Astronomers discover 3I/ATLAS – Third interstellar object to visit Solar System

This one is coming in fast, it has an eccentricity of over 6 with the current fits. For point of reference, 1I and 2I have eccentricities of 1.2 and 3.3.

Right now it is mostly just a point on the sky, it is difficult to tell if it is active (like a comet) yet. If it is not active, IE: asteroid like, then the current observations put it somewhere between 8-22km in diameter (this depends on the albedo of the surface). From what we know, we would expect it to likely be made up of darker material meaning given that range of diameters it is more likely to be on the larger end. However if it is active, then the dust coming off can make it appear much larger than it is. As it comes in closer to the sun and starts to warm up it may become active (or more active if its already doing stuff).

It will not pass particularly close to any planet. It will be closest to the sun just before Halloween this year at 1.35 au, moving at 68 km/s (earth orbits at 29-30 km/s). It is also retrograde (IE, it is moving in the opposite direction of planetary motion), for an interstellar object this is basically random chance that this is the case.

Link to an orbit viewer: https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=3I&vi...

The next couple of weeks will be interesting for a bunch of people I know.

Source: Working on my PhD in orbital dynamics and formerly wrote the asteroid simulation code used on several NASA missions: https://github.com/dahlend/kete

What planets is it passing between?

It is inside jupiter's orbit now, it will come inside Mars for a time. It is almost on the plane of the solar system, not very inclined.

I linked an orbit viewer above if you want to look.

> It is almost on the plane of the solar system, not very inclined.

Is this also random chance or is there a reason why it's so close to the plane of the solar system?

It is also a factor of where our surveys look on the sky. A lot of asteroid surveys have biases to look at the plane of our solar system (since this is where a lot of asteroids are).

It is probably random chance, however there may be some biases from where they come from on the sky (I know people who work on that, but I don't know much about it).

N=3 does not provide very robust statistics yet, give us another decade or two.

Good question, especially given the plane of our solar system is almost orthogonal to the greater plane of the Milky Way galaxy that contains us.

From the simulation you linked looks like it is passing closeish to the Mars... but I do know that space is big. However, I am curious of what would happen if an object of this magnitude hit mars at 90km/s.

I would recommend staying on Earth...

Assuming it’s at the upper range of the size estimate above, and of average rocky density, the kinetic energy of the impact would be something like a 10 billion megaton nuke.

If we could steer it to hit one of Mars’s poles, it might do a bit of terraforming for us!

Are you able to calculate whether, by any chance, it will come close to any of the NASA probes around Jupiter, Mars, Venus, etc...? What is its closest approach to the JWST?

The closest it will come is Mars, but when I say close these are quite literally astronomical distances, about 0.2 au from Mars. This is about 75x further than the moon is from the Earth.

If it is an inactive rock, then we will not see it as any more than a point of light during its visit.

Where did my math go wrong? I got about 50,000 megatons. Assuming the high-end of 22km and a rocky/metallic density of 5000 kg/cubic meter (and assuming it's a cube):

  kinetic energy = 1/2 m v**2 = 1/2 * size * density * v**2
  = 1/2 *(22000 m)**3 * (5000 kg/m**3) * (90 m/s)**2 / (4.184E15 J/megaton)
  = 52,000 megaton

If it's an icy comet then the density is more like 500 kg/cubic meter, or 1/10th that number.

Would be wild if a sufficiently large object with a lot of water and organic molecules hit Mars, ejected a lot of material in to Mars’ orbit to then go on to form a sufficiently large moon that tidally massaged Mars’ core to cause a dynamo to generate a sufficiently strong magnetic field to…

Terraform Mars!

Absolutely nothing. Way too small and slow.

1040 x more energy that the Tsar Bomba.

Or 5-ish Tsar Bomba per country on Earth.

Or 3466 Hiroshima nukes.

Or 17 Hiroshima nukes per country.

90 m/s?

Way too slow, it's more like 70km/s (or 90) - seems you left out a k.

I can not confirm this; the parent calculation is the correct one. I can't immediately find what your error was. (edit: It's your [km/s]—you wrote [m/s] by mistake).

    (let* ((ρ ([g (cm -3)] 5))
           (d ([km] 22))
           (m (* ρ (expt d 3)))
           (v ([km (s -1)] 90))
           (ke (* 1/2 m (expt v 2)))
           (kg-tnt ([J (kg -1)] 4.2e6)))
      (values (/ ke kg-tnt)
       (as [megaton] (/ ke kg-tnt))))
    
    5.133857142857142e19 [KG]
    5.133857142857143e10 [MEGATON]

Huh. It looks like on 10/2 it will make its closest pass to a planet, Mars, and on that date it also is in a straight line with Mars, Mercury and the sun, while Earth and Venus are roughly opposite each other. Do you know if this sim accounts for solar or martian gravity diverting its trajectory?

