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<\/picture><\/div>\n<\/div>\nTrajectory of 3I\/ATLAS with positions of the planets on November 22, 2025. (Credit:\u00a0NASA\/JPL<\/a>)<\/h5>\n\nAvi Loeb<\/p>\n
Let us suppose, hypothetically, that the interstellar object\u00a03I\/ATLAS<\/a>\u00a0is a mothership that was designed to seed Jupiter with technological devices. What would be the largest distance from Jupiter that this interstellar gardener should arrive at?<\/p>\nFor that purpose, 3I\/ATLAS must arrive within Jupiter\u2019s radius of gravitational influence \u2014 the so-called\u00a0Hill radius<\/a>, inside of which Jupiter\u2019s gravity overcomes the gravitational tide from the Sun. Interior to that radius, Jupiter\u2019s gravity wins over the Sun\u2019s gravity and can keep low-speed orbiters bound without the Sun ripping them away. The Lagrange points L1 and L2 of force equilibrium are located at the Hill radius and are ideal locations for technological satellites, since orbital corrections and fuel requirements are minimal there.<\/p>\nJupiter\u2019s\u00a0Hill radius<\/a>\u00a0is given by the equation:<\/p>\nH=R*(m\/3M)^{1\/3},<\/em><\/p>\nwhere\u00a0R<\/em>\u00a0is Jupiter\u2019s distance from the Sun at the particular time of interest,\u00a0m<\/em>\u00a0is Jupiter\u2019s mass and\u00a0M\u00a0<\/em>is the Sun\u2019s mass.<\/p>\n3I\/ATLAS is expected to get to its closest distance from Jupiter on March 16, 2026. The Jupiter-Sun separation on that date will be\u00a0R=<\/em>783.8 million kilometers. Substituting this value in the above equation together with (m\/3M)^{1\/3}=0.06826, yields the Hill radius of Jupiter on March 16, 2026:<\/p>\nH<\/em>=53.502 million kilometers.<\/p>\nThe distance of closest approach of 3I\/ATLAS to Jupiter is calculated by NASA\u2019s\u00a0JPL Horizons<\/a>\u00a0code based on orbital data gathered by about 230 observatories regarding its motion in the sky. This data includes the recently measured non-gravitational acceleration of 3I\/ATLAS during perihelion, leading JPL Horizons to forecast that on March 16, 2026 3I\/ATLAS will arrive at the following minimum distance from Jupiter:<\/p>\nMin{D}<\/em>= 53.445 (+\/- 0.06) million kilometers<\/p>\nWhat an extraordinary coincidence. The values of\u00a0H<\/em>\u00a0and min{D}\u00a0<\/em>are identical within one standard deviation of 0.06 million kilometers. The near coincidence of these numbers was brought to my attention by\u00a0Steve Fairfax<\/a>.<\/p>\nThe measured value of the non-gravitational acceleration of 3I\/ATLAS, acquired during the month-long passage of 3I\/ATLAS near perihelion, changed the value of\u00a0min{D}<\/em>\u00a0at a level of 0.1 million kilometers. This magnitude of displacement in the minimum distance of 3I\/ATLAS from Jupiter results from the measured non-gravitational acceleration value of 5×10^{-7} au per day squared as reported\u00a0here<\/a>, after the month-long perihelion crossing (where au is the Earth-Sun separation).<\/p>\nIn other words, the non-gravitational acceleration introduced a small course correction of exactly the magnitude needed to bring the minimum distance of 3I\/ATLAS from Jupiter to the value of Jupiter\u2019s Hill radius. 3I\/ATLAS would have missed the edge of the Hill sphere otherwise.<\/mark><\/p>\nThis suggests that the level of non-gravitational acceleration was finely tuned to result in\u00a0min{D}=H<\/em>\u00a0and bring 3I\/ATLAS exactly to the radius of Jupiter\u2019s gravitational influence.<\/p>\nIf 3I\/ATLAS is technological in origin, it might have fine-tuned its trajectory with the help of thrusters so as to arrive at Jupiter\u2019s Hill radius. In that case, the multiple jets observed around 3I\/ATLAS in its post-perihelion images (as reported\u00a0here<\/a>,\u00a0here<\/a>,\u00a0here<\/a>\u00a0and\u00a0here<\/a>) might have been used for the slight orbit correction needed to result in\u00a0min{D}=H<\/em>. The optimal time for any such maneuver is close to perihelion when a spacecraft can take advantage of the gravitational assist from the Sun (as pointed out\u00a0here<\/a>). In addition, 3I\/ATLAS arrived at perihelion while being hidden behind the Sun for Earth-based observatories. We therefore do not know whether it just maneuvered slightly to satisfy\u00a0min{D}=H<\/em>\u00a0or also released technological devices near perihelion.<\/p>\nHow statistically rare is the coincidence between the values of\u00a0min{D}<\/em>\u00a0and\u00a0H<\/em>? A margin of 0.06 out of 53.5 million kilometers corresponds to a coincidence of one part in a thousand. But given the full diameter of Jupiter\u2019s orbit around the Sun, this coincidence amounts to one part in 26,000.<\/p>\nIf 3I\/ATLAS were to deposit devices within the Hill sphere of Jupiter on March 16, 2026, these devices would need to fire their engines in order to cancel out the high speed of 3I\/ATLAS relative to Jupiter, which is 65.9 kilometers per second. The escape speed from Jupiter\u2019s gravitational potential well at H=53.5 million kilometers is just 2.2 kilometers per second.<\/p>\n
