Elon Musk has had his fair share of space-related problems over the past couple of weeks, but it looks like he can take a SpaceX rocket crash with the Moon off his list.
Last month, astronomers and space enthusiasts spied a hefty chunk of space junk looping around the Earth which would, within a matter of weeks, meet its fiery end on the far side of the Moon.
The culprit, they thought, was a spent stage from a SpaceX rocket — one that helped ferry a NASA probe to sit between Earth and the Sun.
Now, the hunk of junk is more likely the third stage of a Long March 3C rocket, launched by China in 2014, for a mission to the Moon.
Bill Gray, a US data analyst who tracks objects such as asteroids sailing throughout the Solar System, published the correction on his blog on Saturday.
This new development is based on circumstantial evidence, Mr Gray wrote on his blog.
Why did astronomers think it was a SpaceX rocket stage?
The rocket stage was first spotted way back in early 2015 by the University of Arizona's Catalina Sky Survey, which scans the heavens and tracks objects such as comets on trajectories that bring them close to Earth.
The mystery object was spied zooming closely past the Moon.
At first, astronomers thought it might have been an asteroid.
But that was quickly ruled out: the mystery object circled our planet, behaviour much more in line with something humans hurled up there. An asteroid, on the other hand, would circle the Sun.
Mr Gray and others suspected it might be a stage from a SpaceX Falcon 9 rocket which, just days before the mystery object was spotted, had blasted off with the Sun-monitoring DSCOVR probe sitting atop it.
"The object had about the brightness we would expect, and had showed up at the expected time and moving in a reasonable orbit," Mr Gray wrote.
So that was generally accepted, until Mr Gray received an email on Saturday.
So why is it part of a Chinese rocket?
The email came from Jon Giorgini, an engineer at NASA and Caltech's Jet Propulsion Laboratory.
Mr Giorgini developed Horizons, an online database of stuff moving in our Solar System, from the Sun all the way down to individual spacecraft.
The Horizons system showed the Falcon 9 rocket's trajectory didn't take it near enough to the Moon for it to be the mystery object first detected by the Catalina Sky Survey in 2015.
So Mr Gray looked for other launches that might fit the bill.
He hit on China's Chang'e 5-T1, which launched on a three-stage rocket on October 23, 2014.
The mission was a test run of sorts for another, more ambitious mission to bring back to Earth the first fresh Moon rocks in decades.
(It wouldn't be till the end of 2020 when the real mission, Chang'e 5, would successfully land on the Moon's surface, drill a couple of metres down, and return with its haul of lunar rocks and dust.)
But back in 2014, Chang'e 5-T1 consisted of a sample return capsule attached to a spacecraft, which was sent out to do a lap around the Moon before heading back to Earth.
The capsule separated from the spacecraft, re-entered the atmosphere and parachuted into Mongolia for a safe landing.
And the rocket stages were left to tumble around in space.
Where does this leave SpaceX?
The identity of the projectile may have changed, but everything else stays the same, according to Mr Gray.
The rocket stage will still crash on Friday, March 4 at 11.25:58am AEDT (give or take a few seconds) in the Hertzsprung crater.
It's likely we'll see more rocket parts slamming into the Moon's hard, unforgiving surface down the track, RMIT University space scientist Brett Carter said.
"As human activity increases, particularly as part of [NASA's] Artemis program, and we send people back to the Moon as a platform to get to Mars, this type of thing is set to become more commonplace."
SpaceX copped a bit of heat for its (mistaken) role in the whole affair, but the space company — and China's National Space Administration — simply do what NASA and Roscosmos have done for decades.
It's just too expensive to bring equipment like spent rocket stages back down to Earth — especially those that travel as far as the Moon, Dr Carter said.
That's because rocket stages that push spacecraft out into the further reaches of Earth's orbit don't generally get in the way of, for instance, communications satellites, which are concentrated in low-Earth orbit.
Which is where SpaceX recently ran into strife.
A burst of radiation from the Sun "puffed up" the Earth's atmosphere, and a suite of newly launched Starlink internet satellites, orbiting the planet around 200 kilometres up, found themselves in a much denser atmosphere than expected.
With extra density comes more drag, and this ended up pulling at least 40 of the 49 satellites down where they burned and disintegrated on re-entry.
SpaceX is launching thousands of satellites, and a certain percentage simply won't work up there, Dr Carter said.
So initially sending up flocks of satellites into this very-low-Earth orbit is, on one hand, a good move.
"Those that get up there and don't work, you can just leave them alone, and they'll decay and burn up," Dr Carter said.
But things will get a bit spicier in the coming years. That's because the Sun's activity broadly works on an 11-year cycle, and it's just building up to what's known as the "solar maximum".
And companies like SpaceX will have to contend with more burps and blasts from the Sun.
"SpaceX are going to have to find that balance between deploying at low-enough altitudes so that drag brings down any dysfunctional satellites, and high-enough altitudes to give them enough time to undergo their initial testing," Dr Carter said.
'And, presumably, beneath the International Space Station altitude, so that people aren’t put in harm's way."
