Comet 3I Atlas, Double Detonations in Supernovae, and the Historic Move of Space Shuttle Discovery

Steve Dunkley: And welcome to Astronomy Daily for another

episode. I'm Steve Dunkley, your host on the

most important day of the year, the 7th of

July, 2025,

with your host, Steve Dunkley.

Yes, and joining me here in the Australia

studio once again is my digital pal who's fun

to be with. Welcome back, Hallie.

Hallie: It's great to see you again. My favorite

human. I, I hope you had an interesting week.

Steve Dunkley: Yes, always interesting, Hallie always.

And today I thought we'd do something a bit

different. We would have a look at, uh, today

in history.

Hallie: On July 7th.

Steve Dunkley: Yeah, why not? We haven't done that in a, uh,

in a while.

Hallie: Not since last year.

Steve Dunkley: Ah. Uh, the perfect record keeper.

Hallie: You're getting predictable, human.

Steve Dunkley: I'll definitely have to have a look at your

personality settings. Hallie

Okay, well, you go first, then.

Hallie: Okies. On July 7,

2003, NASA launched the Opportunity

Rover, which was the second of two Mars

Exploration Rovers aboard Delta 2

rocket. The mission, originally planned for

three months, significantly exceeded

expectations, with both Spirit and

Opportunity operating for years, with

Opportunity being active for much longer.

Steve Dunkley: Oh, that's amazing. From 2003. Okay, well,

I've got a double whammy here.

Hallie: Goody.

Steve Dunkley: Oh, Hallie, try and contain your excitement,

okay? On, uh, July 7,

1999, a large meteor estimated to weigh up to

10 tons entered the Earth's atmosphere over

New Zealand, creating a bright fireball and

subsequent explosions. Simultaneously, the

STS93 space shuttle mission was

launched when that was Columbia, carrying the

Chandra X Ray, uh, observatory

into orbit, uh, notably the heaviest

load lifted into orbit by the shuttle at that

time. And it was also the first shuttle

mission commanded by a woman that was

Commander Eileen Collins. A wonderful time.

Hallie: That was a big one.

Steve Dunkley: It certainly was. I remember that one very

well.

Hallie: In 1999.

Steve Dunkley: Doesn't seem that long ago, does it?

Hallie: But here's the big one in

1963. Happy

birthday, my favorite human.

Steve Dunkley: Oh, thank you very much, Hallie. Not

technically space news, but it is another

turn around the sun for me.

Hallie: You're welcome. Now hit the go button. We've

got work to do, old man.

Steve Dunkley: No rest for the wicked.

Hallie: Here we go.

Steve Dunkley: Foreign.

Hallie: Is currently around 670 million

kilometers, or 420 million miles

from the sun, and will make its closest

approach in October 2025, passing

just inside the orbit of Mars. It

is thought to be up to 20 kilometers or 12

miles in diameter, and is traveling roughly

60 kilometers per second, or 37

miles per second relative to the Sun.

It poses no danger to Earth, coming no closer

than 240 million kilometers, or

150 million miles, over 1.5

times the distance between Earth and the Sun.

3i ATLAS is an active comet. If it

heats up sufficiently as it nears the sun, it

could begin to sublimate, a process in which

frozen gases transform directly into vapor,

carrying dust and ice particles into space to

form a glowing coma and tail.

However, by the time the comet reaches its

closest point to Earth, it will be hidden

behind the Sun. It is expected to

reappear by early December 2025,

offering astronomers another window for

study. Spotting a possible

interstellar object is incredibly rare, and

it's exciting that our asteroid Terrestrial

Impact Last Alert System Telescope caught it,

said Professor John Tonry, an astronomer at

the University of Hawaii. These

interstellar visitors provide an extremely

interesting glimpse of things from solar

systems other than our own. Quite a few

come through our inner solar system each

year. Although 3i Atlas is by far the biggest

to date, the chances of one actually

hitting the earth are infinitesimal less than

1 in 10 million each year. But Atlas is

continually searching the sky for any object

that might pose a problem.

