A camera atop Hawaii's tallest mountain has captured what looks like a spiral swirling through the night sky.
Researchers believe it shows the aftereffects of a SpaceX rocket launch when the company's Falcon 9 rocket sent a GPS satellite into orbit.
The images were captured on January 18 by a camera at the summit of Mauna Kea outside the National Astronomical Observatory of Japan's Subaru telescope.
A time-lapse video shows a white orb spreading out and forming a spiral as it moves across the sky. It then fades and disappears.
Ichi Tanaka, a researcher at the Subaru telescope, said he was doing other work that night and didn't immediately see it. Then a stargazer watching the camera's live stream on YouTube sent him a screenshot of the spiral using an online messaging platform.
When I opened Slack, that is what I saw and it was a jaw-dropping event for me, Tanaka said.
He saw a similar spiral last April, also after a SpaceX launch, but that one was larger and fainter
The location of the January 18 spiral matched where the second stage of the SpaceX rocket was expected to be after its launch.
SpaceX didn't respond to an email sent on Friday seeking comment.
Tanaka said the observatory installed the camera to monitor the surroundings outside the Subaru telescope and to share Mauna Kea's clear skies with the people of Hawaii and the world.
Someone watching the sky in less clear conditions, for example from Tokyo, might not have seen the spiral, he said.
The live stream is jointly operated with the Asahi Shimbun, a major Japanese newspaper, and frequently gets hundreds of viewers. Some tune in to watch meteors streak across the sky.
The summit of Mauna Kea has some of the best viewing conditions on Earth for astronomy, making it a favoured spot for the world's most advanced observatories. The summit is also considered sacred by many Native Hawaiians who view it as a place where the gods dwell.