You don't need a magnetic field to terraform Mars, it can hold onto an atmosphere without it for 100M years.

In light of the error in the parent comments math, I retract my previous comment and substitute the following bit of awkward silence:

…

Without a magnetic field, isn’t the surface of Mars subject to sterilising radiation from Sol?

in a somewhat related story, I was on a beach in Costa Rica last week, watching some spider monkeys in a palm tree trying to whack open small nuts. Just then, an American family walked up the beach with two teenage boys. They didn't notice the monkeys I was watching. But one of the boys grabbed a coconut off the sand and became determined to break it open with a rock in front of his parents. So watching the monkeys and the boy simultaneously, I had the distinct feeling of how slowly evolutionary, let alone geological, processes actually move.

Haha, cool, that gave me a chuckle :)

“We'll be saying a big hello to all intelligent lifeforms everywhere and to everyone else out there, the secret is to bang the rocks together, guys.” - The Hitchhikers Guige to the Galaxy, Douglas Adams

Planetary magnetic field only weakly protects against cosmic rays (extra-solar origin).

A thick enough atmosphere will stop pretty much all the charged particles from the normal solar radiation.

We're going to see a lot more of these in the next couple of years due to the new Vera C Rubin observatory.

Also the ELT [1], I believe. (Both come online this year.)

[1] https://en.m.wikipedia.org/wiki/Extremely_Large_Telescope

We all make mistakes, as the Dalek said climbing off the dustbin.

FWiW .. here's mine (or is it?)

One Tsar Bomba ~ 50 megatonne. One Hiroshima bomb ~ 15 kilotonne.

One Tsar Bomba ~ 50,000 / 15 ~ 3,333 Hiroshima bombs.

1,040 x Tsar Bomba ~ 3,466,667 Hiroshima bombs.

If it would be so bad, Earth's polar regions (experiencing aurora borealis) would be inhabitable too. Earth's magnetic field is not magically neutralizing all charged particles from the Sun, just diverts them (some maybe away, but many simply towards poles).

And clearly even our mag field (and Sun's heliosphere) is not enough to shield us from those crazy cosmic rays.

Oops.

Every time I see your username I can’t help but say it in my mind as Defrost Kelly, some kind of frozen Dr. Leonard "Bones" McCoy

My mistaken use of m/s instead of km/s, in a squared term, indeed gives a HUGE difference.

Thanks!

Yes, that was my error - thanks!

This orbit visualization uses a simple 2 body approximation, so only the sun. This is because unless an object has a VERY close approach to a planet the two body approximation is more then enough for this style of visualization.

I did a full proper n-body integration and it is not visually different than this.

ELT's first light is planned for March 2029.[1] Vera is already online I think.

[1] https://www.eso.org/public/announcements/ann25001/

I would expect most visitors would come from the galactic plane.

I know it’s incredibly, vanishingly unlikely but what would happen if an object with these characteristics smacked into Earth?

Closest approach will be October 29, 2025. It’s currently passing Jupiter’s orbit. I’m amazed that even at this speed it will take that long to get here.

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is.” ~Douglas Adams

The end, unless you're a small proto-mammal ;).

An object (depending on consistency) of about 100m is enough to wipe out a city and do enough damage to the environment. Something of 8-20km is in the same category as what wiped out the dinosaurs (10-15km).

8-22km at interstellar speeds? Probably total extinction level.

What is easier? Not mess up this planet, or Terraform Mars?

Username checks out.

It’s going at 68km/s so I think even microbial life could be in trouble.

…and after just a few million years to settle down again, we’ll be ready to visit blue sky on Mars!

I don't know. Have you seen humanity? I think teraforming another planet is probably easier than not fucking up this one

With this much mass and velocity - it would smash the planet, rupturing the entire crust at the very least.

No matter how infinitesimally small the probability - the universe is infinite, and so it probably will happen.

i3 is much bigger than the Chicxulub asteroid that ended the Cretaceous period (and extinct all non-avian dinosaurs).

How fast does something need to be traveling before you’d consider it to be fast? It probably weighs as much as a city and it is traveling tens of times faster than a high-velocity bullet.

Gag Halfront, wasn’t it?

You could very well be right!

It is of the same caliber as the dinosaur ending meteorite. The planet barely shrugged from it. There is suspicion that something the size of pluto has already hit mars once upon a time. And it is way more massive than this speck of cosmic dust.

Sometimes it is hard to think of big space is, especially because we tend to do that while sitting around inside (this is where we have most of our thoughts, after all). Of course space distances are nothing like the distances inside our rooms, no frame of reference.