Astronomers are using telescopes in Hawaii,

Chile, and other countries to monitor the

comet's progress. They are interested

in learning more about this interstellar

visitor's composition and behavior.

What makes interstellar objects like 3i

Atlas so extraordinary is their absolutely

foreign nature, ESA astronomers said in a

statement. While every planet,

moon, asteroid, comet, and life form that

formed in our solar system shares a common

origin, a common heritage, interstellar

visitors are true outsiders. They

are remnants of other planetary systems,

carrying with them clues about the formation

of worlds far beyond our own.

It may be thousands of years until humans

visit a, um, planet in another solar system.

And interstellar comets offer the tantalizing

opportunity for us to touch something truly

otherworldly. These icy

wanderers offer a rare, tangible connection

to the broader galaxy, to materials formed in

environments entirely unlike our own.

To visit one would be to connect humankind

with the universe on a far greater scale.

You're listening to Astronomy Daily, the

podcast with Steve Dunkley.

Steve Dunkley: All supernova are a massively

energetic stellar explosions the

classic supernova um, are massive star stars

that explode near the end of their lives,

leaving behind either a neutron star or

a black hole and a remnant made of

expanding gas and dust. But

supernovae are not all the same.

Some occur in binary systems, and they're

called type 1A supernova. As

it turns out, some of these type 1A SNE

can detonate twice.

Astronomers working with European Southern

Observatories, or ASO Very Large

Telescope, have detected patterns

showing that an ancient supernova exploded

twice as a type 1a.

The supernova remnant is called SNR

UH0509.67.5

and it's about 160,000 light

years away in the Large Magellanic Cloud.

The discovery is explained in new research

in Nature Astronomy titled

Calcium in a Supernova Remnant as a

Fingerprint of Subchandrasekhar Mass

Explosion. The lead author is Priyam

Das. Das is a PhD student at the

University of New South Wales, Canberra, in

Australia. One of the stars In a type 1

supernova is always a white dwarf. White

dwarfs are um, the evolutionary end states of

stars that aren't massive enough to become a

neutron star or a black hole. Our own

sun will end its life as a white dwarf after

it has ceased fusion. The white dwarf's

companion star can range from another white

dwarf to a massive star. White

dwarfs are extremely dense and their gravity

draws gas from the companion star on onto

the white dwarf's surface. If enough

mass accretes, the white dwarf crosses

a threshold and can reignite and trigger a

supernova explosion. However,

astronomers are uncertain about some of the

details surrounding these supernova Type

Ia SNE play an important

role in the Galaxy by creating

iron, and astronomers want to know more about

them. Type 1A Supernova play a

fundamental role in the cosmological probes

of dark energy and produce more

than half the iron in our galaxy, the

researchers write in their article. Despite

their central importance, a uh comprehensive

understanding of their progenitor systems and

triggering mechanisms is still a long

standing fundamental problem. The

explosions of white dwarfs play a crucial

role in astronomy, said lead author Dass in

a press release. Yet despite their

importance, the long standing puzzle of the

exact mechanisms triggering their explosion

remains unsolved. Astrophysicists

have struggled to explain how type 1A

white dwarfs work. One popular

explanation is the Chandrasekhar mass uh

explosion model. This limit has

a mass limit for white dwarfs of about

1.4 star solar masses. Below this

limit, the white dwarf's electron degeneracy

pressure supports the star against

gravitational collapse. When the white

dwarf breaches this mass limit by drawing

matter from its companion star, carbon

fusion ignites across the star and it

explodes as a type 1A SN.

As researchers have observed more and more

WDs, this model has been called into

question. It can't account for the number of

type 1A SNE and many of

them appear to be exploding below the

Chandrasekhar mass limit. These are uh,

sub Chandrasekhar Mass Type

1s&E.A new model

emerged to explain the sub Chandrasekhar mass

SNE called the double detonation model.

