Tag: 3I/Atlas

Interstellar Visitors

As of this writing, three objects have been discovered that have passed through our solar system coming from interstellar space.

1I/’Oumuamua
Discovery Date: 2017-10-19
Perihelion Date: 2017-09-09 (40 days after perihelion)
Perihelion Distance: 0.26 AU
Incoming and Outgoing Speed: 26.4 km/s
Dimensions: approximately 115 m × 111 m × 19 m, or 230 m × 35m × 35m
Object Type: asteroid?

2I/Borisov
Discovery Date: 2019-08-29
Perihelion Date: 2019-12-08 (101 days before perihelion)
Perihelion Distance: 2.01 AU
Incoming and Outgoing Speed: 32.3 km/s
Diameter: 400 m – 1000 m
Object Type: comet

3I/Atlas
Discovery Date: 2025-07-01
Perihelion Date: 2025-10-29 (120 days before perihelion)
Perihelion Distance: 1.36 AU
Incoming and Outgoing Speed: 58.0 km/s
Diameter: 320 m – 5,600 m (most likely 520 m – 748 m)
Object Type: comet

Here are charts showing the direction from which each object entered our solar system, and the direction towards which each object is leaving our solar system.

1I/’Oumuamua came in from the direction of the constellation Lyra
1I/’Oumuamua is exiting in a direction inside the Square of Pegasus
2I/Borisov came in from the direction of the constellation Cassiopeia
2I/Borisov is exiting in the direction of the southern constellation Telescopium
3I/Atlas came in from the direction of the constellation Sagittarius
3I/Atlas is exiting in the direction of the constellation Gemini

1I/’Oumuamua
Incoming Right Ascension (2000): 18h 37m 53.88s
Incoming Declination (2000): +33° 51′ 34.7″
Outgoing Right Ascension (2000): 23h 51m 27.99s
Outgoing Declination (2000): +24° 42′ 33.0″
Angular Separation (Incoming→Outgoing): 67.4°
Deflection Angle: 180° – 67.4° = 112.6°

2I/Borisov
Incoming Right Ascension (2000): 2h 11m 37.54s
Incoming Declination (2000): +59° 27′ 26.6″
Outgoing Right Ascension (2000): 18h 21m 24.19s
Outgoing Declination (2000): -52° 00′ 21.9″
Angular Separation (Incoming→Outgoing): 145.4°
Deflection Angle: 180° – 145.4° = 34.6°

3I/Atlas
Incoming Right Ascension (2000): 19h 40m 04.79s
Incoming Declination (2000): -19° 04′ 21.7″
Outgoing Right Ascension (2000): 6h 20m 55.99s
Outgoing Declination (2000): +19° 48′ 15.6″
Angular Separation (Incoming→Outgoing): 161.3°
Deflection Angle: 180° – 161.3° = 18.7°

It is perhaps not surprising that 1I/’Oumuamua had the greatest deflection angle of the three interstellar objects. It came quite close to the Sun (0.26 AU, well inside the orbit of Mercury) and had the lowest incoming speed (26.4 km/s).

3I/Atlas, on the other hand, had the greatest incoming speed by far (58.0 km/s), so it was deflected by only 18.7° from a straight-line trajectory (angular separation 180° and deflection angle 0°).