Discussion in chat pointed out that the SpaceX Roadster or Starman has a Marsden A1 coefficient.
From solution 10 in Horizons:
EPOCH= 2458164.5 EC= .2585469914787243 QR= .9860596231806226 TP= 2458153.620483722645 OM= 317.3549094214575 W = 177.3203028023227 IN= 1.088451292866039 A1= 2.960683526738534E-9 R0= 1. ALN= 1. NM= 2. NK= 0. SRC= -2.057839421666802E-7...
I wrote about the Marsden parameters in this question a while ago and have linked several sources there. You have to use that in a certain power-law equation and use units of days and AU, so A1 is 2.96E-09 AU/day^2.
Question: Why does Starman/Roadster have radial acceleration? What is causing this? Can the size of the acceleration be understood quantitatively?
Aliens are trying, very slowly, to steal it?
Air leaking out of the tires?