For that purpose, 3I\/ATLAS must arrive within Jupiter\u2019s radius of gravitational influence \u2014 the so-called\u00a0Hill radius<\/a>, inside of which Jupiter\u2019s gravity overcomes the gravitational tide from the Sun. Interior to that radius, Jupiter\u2019s gravity wins over the Sun\u2019s gravity and can keep low-speed orbiters bound without the Sun ripping them away. The Lagrange points L1 and L2 of force equilibrium are located at the Hill radius and are ideal locations for technological satellites, since orbital corrections and fuel requirements are minimal there.<\/p>\n Jupiter\u2019s\u00a0Hill radius<\/a>\u00a0is given by the equation:<\/p>\n H=R*(m\/3M)^{1\/3},<\/em><\/p>\n where\u00a0R<\/em>\u00a0is Jupiter\u2019s distance from the Sun at the particular time of interest,\u00a0m<\/em>\u00a0is Jupiter\u2019s mass and\u00a0M\u00a0<\/em>is the Sun\u2019s mass.<\/p>\n 3I\/ATLAS is expected to get to its closest distance from Jupiter on March 16, 2026. The Jupiter-Sun separation on that date will be\u00a0R=<\/em>783.8 million kilometers. Substituting this value in the above equation together with (m\/3M)^{1\/3}=0.06826, yields the Hill radius of Jupiter on March 16, 2026:<\/p>\n H<\/em>=53.502 million kilometers.<\/p>\n The distance of closest approach of 3I\/ATLAS to Jupiter is calculated by NASA\u2019s\u00a0JPL Horizons<\/a>\u00a0code based on orbital data gathered by about 230 observatories regarding its motion in the sky. This data includes the recently measured non-gravitational acceleration of 3I\/ATLAS during perihelion, leading JPL Horizons to forecast that on March 16, 2026 3I\/ATLAS will arrive at the following minimum distance from Jupiter:<\/p>\n Min{D}<\/em>= 53.445 (+\/- 0.06) million kilometers<\/p>\n What an extraordinary coincidence. The values of\u00a0H<\/em>\u00a0and min{D}\u00a0<\/em>are identical within one standard deviation of 0.06 million kilometers. The near coincidence of these numbers was brought to my attention by\u00a0Steve Fairfax<\/a>.<\/p>\n The measured value of the non-gravitational acceleration of 3I\/ATLAS, acquired during the month-long passage of 3I\/ATLAS near perihelion, changed the value of\u00a0min{D}<\/em>\u00a0at a level of 0.1 million kilometers. This magnitude of displacement in the minimum distance of 3I\/ATLAS from Jupiter results from the measured non-gravitational acceleration value of 5×10^{-7} au per day squared as reported\u00a0here<\/a>, after the month-long perihelion crossing (where au is the Earth-Sun separation).<\/p>\n In other words, the non-gravitational acceleration introduced a small course correction of exactly the magnitude needed to bring the minimum distance of 3I\/ATLAS from Jupiter to the value of Jupiter\u2019s Hill radius. 3I\/ATLAS would have missed the edge of the Hill sphere otherwise.<\/mark><\/p>\n This suggests that the level of non-gravitational acceleration was finely tuned to result in\u00a0min{D}=H<\/em>\u00a0and bring 3I\/ATLAS exactly to the radius of Jupiter\u2019s gravitational influence.<\/p>\n If 3I\/ATLAS is technological in origin, it might have fine-tuned its trajectory with the help of thrusters so as to arrive at Jupiter\u2019s Hill radius. In that case, the multiple jets observed around 3I\/ATLAS in its post-perihelion images (as reported\u00a0here<\/a>,\u00a0here<\/a>,\u00a0here<\/a>\u00a0and\u00a0here<\/a>) might have been used for the slight orbit correction needed to result in\u00a0min{D}=H<\/em>. The optimal time for any such maneuver is close to perihelion when a spacecraft can take advantage of the gravitational assist from the Sun (as pointed out\u00a0here<\/a>). In addition, 3I\/ATLAS arrived at perihelion while being hidden behind the Sun for Earth-based observatories. We therefore do not know whether it just maneuvered slightly to satisfy\u00a0min{D}=H<\/em>\u00a0or also released technological devices near perihelion.<\/p>\n How statistically rare is the coincidence between the values of\u00a0min{D}<\/em>\u00a0and\u00a0H<\/em>? A margin of 0.06 out of 53.5 million kilometers corresponds to a coincidence of one part in a thousand. But given the full diameter of Jupiter\u2019s orbit around the Sun, this coincidence amounts to one part in 26,000.<\/p>\n If 3I\/ATLAS were to deposit devices within the Hill sphere of Jupiter on March 16, 2026, these devices would need to fire their engines in order to cancel out the high speed of 3I\/ATLAS relative to Jupiter, which is 65.9 kilometers per second. The escape speed from Jupiter\u2019s gravitational potential well at H=53.5 million kilometers is just 2.2 kilometers per second.<\/p>\n