52 votes

Can a moon orbit its planet faster than its planet rotates?

What immediately springs to mind is the Martian moon Phobos, orbiting the planet in 7 hours 39 minutes. That's a fair bit quicker than the 24 hour 37 minute sidereal period of Mars. From the surface ...
SE - stop firing the good guys's user avatar
41 votes
Accepted

Why are orbits around a black hole not elliptic?

What this image depicts is the gravitational lensing created by the black hole. Light that passes close to a strong gravity source is distorted by it into characteristic ring-like shapes. (You can see ...
Cadence's user avatar
  • 614
28 votes
Accepted

What processes create an object with an interstellar velocity?

The answer to 'how can it come blazing in with enough energy to exit again' is that if it started outside the solar system it would have been unusual for it to NOT leave again, since it would have ...
GremlinWranger's user avatar
20 votes

What would be the effect of increasing the mass of Mars?

Planets are much, much bigger than you think. The total mass of all the bodies in the main asteroid belt is about half of 1% of Mars's present mass. There's no realistic way to round up enough loose ...
Russell Borogove's user avatar
14 votes
Accepted

Besides retarded gravitation, anything else to worry about when calculating MU69's orbit from scratch?

This is not a complete answer. It is instead an extended comment to the following: I understand I will have to retard the gravity from each source by its particular light-time, as well as correct ...
David Hammen's user avatar
  • 74.8k
14 votes

Why are orbits around a black hole not elliptic?

What you are seeing "bent" around the black hole is light from the accretion disk the path of which is warped by traveling close to the black hole. We see a distorted view of what is "...
antlersoft's user avatar
  • 1,213
13 votes

Is there an elegant method to stop an asteroid's spin?

I found at least 1 paper proposing enclosing the asteroid in a bag filled with gas. https://www.researchgate.net/publication/273913280_SHEPHERD_A_Concept_for_Gentle_Asteroid_Retrieval_with_a_Gas-...
lijat's user avatar
  • 1,798
13 votes

Is there an elegant method to stop an asteroid's spin?

Look at how satellites are commonly de-spinned, and apply it on a larger scale. A commonly done method is the Yo-yo de-spin where you have long ropes with weights, and extending them slowy from the ...
Ferrybig's user avatar
  • 231
12 votes

Can a moon orbit its planet faster than its planet rotates?

Are there any known examples of this situation? Yes! In addition to Phobos mentioned in this answer and from Astronomy SE: How did “oddball” Valetudo, Jupiter's new prograde moon, end up in a wider ...
uhoh's user avatar
  • 149k
12 votes

What processes create an object with an interstellar velocity?

This is a very generic answer: A gravitationally bound system has a tendency to become more compact. As this happens, the gravitational potential energy becomes more negative. The energy that is lost ...
Roger Wood's user avatar
  • 3,864
11 votes

C3 calculation in interplanetary missions

For reasons of convenience, departure excess energy is plotted as $C_3$, and arrival excess energy is plotted as $v_\infty$, where $C_3=v_\infty^2$. The reason is that launch vehicle performance is ...
Mark Adler's user avatar
  • 58.2k
10 votes
Accepted

Why is FORTRAN recommended for astrodynamics rather than MATLAB?

As many of the comments have already mentioned, there are several different reasons people might recommend the use of Fortran over Matlab. One of the most straightforward answers is that a lot of ...
Chris's user avatar
  • 663
9 votes
Accepted

Is Mercury's orbit still considered potentially unstable (in the very long term)?

Here is the first paragraph of the introduction from Abbot et al. (2023): Since the landmark study of Laskar (1994), the potential for Mercury’s orbit to destabilize has been widely recognized. The ...
ProfRob's user avatar
  • 374
8 votes
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Source for up-to-date values of Mars' standard gravitational parameter

The most up-to-date is from the work in this paper, due to be published in July 2016. The actual numbers can be found in this large file, for which the number you seek is the second number in the file,...
Mark Adler's user avatar
  • 58.2k
8 votes
Accepted

Why is the gas giant grand tour interval 175 years when the synodic period of Uranus and Neptune is 171 years?

A couple considerations enter here. We do not expect the alignments to occur every 175 years over the long haul. Rather, they are likely to occur in clusters internally spaced by that interval until ...
Oscar Lanzi's user avatar
  • 8,505
8 votes

Can a moon orbit its planet faster than its planet rotates?

