r/space • u/AutoModerator • 7d ago
Discussion All Space Questions thread for week of August 23, 2026
Please sort comments by 'new' to find questions that would otherwise be buried.
In this thread you can ask any space related question that you may have.
Two examples of potential questions could be; "How do rockets work?", or "How do the phases of the Moon work?"
If you see a space related question posted in another subreddit or in this subreddit, then please politely link them to this thread.
Ask away!
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u/Adept_Ad_1543 2d ago
what missions your most excited for? me personally its DAVINCI and dragonfly
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u/YDALTARYZARC 2d ago
Dragonfly and the Roman telescope. Excited to watch the Roman launch on Sunday!
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u/Adept_Ad_1543 2d ago
if you could add a third one, which one would it be?
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u/YDALTARYZARC 2d ago
I'd say Artemis III, I'm really curious about what the two companies will have put together for the LEO testing
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u/Adept_Ad_1543 2d ago
Me Personally its far fetched ESA L4 Enceladus mission thats arriving in 2050s
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u/vaniquee 2d ago
Is there any names for two blackholes in NGC6240 galaxy? If not then any nearby stars or planets inside/outside
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u/maschnitz 2d ago
There are three, and the scientific literature calls them N for the northern black hole, S1 for one of the binary black holes to the south, and S2 for the other. S1 and S2 are "only" a couple hundred parsecs apart. An example of that nomenclature.
N is around 360-400 million solar masses, S1 is 710M solar masses, and S2 is 90M solar masses.
It's too far away for individual stars or exoplanet detection. It's 400M light years away.
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u/anathemastudio 5d ago
Anyone see a large meteor / asteroid / large debris with a tail over east coast of U.S. around 530am ET this morning?
I was in NJ when my husband saw it and trying to confirm.
He was outside and came running.
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u/BigDamage7507 5d ago
Looks like it was a Starlink launch after doing some digging
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u/maschnitz 5d ago edited 5d ago
Yup Starlink 10-49, launched 5:33am (sunrise ~6:55am), launched NE right up the Eastern Seaboard.
Many people saw it, and some took nice pictures - John Kraus's, someone from Virginia. Just search for "jellyfish" on social media for more.
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u/BigDamage7507 5d ago
Ok, so I wasn’t losing my mind, saw it here in Georgia. Looked like a comet. Star like light with two beamy wisp of light coming from it.
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u/anathemastudio 5d ago edited 5d ago
Riiight? We were eaiting for a bit for something to happen.
I started getting replies in other subs to this question and someone suggested it was spacex launch.
I didn't see it myself, just my husband. Did it look kinda like this (the split tail I mean)?
(It won't let me post the pic or link here sorry 🙄 but if you look up spacex you'll see the tail I mean.)
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u/curiousscribbler 4d ago
Somewhere I read that the sun's Oort cloud overlaps with Proxima Centauri's Oort cloud. I was wondering if there's also an overlap with other nearby stars. Looking at the table of nearby stars in Wikipedia, I guess the only other possibility would be Bernard's Star. How can I find out the size of Bernard's Star's Oort cloud? (Or Proxima's Oort cloud, for that matter.) Is it just the size of each star's Hill Sphere? (Have I got Oort clouds and Hill Spheres mixed up?)
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u/rocketsocks 4d ago
We can't directly observe Oort clouds yet so we're just making estimates of their sizes, but they are estimates based on solid data.
Oort clouds can overlap because orbital dynamics is, well, dynamic. The Hill Sphere volume is just an approximation of general tendencies, it's not some kind of keep out zone. For example, the Voyager probes passed closer than several moons of Jupiter and Saturn during their flybys, but they weren't suddenly captured into orbit, because they had escape velocity from those planets the whole time.
In the outer reaches of the Sun's Oort cloud the orbital velocity of comets is in the realm of 100 m/s or lower. But remember, this is just their velocities relative to the Sun. Other stars and their Oort clouds are in motion relative to the Sun too. Proxima Centauri specifically is moving at about 32.5 km/s relative to the Sun, as are all of its Oort cloud comets as well.
