New NASA satellite will study how space weather meets Earth weather
A new satellite called Global Observations on the Limb and Disc, or GOLD, was sent aloft this week to study the upper boundary of the Earth's atmosphere, where space begins. It is a very active and poorly studied region where weather from our planet meets weather from space.
The very top layer of our atmosphere, from 80 to 900 kilometres up, is poorly studied because it is too high and thin for aircraft or balloons to fly through. Yet the upper portion is where some satellites and the International Space Station travel. The extremely rarefied air in this region interacts directly with powerful radiation from space, and is bombarded by high speed electrically charged particles streaming out from the sun called the solar wind. One beautiful side-effect of this onslaught from above is the eerie display of the aurora, the northern and southern lights.
The GOLD instruments will scan this region from high above. It will monitor interactions that go beyond aurora, measuring chemical changes taking place in the uppermost regions of our atmosphere. Sunlight is so powerful at this altitude that it can strip electrons away from atoms, creating ions, which are electrically charged. Together, those ions are called the ionosphere. HAM radio operators are able to bounce their radio signals off this charged layer to communicate halfway around the planet.
The sun also performs photochemistry on the gases of the upper atmosphere, tearing apart molecules that rearrange into new forms, such as when oxygen is broken down to re-form into ozone, or when water vapour is separated into hydrogen and oxygen, with the lighter hydrogen leaking off into space.
Communication can be disrupted as radio signals travelling from the ground up to satellites and back down again become garbled as they pass through this electrified region.
The GOLD mission will look at the entire Earth from the high perspective of geostationary orbit, 35,000 kilometres above, and will be later joined by another satellite called Ionospheric Connection Explorer, or ICON, which will fly much lower down within the ionosphere itself, so the region can be studied from above and below at the same time.
Magnetic field trembles 'like a giant bowl of jelly'
Scientists are interested in activity up there because it is ever-changing on the scale of minutes or hours. The sun passes through cycles of activity, where solar storms erupt on the surface, hurling large blobs of energetic material toward the Earth. When they strike our planet's magnetic field, it can tremble and distort like a giant bowl of jelly. Geomagnetic storms from this activity can induce unwanted electric currents in high voltage transmission lines on the ground, causing massive blackouts, or they can knock satellites right out of commission.
In the past, most of the focus on the ionosphere has been on changes caused by space weather raining down from above, but there is new evidence that the region is also affected by regular weather from below. Hurricanes or cyclones can create huge waves that lift the atmosphere higher in some places, exposing more of the air to the space environment and accelerating some of the physical and chemical changes taking place. Understanding the region better fills in gaps in our understanding of the Earth's atmosphere from the bottom all the way to the top.
It is interesting to note that the GOLD mission is the first time NASA has done a science mission as a "hosted payload." The mission hitched a ride on a commercial communication satellite that was launched on a European rocket. Very often, there is extra space on big rockets to put smaller satellites such as cubesats, about the size of a loaf of bread, that are usually projects built by university students. NASA took advantage of such an opportunity to send the GOLD instrument, about the size of a microwave oven, into space — an example of how international cooperation can bring down the cost of space exploration.