Scott S. Sheppard of the Carnegie Institution has, with a Chilean telescope, found the shortest-period asteroid: 2021 PH27. Thus beating out 2019 AQ3, at last.
At 113 days, this is near-exactly half Venus' 224.7 days. 2:1 resonances are, I think, unstable; this one gets away with it the way Pluto avoids Neptune: by being inclined 32° from ecliptic. Also like Pluto it's elongated: it crosses Mercury's and Venus' orbits both. Which, as they note, means it suffers relativistic effects at perihelion.
As to Earth-crossers (so off-topic), pace Zimmerman: looking at twilight for near-solar asteroids is not how we find threats to our own little marble. If their orbits are sun-to-planet, chances are very high they are resonant and tilted, so they won't get anywhere near us. Better off looking at night, as the joke goes, for those missiles incoming.
2021 PH27 is a kilometer wide. The astros don't know what it is made of, but they can fairly constrain that it doesn't have any lead or tin - because at peri' it gets to 500 Centigrade. They'll be able to look at it properly early 2022 as it's in solar-opposition against our telescopes currently. Wanted: STL4 and L5 orbiting 'scopes.
And pace Sheppard / Carnegie, I would not bet on a comet here. I think any ol' rock at a Venus-resonant orbit is getting pulled into a trajectory like this one. Keyword missing from the text: "retrograde". That means it's running with the rest of us, not spearing in from Oort or beyond.
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