A glowing metal ring crashed to earth. Nobody knows where it came from

It has been more than a week since reports first emerged of a “luminous ring of metal” falling from the sky and crashing near a remote village in Kenya.

According to the Kenya Space Agency, the object weighed 1,100 pounds and was more than 8 feet in diameter, measured after landing on December 30. A few days later, the space agency confidently reported that the object was a piece of space junk, it was a ring that had come off a rocket. “Such objects are typically designed to burn up upon re-entry into Earth’s atmosphere or to fall over uninhabited areas such as the oceans,” the space agency said told the New York Times.

Since these initial reports were published in Western media, a small group of dedicated space trackers have been using open source data to try to identify exactly which space object fell in Kenya. So far they have not been able to identify the rocket launch that caused the large ring.

Now some space trackers believe the object may not have come from space at all.

Did it really come from space?

Space is becoming increasingly crowded, but large chunks of metal from rockets generally don’t fly around in Earth’s orbit undetected and untracked.

“It has been suspected that the ring is space debris, but the evidence is marginal.” wrote Jonathan McDowell, an astrophysicist working at the Harvard-Smithsonian Center for Astrophysics. McDowell is highly regarded for his analysis of space objects. “The most likely space-related possibility is the re-entry of the SYLDA adapter from the Ariane V184 flight, Object 33155. However, I am not entirely convinced that the ring is even space debris,” he wrote.

Marco Langbroek, another prominent space researcher, believes it is plausible that the ring came from space and therefore continued to investigate for objects that may have returned at the time of the object’s discovery in Kenya. In A blog post written on Wednesday He noted that in addition to the metal ring, other fragments consistent with space debris were found several kilometers from the ring – including material that looks like carbon cladding and insulation foil.

Like McDowell, Langbroek concluded that the most likely source for the object was an Ariane V launch This happened in July 2008 when the European rocket launched two satellites into geosynchronous transfer orbit.

The Ariane V rocket was a fairly unique rocket in that it was designed with the ability to launch two medium-sized satellites into geostationary transfer orbit, a goal that was far more popular in the late 1990s and early 2000s than it is today. To accommodate both satellites, a SYstème de Lancement Double Ariane (SYLDA) envelope was placed over the lower satellite to support mounting a second satellite on top. During launch in 2008, this SYLDA shell was thrown into a 1.6 degree inclined geosynchronous transfer orbit, Langbroek said.

Could it have come from a European rocket?

Over the years, this object has been tracked by the US military, which maintains a database of space objects to help active spacecraft avoid collisions. Due to the lack of tracking stations near the equator, this object is only observed periodically. According to Langbroek, its last observation occurred on December 23, when it was in a highly elliptical orbit and reached a perigee of just 90 miles (146 km) from Earth. This was a week before an object hit Kenya.

Based on his modeling of the possible re-entry of the SYLDA shell, Langbroek believes it is possible that the European object could have landed in Kenya around the time its entry was observed.

An anonymous I posted a thread This suggests that this ring could not have been part of the SYLDA case. Based on images and documentation, it seems clear that neither the diameter nor the mass of the SYLDA component matches the ring found in Kenya.

In addition, Arianespace officials told the newspaper Le Parisien on Thursday that they do not believe the space debris is related to the Ariane V rocket. Basically: If the ring doesn’t fit, you have to acquit.

So what was it?

This story originally appeared on Ars Technica.