Though it's a stretch, GNSS satellites in MEO like GPS, Galileo, GLONASS, etc... are examples of such "moons" orbiting planet Earth, since they're positioned at an altitude lower than ...
Will's user avatar
  • 180
8 votes

Disposing of Obsolete Satellites by Propelling to the Sun

For an object to fall into the Sun, from close to the Earth, its angular momentum, which is conserved in any ballistic trajectory, would have to be reduced close to zero - since its velocity vector ...
ProfRob's user avatar
  • 374
7 votes
Accepted

Calculate flight path angle given semi-major axis, eccentricity and distance from the focal point

One method of calculating the angle involves using the ellipse reflection law. Light from one focus reflects off the ellipse into the other focus. Thus in the picture below (by the author), the ...
Oscar Lanzi's user avatar
  • 8,505
7 votes
Accepted

Is a ballistic Jovian capture using the Galilean moons possible from interplanetary entry?

Yes, but really no. Preamble: I built a little 2D trajectory simulation (2D because the Galilean moons are more or less coplanar) to test out trajectories (Jupiter + Galilean moons gravity, RK4, 10s ...
BrendanLuke15's user avatar
7 votes

What processes create an object with an interstellar velocity?

Assume that 'Oumuamua was gently ejected from whatever environment it formed in. Then, how is it that it entered the solar system at 26.33 km/s? This is actually expected. The velocity dispersion of ...
John Doty's user avatar
  • 3,304
7 votes

Why do the modified equinoctial elements use the semilatus rectum?

Partial Answer: For the extreme special case of the parabolic trajectory, where Orbital Eccentricity = $e=1$, the semi-major axis hits a singularity at $a=\pm\infty$, whereas the semi-latus rectum ...
notovny's user avatar
  • 5,439
7 votes
Accepted

Is this a typo in the Python Skyfield API? "International Coordinate Reference Frame (ICRF)"?

The quotation correctly (though not completely) describes the International Celestial Reference Frame, so I'm comfortable calling "Coordinate" a typo.
Ryan C's user avatar
  • 7,942
6 votes
Accepted

Python API for JPL Horizons?

callhorizons is depricated now and refers to the python library astroquery which now seems to be the way to go. astroquery (GitHub, readthedocs) is "an astropy ...
Gandalf Saxe's user avatar
6 votes

What would be the effect of increasing the mass of Mars?

As Russell Borogove pointed out, that plan is quite impossible because you need to get that mass from somewhere, and all the other mass is already concentrated on even larger planets. And even when we ...
Philipp's user avatar
  • 9,326
6 votes
Accepted

What is the physical interpretation of the eigenvalues of the monodromy matrix and how are they associated with the invariant manifolds?

Eigenvalues and Eigenvectors Before specifically addressing the monodromy matrix, it's important to make sure you have a physical understanding of what eigenvalues and eigenvectors represent in ...
yeemonic's user avatar
  • 356
6 votes

2 body equations of motion in 3D

$state=[rx,ry,rz,vx,vy,vz]$ $\dot{state}=[vx,vy,vz,ax,ay,az]$ $a=\dfrac{\mu}{r^2}$ (Newton's universal law of gravitation / two body acceleration in scalar form) Division be zero errors are avoided by ...
Alfonso Gonzalez's user avatar
6 votes

Is it possible to detect if orbits intersect or not and positions where they intersect if you know Keplerian elements (2D)?

Where the orbits cross is only part of assessing collision probability. You also have to know the time at which the two spacecraft reach the same point. Unless the crossing happens at the same time ...
Ryan C's user avatar
  • 7,942
6 votes

Why are orbits around a black hole not elliptic?

Photon Ring While other answers describe the gravitational lensing effects of a black hole, the full picture is far more dramatic. Lensing, as the name implies, only affects an image that is already ...
Lawnmower Man's user avatar
5 votes

What would be the effect of increasing the mass of Mars?

The mass of Mars is 6.419 * 10E23 kg, the mass of the largest object in the asteroid belt, the dwarf planet Ceres is 9.393 * 10E20 kg. Adding Ceres to Mars would result in 6.4284 * 10E23 kg, a very ...
Uwe's user avatar
  • 49k

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