composition of the atmosphere: mixing up molecules near the bottom of the ionosphere and sending others on one-way trips into deep space.

While NGIMS picks out particles one by one, the UltraViolet Spectrograph (IUVS) will be making sweeping, planetary-wide maps.

"IUVS and NGIMS are backups for each other," said IUVS Principle investigator Nick Schneider, "They both measure the composition & structure of the atmosphere.

Nick Schneider

And we're complementary in measuring different isotopes. IUVS measures the [ratio of heavy to light hydrogen] and NGIMS measures isotopes of heavier elements."

As the most powerful ultraviolent spectrograph to ever be sent to another planet, IUVS is exquisitely sensitive to composition and temperature variations of entire upper atmosphere.

The temperature and composition of Mars' atmosphere varies dramatically, not only by altitude, but also by orbit.

At perihelion, when Mars is closest to the Sun, it is 40 million miles closer than at aphelion, when it is farthest away.

The difference in distance means that much more of the Sun's energy will be reaching Mars during certain times of year. As a result, we expect ultraviolet readings at perihelion and aphelion to vary widely.

"But we anticipate seeing changes from other causes too: solar storms like flares and Coronal Mass Ejections (CME's), and dust storms on Mars too," said Schneider.

"These each have the potential to control atmospheric escape on Mars, so we'll be watching them all."

NGIMS instrument, just prior to integration with into the MAVEN spacecraft. Credit: NASA/Goddard