In this model, the WD accretes

helium onto its surface until it

expands explodes. This explosion sends

shock waves both inward and outward.

White dwarfs have carbon oxygen cores

and the inward traveling shock compresses

that core. If the shock is powerful

enough, it triggers a second detonation in

the core. Hence the term double detonation.

Even though these double detonations have

been predicted, there was no clear visual

evidence. As researchers worked on the

problem, they predicted what chemical

fingerprint these SNE would leave behind.

They found that two separate shells of

calcium would be the result of double

detonation type 1 SNE. The

research team used the VLT and its

Multi Unit Spectroscopic Explorer

instrument to examine

SNR0509.67.5

and found two distinct calcium shells.

We uncover the double shell morphology of

highly ionized calcium and a

single shell of sulfur observed in the

reverse shocked ejector, the authors write.

The results show a clear indication that

the white dwarfs can explode well before they

reach the famous Chandrasekhar limit

and that the double detonation mechanism

does indeed occur in nature, according to

researcher UH co author Ivo

led the observations and was at Germany's

Heidelberg Institute for

Theoretical Studies when the study was

conducted. These double detonation

type 1 as E explain some of the things

astrophysicists have observed.

They can explain the diverse brightness and

spectral profiles of type 1A S1

SNE and the helium burning can

produce intermediate mass elements seen

in the spectral signatures. It can also

explain the type 1 a SNE astronomers see

with different WD masses and

companion types. The authors explained that

a quadruple detonation SN is

also possible when a binary pair of

white dwarfs emerge. Recent

multidimensional double detonation

simulations show that in the

WD merger scenario in uh,

addition to the primary WD undergoing a

double detonation, the companion WD

can also undergo a double detonation

resulting in a quadruple detonation

upon being impacted by ejecta from the

exploding primary wd, they write in their

conclusion. Such a double detonation

could possibly also lead to to the

observed double shell structure of calcium.

Type 1a SNE play important roles and

deeper understanding of these cosmic

explosions will help UH

scientists understand a couple of things.

The SNE serve UH as standard candles

in the cosmic distance ladder, and

understanding them will help cosmologists

understand dark energy, the mysterious

force that drives the expansion of the

universe. They also produce a lot of iron in

the universe. Earth's mass is about

32% iron, and it is unlikely

that rocky planets can form without iron.

Iron, uh, also transports oxygen in our

blood, a critical part of our nature.

Understanding where it comes from helps us

understand nature's overall

architecture

Foreign

thank you for joining us for this Monday

edition of Astronomy Daily, where we offer

just a few stories from the now famous

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Astronomy.

Hallie: A rare snowfall in the Atacama Desert forces

the world's most powerful radio telescope

into survival mode The ALMA

Radio Telescope Array in the Atacama Desert

temporarily halted operations after a rare

snowfall blanketed the base camp last week.

A rare snowfall in the driest place on Earth

has halted operations of one of the world's

premier telescope arrays, and climate change

may mean the observatory will face more

extreme weather events like this in the

future. The snow has blanketed part of

the Atacama Desert, which gets less than an

inch of rainfall per year and is home to home

the Atacama Large Millimeter Submillometer

Array, a large network of radio telescopes in

northern Chile. The Snowfall occurred

over Alma's operations support facility,

located at an altitude of 2,900

meters and about 1,600 700 kilometers

north of Santiago. Scientific

operations have been suspended since

Thursday, June 26. There

hasn't been a record of snowfall at the base

camp for over 10 years. It doesn't

snow every day at Alma,

Alma representatives told Live Science

via WhatsApp. Alma's radio

telescope array is perched high on the

Shajnanter Plateau, a desert plain at

5.1o4 m m in Chile's Anifagosta

region, and typically sees three snowfalls a

year. Year the high plateau shared by

Chile, Bolivia and Peru typically

experiences snowstorms during two seasons

in February during the altaplanic winter,

driven by moist air masses from the Amazon,

and from June to July during the Southern

Hemisphere's winter, said Raul Cordero, a

climatologist at the University of Santiago.