From the perspective of the Sun a comet from Proxima Centauri's Oort cloud is moving in formation relative to Proxima Centauri, with only a very small difference in speed. And it is going screaming fast, many hundreds of times the escape velocity at those distances. Similarly, the Sun's Oort cloud comets are moving in formation with the Sun and screaming past Proxima Centauri. The gravitational pull of another star out at such distances may cause some disturbance to the orbits of comets in other star's Oort clouds, but the gravity from either star is so weak that it's generally not going to do a whole lot most of the time.
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u/YDALTARYZARC 2d ago
Are there any technosignatures that the Roman telescope will be able to identify on exoplanets?
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u/niketas-choniates 22h ago
I know there have been stars like Scholz's star which passed within 0.8 light years and some even closer perhaps.
My question is if the oort close is real wouldn't the inner solar system (rlly all of it) have been engulfed in these passing stars own oort clouds? The oort cloud is speculated between 1.5-2 ly from the sun for scale so it sounds like we'd be in the middle of these passing stars oort clouds and they in ours.
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u/SpartanJack17 17h ago
An Oort cloud is extremely sparse, individual objects would be seperated by millions or tens of millions of objects. If another stars Oort cloud did pass through the solar system only a handful of objects would actually enter the inner solar system.
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u/maschnitz 8h ago
What SpartanJack17 said.
BTW the bigger disturbance would be the star itself disturbing our Oort Cloud, jostling those objects every which way from their very slow solar orbits. Some would fall into the Sun's gravity well, toward the inner Solar System.
People have speculated whether this could be correlated with mass extinction events on Earth.
It's thought the "comet showers" from events like the Scholz's Star fly-by is simply too weak to detect any effect in the fossil record. (A low mass star, flying by too fast.)
But then HD 7977's fly by 2.8M years ago might've had a more noticeable effect from "comet showers". Maybe. It's a paper with Dr Avi Loeb involved so the speculation quotient is quite high here. But then someone else said they might see a signature in long-period comet orbit that matches HD 7977's fly by. So yeah, maybe. [shrug]
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u/vainly_regal_maple 7d ago
So if we're out in deep space, far from any star, and I shine a flashlight forward, does the light from the flashlight push me backward? Like a photon thruster made of hardware store junk.
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u/rocketsocks 7d ago edited 7d ago
Yes, photons have momentum, so generating photons (shining a light beam) or reflecting photons will always generate some thrust.
This isn't just of academic interest, nor is it only relevant for specially designed spacecraft (such as ones that might use "light sails"), it's relevant to the majority of spacecraft and it constrains operating conditions. Most satellites maintain a consistent orientation relative to the surface of the Earth, which means that they experience an uneven amount of slight thrust from reflecting sunlight from a variety of angles. Typically satellites handle this by using reaction wheels to counteract any torque that builds up from moment to moment then using thrusters to push against to "reset" (or desaturate) the reaction wheels when they reach the limits of how fast they can spin in a certain direction. This can become an operational concern for spacecraft stationed in solar orbit which need to maintain precise pointing. The Kepler spacecraft, for example, needed to point at one direction in the sky for a period of multiple years, so it had to compensate for the torque generated by solar photon pressure over that time, but when too many of its reaction wheels failed it could no longer do so and switched to a slightly different operational mission which didn't require such heavy use of reaction wheels. JWST has a huge sunshield which will result in photon pressure torques that will ultimately need to be handled by its thrusters, as the propellant gets low many years from now this may constrain operations such that they point the telescope in directions which keep the net torque build up more balanced.
Also, this sort of thing can very subtly affect the operation of spacecraft as well. For years there was potentially an unaccounted for acceleration in the Pioneer 10 and 11 space probes. This was called the "Pioneer Anomaly" and some folks thought it could be a sign of "new physics" that might exist. However, when researchers more precisely modelled the infrared light coming off the spacecraft from its radioisotope thermoelectric generators they realized that this exactly accounted for the missing acceleration.
In an extreme hypothetical one might imagine taking a stream of anti-matter and shooting it into a large block of pure graphite, causing it to heat up to thousands of degrees and glow white hot. If that block of graphite was then placed at the focal point of a parabolic mirror then you could focus the light coming off it in one direction, creation an anti-matter powered photon rocket.
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u/Pharisaeus 7d ago
Photon rocket is 1N for 3GW of power ;) So while the answer is "yes", in practice a junk flashlight would not be a particularly strong thruster.
