Space and Astronomy News for the 20th of September 2025

 Comet 3I/ATLAS: How rare are interstellar visitors?

"There's almost always one within the solar system."

The third known interstellar visitor to our Solar System, Comet 3I/ATLAS, is in the news at the moment, and there's going to be more updates as further observations are made by astronomers. We'll be doing a further deep-dive into this cosmic visitor in an upcoming BINTEL blog.

3I/ATLAS glowing green during the recent lunar eclipse. | Credit: Michael Jäger/Gerald Rhemann

The "3I" in this comet's name indicates it's the third interstellar object we've found in in the Solar System so far. Astronomers have conjectured that these comets and rocky bodies, travelling through the Milky Way too fast to be captured by stars they encounter, are likely quite numerous. Since the first interloper, 'Oumuamua, was found in 2017, the question has been, what else have we missed?

This issue was address at the Europlanet Science Congress (EPSC) and Division for Planetary Sciences (DPS) joint meeting, which was held in Helsinki last week. 

"These sorts of interstellar objects are the most common macroscopic objects in the galaxy," Chris Lintott, a professor of astrophysics at the University of Oxford, said during the meeting. "The fact that we've only found three of them is quite fun."

Many researchers think the number of interstellar objects found in the Solar System will jump dramatically from the current three once more powerful instrument such as the Vera C. Rubin Observatory commence extended and regular programs. 

The latest estimate by some astronomers this week including Chris Lintott is that interstellar objects in the Milky Way may number from a hundred million trillion to a staggering trillion trillion. This make them the most numerous type of body in the galaxy. In much the same way we now think that rogue planets, those not in set orbits around stars outnumber planets like those in our own Solar System, there might be vastly more comets and asteroids in interstellar space compared to those orbiting stars.

NASA’s Tally of Planets Outside Our Solar System Reaches 6,000

It's amazing to think that when the Hubble Space Telescope (HST) was launched in 1990, there were no confirmed planets around other stars. As far as we knew, the Earth and the other planets that make up the Solar System were unique in our galaxy. 

The number of confirmed exoplanets passed the 6,000 count this week and continues to rise. 

Since the first confirmed discovery of an exoplanet, or a planet outside our Solar System, in 1992* and the discovery of a planet around a regular star in 1995, the number has been rising steadily. Astronomers use a variety of techniques to find exoplanets, including wobble in their host stars, dips in the star's light as planets pass between the star and observers here on Earth and more. In a small handful of cases, we've been able to even directly image stars around other planets. 

A question we get asked now and then here at BINTEL is "can I see planets around other stars?" The answer to that is sadly, a firm no. 

If you'd like to check out the NASA Exoplanet Catalogue to keep up with the latest discoveries, visit it here.

Cheers,

Earl White

BINTEL

20th September 2025

*The earliest recorded evidence of an exoplanet was made in a 1917 using the 60 inch at Mt Wilson. A white dwarf star was found back then that had an unusual and unexplainable spectrum. In 2016 this was was found to be the result of an exoplanet being broken up by the star's gravity and material from its planet falling into the star causing the strange spectrum!