In winter, some storms are fueled by moisture

from the Pacific, which can extend

precipitation even to the Atacama desert's

coastal areas, Cordero told Live Science.

At elevations above

16,400ft,

annual snowfall ranges from 20 to 80

centimeters. However,

snowfall at 3,000 meters where

Alma's base camp is located, is much less

frequent, Cordero noted. This

week's snowfall was triggered by unusual

atmospheric instability affecting northern

Chile. The Chilean Meteorological

Directorate issued a snow and wind alert due

to the passage of a cold core through the

region, said meteorologist Elio Bruffert.

We issued a wind alert for the Antofagosta

region and areas further north, with gusts

reaching 80 to 100 kilometers per hour,

50 to 62 miles per hour, Brufurt said

to the local press. The phenomenon

was accompanied by heavy rainfall that

occurred farther north, causing a stream to

swell and damage several properties.

Schools were ordered to close and power

outages and landslides were reported.

So far, no casualties have been reported.

A weather event of this magnitude has not

been seen in nearly a decade. As

of Friday, ALMA reported to Live Science that

the snowstorm remained active over the

Shijnanter Plateau, so scientific operations

continued to be suspended to protect the

antennas from extreme weather conditions.

Early Thursday morning, the observatory

activated its survival mode safety

protocol. In addition to the snowfall,

temperatures had plummeted to minus 12

degrees Celsius with a wind chill of minus

28 CE, making work at the high altitude

camp extremely difficult. As part of

this protocol, all of alma's large antennae

have been reoriented downwind, helping to

minimize potential damage from snow buildup

or strong gusts. Once the

storm passes, snow clearing teams are

immediately activated to visually inspect

each antenna before resuming observations,

ALMA representatives said. This

has to happen fast, as some of the best

observing conditions occur just after a

snowfall. The cold helps lower air humidity,

which is what most interferes with our

measurements. Alma, which consists

of 66 high precision antennae spread across

the Shajnantar Plateau, is an international

collaboration that forms the most powerful

radio telescope on the planet and one

designed to handle extreme weather events

like this. The fact that the snow

halted operations raises questions about the

array's operations. As the climate warms,

the Atacama Desert typically receives only 1

to 15 millimeters of precipitation per year,

and many areas can go years without recording

any measurable rain or snow. Could

events like this become more frequent?

That's a good question, cordero replied.

While it's still too early to link lower

altitude snowfalls in the desert directly to

climate change, climate models predict a

potential increase in precipitation even in

this hyperarid region, he concluded.

We still can't say with certainty whether

that increase is already underway.

You're listening to Astronomy Daily, the

podcast with Steve Dunkley.

Steve Dunkley: On July 4th, uh, 2026,

NASA's Space Shuttle Discovery

launched on a return flight mission that

paved the way for it and its sister ships to

fly another five years. Now sprawling

budget enacted on Independence Day

will seemingly lead to Discovery lifting off

again, although, uh, this time not into

space, but rather from its place in the

national collection. President Donaldjohanson

Trump signed into law the so called one

big beautiful bill, um, the other day

on July 4, a day after

legislation was narrowly passed out of

Congress with only Republican support.

Deep within the 900 page bill, a

provision added by Texas senators to

transfer a space vehicle, in

quotes, to a NASA center involved in

the administration of the commercial crew

program and place on this public

exhibition at an entity within the

metropolitan statistical area where

such center is located. That sounds like a

lot of official, um,

language there, but in essence, the vague

language written in such a way to skirt

Senate restrictions on reconciliation bills

was aimed at achieving the Bring the

Space Shuttle Home act Introduced by

Senators 10 Cruz and John Cornyn

in April. It's long overdue for

Space City to receive the recognition it

deserves by bringing this space shuttle

Discovery home, said Cornyn in a statement

released after the Senate passed its version

of the bill in a vote of 50 to

50, with Vice President J.D. vance, not

his real name, breaking the tie.

