Earth and Saturn were positioned like this March 28, 2013. Both planets were on the same side of the Sun in their orbits. At that time, the Solar Dynamics Observatory (SDO) was gathering data in images of the Sun at 10 different wavelengths every 10 seconds. SDO helps monitor solar storms for possible negative effects here on Earth.
Around March 28, emission from the Sun was directed toward Saturn and almost at Earth. Astronomers could see that from Earth via SDO. Two months later, the effects of the energetic emission were observed at Saturn by the Cassini spacecraft and the Hubble telescope. Bright displays of aurorae at the north and south polar regions of Saturn were recorded and are viewable later in this post.
Emissions from the Sun
One of the instruments records images at 211 Ångströms (1 Ångström = 10-10 meter). That wavelength is emitted by excited iron-14 at 2,000,000 K. These images help monitor the hot and magnetically active parts of the solar corona, the bright parts around the Sun. It is coded as a pink color in this short video I requested from the Helioviewer image site for SDO sponsored by NASA and ESA. The video spans one week of solar activity.
Of particular note in the video above is the dark region that traversed the face of the Sun. That is called a coronal hole. The Sun has a lot of magnetic field structure that continually changes. It is caused by the circulating patterns of charged gases within the Sun. Normally, the magnetic field lines emerge from the surface and loop back into the Sun. They capture and guide the charged protons and electrons to follow them. The particles are at very high temperatures and appear as the brightest regions in the video.
In a coronal hole, the magnetic field lines emerge from the surface and don’t loop back into the Sun. The particles of protons and electrons follow those lines and stream away from the Sun at high speed. This causes a solar wind of particles to flow from the Sun. If the coronal hole and subsequent solar wind are directed at Earth, we can see some geomagnetic activity such as aurorae, northern and southern lights. It does not usually cause intense activity.
I requested a second video from Helioviewer for the same one week time period. This video recorded activity at 193 Ångströms. Regions are labeled in this video as CH for coronal hole. Note that there are several. The region of most interest is that directed more toward Earth. It actually missed the Earth and was headed toward Saturn. It took about two months to reach Saturn.
Arrival at Saturn
The fast solar wind streamed protons and electrons from the coronal hole toward Saturn. On the way, this high-speed stream caught up to the slower solar wind ahead of it. That collision formed a more intense region of solar wind. It crashed into Saturn’s magnetic field in May 2013, causing bright auroral displays.
NASA’s Cassini spacecraft in orbit around Saturn and the Hubble Space Telescope both provided us with views of the aurorae. In the first part, Hubble shows some activity. Look for the ring of bright activity at the top north polar region of the planet. This is followed by closer more detailed images from Cassini. Activity at the south pole of Saturn is the green and red portion of the video.
I find it fascinating to be able to observe this cause-effect relationship over such great distances and time. I hope you enjoyed it, too.