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ZTm0038: Did we just dodge a bullet? by jpo234 on 15 Aug, 2023 22:26
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#1 by whitelancer64 on 15 Aug, 2023 23:11
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Depending on its orbit, it may have dodged us.
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#2 by deltaV on 16 Aug, 2023 02:34
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According to a table in https://en.wikipedia.org/wiki/Impact_event a 400m impactor diameter produces an impact crater of roughly 6 km, impact energy 2800 Mt (~50x the largest atomic bomb ever), and a frequency of roughly 100k years. https://en.wikipedia.org/wiki/List_of_impact_craters_on_Earth has the most recent crater of 6 km or more diameter about 900k years ago and a total of 6 craters that big in the past 10M years. Either that 100k year frequency estimate is too low or a lot of impact events didn't produce craters that we've discovered (e.g. because they were in the ocean). It looks like ZTm0038 should probably have been a 4 on the Torino scale but it's very close to being a 5: https://en.wikipedia.org/wiki/Torino_scale. The description of Torino 4 includes "regional devastation" and "Attention by public and by public officials is merited if the encounter is less than a decade away." So it seems strange that the merited attention by the public didn't happen.
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#3 by Hobbes-22 on 16 Aug, 2023 07:14
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From Ycombinator:Quote
When a new potentially-hazardous asteroid is discovered, it's normal for the probability of impact to go up a couple times before abruptly plummeting to zero, as the radius of uncertainty shrinks until it shrinks past the Earth. See https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apophis_ellipse.svg
A 3% chance of impact right after discovery with the initial error ellipse isn't all that unusual; it will almost certainly be revised to 0 with more observation (and if it's not, you'll hear about it). -
#4 by hoku on 16 Aug, 2023 08:42
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Impact probability: 0.034 (~3%)
https://newton.spacedys.com/neodys2/NEOScan/risk_page/ZTm0038/index_summary_ZTm0038.html
I call BS. "NickAstronomer" didn't even bother to do a simple consistency check.
From https://minorplanetcenter.net
ZTm0038* C2023 08 12.49542 06 32 33.23 +15 57 35.5 18.86rUNEOCPI41
ZTm0038 C2023 08 12.50028 06 32 33.17 +15 57 37.9 18.83rUNEOCPI41
ZTm0038 C2023 08 12.50271 06 32 33.15 +15 57 39.6 18.74rUNEOCPI41
ZTm0038 C2023 08 12.50514 06 32 33.06 +15 57 40.9 19.05rUNEOCPI41
ZTm0038 C2023 08 13.49775 06 32 33.04 +15 57 47.4 18.93rUNEOCPI41
ZTm0038 C2023 08 13.50020 06 32 33.00 +15 57 48.5 19.00rUNEOCPI41
ZTm0038 C2023 08 13.50263 06 32 33.04 +15 57 49.5 19.05rUNEOCPI41
ZTm0038 C2023 08 13.50506 06 32 33.05 +15 57 50.9 18.90rUNEOCPI41
Two sets of observations, taken 1 day apart, yet the "NEO" hardly moved, while the observers reported apparent movement during their individual 15 to 20 min observing sessions. The observers might have detected a transient background source (variable star in the Milky Way, distant supernova, etc.) in their low angular resolution(?) monitoring.
Edit: data were recorded and reported (automatically) by the Zwicky Transit Facility (ZTF) - see https://www.ztf.caltech.edu/index.html -
#5 by whitelancer64 on 16 Aug, 2023 16:20
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https://twitter.com/NickAstronomer/status/1691762822819033402
Running the MPC data through orbital calculator shows ztm0038 not getting anywhere near as close as JP:/NEOdys have it... Like , orders of magnitude variance.
Going to wait now until I hear more/see better data
3:44 AM · Aug 16, 2023
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#6 by launchwatcher on 16 Aug, 2023 18:09
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it appears that in its latest run, NEOScan has split the observations - it now has separate pages for "ZTm0038" and "Ztm0038", each with 4 observations and with very different parameters:
https://newton.spacedys.com/neodys2/NEOScan/index_risk.html
https://newton.spacedys.com/neodys2/NEOScan/risk_page/ZTm0038/index_summary_ZTm0038.html
https://newton.spacedys.com/neodys2/NEOScan/risk_page/ZTm0038/index_summary_ZTm0038.html
Both are flagged withQuoteWARNING! This case is not significant because the arc length is less than 20 minutes and/or there are less than three observations.