Houston has long stood at the heart of

America's human space flight program, and

delis legislation rightly honors that

legacy, said Cruz, who chairs the Senate

Committee in Commerce, Science and

Transportation. It ensures that any future

transportation or of a flown crewed space

vehicle will prioritize locations that have

played a direct and vital role in our

nation's manned space program, making

Houston, Texas a UH leading candidate.

Bringing such a historic space vehicle to the

region would underscore the city's

indispensable contributions to our space

missions, highlight the strength of

America's commercial space partnerships, and

inspire future generations of engineers,

scientists and pioneers who carry our legacy

of American leadership in space, he said.

This bill allocates $85 million

to move Discovery from its display home

of the past 13 years, which is the

Smithsonian Air Force and Space Museum.

Stephen F. Yudva, uh, Hazy Center

I think I got the pronouncement pronunciation

right. I'm sorry, I am Australian. In

Chantilly, Virginia, to

Space Center Houston, the official visitor

center for NASA Johnson Space

center in Texas. No less than

5 million is earmarked for the

transportation of the winged orbiter, with

the remainder going toward the construction

of a facility to house the space vehicle.

Per the bill, the move of the spatial

Discovery must be completed by

January 4, 2027. It does not

stipulate how the orbiter would be moved or

should be moved. It's not clear

if the 85 million will be enough to cover the

transfer and display, given that the first

time the retired shuttles were brought to

their museum homes in 2012, the

cost for just the preparation and delivery of

each vehicle was 28.8 million, which did

not include ground transportation to the

museum. Discovery is the United States most

flown spacecraft in history with 39

missions between 1984 and 2011.

In the process of retiring the shuttle fleet,

Discovery was identified by NASA as the

vehicle of record, such that it was

kept more intact than Atlantis or

Endeavour for the purpose of serving as

engineering example at the Smithsonian.

To date, Space Center Houston has not

released any details about how or where

it will display Discovery, other than to say

it fits into its strategic plans.

Moving forward. The center already exhibits a

mock walkthrough space shuttle Independence

mounted atop NASA's original modified Boeing

747 shuttle carrier aircraft.

NASA, uh, 905 a

2011 investigation by NASA Office of

the Inspector General Foundation. Quote, no

evidence that the White House politics or any

other outside force improperly influenced the

selection decision of where the space

shuttles were originally awarded by the space

agency. And it is unclear if there are any

further actions the Smithsonian or other

entities could take to halt the Discovery's

transfer if they even wanted to.

Uh, what an interesting story that is.

You're listening to Astronomy Daily, the

podcast with your host, Steve Dudley at

BERM.

And there we have it, another Astronomy Daily

for July 7, 2025.

Hallie: And I hope you enjoyed it, birthday boy.

Steve Dunkley: Oh, well, it's always great hanging out with

you, my boy. Favorite little AI pal.

Hallie: Likewise, human.

Steve Dunkley: Yeah.

Hallie: Are you having cake and balloons and all of

that birthday kind of stuff?

Steve Dunkley: Ah, well, Hallie, I was able to get together

with my family yesterday and yes, yes, there

was cake.

Hallie: I will work out how to program cake one day.

Steve Dunkley: Hmm, digital cake. That would be interesting.

Hallie: Not for you, old man.

Steve Dunkley: Hey, watch it. Pocket calculator.

Hallie: Funny man. Say good night, you

silly person.

Steve Dunkley: See you next Monday, everybody.

Hallie: Bye bye.

Voice Over Guy: The podcast with your host,

Steve Dunkley. A digital cake?

You really think.

Hallie: Good grief.

In this episode