New study reveals potentially fiery fate of inner Venus asteroid ‘Ayló’chaxnim: ScienceAlert

There are a lot of asteroids in the solar system that orbit around the Sun.

We know about 1 million of them. And almost all of these asteroids lie beyond Earth’s orbit, in the outermost regions of the middle and outer solar system. Only a few have been discovered entirely inside Earth’s orbit.

Models suggest that there should be a population of asteroids even closer to the Sun, entirely confined within the orbit of Venus. To date, we have only found one: the asteroid ‘Ayló’chaxnim, discovered in 2020. Its name means ‘Venus girl’ in the Luiseño language.

Yet ‘Ayló’chaxnim defies our expectations: it’s a size that, according to models, is too large to be an asteroid inside Venus.

Scientists have taken a closer look at the rock to see if they can figure out what it is, how it got there, what its future holds and if it can lead us to more asteroids inside of Venus.

A paper describing the findings, led by Caltech astronomer Bryce Bolin, has been accepted by Royal Astronomical Society Monthly Notices and is available on the arXiv preprint server.

According to models based on the known population of near-Earth asteroids, the asteroid population in Venus’ interior should consist of rocks about 1 kilometer (0.62 miles) in diameter or less.

However, finding these asteroids is difficult; they tend to be quite close to the Sun in the sky, which means we can only find them in the short time between sunset (or sunrise) and total darkness. Because they’re small and remote, that’s no small feat.

Initial observations of ‘Ayló’chaxnim, first detected using the Zwicky Transient Facility, and tracked using a number of different instruments, suggested the asteroid is around 2 kilometers in diameter. It has a reddish tint, consistent with S-type asteroids from the inner main belt of asteroids that orbit the Sun between Mars and Jupiter.

At the edge of its orbit, the asteroid flies about 0.65 astronomical units from the Sun. The orbital distance of Venus is 0.72 astronomical units.

By collecting all the sightings, analyzing the data, and running simulations, Bolin and his colleagues determined that ‘Ayló’chaxnim is about 1.7 kilometers across and migrated to its current position from the Main Belt.

This is consistent with previous findings and modeling which suggest that any asteroid with the orbital profile of ‘Ayló’chaxnim should come from the Main Belt.

However, Bolin and his team also discovered that ‘Ayló’chaxnim only came to its current position relatively recently, from a cosmic perspective, within the last million years or so. And he’s not likely to stay there long. In the team’s simulations, 90% of the ‘Ayló’chaxnim clones had a gravitational interaction with a planet that resulted in a collision with a planet or the Sun within 30 million years.

Of the surviving clones, within 50 million years, 13% collided with the Sun, while 13%, 52%, 16% and 2% collided with Mercury, Venus, Earth and March, respectively.

The remaining 4% of that 10% survives more than 50 million years, or they eventually get ejected from the solar system entirely. This gives ‘Ayló’chaxnim a survival rate of only 0.04% beyond 50 million years.

This relatively short stability time could explain why we haven’t found many asteroids inside Venus. It should also be noted that the first objects found in any cosmic population tend to be the outliers, giving us a signal large enough to detect.

‘Ayló’chaxnim is bigger than the models thought, but it could be a big oddball, and the smaller swarm is outside of our current detection capabilities – or we just need to look a little further .

And that’s what Bolin and his team recommend we do. The team’s simulations suggest that ‘Ayló’chaxnim could have a 0.16% chance of colliding with Earth within 50 million years. These are small odds, but still not zero. If there are more asteroids with these ratings, we want to know more.

“The twilight sky within 50 degrees of the Sun is relatively unexplored, and comparison between observations and asteroid population models requires future exploration of this phase space,” they write in their paper.

“Observations of the sky near the Sun by current surveys…as well as future surveys…will provide coverage of the sky near the Sun and the asteroid population inside Venus.”

As ‘Ayló’chaxnim was the first of these asteroids to be officially detected, identified and named, the team proposes that this population be referred to as ‘Ayló’chaxnim asteroids.

The research was accepted in the Royal Astronomical Society Monthly Notices and is available on arXiv.

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