[HN Gopher] Images reveal exocomets around nearby stars
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Images reveal exocomets around nearby stars
Author : gmays
Score : 90 points
Date : 2025-01-31 15:00 UTC (17 hours ago)
(HTM) web link (skyandtelescope.org)
(TXT) w3m dump (skyandtelescope.org)
| AtlasBarfed wrote:
| Doesn't that practically guarantee Exoplanets in those systems?
| tantalor wrote:
| The article says we already knew that:
|
| > astronomers knew disks of debris leftover from planet
| formation were common around newborn stars
|
| The new result allows much more insight:
|
| > only a few have been resolved in sufficient detail to study
| their internal structure. "This is the first time we can make a
| statistical analysis of what's going on in these disks,
| divbzero wrote:
| I always thought that comets come from the Oort cloud, but
| apparently short-period comets come from the Kuiper belt or its
| associated scattered disk--similar to the exocometary belts in
| these images.
| araes wrote:
| It's a neat result, its maybe a bit to specify sizes. At least
| with the images provided in the article, they're getting maybe:
|
| 10 pixels, across across objects of >1 astronomic unit
| (149,597,870 km). If those rings are like our own Kuiper belt
| objects, then those are more like 25-50 AU. If they're like the
| asteroid belt in the inner solar system, then maybe 2-5 AU.
|
| If those are images from the nearest 74 solar systems, then those
| are somewhere from 4 ly to 20 ly away (~4e13 km to 2e14 km away).
| [1][2] They're probably further away.
|
| Based on the stated resolution, ALMA is supposed to get ~10
| milliarcseconds (10-7 radians) resolution. [3] With the small
| angle approx. that means it can resolve: (~4e13
| km to 2e14 km) * 10^-7 = 4e6 km to 2e7 km = 0.025
| AU to 0.125 AU
|
| It's cool though, as it at least implies disc path clearing,
| orbital harmonics resulting in ring formation, and probably a lot
| of other implications. Likely gives excellent regions to try
| looking for further planets, planetoids, or planetesimals.
| Provides some idea of how likely it is for the conditions in our
| own solar system to cause similar formations in further away
| solar systems. Mostly a lot of single rings, not that many double
| ring groups. Quite a few that end up looking more like bloby
| clouds.
|
| [1] 100 Nearest Star Systems,
| http://www.recons.org/TOP100.posted.htm
|
| [2] GJ 1005 (#74), https://en.wikipedia.org/wiki/GJ_1005
|
| [3] Atacama Large Millimeter Array,
| https://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array
| hinkley wrote:
| Someone once broke my brain about hostile alien movies. They said
| if the aliens were here to take, they could stay in the Oort
| Cloud or outer planets where the gravity well is shallow, and
| strip mine our system for natural resources and we wouldn't even
| be able to throw anything that high to stop them.
|
| We could just watch and shake our fists as they steal our future
| at their leisure. They wouldn't even have to send their people.
| They could use robots on ten systems at once.
| ceejayoz wrote:
| > we wouldn't even be able to throw anything that high to stop
| them
|
| Worse, they could throw bits of the Oort Cloud _at us_.
| hinkley wrote:
| When you're standing at the bottom of a well, don't mouth off
| to the person standing at the top.
| ridgeguy wrote:
| It takes just as much [?]V to throw a rock from the Oort
| cloud to Earth as to throw the same rock from Earth to the
| Oort cloud. The aliens don't get an energy advantage by
| holding the high ground.
| ceejayoz wrote:
| > It takes just as much [?]V to throw a rock from the Oort
| cloud to Earth as to throw the same rock from Earth to the
| Oort cloud.
|
| Yes, but _they_ clearly have the capability to get _to_ the
| Oort Cloud, and we (other than a small probe) do not.
| Having the high ground (both physically and
| technologically) makes holding the Oort Cloud a pretty good
| spot to be in.
|
| (It also takes substantially less [?]V to _nudge_ an
| existing rock into a nastier trajectory, and we 're
| essentially a big easy to hit static target.)
| lazide wrote:
| No it doesn't, at all.
|
| The whole point of the high ground is someone just needs to
| 'drop' something in, which is cheap and easy, but someone
| on the 'low ground' needs to make up all the energy to get
| up there before they are even at the same level.
|
| The energy involved in de-orbiting something and dropping
| it to the surface of earth (at very high speed) is orders
| of magnitude less than it would take to get the same mass
| to even earth orbit from the surface.
|
| Holding a brick over the opening of a well is a much more
| credible threat to someone at the bottom, than that someone
| with the same brick threatening to throw it back out.
| ianburrell wrote:
| The first valuable thing on Earth is life. Life may be rare
| enough, or diverse enough, that worth sampling the unique life
| on Earth. The intelligent monkeys can be useful, but can be
| knocked down is cause problems.
|
| The second valuable thing is intelligent life. The intelligent
| monkeys are worth preserving and talking to. But their advanced
| civilization has lots of potential dangers so need controlling
| protectorate.
|
| The third valuable thing is better minerals. The active
| processes of the Earth concentrates minerals. They could grind
| up a whole asteroid, but cheaper to take from Earth. Also,
| biologic processes make minerals; vacuuming up coal is cheaper
| than making it. These wouldn't be whole civilization but
| pirates grabbing some cheap loot before the authorities and
| natives notice.
|
| The fourth valuable thing is Earth itself. Inhabitable planets
| are rare. The expected way would be apocalypse or annihilation.
| But I think it would be more interesting to have alien invasion
| where they ignore us. They settle the arctic, and don't do
| anything until attacked. Then they start removing CO2 until the
| temperatures drop and ice age returns.
| holoduke wrote:
| I always wonder. If we theoretically could know for each photon
| the direction vector and distance travelled, then could we make a
| collector that could image an exoplanet? Or is this simply
| impossible?
| wongarsu wrote:
| We actually already have multiple images of exoplanets. [1] and
| [2] were both taken with the Very Large Telescope in Chile.
| Granted, you can't see much beyond reddish blobs. But they are
| not _that_ much worse than Hubble 's images of Pluto [3].
|
| We probably can't do much better with earth-based telescope
| arrays due to atmospheric distortions. But with satellite
| launch costs coming down we will see large telescope arrays in
| orbit in a couple decades, and those might do a lot better
|
| [1] https://science.nasa.gov/resource/2m1207-b-first-image-of-
| an...
|
| [2] https://www.eso.org/public/images/eso2011b/
|
| [3] https://esahubble.org/images/opo1006h/
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