Stellar Surprises; The Interstellar Comet 3I ATLAS and Upcoming Comet LEMMON

0:00 Avery: Welcome to Astronomy Daily. I'm Avery, and

0:03 as always, I'm joined by my co host, Anna.

0:05 We're here to bring you the latest and most

0:07 fascinating news from the cosmos. Breaking

0:10 down complex discoveries into conversations

0:12 you'd have with your space obsessed friends

0:14 over coffee.

0:15 Anna: Hey, everyone, I'm Anna. And wow, do

0:18 we have an incredible lineup for you today.

0:20 We're talking about not one, but two amazing

0:23 comets making headlines right now. Plus some

0:25 groundbreaking observations from the James

0:27 Webb Space Telescope that are helping us

0:30 understand what it's like on pot. Potentially

0:32 habitable worlds beyond our solar system.

0:34 Avery: That's right. And what makes today's, uh,

0:36 episode especially exciting is that we're

0:38 covering some truly rare cosmic visitors.

0:41 Anna, when I first read about our first story

0:44 today about interstellar comet

0:46 3I ATLAS, I had to

0:49 do a double take. We're talking about only

0:52 the third known comet from outside

0:54 our solar system.

0:56 Anna: I know, right? It's absolutely mind blowing.

0:59 Let's dive right into this because the Gemini

1:02 South Telescope just captured some stunning

1:05 new images of three I ATLAS. And what they're

1:07 showing us is fascinating. This interstellar

1:10 visitor was discovered on July 1,

1:13 2025 by the Atlas survey in Chile. And

1:16 it's becoming increasingly active as it

1:18 travels through our inner solar system.

1:20 Avery: So, Anna, help me understand this. When we

1:22 say it's becoming more active, what exactly

1:24 are we seeing?

1:26 Anna: Great question. The latest Observations show

1:28 that 3i ATLAS is developing a

1:31 prominent tail and a glowing coma.

1:34 That's the fuzzy atmosphere around the

1:36 comet's nucleus. As it gets closer to our

1:38 sun, the solar radiation is heating up the

1:41 comet's surface, causing dust and ice to

1:43 sublimate and create this beautiful glowing

1:45 display. What's really remarkable is that the

1:48 composition appears to be very similar to

1:50 comets from our own solar system.

1:53 Avery: That similarity in composition is what really

1:55 gets me excited because it suggests that

1:58 comet formation processes might be remarkably

2:01 consistent across different star systems.

2:03 I mean, think about it. This object formed

2:05 around a, uh, completely different star,

2:08 potentially billions of years ago, yet it's

2:11 made of the same basic materials as comets we

2:13 see regularly in our own neighborhood.

2:16 Anna: Exactly. And speaking of age, Avery, here's

2:19 something that blew my mind. Scientists think

2:21 this could be the oldest comet we've ever

2:23 observed. We're potentially looking at a

2:26 relic from the very early universe, a time

2:28 capsule that's been wandering through

2:30 interstellar space for eons before finally

2:33 making its way into our solar system.

2:35 Avery: That's incredible. And it's not just passing

2:38 through either. 3i ATLAS is going to make

2:40 close passes by The Sun, Earth, Mars, and

2:43 Jupiter. This gives astronomers an

2:45 unprecedented opportunity to study an

2:47 interstellar object up close as it interacts

2:50 with our solar system.

2:52 Anna: Those close approaches are going to provide

2:54 us with so much valuable data. Every time we

2:57 get a chance to study one of these

2:58 interstellar visitors, we learn something new

3:00 about how planetary systems form and evolve

3:03 throughout the galaxy.

3:04 Now, speaking of comets making news, we have

3:07 another fascinating visitor to talk about.

3:09 And this one might actually be visible to the

3:11 naked eye.

3:12 Avery: Oh, yes. Comet C 2025

3:14 A6, also known as Comet

3:17 LEMMON And this is the kind of story that

3:19 gets amateur astronomers really excited,

3:22 because there's a chance chance that people

3:25 might be able to step outside in October and

3:27 see this comet with their own eyes.

3:30 Anna: That's right. This comet was discovered by

3:32 the Mount Lemmon survey in Arizona, and it's

3:35 approaching Earth right now. The closest

3:37 approach will be on October 20th, when it'll

3:39 pass by at about 55.41 million

3:42 miles away. Now, that might sound far, but

3:45 in cosmic terms, that's practically next

3:47 door.

3:48 Avery: And here's where it gets interesting for

3:50 skywatchers. The comet will reach perihelion,

3:53 its closest point to the sun, on November.

3:56 But the brightness predictions are all over

3:59 the place, which honestly makes this even

4:01 more exciting because we're not quite sure

4:03 what we're going to get exactly.

4:05 Anna: Some predictions suggest it could reach

4:08 magnitude 4 to + 5,

4:10 which would make it easily visible to the

4:13 naked eye, even from moderately light

4:15 polluted areas. But other estimates

4:18 put it at magnitude 7.3,

4:22 which would require binoculars or a small

4:24 telescope to see clearly.

