The continued search for interstellar meteors
Many people on social media saw a bright flash in the sky above Portugal and Spain a few weeks ago (5/18). Was it interstellar?
Disclaimer: This post is a bit nerdy. It doesn’t contain any conjecture about the current state of the bizarre situation wrt extraterrestrial intelligence and the USG as portrayed in the popular media (as well as on the floor of Congress.) Again, I don’t anticipate anything worth noting on that front until perhaps the next expedition to the IM1 impact zone and I don’t want to waste everyone’s time.
After seeing the above videos on social media and seeing its estimated very high speed relative to Earth reported by the ESA (~28 miles per second), I was curious to know whether this brilliant display came to us from another star system (and I was too impatient to wait for Avi.) Although I have no astrophysics background, I was roughly familiar with what it would take to determine the answer given Avi Loeb’s team’s papers regarding IM1 and IM2. In these papers, use of a software package called REBOUND is cited. I knew their data source was the CNEOS fireball catalog so I set to figuring out how to use the software (along with Astropy) to determine the answer. It took about two days of tinkering with it to come up with sane output.
Here is the orbit I calculated at the time of impact (units are kilometers):
This plot only includes the inner solar system to make it more readable but the simulation used to calculate this orbit included all of the major planets’ orbital parameters by querying JPL Horizons’ data. The black ellipse represents the meteor’s final turn around the Sun and into Earth. The “Vhel” value was the velocity of the meteor relative to the Sun at the time of impact. In order for the meteor not to have been bound to the solar system this value would’ve had to have been about 41.2 km/s. For reference, Earth’s Vhel is around 30 km/s.
In addition, I also calculated and plotted the orbits of every meteor in the CNEOS catalog along with a crude estimate of their material strengths given the method described by Loeb et al. for calculating their ram pressure. I also used an atmospheric model provided by the U.S. Naval Research Laboratory. For this particular meteor, I came up with a value of 0.06 megapascals (MPa). This would imply the 4th weakest material composition in the entire CNEOS catalog.
I also compared the values and orbits I calculated to known values by comparing my results to those in Loeb et al.’s papers (and others) for IM1 and IM2 as well as to data on the Chelyabinsk meteor. It appeared to confirm my calculations are in rough agreement with others.
Here is my plot of IM1:
The full ellipse is not visible because the relative velocity to the Sun implies this meteor was not local to our solar system. It seems to have rocketed into our solar system at a very high speed from below and smashed into us from behind. This is why its heliocentric speed was much faster than the recorded speed relative to Earth (44.8 km/s).
It is very clear that IM1 and IM2 are unique standouts among the rest of the catalog:
When sorting by heliocentric velocity, they are clear standouts, with IM1 being particularly unique. (Note that Loeb et al.’s Vhel for IM1 is mentioned as ~60 km/s whereas mine is ~62 km/s. So I assume most of my values are at least in error of +/- 1-2 km/s but likely more.) Even if large errors are assumed, it seems very likely IM1 was unbound at the time of impact. You’ll notice my data shows around 30 or so of the meteors look to have been on hyperbolic (unbound) orbits but the vast majority should be regarded as within error limits and not likely to have been truly interstellar.
Another property of these meteors also stands out:
When sorting by ram pressure, it’s clear IM1 is again a major outlier. Loeb et al. calculated ~ 194 MPa but it’s not mentioned which atmospheric model they used for their calculation. Others have calculated it as 222.8 +/- 67.6 MPa so we all seem to be in rough agreement. For reference, iron meteors, which are fairly rare, are expected to yield a ram pressure of ~ 50 MPa. It is these two reasons that make IM1 such an intriguing object to study.
So now I hope maybe you better understand why this particular meteor is worth scouring the South Pacific for. If you would like to view/run my code for processing the CNEOS fireball catalog you can find it here: https://gist.github.com/markbeef1234/1645e5b1dbf2e8d7890297af80da444a
(Disclaimer: Again, I am not an astrophysicist and only verified rough agreement using a handful of public data I could find from others. Use at your own risk!)
Thanks for reading!