The Astronomy Thread

Guess we know where Gozer is being summoned at least

Thought the relatively close approaches of 3I/Atlas by Mars and Jupiter both was interesting and asked Grok what the odds are of that... C3P0 gave better odds of successfully navigating an asteroid field. Grok's estimate for this two-planet pass trajectory was 114,000 to 1:

3. Geometric Probability of Passing Close to One Planet The solar system’s ecliptic plane, where 3I/ATLAS crosses, is where planets are most likely to be encountered. Let’s estimate the probability of a random interstellar object passing within a given distance of a planet:

• Solar System’s Cross-Section: Assume the comet crosses the ecliptic within 5.2 AU (Jupiter’s orbital radius), as 3I/ATLAS’s perihelion is 1.357 AU and its Jupiter encounter occurs near 5.2 AU. The cross-sectional area of the ecliptic plane out to 5.2 AU is:
  Asolar=π×(5.2 AU)2≈85 AU2≈1.9×1022 m2.A_{\text{solar}} = \pi \times (5.2 \, \text{AU})^2 \approx 85 \, \text{AU}^2 \approx 1.9 \times 10^{22} \, \text{m}^2.A_{\text{solar}} = \pi \times (5.2 \, \text{AU})^2 \approx 85 \, \text{AU}^2 \approx 1.9 \times 10^{22} \, \text{m}^2.
• Mars’s Target Area: For a close approach within 0.2 AU of Mars (radius of Mars’ orbit ~1.52 AU), the target area is:
  AMars=π×(0.2 AU)2≈0.1256 AU2.A_{\text{Mars}} = \pi \times (0.2 \, \text{AU})^2 \approx 0.1256 \, \text{AU}^2.A_{\text{Mars}} = \pi \times (0.2 \, \text{AU})^2 \approx 0.1256 \, \text{AU}^2.
  Probability of passing within 0.2 AU of Mars:
  PMars=0.125685≈0.00148 or 0.148% (1 in 676).P_{\text{Mars}} = \frac{0.1256}{85} \approx 0.00148 \text{ or } 0.148\% \text{ (1 in 676)}.P_{\text{Mars}} = \frac{0.1256}{85} \approx 0.00148 \text{ or } 0.148\% \text{ (1 in 676)}.
• Jupiter’s Target Area: For a close approach within 0.4 AU of Jupiter (orbital radius ~5.2 AU):
  AJupiter=π×(0.4 AU)2≈0.5024 AU2.A_{\text{Jupiter}} = \pi \times (0.4 \, \text{AU})^2 \approx 0.5024 \, \text{AU}^2.A_{\text{Jupiter}} = \pi \times (0.4 \, \text{AU})^2 \approx 0.5024 \, \text{AU}^2.
  Probability of passing within 0.4 AU of Jupiter:
  PJupiter=0.502485≈0.00591 or 0.591% (1 in 169).P_{\text{Jupiter}} = \frac{0.5024}{85} \approx 0.00591 \text{ or } 0.591\% \text{ (1 in 169)}.P_{\text{Jupiter}} = \frac{0.5024}{85} \approx 0.00591 \text{ or } 0.591\% \text{ (1 in 169)}.

These probabilities assume the comet’s entry point into the ecliptic is random, which is reasonable for interstellar objects like 3I/ATLAS, whose trajectories are determined by their origins in the galactic disk or other star systems and are not influenced by the solar system’s structure until they approach closely.4. Odds of Passing Close to Both Mars and Jupiter Since Mars and Jupiter are at different heliocentric distances (1.52 AU vs. 5.2 AU), their positions are independent in the context of a fast-moving interstellar object crossing the ecliptic. The comet’s trajectory is nearly straight (hyperbolic, eccentricity 6.14), and its high speed (58–68 km/s) means it crosses the solar system in months, so we can treat the Mars and Jupiter encounters as independent events for a first-order approximation:

• Joint Probability: The probability of passing within 0.2 AU of Mars and 0.4 AU of Jupiter is the product of the individual probabilities:
  Pboth=PMars×PJupiter=0.00148×0.00591≈8.75×10−6 or 0.000875% (1 in 114,286).P_{\text{both}} = P_{\text{Mars}} \times P_{\text{Jupiter}} = 0.00148 \times 0.00591 \approx 8.75 \times 10^{-6} \text{ or } 0.000875\% \text{ (1 in 114,286)}.P_{\text{both}} = P_{\text{Mars}} \times P_{\text{Jupiter}} = 0.00148 \times 0.00591 \approx 8.75 \times 10^{-6} \text{ or } 0.000875\% \text{ (1 in 114,286)}.
  This suggests that for a random interstellar object, the odds of passing within 0.2 AU of Mars and 0.4 AU of Jupiter are extremely low, about 1 in 114,000.

Only the third interstellar object ever witnessed, has some early on strange characteristics (bright, massive?), just happening to pass in on an extremely unlikely trajectory that gets it relatively close to a couple planets. Just saying...

• q = periapsis (closest distance to the sun)
• a = semi-major axis (longest diameter of the orbit)
• AU = astronomical unit
• Ga = Giga annum = a billion years ago
• Gyr = Gigayear = 1 billion years

Wiki says Ga and Gyr meanings are switched from above, but that wouldn't read correctly in this paper(?).

Frankly it's wild that we can find these things at all. It's an ice ball less than 400 km in diameter and ~8 billion miles away.

At least Congress is growing some balls and pushing back against the cuts. You know all these science cuts are Vaught's idea - that worthless piece of shit has such a hard-on for gutting our nation's science programs

I don't disagree, although if you look back at why SLS was probably approved to begin with, its because the manufacture of it involves multiple states.

SpaceX needs to get Starship actually functional as advertised

Avi Loeb and a couple others just put out a draft paper on the possibility of 3I/Atlas being something "technological" - expanding on the thing I pointed out above that it gets improbably close to multiple planets, in addition to other improbable characteristics. Multiple times from the start to the end of their paper they highlight that it is probably a comet... and they await the data proving that - but they have yet to see the data proving that's what it is. And so until then, due to the improbable characteristics, they think that the possibility this is something of intelligent design has to be considered.. just saying.

20km - currently high end of this thing's estimated size - was the diameter of Rama btw!

https://lweb.cfa.harvard.edu/~loeb/HCL25.pdf