By Anne W. Semmes
July of 2025 became historic with the July 1 spotting of perhaps the world’s oldest comet having arrived at great velocity from outside our solar system. It’s also the third interstellar object (ISO) discovered since 2017. It’s been named 3I/ATLAS by NASA having been seen by one of NASA’s five world-wide telescopes in its Asteroid Terrestrial-impact Last Alert System, or ATLAS, that watches for space rocks that might be on a collision course with Earth.
But NASA has stated that 3I/ATLAS “poses no threat to Earth and will remain at a distance of 160 million miles.” Time to reach out to my astronomer stepbrother Michael Snowden, based in Christchurch, New Zealand. Michael had, three years ago, described for this newspaper five of the most important astronomy projects around the world.
So, what grabs Michael about 3I/ATLAS? “You’re looking at material from very early in the universe!” Yes, older than our 4.6 billion years old solar system – with some saying the comet’s velocity could date it back 7 billion years. “What’s exciting is almost certainly it was twisting around another star and got kicked out of its home turf, sailed off in space and finally got sucked into our solar system by gravity from the sun. And it comes in this remarkable hyperbolic orbit. And real interesting to me is that it’s going so close to Mars.”
And located on Mars are those rovers placed there by us. “They’re designed to look at the ground and look at the soil of Mars and the atmosphere,” he said, but he’d recently seen an image of a starfield taken by the rover Perseverance. “Those rovers are able to shoot stars!” So, another avenue to capture images in deep space. And back on Earth, in the Chilean Andes the extraordinary Vera Rubin Telescope is debuting.
Vera Rubin Telescope role
Michael cited the Vera Rubin telescope as having “the world’s largest and most powerful camera ever created…it weighs like a ton and goes at the top end of the telescope.” But he noted that telescope “didn’t have a lot of additional adjustments” completed thus that comet was not spotted. That camera recently had its “first light” and had taken the “first images that were remarkably good…and one of the things that popped out were all these asteroids running about.” Yes, that Rubin telescope found 2,104 asteroids in just a few days.
It is those Chilean Andes, the lower mountains, the desert, and the stable atmosphere that make that location so sought after by European and American astronomers. Indeed, it was that Chile-based NASA telescope that found 3I/ATLAS on July 1.
Michael also cited the island of Hawaii as “probably the best in the world for its stable atmosphere, with its volcano very rounded.” It was there that the first rogue interstellar comet was discovered called Oumuamua, spotted with its cigar shape in 2017, and the second comet 2I/Borisov was discovered in 2019 by the MARGO Observatory in Ukraine.
Comets up close and personal
Michael then described the differences between comets and asteroids as seen from those telescope images. “I’m speaking from the last 24 hours as things are changing so fast. The Hubble Space Telescope image is the best…You’re seeing a round image which is slightly blurred and with a little bit of dusty elongation… We don’t know if it’s a dusty tail or if it’s gas that’s spewing out.” But “we now know that if it has a tail and something is spewing out, it’s a comet.” Whereas if it’s an asteroid, “They’re just big rocks.”
And what about the size of a comet? “People are scratching their head a bit about the size. I don’t think they really know anything about the size or the age.” Some reports say perhaps “12 miles wide” … “bigger than the space rock that wiped out the non-avian dinosaurs.” “We need more time. Probably we’ll get a pretty good measurement of the size at some point.”
Michael has a speculation. “The fact that we’ve discovered three comets in such a short period of time suggests to me that once the Vera Rubin telescope with its massive camera is underway, it’ll be finding comets all over the place mixed in with those 2,000 plus asteroids.”
But how long will comet 3I/ATLAS be in sight before it returns to the cosmos from whence it came? Its closest path to the sun will be the end of October. “And when it goes behind the sun,” said Michael, “that means a period of blank time where we can look, but it would come out on the other side, and we can resume work on it.” And come December it will be the closest to earth, at 160 million miles.
Following the path of 3I/ATLAS
During those comet visiting days Michael will be on top of developments and discoveries while attending a weekly seminar at the University of Canterbury in Christchurch, run by planetary astronomer Michele Bannister, Senior Lecturer Above the Bar in the School of Physical & Chemical Sciences. Bannister engages her seminar students individually to share “something interesting” they’ve learned of in our solar system. “They know better than I know what’s going on,” noted Michael, “because they’re all tuned in.” Count in undergrads, grads getting their master’s or doctorate, “one or two professional scientists, and one retired astronomer, me.”
The challenge these students face, Michael shared, “is the quantity of data that’s coming out of those telescopes on a nightly basis.” So, he’s hearing from those students their need to develop technology to examine that data, and “some are working on theses that develop the technology to observe…examine…interpret the data.”
It is astronomers, Michael noted, who have been leading the world “for centuries” in examining the technology of images. “Even the military comes to astronomers for advice on the surveillance of satellites…on any kind of imaging technology, on understanding what our pictures are telling us.” And AI he said is going to “play a big role in the assessment of these images. The students are already working right now before the telescopes are even finished to develop the technology for doing that.”
But now one of the “massive headaches” facing those powerful telescopes’ revelatory images are the smears coming from the growing number of satellites produced by SpaceX and others “because they put streaks across the images. They just saturate the telescope images. But students are working on techniques to deal with those streaks, and that’s a whole story in itself.”
Postscript: The late science fiction writer Arthur C. Clarke’s 1973 novel “Rendezvous with Rama” that addresses a sizeable interstellar starship of intelligent origin entering our solar system will be a film shared Michael Snowden, old time friend of Clarke’s.
