Ancient Bacteria Saw Northern Lights, Too!

 Working late into the night, the scientist checks the detector status. Operations at the remote Air Force base proceed smoothly as the detector settles into a steady course of data-taking. Seeing green lights across the board, the scientist relaxes and starts to catch up on his backlog of email correspondence. For the next half-hour, the detector will diligently monitor the sky for any gamma-ray excess.

Without warning, alarms trip and detector operations grind to a halt. The scientist quickly checks through a standard list of problems. Nothing changed in the lab. The weather monitor shows no clouds, fog, or frost. As he steps outside and glances to the north, the reason for the detector stoppage becomes obvious.

Ground-based gamma-ray detectors require exceptionally dark conditions for operation. Even the Moon can cause damage to certain (expensive) electrical components. Consequently, researchers monitor the brightness of the sky and shut the detector down when the sky gets too bright. My most recent work in gamma-ray astronomy with the STACEE collaboration took me to Kirtland Air Force Base outside of Albuquerque, NM. One night, as I attempted to find the reason for the detector shutting down, I walked outside and witnessed a beautiful display of the northern lights, similar to the picture above.

The aurora borealis (and aurora australis in the southern hemisphere) results from the protection provided by Earth’s magnetic field. The Sun occasionally emits blobs of high-velocity charged radiation toward our planet. The magnetic field deflects most of this radiation toward the poles, thus shielding the atmosphere from being sputtered away into space. As the charged particles interact with the atmosphere at the magnetic poles, the auroral lights result.

Since the magnetic field around Earth arises from complex fluid motions within the planet’s core (called a geodynamo), scientists seek to understand how these processes operated throughout history. In particular, researchers expect that the amount of heat contained within the core and the size of the solid component of the core affects the strength and behavior of the magnetic field. A formation in Montana contains rocks that help reconstruct the magnetic field from 2.7 billion years ago. Analysis of these rocks indicates the strength of Earth’s magnetic field has remained constant over the last 2.7 billion years. While the bacteria may not have appreciated the display, the auroras were in full operation eons ago.

Even though the solid core has grown and the heat generated has decreased (because the amount of radioactive isotopes decreased over time), these results show that Earth maintained its protective magnetic field. In contrast, the original magnetic fields of Venus and Mars decayed away long ago. The lack of protection from the relentless solar wind played a significant role in these two “sister” planets of Earth losing all the liquid water from their surfaces. The fine-tuning of processes in Earth’s interior to maintain a strong magnetic field comports well with the idea that a Designer fashioned Earth to teem with life.