Apophis: A Dance Before Its Date with Earth express
A spinning top launched into weightlessness doesn't just rotate around its axis: it also wobbles, like a drunken sailor. That's exactly how the asteroid Apophis behaves: it doesn't spin neatly but tumbles through space. On April 13, 2029, this celestial wanderer will whiz past at about 38,000 kilometers from Earth — closer than communications satellites. Our planet's gravity will yank it like a strong gust of wind tugging a weather vane, forcing it into a new spin.
To predict how Apophis's dance will change after the encounter, we need to know its current motions precisely. Astronomers took old photographs of the asteroid from 2012–2013 and 2020–2021 and applied the light-curve method (graphs of brightness variation). These brightness fluctuations, like fingerprints, reveal how the object tumbles. This yielded several rotation models, but none could be singled out — the data weren't enough. It's like trying to guess how a coin is spinning when you see it through frosted glass.
The puzzle is that all viable models show roughly the same orientation of the asteroid before the encounter. The reason is a lucky coincidence: the interval between the 2012–2013 and 2020–2021 observations (8 years) equals the gap from 2021 to 2029. Nature seems to have given us a synchronization: the asteroid is now facing the same way it did 8 years ago. But after the April encounter, uncertainty will spike: Earth's gravitational pull could set Apophis spinning in any of several directions. Fortunately, there's good news: most likely, the asteroid will keep rotating around its shortest axis, like a figure skater pulling in their arms.
Asteroid Apophis is named after the ancient Egyptian serpent of destruction, who tries to swallow the sun's barge every night. But unlike the myth, the real Apophis poses no threat to Earth for at least the next hundred years.
In Arthur C. Clarke's novel Rendezvous with Rama, humanity also tracks a cosmic wanderer whose rotation and trajectory hold a mystery. Apophis, like Rama, makes us gaze at the sky with awe and curiosity.