Michele Bannister Jul 9
It's paper day! We use our Ōtautahi-Oxford model of the Galaxy's interstellar object population to understand the origins of 3I/ATLAS, from only its velocity @astrohopkins.bsky.social, Dorsey, @redshiftless.bsky.social, @astrokiwi.bsky.social, @chrislintott.bsky.social & Leicester, submitted A 🧵🔭

From a Different Star: 3I/ATLA...
Show threadMichele Bannister Jul 9
As interstellar objects are unbound from their home systems, they carry with them the memory of where they formed in the protoplanetary disk. Greater distances out in the disk = where it is cold enough to condense different types of ices, which then go into the composition of the future ISO
Show threadMichele Bannister Jul 9
The metallicity and mass of disks seem to scale with their star. So an ISO has a link to its star's metallicity, even long after that star may be no more; rocks continue drifting in the Galaxy
Show threadMichele Bannister Jul 9
There's something cosmic in scale that building a model of the interstellar object population means taking into account all the stars that have ever lived in the Milky Way. ISOs are our record-keepers, even after light itself has left
Show threadMichele Bannister Jul 9
From every system, the drifting interstellar objects are then moving out in long tidal streams, and being gently mixed around the whole Galaxy. We used Gaia's snapshot of what's nearby (stars within 200 pc of the Sun) to build a model of what ISOs are nearby

Predicting Interstellar Object...
Predicting Interstellar Object Chemodynamics with Gaia

The interstellar object (ISO) population of the Milky Way is a product of its stars. However, what is in fact a complex structure in the solar neighborhood has traditionally in ISO studies been described as smoothly distributed. Using a debiased stellar population derived from the Gaia Data Release 3 stellar sample, we predict that the velocity distribution of ISOs is far more textured than a smooth Gaussian. The moving groups caused by Galactic resonances dominate the distribution. 1I/'Oumuamua and 2I/Borisov have entirely normal places within these distributions; 1I is within the noncoeval moving group that includes the Matariki (Pleiades) cluster, and 2I within the Coma Berenices moving group. We show that for the composition of planetesimals formed beyond the ice line, these velocity structures also have a chemodynamic component. This variation will be visible on the sky. We predict that this richly textured distribution will be differentiable from smooth Gaussians in samples that are within the expected discovery capacity of the Vera C. Rubin Observatory. Solar neighborhood ISOs will be of all ages and come from a dynamic mix of many different populations of stars, reflecting their origins from all around the Galactic disk.

ADS
Show threadMichele Bannister Jul 9
And this model makes predictions! The Ōtautahi–Oxford model predicts correlations between ISO velocity and properties such as composition and age. So with just 3I's velocity, which is well-measured by all that hard work people already put into measuring its orbital arc, we can draw from the model...
Show threadMichele Bannister Jul 9
What does the Ōtautahi–Oxford model tell us? 3I/ATLAS is coming in fast, but well within what's expected. Its large vertical velocity suggests it's here from a part of the Galaxy known as the thick disk - different from the part the Sun lives within
Show threadMichele Bannister Jul 9
We can also predict that 3I/ATLAS came from a metallicity of star that was more metal-poor; ISOs from these stars tend to be more water-rich. So, a prediction for observers! As we found yesterday, no gas emission yet in VLT/MUSE spectra, but maybe we'll see some as 3I gets more heated by the Sun?
Mike MalaskaJul 9
Show threadMichele Bannister
3I/ATLAS also seems like it could be somewhat older than 1I and 2I were. It's pretty incredible to think of this new-seen tiny world as wandering our Galaxy for upwards of 8 billion years.
Jul 9 at 4:25amWeb
Show threadMichele Bannister Jul 9
So no, we're not going to be able to trace 3I/ATLAS back to any home star. And based on how it is moving, that star or star cluster was a different one to either of the origin stars of *both* 1I or 2I. We just have to work with the memories that 3I brings with it.
Show threadMichele Bannister Jul 9
That thick-disk origin means 3I/ATLAS is infalling from a more southerly direction than most of the interstellar objects that the Ōtautahi–Oxford model suggests, which come in from the North. This makes its orbit one that would be pretty unusual for @vrubinobs.bsky.social to see, for instance!
Show threadMichele Bannister Jul 9
From the Ōtautahi–Oxford model, 3I/ATLAS is our first interstellar object from the Galaxy's thick disk. It'll be exciting to see what the current and upcoming observations can help tell us about our new visitor over the next few months. /fin

From a Different Star: 3I/ATLA...
From a Different Star: 3I/ATLAS in the context of the ĹŚtautahi-Oxford interstellar object population model

The discovery of the third interstellar object (ISO), 3I/ATLAS (`3I'), provides a rare chance to directly observe a small body from another Solar System. Studying its chemistry and dynamics will add to our understanding of how the processes of planetesimal formation and evolution happen across the Milky Way's disk, and how such objects respond to the Milky Way's potential. In this Letter, we present a first assessment of 3I in the context of the ĹŚtautahi-Oxford model, which uses data from Gaia in conjunction with models of protoplanetary disk chemistry and Galactic dynamics to predict the properties of the ISO population. The model shows that both the velocity and radiant of 3I are within the expected range. Its velocity suggests an origin within the Milky Way's thick disk, making it the first ISO from this population, and predicts a high water mass fraction, which may become observable shortly. We also conclude that it is very unlikely that 3I shares an origin with either of the previous two interstellar object detections.

arXiv.org