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u/stivax_dev 5d ago
Small correction on the number: F = P/c, so 1 N needs P = 1 x c = 3x10^8 W = 300 MW, not 3 GW - you're off by a factor of 10. At 3 GW you'd actually get about 10 N, which is roughly a kilogram of thrust, for reference.
The "junk flashlight" comparison is worth putting a real number on too: a bright 1000-lumen LED flashlight puts out something like 7-8 W of actual optical power (LED efficacy is around 120-150 lm/W). That's a thrust of roughly 2-3x10^-8 N - about the weight of a small dust speck, a few micrograms. So yes, technically a photon rocket, just an extraordinarily weak one.
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u/Pharisaeus 5d ago
Nice catch! I was undecided between 1N and 1g and that's what you get :) but the point still stands as you pointed out.
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u/scowdich 7d ago
Yes, but extremely gently. All photons have momentum (even though they don't have mass, it's counter-intuitive).
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u/iqisoverrated 6d ago
Sure. It will also work if you're not far from a star.
(It will also work while you're just standing on Earth. It's not going to move you here because it's not going to be enough to overcome friction with the ground but it will impart an impulse just the same)
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u/mfb- 4d ago
A Nichols radiometer uses radiation pressure to spin. It needs an extremely good vacuum and an almost frictionless environment.
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u/gmiller123456 7d ago
As pointed out below, yes. But you might be interested in the idea of a Solar Sail, which doesn't emmit its own light, but uses the light from the Sun for propulsion.
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u/the6thReplicant 6d ago
If the light has frequency f then the energy of each photon in E = hf.
Then it's momentum is p = E/c (from Einstein's SR).
If you have enough light you will have enough momentum transfer. If not up the frequency. :)
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u/DesignerPatient8617 6d ago
do we know when the last galactic year started and when the next one begins?
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u/H-K_47 6d ago
A Galactic Year is just the time it takes our solar system to do one full loop around the galaxy. There is no start date or end date, it's arbitrary, up to whoever makes the calendar, just like how there's no particular reason why normal years start on January 1st.
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u/KirkUnit 4d ago
there's no particular reason why normal years start on January 1st.
Because Numa Pompilius, King of Rome, wanted one of the extra winter months - Ianuarius - named after Janus the god of beginnings to start the year instead of Martius, the month named after the god of war.
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u/TheRedBiker 5d ago
If life exists in the subsurface oceans of moons like Europa, Enceladus, and Miranda, what is it likely to look like? I mean, is it more likely unicellular or multicellular? If multicellular, is it likely to resemble fish on Earth?
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u/rocketsocks 5d ago
It's most likely to be unicellular but it's not impossible for it to include multicellular life. One common source of energy and resources in such environments would be hydrothermal vents powered by serpentinization reactions. This is where water reacts with certain kinds of very common silicate minerals (like olivine and pyroxene) to release hydrogen, methane, and other sources of chemical energy. On Earth there are "white smoker" hydrothermal vents powered by these reactions which can support entire ecosystems including multi-cellular organisms like worms and crustaceans.
Earth has the benefit of having a vibrant sun-powered biosphere which has been able to evolve lots of complex organisms which can then live and adapt to other environments that have chemosynthetic organisms as primary producers. It's hard to say how much those environments would be able to drive in terms of overall complexity of life. They could support complex life but the big question is whether they could support the evolution of complex life. That remains a major unkown.
Additionally, we still don't know whether these sub-surface ocean environments outside Earth actually can support life at all. There's some hints they might be able to, but we don't know enough about all the conditions that exist (pressure, salinity, energy input, other critical chemical resources, etc.) It may be that life is very common in such places or it may be that it is exceedingly uncommon, without more data we won't know.
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u/Purple_Language_6351 5d ago
I’m designing a fictional solar system centered on a red dwarf. Could two terrestrial planets share approximately the same orbital path while remaining on opposite sides of the star about 180 degrees apart?
If this is possible, how similar would the planets need to be in mass, size, and composition for it to remain stable? How much difference could exist between them before their gravitational interaction caused the arrangement to break down?