Instead, go out to the ocean on a clear day, and observe how absurdly vast the ocean is. Just ocean, as far as you can see. Look around and realize you’ve gained absolutely nothing in terms of comprehending the vastness of space, to which the difference between your room and the most sweeping views on Earth are just totally insignificant.

Belter, our future is in orbital habs. Going downwell is for tourism and archaeology.

The single best depiction of the Solar System to help grok size and distance is Josh Worth's "If the Moon were only 1 pixel":

https://www.joshworth.com/dev/pixelspace/pixelspace_solarsys...

No no no no no.

"If life is going to exist in a Universe of this size, then the one thing it cannot afford to have is a sense of proportion." -DNA

> Source: Working on my PhD in orbital dynamics and formerly wrote the asteroid simulation code used on several NASA missions:

This is one of the big reasons I love HN

I agree and I’m old enough to remember when Reddit was like this

An even better visualization of the size of the Solar System. It shows traveling from the Sun out to forever at the speed of light. Be prepared to spend hours watching the paint dry. I suspect traveling in space will be like war, long periods of boredom punctuated by brief moments of sheer terror.

https://www.youtube.com/watch?v=1AAU_btBN7s

[edit] arrgh. brain spaz forgot to put in the URL

Can you walk and chew gum?

From the first link I get:

"specified object was not found"

What do you mean by 'active' here - has a plume?

Max Quordlepleen

Nice story.

But are you implying that we are somehow more evolved than the monkeys? Both the human and the monkey in the story have evolved for the same amount of time since our last common ancestor.

I can't believe that all those super-intelligent astronomers, who spend hours on their own in the dark, couldn't come up with a better name than 'Extremely Large Telescope'. ;0)

That argument always struck me as vacuous. Dump a barrel of ball bearings on the top of a craggy hill. Wait as they all bounce around, some getting stuck in local minima and some bouncing over obstacles and covering large distances.

Would you claim that they all traveled the same distance because they all traveled for the same amount of time?

Evolutionary space is very high dimension, which makes the argument that just projecting onto the (1d) time axis is misleading even stronger.

It’s not worth doing because it is easier, but because all of our eggs are in one basket (planet). We know of disasters that can wipe out almost all life on a single planet. Of course, there are also disasters that can wipe out all life in one star system (and one region of the Galaxy). So, ideally we need to colonize many worlds in many different parts of the Galaxy, but baby steps. Step one is to have a sustainable population on multiple moons/planets/stations of this star system before we jump to other star systems.

Thanks for sharing this info. Does "eccentricity" refer to the orbit, or the shape of the object?

For ‘Oumuamua in 2017, some method was used to determine its shape, which is (apparently) remarkably elongated. Is it possible to determine the elongation of the new object?

https://science.nasa.gov/solar-system/comets/oumuamua/

Thanks for sharing your expertise! What really bends my mind is the relative speeds involved. Reddit's /r/space has a great visual[1] which depicts it as basically going straight through our solar system, only bending slightly as it passes Sol. This is only possible if the object moving at 68 km/s is also moving sideways at 230 km/s so as to match our galactic orbit, and moving up at a mind-boggling 600 km/s (relative to CMB). This is all basic stuff of course, but something about having the object actually pass by us is making it more real than usual...

Hell, maybe it's only orbiting the galaxy at a leisurely 160 km/s, and from its perspective we're a spinning disc of chaos zipping past it for the first time in a few million years! I don't even know how I would start to analyze its orientation in relation to the galactic center, but I'll be keeping this as my little "headcannon" until proven wrong, that's for sure.

[1] https://www.reddit.com/r/space/comments/1lpw4as/new_interste...

Eccentricity refers to the shape of the orbit, derivable from the highest and lowest distances in the orbit of the orbiting body (there's actually a bunch of ways to calculate it that are mathematically equivalent). It's related to modeling orbits as conic sections. An eccentricity of 0 is a perfect circle, <1 is a normal elliptical orbit, >=1 is an escaping trajectory.

For example, Earth's orbit around the sun is ~0.0167, Pluto's is 0.248.

I found it by searching an alternate designation:

C/2025 N1

Edit: does this link work?

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=C%2F2...

I'm not sure more/less evolved is a meaningful concept in Darwinian terms. Organisms have a level of fitness for their environment. Perhaps you are talking about cultural evolution?

Based on the corrected 90 km/s instead of m/s it should be 52 pt (peta-ton) impact.

Yes, thanks!

Getting a "specified object not found" on the orbit viewer.

We don't have enough data of the object yet to say basically anything at all about its shape.

I guess they should have SuperSized™ it.

I also like this solar system model from NASA, https://science.nasa.gov/learning-resources/how-big-is-the-s....

They compare it to a US football field.