4:26 Avery: The uncertainty is part of what

4:28 makes comet watching so thrilling. Comets

4:31 are notoriously unpredictable. They can

4:33 suddenly brighten dramatically, or

4:36 sometimes they just fizzle out. For Comet

4:39 Lemmon, the best viewing opportunities look

4:41 like they'll be in early October. And

4:43 starting October 12, it should be visible in

4:46 the evening sky.

4:47 Anna: And here's a fun detail for anyone planning

4:50 to observe it. Comet LEMMON is expected

4:53 to display a greenish color, which is

4:55 likely caused by dicarbon molecules in its

4:58 coma. That green glow is actually a

5:01 pretty common feature in comets, and it

5:04 creates this beautiful, otherworldly

5:06 appearance against the night sky.

5:08 Avery: What I find fascinating about this comet

5:11 is its orbital period. It's

5:13 approximately

5:14 1,350 years.

5:17 But here's the kicker. That period has

5:20 actually been shortened due to an encounter

5:22 with Jupiter. It's yet another

5:25 example of how the giant planets in our solar

5:27 system act as gravitational shepherds,

5:30 influencing the paths of these cosmic

5:33 wanderers.

5:34 Anna: Jupiter really is the heavyweight champion of

5:36 our solar system when it Comes to altering

5:38 orbits.

5:40 Now let's shift gears from these relatively

5:42 nearby visitors to something much

5:45 distant but equally fascinating. The

5:48 the James Webb Space Telescope has been

5:50 studying Trappist1e, an earth

5:53 sized planet in the habitable zone around a

5:56 red dwarf star about 40 light years

5:58 away.

5:59 Avery: The Trappist 1 system has been on

6:02 everyone's radar since its discovery because

6:05 it has seven Earth sized planets and

6:07 several of them orbit in the habitable zone

6:10 where liquid water could potentially exist on

6:13 the surface. Trappist1e

6:15 is particularly interesting because it's

6:18 right in the middle of that Goldilocks zone.

6:22 Anna: Right. And what JWST has been doing

6:24 is observing transits, basically

6:27 watching as the planet passes in front of its

6:30 host star. From our perspective, based on the

6:33 first four transit observations, the results

6:36 are both revealing and somewhat

6:38 disappointing for those hoping for signs of a

6:41 thick, potentially life supporting

6:43 atmosphere.

6:44 Avery: So what did they find, Anna? Uh, I, um, know

6:47 the results suggest the planet likely lost

6:49 its primary atmosphere, but can you break

6:52 that down for us?

6:53 Anna: Sure. The main finding is that

6:55 Trappist1e has probably lost its primary

6:58 atmosphere due to stellar flaring from its

7:01 red dwarf host star. Red dwarfs are

7:03 notorious for being very active, especially

7:06 when they're young, producing intense

7:09 radiation and particle bombardment that can

7:11 strip away planetary atmospheres.

7:14 JWST didn't detect the thick

7:16 hydrogen atmosphere that some models might

7:19 have predicted was present.

7:21 Avery: But here's the thing, and this is why

7:24 I love science. The results don't completely

7:26 rule out the possibility of a secondary

7:29 atmosphere. Right. There could still be an

7:31 atmosphere that formed after the primary one

7:34 was stripped away.

7:35 Anna: Absolutely. And in fact, there are some

7:38 intriguing hints in the data. The

7:40 observations suggest there might be trace

7:43 amounts of methane in what could be a, uh,

7:45 nitrogen rich atmosphere. Now,

7:48 methane in an atmosphere is particularly

7:50 interesting because it can be produced by

7:53 both geological and biological

7:55 processes, Though we.

7:58 Avery: Have to be careful not to get too excited

8:00 about the biological implications just yet.

8:03 The challenge with these observations is that

8:06 they're complicated by stellar contamination

8:08 from the red dwarf's flaring activity. When

8:11 the star flares, it can create signals that,

8:14 uh, mimic or mask atmospheric

8:17 features.

8:17 Anna: Exactly. And that's why the

8:19 JWST team has developed a really

8:22 clever technique to deal with this problem.

8:25 They're planning 15 more observations

8:28 and they're going to compare Trappist 1e to,

8:31 with its neighboring planet, Trappist 1b,

8:34 to filter out those stellar artifacts.

8:37 By observing both planets, they can better

8:40 separate the star's contribution from the

8:43 actual planetary atmospheric signals.

8:46 Avery: That's brilliant. It's like having A control

8:48 group in the Same star system, Trappist 1b,

8:51 orbits much closer to the star, so it's

8:54 definitely had its atmosphere stripped away,

8:56 making it the perfect reference point for

8:58 understanding what signals are coming from

9:00 the star versus the planet we're actually

9:03 interested in.

9:04 Anna: And this technique could revolutionize how

9:06 we study exoplanet atmospheres around active

9:09 stars. Red dwarfs make up about

9:12 75% of all stars in our

9:15 galaxy, and many potentially habitable

9:17 exoplanets orbit these stars. So

9:20 figuring out how to reliably detect

9:23 atmospheres around them is crucial for

9:25 understanding habitability throughout the

9:28 cosmos.