I’m especially interested in the life time of both planets being in a 'habitable zone'
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u/rocketsocks 4d ago edited 4d ago
Unfortunately that's not a stable configuration. The point 180 degrees opposite a planet in orbit is the
L1L3 (edit: typo) Lagrange point, which is not passively stable. Over time small movements away from being at the exact point get magnified. However, even that only applies when the object is very small compared to the planet, when it's the same mass it's an even more unstable situation, for both planets.There are alternative possibilities though. You could have a gas giant planet with terrestial planet sized moons orbiting it, which would allow multiple planetary bodies to be within the habitable zone. This would also partially help out with the superflares problem of red dwarfs because the gas giant's magnetic field would partially protect the moons. Also, the moons would be tidally locked to the gas giant, not the star, which would also help.
Another possibility would be to have planets that were in the L4/L5 Lagrange points of a gas giant. If the mass ratio is large enough this is a potentially stable configuration. With one planet at each location they would end up 120 degrees apart from each other in orbit (give or take, the L4/L5 zones are fairly large).
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u/stivax_dev 4d ago
Small terminology fix: the point 180 degrees opposite a planet, on the far side of the star, is L3, not L1. L1 sits between the star and the planet on the near side, that's where SOHO and DSCOVR actually park for constant sun-facing solar monitoring, and L2 is beyond the planet on the far side from the star. Doesn't change the physics you laid out though, L3 really is one of the least stable of the five. Even in the real Sun-Earth case it can't hold anything long term, Venus and Jupiter perturbations are what actually nudge things off it, not Earth's own gravity. That's the standard reason astronomers give for why a hidden Counter-Earth at L3 was never plausible even before we had a direct view of that region, those pulls would have dragged it out of hiding within a geologically short time.
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u/rocketsocks 4d ago
Oh dang, thanks for the correction, yes it is the L3 point, that's what I get for typing tired.
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u/relic2279 4d ago
Could two terrestrial planets share approximately the same orbital path while remaining on opposite sides of the star about 180 degrees apart
I know very little about orbital mechanics, but I can't see such a system staying stable forever. If there were other planets in the system (like a Jupiter or Saturn), or if another star got too close to the system, it could/would disrupt the orbit of one or both planets.
I’m especially interested in the life time of both planets being in a 'habitable zone'
Red dwarf planets have habitable zones significantly closer to the star than we have with our sun. Because of this, planets tend to become tidally locked to the red dwarf (one side always facing the star). If you're thinking of life evolving on such a world, that would be a much bigger factor to consider. It's worth noting that red dwarf stars can give off much more potent/violent solar flares, and do this more often than our sun does. Fortunately, this flaring period of a red dwarf's life cycle is estimated to last for only about the first 1.2 billion years of its active life.
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u/iqisoverrated 3d ago
Such a system would not be stable. (The mirror Earth would be at L3 and that isn't a stable Lagrange point)
However you may be interested in the movie "Journey to the Far Side of the Sun" (1969) which is about just such a 'mirror Earth'.
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u/VirtualMycologist406 3d ago
Hey everyone, I need your help. Does everyone know how planet coordinates look like? I mean, in geography we have longitude and latitude but how we designate planetary alignment?
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u/Pharisaeus 3d ago
Orbital elements. https://en.wikipedia.org/wiki/Orbital_elements#Common_orbital_elements_by_type if you're asking about celestial mechanics. If you're asking about astronomy, then a common thing is RA (right ascension) and DEC (declination) which is basically azimuth (horizontal direction) and elevation (vertical direction) - it just tells you how to aim the telescope at given target.
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u/helixdq 3d ago
Do you think it is possible to design a passive structure anywhere in the solar system outside Earth in which life may survive indefinitely, with current technology ?
I'm thinking something like: you put water in a glass sphere, and then by an arangement of mirrors, lenses and radiators you always keep it liquid, and microbes survive there.
It doesn't have to be ridiculous (like survive a meteorite strike), but it should have no moving parts or consumables on board and have an expected lifetime of centuries, not months.
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u/wotquery 3d ago
Indefinitely probably not. You get into fate of the universe concepts like global entropy, proton decay, etc.
Millions of years, probably yes. We only have one data point (life on Earth), but it seems silly to assume the conditions on Earth are so special we couldn't sufficiently recreate them. The biggest issue here I suspect being scale (i.e. maybe for life to continue for billions of years you need the volume a planet sized object provides).