"On this scale, the Sun, by far the largest thing in our solar system, is only a ball about two-thirds of an inch (17 millimeters) in diameter sitting on the goal line — that's about the width of a U.S. dime coin. ...

The inner planets — Mercury, Venus, Earth and Mars — are about the size of grains of sand on a football field scale. They would be dwarfed by a typical flea, which is about 3 millimeters long.

Closest to the goal line is Mercury, just under a yard from the end zone (.8 yards to be specific). ... At this scale, Mercury's diameter would be scarcely as large as the point of a needle.

Venus is next. It is 1.4 yards from the end zone. ...

On to Earth, sitting pretty on the 2-yard line. ...

Mars is on the three-yard line of our imaginary football field. ...

Jupiter remains pretty close to our end zone on the 10.5-yard line. ...

Saturn is on the field at 19 yards from the goal line. ...

Uranus ... is about 38 yards from our end zone.

Neptune is where things start to get way out. It is 60 yards from our solar goal line on the imaginary football field. ...

Tiny Pluto is much closer to the opposing team's end zone. It's about 79 yards out from the Sun ...

On this scale, our little friend Voyager 1 has left the game and is well out in the stadium parking lot or beyond."

Let's see if I get this math right.

Mauna Loa is about 95,000 km3 in volume says https://www.usgs.gov/volcanoes/mauna-kea/science/geology-and... . Density of TNT is 1.6g/cm3:

  95000 km3 * (1000m/km)**3 * 1600 kg/m3 = ~1.5E17 = 150 pt.

1/3rd of the mountain in TNT.

Nope, I can't conceive of that much energy.

At this point, it is tradition.

https://upload.wikimedia.org/wikipedia/commons/c/c5/Comparis...

And the horizon you see standing on the beach is just about 5km or 3 miles away!

Do not we humans and those monkeys largely share the same environment?

Which one is more numerous, less prone to natural forcings?

I like planetary trails, where the orbits of the planets (or other celestrial objects) are proportionally reduced and placed in the landscape.

For example, this image from a park in Halle (Germany) shows the inner solar system: https://dubisthalle.de/wp-content/uploads/2023/06/Planetenwe... -- but one has to walk 500 meters to reach Pluto.

The German Wikipedia has quite a long list of planetary trails: https://de.wikipedia.org/wiki/Planetenweg

Primo Levi wrote a short story [1] about this. Our words/measurements are inadequate when tasked with describing the cosmos.

[1] https://www.newyorker.com/magazine/2007/02/12/a-tranquil-sta...

> long periods of boredom

Not if it's at the speed of light, the journey will be instantaneous for the (massless) traveller.

Seems like it arrives with a bit more energy than a 10 on richter scale: https://www.edinformatics.com/inventions_inventors/richter_s...

No, I can’t really imagine what that means, either.

frame of reference matters, from the center of the sun or galactic core they all most certainly moved the same distance in the same amount of time and it was much further than the hill was tall.

Sure? What is the analog to this other frame of reference in the evolution case though? Or are you just stepping out of the analogy's applicability range to show that it can be pushed too far (which is of course true of an analogy)?

They can't go C though, just 0.99999 C or whatever. So almost frozen in time :)

Vastly easier to not only stop but also undo all the damage here than to do anything of consequence on Mars.

We have numbers with a wide error bar.

> It is almost on the plane of the solar system, not very inclined.

except that it's going the wrong way :)

Would be pretty hard to fuck up Mars’ biosphere.

A Molecular clock would be gravity in your model, when ever you called stop all your marbles would have experienced the same amount of gravitational force. That is the intent of "experienced the same amount of evolution" and similar.

Where I see the model flounder is; the hill provides the fitness context. You implied distance "means" more evolved, but for life it is all about making it to the next round, in your marble game how many of those furthest marbles will ever be found for the next round?

With life big changes are dangerous, you may find yourself improved out of options.

Imagine how I feel every time I see "Dalek" instead of my surname.

It's illegal to mention the solar system and football without mentioning one of the greatest pieces of science fiction on the two, Jon Bois' 17776 https://en.wikipedia.org/wiki/17776

The best way I heard this put: Before we worry about terraforming Mars, maybe first we should stop Venusforming Terra.

To add what others said, eccentricity is also a way to tell if the object is captured or not. 0 means perfectly circular orbit, >=1 means escape, >=2 means hyperbolic.

Not terribly related but I got curious, the ELT has a reported angular resolution of 0.005 arcseconds. The sad state of public trust has resulted in many people no longer accepting the US landed on the moon at all. Tossing the question of what it would take to resolve the lunar landing sites into a LLM gives a broad requirement of 0.0005 arcseconds. Even still, you could never "prove" it to most people unless it's glass the entire way with no "hoax generating" computers involved.

It's a fun idea thought though.