14/11/2025
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Since comet 3I/ATLAS, the third identified interstellar object, was found on 1 July 2025, astronomers worldwide have labored to foretell its trajectory. ESA has now improved the comet’s predicted location by an element of 10, due to the revolutionary use of statement knowledge from our ExoMars Hint Gasoline Orbiter (TGO) spacecraft orbiting Mars.
By with the ability to use Mars-based knowledge for an uncommon statement, we discovered extra in regards to the interstellar comet’s path by means of our Photo voltaic System in a invaluable take a look at case for planetary defence, despite the fact that 3I/ATLAS doesn’t pose any hazard.
Special approach from Mars unlocks precision
Till September, determining the situation and trajectory of 3I/ATLAS relied on Earth-based telescopes. Then between 1 and seven October, ESA’s ExoMars TGO turned its eyes in direction of the interstellar comet from its orbit round Mars. The comet handed comparatively near Mars, approaching to about 29 million km throughout its closest section on 3 October (extra on the observations).
The Mars probe bought about ten occasions nearer to 3I/ATLAS than telescopes on Earth and it noticed the comet from a brand new viewing angle. The triangulation of its knowledge with knowledge from Earth helped to make the comet’s predicted path rather more correct.
Whereas the scientists initially anticipated a modest enchancment, the end result was a formidable ten-fold leap in accuracy, decreasing the uncertainty of the item’s location.
As a result of 3I/ATLAS is passing by means of our Photo voltaic System quick, travelling with speeds as much as 250 000 km/h, it can quickly vanish into interstellar house, by no means to return. The improved trajectory permits astronomers to goal their devices with confidence, enabling extra detailed science of the third interstellar object ever detected.
From Mars knowledge to correct predictions
It was a problem to make use of the Mars orbiter’s knowledge to refine an interstellar comet’s path by means of house. The CaSSIS instrument was designed to level in direction of the close by martian floor and have a look at it in excessive decision. This time, the digital camera was aimed on the skies above Mars to catch the tiny, distant 3I/ATLAS sweeping by throughout a starry backdrop.
The astronomers within the planetary defence workforce at ESA’s Close to-Earth Object Coordination Centre, used to figuring out the trajectories of asteroids and comets, needed to account for the spacecraft’s particular location.
Often, trajectory observations are constituted of mounted observatories on Earth, and infrequently from a spacecraft in near-Earth orbit, just like the NASA/ESA Hubble Area Telescope or NASA/ESA/CSA James Webb Area Telescope. The astronomers are well-practiced in contemplating their location as they decide the long run places of objects, known as ephemeris.
This time, the ephemeris of 3I/ATLAS, and specifically the prediction’s precision, trusted accounting for the precise location of ExoMars TGO: at Mars and in a quick orbit round it. It required working collectively in a mixed effort by a number of ESA groups and companions, from flight dynamics to science and instrument groups. Challenges and subtleties which are normally negligible, needed to be tackled to cut back the margins as a lot as doable, in an effort to obtain the best accuracy doable.
The resulting data on comet 3I/ATLAS is the primary time that astrometric measurements from a spacecraft orbiting one other planet have been formally submitted and accepted into the Minor Planet Center (MPC) database. The database acts as a central clearing home for asteroid and comet observations, streamlining knowledge collected by totally different telescopes, radar stations and spacecraft.
A take a look at case for planetary defence
Though 3I/ATLAS poses no risk, it was a invaluable train for planetary defence. ESA routinely screens near-Earth asteroids and comets, calculating orbits to offer warnings if required. As this ‘rehearsal’ with 3I/ATLAS reveals, it may be helpful to triangulate knowledge from Earth with observations from a second location in house. A spacecraft may additionally occur to be nearer to an object, including much more worth.
Practising with spacecraft knowledge past Earth orbit hones vital expertise and demonstrates the worth of leveraging sources not designed for asteroid detection, boosting readiness in case of a risk.
What’s subsequent?
The comet is at the moment being noticed with our Jupiter Icy Moons Explorer (Juice). Although Juice is farther from 3I/ATLAS than the Mars orbiters have been final month, it’s seeing the comet simply after its closest method to the Solar, when it’s in a extra energetic state. We don’t anticipate to obtain knowledge from Juice’s observations till February 2026 – discover out why in our FAQs.
We must always not solely depend on spacecraft hopefully being within the neighborhood of hard-to-observe objects which may pose a risk. Due to this fact, ESA is making ready the Neomir mission, to cowl the identified blind spot that the Solar causes for asteroid observations, its shiny glow outshining the faint glimmer of an asteroid or comet. Neomir can be positioned between the Solar and Earth to detect near-Earth objects coming from the Solar’s route at the very least three weeks upfront of potential Earth affect.
Icy wanderers reminiscent of 3I/ATLAS supply a uncommon, tangible connection to the broader galaxy. To really go to one would join humankind with the Universe on a far larger scale. ESA is making ready the Comet Interceptor mission that may be taught extra a couple of comet – with luck, it simply could be an interstellar one.
