Hacker News Reader

Comment by 1970-01-01 | Hacker News Reader

1970-01-01

Launch a probe already! If the anomaly is a planet, ~you've discovered a new planet~ If the anomaly is a black hole, then ~you've discovered a local black hole~ If there is literally nothing there, use the probe for interstellar science.

View on HN

"literally nothing there"

1. Space is big.

2. Space is REALLY big!

3. This thing would be tiny.

4. This thing would be invisible.

Combine these four together and you'll quickly realize just how difficult even scoping out the probe's requirements and such would be. Would be cool though.

You might be interested in Ed Witten's paper about this exact problem:

"Searching for a Black Hole in the Outer Solar System", https://arxiv.org/abs/2004.14192

Thanks for sharing! Some interesting things --

"And one would like to launch hundreds of spacecraft (at least) in different directions so that some would come within dozens of AU of Planet 9, rather than hundreds of AU."

Their example of a neat-but-good-luck project could actually achieve the goal is [1]. The spec requires ground lasers that's powered by a 1GW nuclear power plant for propulsion. And, "According to The Economist, at least a dozen off-the-shelf technologies will need to improve by orders of magnitude." [2]

[1] https://breakthroughinitiatives.org/initiative/3 [2] https://en.wikipedia.org/wiki/Breakthrough_Starshot#Technica...

Would gravitational lensing be usable to detect one of these tiny black holes?

I don't think so. The black holes are, by assumption, tiny and only light passing by very very closely would experience significant lensing. Farther away, the lensing would be the same as near any other planet.

I think we would be able to detect it. We can navigate spacecraft with high accuracy.

If you can get a spacecraft somewhere in the vicinity of a black hole of decent mass (like a 10km asteroid equivalent) we could probably detect changes in trajectory of the spacecraft from the gravitational attraction.

Or, here's an idea, blow out a tonne of radar chaff in the vicinity of the black hole and watch for how it disperses via radar.

We could also try detecting Hawking radiation that a BH should generate, though that might be pretty faint (I have not done the math).

You are correct. At about Luna-mass, then it is hotter than the 3K cosmic background. If it is heavy enough to be a 9P candidate, it would be colder than 3K. You couldn't detect by temp.

You'd have to look for a very precise spike in the EM spectrum at the electron-position annihilation energy equivalent.

Despite being raised on space opera and hard-sf and having a science degree, I am pretty bearish on most space exploration. Having said that, a nearby black hole wouldn't merely be nifty. For reasons we do not understand, the event horizon stops honoring conservation of baryon number (and lepton number, and other numbers). I consider this important because replication of that would allow for direct conversion of uncharged mass to energy, just as any neutral particle crossing the event horizon has its energy (eventually) returned to us. If Hawking radiation is true (we have yet to experimentally verify it), then we know that mechanism exists. Can we do it without a black hole?

Would a small BH have enough of an accretion disc to emit sufficient X-rays to be detectable? While the density of matter in the Oort cloud is low, it is not as low as interstellar space.

Depends on size. That size? No, no accretion disc. That kind of effect would evaporate as you scale down.

Friend, let me repeat: Space is BIIIIIIIIIIIIIIG.

What if we create a time loop, launch the spacecraft in a random direction, and reset the loop if nothing is found?

We might just find it after 390.03 years!

I assume that's 9,318,054 * 22 minutes, not counting leap years?

ding!

To quantify this a bit, the search area for Planet X is in the region of many hundreds of AU from the sun. That’s many millions of cubic AU to hunt around in. That’s a lot of chaff, without even considering how we would detect and track the chaff from this far away.

It's sort of the equivalent of trying to find your headphones by walking around with the bluetooth menu open on your phone and waiting to see if they pop up then they must be nearby, except all you know is that they're somewhere on Earth and you don't know where until you come within ten feet or so of them. And in reality it's even harder than that, since the surface of Earth is essentially two-dimensional as far as finding things goes, but a search for a planet would need to cover most of the volume of the greater solar system.

So essentially, we need a lot more clues to narrow this search radius down.

Any singular probe would needed to know where to go searching. Any scanning instruments it could carry we can build and use better at Earth (soon Moon [1], fingers crossed). Your idea would require a swarm, an array, with Earth as a centre piece, effectively forming search beam rotating outwards.

I agree tho, #LaunchTheProbe #NASA

[1] - https://en.wikipedia.org/wiki/Lunar_Crater_Radio_Telescope

launch where exactly?

That's the key, you absolutely need to design a probe where gravity is the guidance system. My take is a primary probe containing hundreds of hyper reflective microprobes, which scatter for billions of miles into space. After a few decades, the primary probe locates where the majority of mircoprobes went, and now you steer the primary probe into Planet 9's gravity well.

I think you're underestimating the area you need to search. See the wiki page[1]. There's so much space to look near, you need a much better guess before you can send any probes. A 9k year orbit, that starts at 340 AU, and has a lot of uncertainty in all the parameters, just leaves too much volume to check naively. And that doesn't even get into the fact that there's not enough light out there to feasibly find probes from their reflections.

1: https://en.wikipedia.org/wiki/Planet_Nine

Uhhhh, we've got all those "microprobes" which are all of the known objects in the Solar System. A couple of them are a bit macro though (Jupiter in particular).

It would fly directly into the Sun

planet nine is not the eye of the universe

Reply on news.ycombinator.com