On the first of July, an Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope in Chile discovered a celestial body hurtling through our solar system. Astronomical review of prior sky images enabled the creation of an early path projection which showed that the body was expected to pass Mars and Jupiter. As the third recognized interstellar object entering the sun’s gravitational domain, this body has been labeled 3i/ATLAS in reference to the credited institute.
3i/ATLAS travels near the ecliptic in a retrograde hyperbolic trajectory at over sixty kilometers per second – about six times earth escape velocity and over twice the speed that the earth orbits the sun. Despite being invisible to the unaided eye, its fast approach and unique chemical characteristics have caught popular attention.
In August, Webb photographed 3i/ATLAS in infrared (i.e., electromagnetic wavelengths longer than visible light). Two years ago, NASA dispatched Psyche, an eponymous probe, towards this metal-rich asteroid in order to conduct spectroscopic measurements. And just this past September, NASA began to train its imagers on 3i/ATLAS. Meantime, 3i/ATLAS brightened enormously and changed color as the sun’s energy intensified.
On 03 October, 3i/ATLAS made its closest Martian approach. During this flyby, the Mars Reconnaissance Orbiter and Mars Atmospheric and Volatile Evolution (MAVEN) probe both photographed 3i/ATLAS, the latter using ultraviolet spectroscopy. In mid-October, the joint NASA and European Solar and Heliosphere Observatory (SoHO) that is traveling in solar orbit employed repeated exposures to capture images of 3i/ATLAS.
The comet’s perihelion (closest position to the sun) occurred 29 October, with earth being on the opposite side. Nonetheless, the Martian orbiters revealed enormous increases in brightness as well as color changes during that interval. On 19 December, 3i/ATLAS will reach earth’s closest approach at 1.80 astronomical units (AU or equivalent distance ratios of earth to sun). As it approaches, in addition to the Vera C. Rubin terrestrial observatory in Chile, orbiting telescopes Hubble and Webb will also be able to investigate with additional imagery.
Next 16 March, 3i/ATLAS will reach its closest approach to Jupiter. Unfortunately, Juno remains the only probe in that vicinity, and its ongoing operation seems uncertain. NASA’s Europa Clipper and Europe’s Jupiter Icy Moons Explorer do not reach the Jovian satellites until respectively early 2030 and mid-2031 – long after this comet’s departure from our planetary neighborhood.
Closer to home, a meteor exploded near Papua New Guinea almost a dozen years ago, leaving hundreds of tiny spherules. According to an analysis report authored by Avi Loeb at Harvard, its peculiar chemical composition offers another potential candidate for arrival from an interstellar cradle.
The coma of dust surrounding 3i/ATLAS extends about two earth diameters. The sun’s radiation causes comets in the vicinity to release volatile materials, thereby producing an extended dust tail pushed by solar particle wind, and sometimes also plumes of sublime ejecta. The cloud around 3i/ATLAS emanates from a central core estimated at less than half the size of Halley’s comet (or about one quarter the length of Manhattan).
Typical comets in elliptical orbits around the sun possess extensive water ice, and after repeated solar approaches have lost much of volatile mass to produce only modest tails. By contrast, and as revealed by Webb, 3i/ATLAS releases far more carbon-oxide compounds and exhibits plumes in multiple directions.
Most observers interpret this rapidly traveling object as an untypical comet from elsewhere in our galaxy and estimate that it is possibly older than our sun. A few specialists by contrast, and most notably Professor Loeb again, speculate an artificial origin of 3i/ATLAS, citing anomalies such as thrust from plumes that adjust its Jupiter approach near the null intersection of Jovian and solar gravitational influences. Loeb envisions a potential release of some non-natural “device” from the core during its flyby and proposes diverting the Juno probe for closer inspection.
For what it’s worth, the transit of 3i/ATLAS will be so distant and momentary to preclude definitive determination with current instrumentation, although the comet consensus is expected to prevail. Perhaps in the near future, another such object will venture into our proximity which will allow us to obtain a more complete glimpse of our neighboring stellar composition and confirm the particular sources of our mysterious visitors from beyond.
Photo Credit- Popular Science and NASA.
The plume directionality you mentioned is actually the most interesting part. Typical comets degas pretty predictably based on solar heating, but this thing throwing jets in multiple directions near the Lagrange point does feel weird. That said, Loeb's artificial origin theory needs way more evidence before it can hold water. Still, the fact that we can track something this small at such speed across interstellar distances is pretty incredible.
Why would an alien interstellar spacecraft look like a comet?