Intergalactic planetary, planetary intergalactic
October 25, 2021 2:21 PM Subscribe
Just thirty years ago, we could only speculate what planets might exist around other stars. That changed in 1992, with the first confirmed detection of an extrasolar planet. Since then, progress has been rapid: there are now 4,843 confirmed exoplanets in 3,579 planetary systems. So far, all of these have been relatively nearby. But a new paper, published today in Nature Astronomy, reports the first evidence of a planet in a whole other galaxy. The potential planet, 28 million light years away, was detected as it passed in front of a bright X-ray binary star in the M51 galaxy, causing a three-hour blip in its X-ray emissions. BBC article and link to the paper itself.
A friend of mine was in the exoplanet-discovery business for a while. Famously among our social group, he once found a planet and was very pleased at its properties. Then a year later, his housemate disproved the existence of said planet. What an awkward dinner they must have had that night.
posted by knile at 3:21 PM on October 25, 2021 [21 favorites]
posted by knile at 3:21 PM on October 25, 2021 [21 favorites]
not bad for a bunch of barely sentient hominids
posted by lalochezia at 3:36 PM on October 25, 2021 [2 favorites]
posted by lalochezia at 3:36 PM on October 25, 2021 [2 favorites]
That's mind-blowing. If my quick back-of-envelope calculations are correct, it's like detecting a single water molecule from 1000 km away.
posted by justkevin at 3:45 PM on October 25, 2021 [1 favorite]
posted by justkevin at 3:45 PM on October 25, 2021 [1 favorite]
And that makes me think that some enterprising astronomer should set up a Twitter bot or something that lets us know every time a new star could be home to someone detecting Earth via a transit at that moment. Sure, there are bajillions of stars and all, but you have to be out there in juuuust the right detection to see Earth pass in front of the sun, right?
You have nerdsniped me into doing the math on this.
The sun's diameter, let's call that D, is 1.39 million km. Earth's, d, is 12,742km. They're about 150 million km apart, let's call that r.
If I've derived the trig right, then the angle of sky, θ, within which the sun is at least partially obscured by Earth is given by:
θ = 2tan⁻¹((D+d)/2r)
for which I get 0.53 degrees, or 32.1 arc seconds. Taking that as the diameter of a circle in the sky gives a figure of 812 square arc seconds of sky in which the Earth could be seen transiting.
This thread estimates that there are around 5.7 stars in our galaxy per square arc second of sky.
Which means that at any given moment, there are something like 4500 stars from which Earth could be observed transiting the Sun. And with the Earth orbiting the sun at around one degree per day (360 / 365), you would have a whole new batch of stars to consider every 12 hours.
I think it's safe to say that your Twitter bot would be banned for spam.
posted by automatronic at 4:50 PM on October 25, 2021 [15 favorites]
You have nerdsniped me into doing the math on this.
The sun's diameter, let's call that D, is 1.39 million km. Earth's, d, is 12,742km. They're about 150 million km apart, let's call that r.
If I've derived the trig right, then the angle of sky, θ, within which the sun is at least partially obscured by Earth is given by:
θ = 2tan⁻¹((D+d)/2r)
for which I get 0.53 degrees, or 32.1 arc seconds. Taking that as the diameter of a circle in the sky gives a figure of 812 square arc seconds of sky in which the Earth could be seen transiting.
This thread estimates that there are around 5.7 stars in our galaxy per square arc second of sky.
Which means that at any given moment, there are something like 4500 stars from which Earth could be observed transiting the Sun. And with the Earth orbiting the sun at around one degree per day (360 / 365), you would have a whole new batch of stars to consider every 12 hours.
I think it's safe to say that your Twitter bot would be banned for spam.
posted by automatronic at 4:50 PM on October 25, 2021 [15 favorites]
That's amazing! WOW!
posted by doctornemo at 5:09 PM on October 25, 2021
posted by doctornemo at 5:09 PM on October 25, 2021
Hm, actually that number I just came up with isn't crazy on its own. 4500 new stars in the transit zone every 12 hours, is only one every six minutes. If you also tweeted when the transit ends, that's every three. And as the Every Three Minutes account demonstrates perfectly, that's an acceptable tweet rate.
