What is the rare interstellar object made of? New observations give clues
A mysterious visitor from outside our solar system has once again captured global attention — and researchers from KTH Royal Institute of Technology played a key role in uncovering what it really is.
The object, known as 3I/ATLAS, is only the third confirmed interstellar object ever observed passing through our planetary neighbourhood. Since its discovery in July 2025, it has sparked a range of reactions, from scientific curiosity to online speculation about alien spacecraft.
Now, new observations using the MeerKAT radio telescope in South Africa have revealed a clear signal from hydroxyl (OH) molecules surrounding the object — a classic fingerprint of a comet. The findings were made by an international research team including Lorenz Roth and Mykola Ivchenko from the Space and Plasma Physics division at KTH.
“Detecting the hydroxyl signal is an important confirmation that 3I/ATLAS behaves like a comet, namely that the object contains some ice on the surface,” says Lorenz Roth, associate professor at KTH. The first two interstellar objects showed quite different characteristics - one was more like a rocky asteroid than an icy comet.
Rare opportunity to study an interstellar comet
When comets approach the Sun, solar radiation heats their icy surfaces, releasing water molecules. These break apart into hydrogen and hydroxyl, which can emit characteristic radio signals detectable from Earth.
MeerKAT observed 3I/ATLAS during several short “windows” when conditions were ideal. On 24 October, the telescope detected clear emissions in two specific radio frequencies — exactly where they should appear if the object is outgassing like a typical comet. Further observations on 4 and 6 November showed the signal disappearing and reappearing.
“This is a very small and faint object, so catching these signals at all is a technical achievement,” says Mykola Ivchenko, professor at KTH.
No signs of technological signals
Alongside the comet-focused observations, the Breakthrough Listen project analyzed the data to search for any narrowband radio signals — the kind associated with artificial, technological sources. None were found.
Strong standing in planetary research at KTH
The study showcases KTH’s broad research activities in space science in the solar system, from generation of polar lights on Earth to gas around an interplanetary object.
“This is exactly the type of research we aim to expand,” says Roth. “Interstellar objects offer a rare window into materials formed around other stars, and radio observations are key to understanding them.”
Press release from SARAO: South African telescope detects natural radio emission – and no signal of technological origin – from the interstellar visitor 3I/ATLAS
The study was led by researchers at the University of Cape Town, Rhodes University, SARAO, KTH, and the Breakthrough Listen initiative.
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