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\u00b7 The retrograde trajectory of 3I\/ATLAS is aligned with the ecliptic plane of the planets around the Sun to within 5 degrees, with a chance probability of 1 in 500 (as discussed\u00a0here<\/a>). This coincidence brings 3I\/ATLAS to pass within several tens of millions of kilometers from Mars, Venus and Jupiter.<\/p>\n \u00b7 The diameter of the nucleus of 3I\/ATLAS has an upper limit of 46 kilometers (as derived\u00a0here<\/a>), which would make it a million times more massive than the interstellar comet\u00a02I\/Borisov<\/a>. On October 3, the HiRISE camera on the Mars Reconnaissance orbiter will be able to image 3I\/ATLAS with a pixel resolution of 30 kilometers, providing the best limit on the diameter of its nucleus.<\/p>\n \u00b7 For a couple of months after its discovery \u2014 when 3I\/ATLAS was at a heliocentric distance of 3\u20134.5 times the Earth-Sun separation, it featured a glow, ten times longer than it is wide, towards the Sun and not in the opposite direction \u2014 as expected from a cometary tail. This feature of an\u00a0anti-tail<\/em>\u00a0was never observed before for comets (as analyzed\u00a0here<\/a>).<\/p>\n \u00b7 The plume of gas around 3I\/ATLAS is composed primarily of carbon dioxide \u2014 CO2 (87% by mass) with traces of carbon monoxide \u2014 CO (9%), and water \u2014 H2O (most of the remaining 4%), as derived\u00a0here<\/a>. It also features nickel without iron (as known to exist in industrially-produced nickel alloys) and cyanide, both rising sharply with decreasing heliocentric distance (as reported\u00a0here<\/a>).<\/p>\n \u00b7 3I\/ATLAS is characterized by an extremely deep and narrow negative polarization of \u22122.77 percent with a low inversion angle of 6.41 degrees (as reported\u00a0here<\/a>). This polarimetric behavior is significantly different from all known comets, either interstellar or bound to the Solar System. 3I\/ATLAS is the first object known with this combination of low inversion angle and extreme negative polarization. Its anomalous polarization might be the result of the very elongated configuration of scattered sunlight around it with a 10:1 aspect ratio.<\/p>\n Posted by Avi Loeb<\/p>\n