But as the same source points out, that figure of 5.7 stars per square arc second is an average. In the direction of the galactic core, which is not that far off the ecliptic, there might be more like 100 times that number, so your bot would need to be tweeting every couple of seconds at certain times of the year.
And we don't have names, or even numbers, for all those stars. The largest star catalogues include only a couple of billion stars, out of some 400 billion in our galaxy.
posted by automatronic at 5:19 PM on October 25, 2021 [1 favorite]
But as the same source points out, that figure of 5.7 stars per square arc second is an average. In the direction of the galactic core, which is not that far off the ecliptic, there might be more like 100 times that number, so your bot would need to be tweeting every couple of seconds at certain times of the year.
And we don't have names, or even numbers, for all those stars. The largest star catalogues include only a couple of billion stars, out of some 400 billion in our galaxy.
posted by automatronic at 5:19 PM on October 25, 2021 [1 favorite]
This thread estimates that there are around 5.7 stars in our galaxy per square arc second of sky.
Which means that at any given moment, there are something like 4500 stars from which Earth could be observed transiting the Sun. And with the Earth orbiting the sun at around one degree per day (360 / 365), you would have a whole new batch of stars to consider every 12 hours.
that's with infinitely sensitive tech, though, right? the estimate of 5.7 stars per arc second is for a slice emanating from the galactic center and extending to the edge, i think. but some stars on that slice might be so far that they wouldn't have the tech to resolve earth in front of the sun from their distance, depending on how far they are and how good their telescopes are.
posted by wibari at 10:19 PM on October 25, 2021
Which means that at any given moment, there are something like 4500 stars from which Earth could be observed transiting the Sun. And with the Earth orbiting the sun at around one degree per day (360 / 365), you would have a whole new batch of stars to consider every 12 hours.
that's with infinitely sensitive tech, though, right? the estimate of 5.7 stars per arc second is for a slice emanating from the galactic center and extending to the edge, i think. but some stars on that slice might be so far that they wouldn't have the tech to resolve earth in front of the sun from their distance, depending on how far they are and how good their telescopes are.
posted by wibari at 10:19 PM on October 25, 2021
That's mind-blowing. If my quick back-of-envelope calculations are correct, it's like detecting a single water molecule from 1000 km away.
I guess it's like detecting a single water molecule that occasionally completely blocks a tiny laser?
posted by clawsoon at 11:32 PM on October 25, 2021 [1 favorite]
I guess it's like detecting a single water molecule that occasionally completely blocks a tiny laser?
posted by clawsoon at 11:32 PM on October 25, 2021 [1 favorite]
automatronic: Which means that at any given moment, there are something like 4500 stars from which Earth could be observed transiting the Sun.
I was about to say that this feels like a dramatic underestimate. I was thinking that the plane of the solar system would be in the same plane as the Milky Way and therefore visible via transit to half or a third of the 100-400 billion stars in the galaxy over the course of a year... but it turns out that we're going around the sun at an angle of about 60 degrees to the plane of the galaxy, and our solar system as a whole goes up and down through the galactic plane every 40 million years or so.
So I guess that means our discoverability would vary dramatically along the lines that automatronic pointed out? Whenever Sagittarius is directly overhead at midnight, billions of them are watching us?
posted by clawsoon at 12:03 AM on October 26, 2021 [2 favorites]
I was about to say that this feels like a dramatic underestimate. I was thinking that the plane of the solar system would be in the same plane as the Milky Way and therefore visible via transit to half or a third of the 100-400 billion stars in the galaxy over the course of a year... but it turns out that we're going around the sun at an angle of about 60 degrees to the plane of the galaxy, and our solar system as a whole goes up and down through the galactic plane every 40 million years or so.