9:29 Avery: Speaking of keeping our eyes on space

9:30 activity, Anna, um, we should definitely tell

9:33 our listeners about this weekend's launch

9:34 activity. There's a really interesting SpaceX

9:37 mission coming up that I think will be worth

9:39 watching.

9:40 Anna: Oh, yes, the CRS

9:42 NG23 mission. This one's

9:44 launching on Sunday, September 14th at

9:47 exactly 8 hours, 11 minutes and 49 seconds PM

9:50 Eastern Time from Cape Canaveral. What makes

9:53 this launch particularly interesting is that

9:55 it's using a Northrop Grumman style Cygnus

9:58 XL spacecraft. That's the stretched

10:01 version with significantly more cargo

10:03 capacity.

10:04 Avery: Right. And that XL designation isn't just

10:07 marketing. We're talking about a spacecraft

10:09 that can carry up to 1,300kg more mass

10:12 than the previous Cygnus versions. That's a

10:14 substantial increase in capability, which

10:17 means more supplies, experiments, and

10:19 equipment heading to the International Space

10:21 Station crew.

10:22 Anna: And there's actually a bit of a story behind

10:24 this mission. Avery to this Cygnus is

10:27 stepping in to replace the NG22

10:30 spacecraft that was damaged in transit.

10:33 The space industry really shows its

10:35 resilience in moments like these. When one

10:38 spacecraft can't make it, there's always a

10:40 backup plan. This particular Cygnus

10:43 will be named after William Willie C.

10:46 McCool, the naval aviator and

10:48 astronaut.

10:50 Avery: What I find fascinating about this mission is

10:52 the booster story. SpaceX is using

10:54 B1094 and this will be its fourth flight.

10:57 Another example of how routine booster reuse

11:00 has become. But here's what makes it even

11:02 more interesting for viewers. This booster is

11:05 going to perform a return to launch site

11:07 landing at landing zone 2. Which means if

11:10 you're watching the launch, you might

11:12 actually get to see the landing burns and

11:14 touchdown as well.

11:15 Anna: I love those double features. Launch

11:18 and landing. And speaking of international

11:21 collaboration, it's worth mentioning that

11:23 this Cygnus was built by Thalis Alenia

11:26 Space, with facilities in both France and

11:29 Italy. It's always amazing to see how these

11:32 cargo missions represent this incredible

11:35 global effort to keep the International Space

11:37 Station supplied and operational.

11:40 Avery: So if you're free Sunday evening around

11:41 8:11pm Eastern, it's definitely worth

11:44 stepping outside or tuning in to the

11:46 livestream. There's something special about

11:48 watching these routine supply missions. They

11:50 remind us that we literally have people

11:52 living and working in space right now, and

11:55 missions like this keep that incredible

11:57 achievement going. You know Anna, what

11:59 strikes me about all of these stories is how

12:02 they represent different scales of

12:03 exploration. From interstellar visitors in

12:06 our own solar system to naked eye comets we

12:09 can observe from our backyards to detailed

12:11 atmospheric analysis of worlds dozens of

12:14 light years away, it's this incredible range

12:16 of astronomical discovery happening all at

12:19 once.

12:19 Anna: That's such a great point. And what I love is

12:22 how each discovery builds on our

12:24 understanding of the bigger picture. Whether

12:27 it's learning that interstellar comets have

12:29 similar compositions to our local ones,

12:32 or figuring out how to detect atmospheres

12:35 around distant worlds, every observation

12:37 helps us understand our place in the universe

12:41 a little bit better.

12:42 Avery: And for our listeners who might be inspired

12:44 by today's comet stories, October is

12:47 shaping up to be a fantastic month for

12:49 skywatching. Whether Comet LEMMON reaches

12:52 naked eye, visibility or requires

12:54 binoculars, it's going to be worth looking

12:57 for. There's something magical about seeing

12:59 these ancient wanderers with your own eyes.

13:02 Anna: Absolutely. And remember, even if you need

13:05 binoculars to see Comet LEMMON clearly,

13:08 you'll still be looking at something that

13:10 last visited our inner solar system over a

13:13 thousand years ago ago. That's perspective

13:15 that never gets old.

13:17 Avery: Thanks for joining us on today's Journey

13:19 through the Cosmos, everyone. I'm Avery

13:21 alongside Anna, and we'll be back soon with

13:23 more fascinating discoveries from the

13:25 universe. Until then, keep looking up. And

13:28 remember, every clear night is an opportunity

13:31 to connect with the cosmos.

13:33 Anna: Thanks for listening to Astronomy Daily.

13:35 Whether you're planning to hunt for Comet

13:37 Lemmon in October, or just marveling at the

13:40 fact that we can study the atmospheres of

13:42 worlds light years away from, remember that

13:44 we're living in an incredible age of cosmic

13:47 discovery. Clear skies everyone, and keep

13:50 looking up.