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

(www.abc.net.au)
306 points gammarator | 16 comments | 03 Jul 25 03:19 UTC | HN request time: 1.881s | source | bottom

Minor Planet Electronic Circular: https://minorplanetcenter.net/mpec/K25/K25N12.html
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ddahlen ◴[03 Jul 25 05:43 UTC] No.44451980[source]▶
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

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1. noduerme ◴[03 Jul 25 05:48 UTC] No.44452015[source]▶
What planets is it passing between?
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2. ddahlen ◴[03 Jul 25 05:50 UTC] No.44452027[source]▶
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.

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3. Teever ◴[03 Jul 25 06:09 UTC] No.44452115[source]▶
> 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?

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4. ddahlen ◴[03 Jul 25 06:18 UTC] No.44452157{3}[source]▶
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.

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5. defrost ◴[03 Jul 25 06:20 UTC] No.44452174{3}[source]▶
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.
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6. noduerme ◴[03 Jul 25 07:34 UTC] No.44452570[source]▶
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?
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7. sgt101 ◴[03 Jul 25 08:00 UTC] No.44452708{4}[source]▶
We're going to see a lot more of these in the next couple of years due to the new Vera C Rubin observatory.
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8. JumpCrisscross ◴[03 Jul 25 08:05 UTC] No.44452743{5}[source]▶
Also the ELT [1], I believe. (Both come online this year.)

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

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9. ddahlen ◴[03 Jul 25 09:23 UTC] No.44453187{3}[source]▶
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.

10. cyberlimerence ◴[03 Jul 25 09:59 UTC] No.44453399{6}[source]▶
ELT's first light is planned for March 2029.[1] Vera is already online I think.

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

11. rbanffy ◴[03 Jul 25 11:10 UTC] No.44453803{4}[source]▶
I would expect most visitors would come from the galactic plane.
12. hermitcrab ◴[03 Jul 25 15:06 UTC] No.44455823{6}[source]▶
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)
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13. mcswell ◴[03 Jul 25 17:43 UTC] No.44457460{7}[source]▶
I guess they should have SuperSized™ it.
14. Tuna-Fish ◴[03 Jul 25 19:18 UTC] No.44458310{7}[source]▶
At this point, it is tradition.

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

15. NooneAtAll3 ◴[04 Jul 25 02:08 UTC] No.44460569[source]▶
> It is almost on the plane of the solar system, not very inclined.

except that it's going the wrong way :)

16. zorton ◴[05 Jul 25 10:45 UTC] No.44471755{6}[source]▶
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.