r/askastronomy

Hi r/astrophysics, I previously asked a much more broad version of this question, which turned out to be way too hard to answer. Hopefully this is a little more "possible" haha.

That being said:

Do all planetary bodies which become spherical later begin spherically, OR is it possible for the early stages of many planets to be irregularly shaped, until more mass is accumulated?

For example, in the very first/early stages of a planet's formation, would we be looking at something sort of bumpy, potato shaped, and not-very-round? Or would we be looking at something spherical right off the bat, albeit very small?

If it IS possible for something irregularly shaped to then accumulate mass until it's gravitational force forces it round-- what are the chances of an asteroid or planet-shard becoming a planet?

Thank you for taking the time to read! Hopefully this wasn't too confusing. I haven't been able to find any answers online and would appreciate any insight, however small.

Hi r/astrophysics, I've been thinking about this for a few days. There's a few questions here, so bear with me.

Firstly, do all planetary bodies which become spherical begin spherically, or are the early stages of many bodies irregularly shaped, until more mass is accumulated?

Next, why aren't some of even the largest asteroids then, for example, not spherical? Where's that "tipping point" in size, volume, and mass that causes a spacial object to become (or begin) a spherical shape?

Lastly, is it possible for an irregularly shaped, non-round body to become spherical later due to mass accumulation?

Thank you for taking the time to read. Really looking forward to the answers.

reading Cixin Liu's, "the wandering earth" today, which narrates a quest to move the earth from its orbit to our sun to one around proxima centauri via massive fusion thrusters. my thought after reading the very first page of the story was "obviously proxima centauri would be no good because that is a flare star". I haven't gotten to the point of modeling orbits or reading papers on this, but my guess is that alpha centauri a and b are also too close together and share too elliptical an orbit to stably place the earth around either or both at an appropriate distance. looking down the list of nearest stars on wikipedia, Lalande 21185 is the closest singlet non-flare stare, so i land on that as a tentative answer, but am not sure how much it's been studied. better known stars like eridani and tau ceti seem somewhat viable though a bit further, but with obvious drawbacks compared to our own star. does anyone else have thoughts on this?

If we were to detect a long period comet say close to the size of Greenland with less than one year notice headed directly for Earth is there anything that we could do about it to deflect its course?

When I tried to answer this question myself the answer I got was grim and basically said “forget it, with current technology it will be complete sterilization of life on the surface of the earth”. So maybe some experts can point out something? If not with technology today, what would it take besides early detection? Or is that really the only defense?

Would Earth as a planet survive the impact?

The moral obligation is interesting to me. Would governments just not say anything because there’s nothing we can do about it?

As astronomers, what is your role here? How do you inform agencies?

At least in the US even if astronomers detected it, the anti-science movement which includes a very large portion of citizens would likely ignore it and just deny, deny, deny, but other parts of the world might believe what they actually see.

I just don't understand why this is a thing because it violates basic logic itself, as far as I'm concerned the flat earth theory model presents a large flat earth with a miniature sun and moon moving in a circular path over head.

If this were true the sun would be visible at all times regardless of how far away it moves and it wouldn't be reflecting light all the way off of other planets. And not to mention that every single object observed in space is not a flat disc and any object large enough appears to be a perfect sphere and all stars are large with sphere planets revolving around them and are not miniature light bulbs circling overhead giant flat disc planets.

But somehow this isn't all just a trolling scheme and it's not only regurgitated by kids or random rednecks working at Walmart, some of these flat earth advocates seem to be somewhat sophisticated and have a lot of money and technical knowledge which they use to run extensive experiments trying to prove the earth is flat. It just doesn't make any sense.

This is what has been on my mind for a while now.

When there is a true New Moon (0% illuminated), the Moon is in the sky, but one cannot see it since the illuminated part of the Moon faces away from us. This being the case, the Moon should occult stars located directly behind it. This made me think of the following questions: Has anyone noticed or captured a bright star like suddenly disappearing behind the unseen new moon? Has the New Moon ever occulted any planet like Venus or Jupiter or any other bright body? If yes, has someone ever observed or even managed to take a picture of this phenomenon?