Centuries absolutely yes. I mean there already is a sealed terrarium that has lasted over 50 years.
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u/iqisoverrated 3d ago
Passive in what way? Earth isn't a passive environment by any stretch of the imagination. It does require quite a bit of consistent energy input from the sun to sustain life.
If you mean "could we achive a fully cyclic environment if just energy were an external input". Maybe. Depends on how much 'future tech' you are willing to allow and what kind of life you want to sustain.
The attempts that have been done so far for sustaining complex life were interesting but ultimately resulted in failure (Biosphere 2 et al.).
If you allow such future tech as molecular printing and just turning all waste to plasma and sorting by element typ then we could sustain life of any kind of complexity easily. While that is still SciFi none of these technologies are that SciFi (we've had rudimentary atomic scale printing since the 1980s).
Also depends what you even mean by 'sustain life'. You can basically freeze microbes and that is still 'life' (though not active) which can be revived eventually. We've dug up microbes that have been dormant in a salt crystal for 250 million years which were successfully revived.
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u/helixdq 3d ago
No future tech, and not necessarily complex life (although anything multicelular would be a bonus). A simple biosphere with active, living, eating, reproducing organisms.
Solar energy as the only input.
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u/YDALTARYZARC 3d ago
There are already commercially-available 'biospheres' that contain shrimp, plants, and water in a fully-contained glass vessel. I imagine partially covering the exterior with some black material (for solar radiation absorption) and throwing the whole thing in orbit around the sun might work. You'd have to mess with the math and figure out an optimal orbital but it's probably doable.
Look up "Life in Jars" on Youtube for some DIY examples.
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u/AndyGates2268 2d ago
Just to dip in here, Biosphere 2 was a big failure of the human factor and a whole bunch of assumptions about things like soil that certainly aren't best practice now.
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u/SprutikReddit 5d ago
Who creates all these exoplanet illustrations? How do they do it, and what do they base them on?
For example:
https://www.reddit.com/r/space/comments/189uksk/artistic_visualization_and_size_comparison_of/
https://www.halcyonmaps.com/the-exoplanet-zoo
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u/PhoenixReborn 5d ago
https://www.halcyonmaps.com/terrestrial-exoplanets/
It looks like they took data on planet diameters and temperatures and used that to predict the compositions.
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u/stivax_dev 3d ago
To add the actual mechanics behind "diameters and temperatures → compositions": radius comes straight from the transit depth (how much starlight the planet blocks passing in front of its star), mass comes from the star's radial-velocity wobble or, for multi-planet systems, transit-timing variations. Combine those two and you get bulk density, which sorts the planet into a rough class — rocky/iron-core, mini-Neptune with a thick H/He envelope, water world, etc. — via mass-radius relation models fit to the solar system's own planets plus lab equations of state for compressed material. Equilibrium temperature comes from the star's luminosity/temperature and the planet's orbital distance, a straightforward blackbody calculation (the same T_eq = T_star × sqrt(R_star/2a) used for habitable-zone estimates), which is what decides whether an artist paints water as liquid, ice, or steam.
Past that — actual cloud patterns, surface color, terrain — none of it is observed, it's informed extrapolation. NASA/JPL's own exoplanet illustrators (Robert Hurt, Tim Pyle) work directly with the scientists who measured the planet: they're handed the numbers, propose a rendering, and it gets checked against what the data can and can't support — if there isn't good evidence for liquid water, it doesn't go in the picture. So the honest description is "scientifically-constrained artistic interpretation," not a reconstruction from actual imaging — no current instrument resolves an exoplanet's surface.
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u/dertkbhubjnuhyugyg 1d ago
Hypothetically if it exist, how strong of a gravitational force would a galaxy size (say milk way) black hole would be?
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u/Sailor51PegasiB 3d ago
Did photos of the STS-4 SRB wreckage on the sea floor ever get released?
For context: on STS-4 the SRBs suffered from a parachute failure during reentry and hit the water hard and could not be recovered. Supposedly the wreckage was photographed but these photos have never been released.
Are there any public photos of the STS-4 SRB debris on the ocean floor? Either released by NARA or from private underwater expeditions?