A mysterious fireball that exploded over Greenland earlier in the year has provided a unique test-case to study the structure of distant, ice-coated alien worlds, new research reports.
For months, we haven't known a lot about what the meteorite event in July entailed, although early data showed it was one of the most energetic fireballs of 2018.
For residents of Qaanaaq – one of Greenland's (and the world's) northernmost towns – the fireball lit up the evening sky and caused the ground to shake, leading local police to think a meteorite strike might be responsible.
That was at about 8 pm on July 25, but the first time most of the outside world heard about any of this was almost a week later, when NASA scientist Ron Baalke issued the following tweet:
A fireball was detected over Greenland on July 25, 2018 by US Government sensors at an altitude of 43.3 km. The energy from the explosion is estimated to be 2.1 kilotons. pic.twitter.com/EePuk14Pqd— Rocket Ron ? (@RonBaalke) July 31, 2018
A subsequent tweet from nuclear weapons researcher Hans M. Kristensen pointed out that the explosion occurred perilously close to the US Air Force base at nearby Thule, but noted: "We're still here, so they [the Air Force] correctly concluded it was not a Russian first strike".
Phew. For its part, Thule Air Base was conspicuously silent about the phenomenon occurring so close to its strategic base of operations, especially since it resulted in such a powerful explosion.
Now we have new evidence to interpret this fireball event, thanks to a lucky coincidence of time (and space).
In May, just a few months before the August fireball, researchers with a project called the Seismometer to Investigate Ice and Ocean Structure (SIIOS) had begun installing a seismic array just 70 kilometres (43 miles) to the north of Qaanaaq.
The purpose of the SIIOS research is to use seismometers to measure how earthquakes might play out on icy alien worlds and moons (like Jupiter's icy moon Europa and Saturn's icy moon Enceladus), using Earth-based analogues – such as the Greenland ice sheet – as a terrestrial proxy.
What we can learn about the thick ice crusts that cover these environments could be the key to finding and accessing water on future missions in space – but the same infrastructure also gives us a unique glimpse into what exactly happened with the Qaanaaq fireball.
In a new paper presented at the American Geophysical Union annual meeting in Washington, DC last week, a team led by geophysicist Nicholas C. Schmerr from the University of Maryland report their sensors enabled them to isolate a "candidate seismic event consistent with the trajectory of the projected impact point of the fireball".
The new research hasn't yet been peer-reviewed, but the preliminary data suggest the epicentre of the "putative impact" was situated "in the vicinity of Humboldt glacier on the Greenland ice sheet".
There's still a lot we don't know about the Qaanaaq fireball, but thanks to SIIOS's infrastructure we've got an unprecedented new lead on the mysterious meteorite, and – according to the researchers – a new world-first in astronomical research.
"This candidate seismic impact event recorded by a lander-based seismic system is the first high-fidelity seismic analog for icy world impact events," the authors explain in their abstract, "and will inform impact science across objects throughout the Solar System."
The findings were presented at the annual meeting of the American Geophysical Union in Washington, DC last week.