"the system looses its weight depending on the temperature."
https://patents.google.com/patent/WO2001009509A2/en
"the circular mark was between 4 to 5 tons, but that according to analysis, the temperature that made the circular markings was likely to be around 300 to 600 Celsius, or between 500 to over 1,000 degrees Fahrenheit."
https://www.ufoinsight.com/ufos/cover-ups/ufo-encounters-physical-evidence
"The fundamental physics behind a hot air balloon is buoyancy, which generates lift. A hot air balloon consists of a large envelope bag with a basket suspended below. The basket holds a flame used to heat the air inside the balloon through an opening. Therefore, a lift is generated by the heat produced."
https://byjus.com/physics/hot-air-balloon/