Unlike planets like earth the sun is a star made of gas and radiating light outward indefinitely. I see no reason that the gas and radiating light would travel and decay by density countinously, which might make it difficult to tell where it begins and ends.

For a distance from the center can we tell what is considered inside the sun?

Given that we have 8 recognized planets all that follow a similar equatorial plain of orbit to that of the sun and that we have found thousands of solar systems in the milky way I pose the question. Is our solar system unique in its abundance of planets? because I find it hard to believe that other solar systems only have a few rocky planets and no ice giants or gas giants further away from their sun that we can’t detect.

I have gathered around 100 reports from the press during this period (sognifocant but early days in public discussion of what would become UFOs in the 50s). Now though I've hit a wall. Does anyone know of any reports of odd things from this time? The term Flying Saucer became popular c. mid 1947 and there was an awareness of strange rockets from a year earlier. However there are many other ways that people described anomalies above. Any help will be appreciated.

Hear me out tho. Say some advanced alien civilization drops me at a completely random point in the universe. I have all the tech needed for deep space travel. Can I find my way back to Earth?

My first instinct was sure, just locate the Milky Way and work backwards. Earth is in the Solar System, Solar System is in the Orion Arm, roughly 26,000 light years from the galactic center. Simple enough chain to follow, right?

But here's where it collapses. The universe has no center, no fixed origin, no absolute coordinate grid. Every positioning system we use is relative to something else. There is no universal address for the Milky Way that exists independently. So step one of the plan is already conceptually broken before I've moved an inch.

Then there's the randomness problem. The observable universe is 93 billion light years across with roughly 2 trillion galaxies, and most of it is just empty void between galaxy clusters. A truly random drop most likely puts me in the middle of nowhere with nothing visible to even orient myself against.

And even if I could see galaxies around me, identifying which specific smudge of light is the Milky Way is genuinely unsolved. We have never observed our own galaxy from the outside. We don't know what it looks like from arbitrary external angles.

The whole premise assumes the universe has an addressing system. It doesn't. Has anyone actually thought about what navigation would even mean in this scenario?

The foundational bottleneck of contemporary astronautics is thermodynamic. Current institutional space flight matrices remain fundamentally constrained by Tsiolkovsky’s Rocket Equation. This physical reality mandates that to accelerate a payload in a vacuum, an equal and opposite mass must be thermally energized and physically expelled from the vehicle. Because
the propellant itself constitutes mass that must be accelerated prior to its consumption, the
required mass ratio scales exponentially against the desired delta-v. When applied to long-range deep-space logistics or multi-ton infrastructure transit, this
exponential curve demands a fuel mass that quickly exceeds realistic economic and resource
limits, rendering standard chemical or thermal reaction propulsion non-viable for sustained,
high-mass commercial space networks

So in my worldbuilding project there's this hycean planet called Michael. It orbits a perfect sun analogue at 1.7AU and is around 2.6 Earth radii. In my head if I made the planet slightly hot it'd result in a massive runaway greenhouse effect with all the water vapour and trace amounts of methane, letting it be near boiling temperature near the "surface", but as I tried recreating it in universe sandbox, it kept wanting to stay at -77c. All the water vapour I poured in immediately condensed in the core. Of course there was still a massive ocean beneath all that, but it's at the thousand atm mark and there's a thick sheet of liquid hydrogen above it. Could there be any other way a hycean planet with seas of super-critical water exist that far from the "goldilocks zone" or was my sci-fi plausible enough and it's universe sandbox's fault for not simulating greenhouse effects properly? The game displayed Michael's habitable range to be at the 0.7AU mark, which definitely feels wrong -- it has a thousand times more methane than Earth, for crying out loud.