So I guess that means our discoverability would vary dramatically along the lines that automatronic pointed out? Whenever Sagittarius is directly overhead at midnight, billions of them are watching us?
posted by clawsoon at 12:03 AM on October 26, 2021 [2 favorites]
There's been research into this question: Which stars can see Earth as a transiting exoplanet?
posted by The Tensor at 1:54 AM on October 26, 2021 [11 favorites]
posted by The Tensor at 1:54 AM on October 26, 2021 [11 favorites]
Wow! Thanks The Tensor, that's a really interesting link. At one point I was thinking of heading into Astrophysics (Chemistry/Environmental Management won out), and reading something like this makes me a little sorry I didn't.
posted by domdib at 4:34 AM on October 26, 2021
posted by domdib at 4:34 AM on October 26, 2021
Here's the Press Release from the Harvard Center for Astrophysics (CfA). The first co-author is a Physics undergraduate.
The lead author is Rosanne di Stefano who is at the CfA.
She has an interesting paper too in 2016 which speculates that Globular Clusters may be the prime candidates for housing advanced inter-stellar civilizations, if there are any.
posted by vacapinta at 4:51 AM on October 26, 2021 [1 favorite]
The lead author is Rosanne di Stefano who is at the CfA.
She has an interesting paper too in 2016 which speculates that Globular Clusters may be the prime candidates for housing advanced inter-stellar civilizations, if there are any.
posted by vacapinta at 4:51 AM on October 26, 2021 [1 favorite]
Oh, actually I got that second bit wrong. Even with the density of 5.7 stars per square arc second, it's 6 stars per minute coming into range, not one every six minutes. And when the earth is between the Sun and the galactic core, it would be hundreds or even thousands every minute.
But as wibari notes, some of those would be too far away to detect Earth successfully. The paper that The Tensor has linked does a much better job of all this - it considers stars within 100 parsecs, and whether an Earth transit would be long enough to detect reliably (they use a figure of ten hours). I'd actually just been looking at the Gaia DR2 data wondering how to do this, so I'm glad it's already been done.
They came up with 508 candidate stars which we'd be visible to in the course of a year - so a Twitter bot is eminently feasible.
Also they confirm that the width of the zone is 0.528°, so I'm pleased to find that I can still in fact do trig.
posted by automatronic at 5:16 AM on October 26, 2021 [3 favorites]
But as wibari notes, some of those would be too far away to detect Earth successfully. The paper that The Tensor has linked does a much better job of all this - it considers stars within 100 parsecs, and whether an Earth transit would be long enough to detect reliably (they use a figure of ten hours). I'd actually just been looking at the Gaia DR2 data wondering how to do this, so I'm glad it's already been done.
They came up with 508 candidate stars which we'd be visible to in the course of a year - so a Twitter bot is eminently feasible.
Also they confirm that the width of the zone is 0.528°, so I'm pleased to find that I can still in fact do trig.
posted by automatronic at 5:16 AM on October 26, 2021 [3 favorites]
Also from the article, the next chance to confirm this via another transit is in ~70 years. Similar to the 76 years we had to wait after Halley predicted the return of the comet.
posted by freecellwizard at 8:42 AM on October 26, 2021
posted by freecellwizard at 8:42 AM on October 26, 2021
your bot would need to be tweeting every couple of seconds at certain times
In spite of the constant plabet detection covfefe
posted by Jon Mitchell at 12:54 PM on October 28, 2021
In spite of the constant plabet detection covfefe
posted by Jon Mitchell at 12:54 PM on October 28, 2021
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Also, that was 28 million years ago. Who knows what that planet is up to now. If there's a black hole eating its [extra]solar system, how long does that usually take?
And that makes me think that some enterprising astronomer should set up a Twitter bot or something that lets us know every time a new star could be home to someone detecting Earth via a transit at that moment. Sure, there are bajillions of stars and all, but you have to be out there in juuuust the right detection to see Earth pass in front of the sun, right?
posted by whatnotever at 3:15 PM on October 25, 2021 [1 favorite]