New Horizons Will Have Little Time to Measure Pluto’s Atmosphere | Hacker News Reader

New Horizons Will Have Little Time to Measure Pluto’s Atmosphere

spectrum.ieee.org

31 pointsomnibrain27 comments

Just last night the SOFIA Observatory observed Pluto during an occultation [1], a very rare event. The main purpose is to help characterize Pluto's atmosphere and, along with New Horizons, the data will help calibrate future Earth-based observations of Pluto.

[1] http://www.nasa.gov/feature/sofia-in-the-right-place-at-the-...

Before anybody opines with "How could Pluto have an atmosphere when it's less massive than the moon (which has no atmosphere)?", it's worth noting that the moon does in fact have an atmosphere.

Interestingly, NASA speculates that Pluto's surface pressure is around 3 µbar, whereas they state that the moon's surface pressure at night is dramatically less than that, at 3.0 × 10^-9 µbar. I'm curious to see what New Horizons' measurements will reveal.

If we're talking outliers then Titan, the largest moon of Saturn has a surface atmospheric pressure 1.4x more than Earth's, while being 2.3% of Earth's weight

And then there's Venus' atmospheric pressure :-)

Curious, but how much of an effect would temperature have on a planet's ability to retain an atmosphere? A colder planet of equal size will presumably be capable of maintaining a thicker atmosphere, but I'm not sure if that'd be a significant factor in this case or not.

Proximity to the sun is a crucial attribute with respect to density of an atmosphere, both due to heat input (hot molecules escape easier) and solar wind density (energetic particles strip away molecules in collisions.)

Fun fact: the new Horizons's (redundant) processors are 12MHz MIPS R3000s.

http://blog.imgtec.com/mips-processors/mips-goes-to-pluto

I am really curious what it uses for storage. I am guessing something much more modern, with extensive redundancy.

It uses dual redundant 8 gigabyte flash storage.

"With the available radio telescope time on Earth, he says, it will take about 1.5 years for the spacecraft to successfully transmit the 60 gigabits of unique data it collected during the encounter."

Every time I hear about quantum entanglement I so desperately want instant communication to be in our near future.

0.159 kB/s

Quantum entanglement does not permit faster-than-light communication, even in theory.

https://en.wikipedia.org/wiki/No-communication_theorem

Sadly even if there is intelligent life out there around other stars we are terminally absolutely alone in the sense that we will never have anything even remotely resembling a conversation.

They're waiting for us to figure out how to warp space so that we can communicate via wormhole. They're not going to wait around for low bandwidth high latency comms. They're not scrubs.

You're assuming that other intelligent life has a lifespan similar to our own, and that our own lifespan will remain the same forever. Remove those assumptions and our galaxy gets a lot smaller even with radio communication and sub-light travel.

Well, faster than light communication would cut down on the latency, but wouldn't necessarily help with the bandwidth. The lightspeed delay to Pluto is "only" about twelve hours. The low transmission speed is mostly because the transmitter isn't very strong, and it's unbelievably far away, thus the signal is ridiculously weak.

That has far less to do with speed of light than with bitrates.

New Horizons apparently achieves about 1,268 bits/second. Crank that up to 100 megabits/s, and it would take only ten minutes. Plus the 4.5 hour ping lag.

> Every time I hear about quantum entanglement I so desperately want instant communication to be in our near future.

Sadly, that's not how that works...

In fairness, it's not like New Horizons will be doing much in that time. It's hopefully going to be visiting a Kuiper Belt object, but other than that it's got all the time in the world to transmit data.

It sucks to get confirmation quantum entanglement isn't what I thought, but the down votes into negative seems overkill!

It's not just about quantum entanglement, it's about confusing bandwidth and latency.

Hmm, the latency is 4.5 hours, the bandwidth average over 1.5 years is 0.159 kB/s.

Instant communication at low bandwidth would still be nice, they are two different ideas. If we had instant communication I would then expect bandwidth of it to improve over time.

0 latency, 0.159 kB/s this year, 0 latency 100 gB/s for the next launch in 10 years.

I should have been more clear in my thinking.

And every time I tell myself it'll happen, I keep being reminded that most of the theories we have right now suggest it won't.

https://en.wikipedia.org/wiki/No-communication_theorem

Meh. :(

It's a little jarring to me to see a result from Physics labelled a 'theorem'. It's clearly a provable mathematical consequence of a particular mathematical model, but to turn that theorem into a physical law you have to demonstrate that the mathematical model is a complete description of how reality works.

Is there a reason why they didn't try to put this probe into orbit around Pluto?

It will simply be traveling too fast, and Pluto is simply too small, for the probe to get into orbit.

For them to have arranged for it to slowly catch up with Pluto and get into orbit, I imagine the path would have taken decades if not hundreds of years. (Assuming the fuel capacities we have to work with.)

Looks like they have gone into some detail on a potential mission like this[1], appears that it would take 17 years, at least with this particular launch window Jupiter alignment.

[1] http://www.esa.int/gsp/ACT/doc/PRO/ACT-RPR-PRO-ISTS2004-Plut...

Just getting close after 7.5 billion km is pretty impressive.

I think it might not carry enough fuel for the orbit insertion.

Slightly longer answer: space is expensive, especially when you try to change your trajectory.

National Geographic and 5WGraphics have produced an infographic of 50 years of space missions. It's interesting to note the count by destination:

Moon: 72, Venus: 40, Mars: 38, Jupiter:8, Saturn: 5, Mercury: 2, Uranus: 1, Neptune: 1, and Pluto: 1.

A related observation is that Mars in the only planet inabited soley by robots.

These aren't unrelated facts.

For more detail see this post addressing the meme "Mars is the only knonw planet inhabited solely by robots". https://ello.co/dredmorbius/post/J7e5V-B-zHe2fNc6hScUXQ

What does it take to get a robotic mission onto a planet (or other solid body)?

1. It's got to be a solid body. That eliminates Jupiter, Saturn, Uranus, and Neptune, straight out.

2. You've got to be able to get there in the first place. Nearer bodies are generally easier to reach, so long as they're not too close to the Sun. It actually took as long to reach Mercury (about 6 years) as it typically does Jupiter, despite the fact that Jupiter is about 10 times further away by distance. Both these and other missions used gravitational assists to reduce fuel requirements, resulting in complex trajectories:

https://upload.wikimedia.org/wikipedia/commons/5/5e/MESSENGE... The Cassini-Huygens probe had a similarly complex trajectory: Earth, Venus x2, Earth, Jupiter, and Saturn. http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?ima...

To get to Pluto has taken New Horizons 9.5 years. That included a gravitational asssit from Jupiter. And on arrival, it's going to be trucking along at 49,600 km/h (30,800 mph). That's approaching the speed of the Chelyabinsk meteor (67,000 km/h, or about 41,750 mph).

3. You've got to be able either enter into orbit or slow down once you get to the destination. Gravity assists or aerobraking both help hugely, as they avoid the need to carry fuel, and the tyranny of the rocket equation (more below).

4. You've got to be able to land, softly, on the surface. Again, an atmosphere helps a lot. Or a nearby body and low gravity for a rocket landing (as in the Moon). Pluto's got low gravity, but is so far away we're travelling fast when we get there.

xkcd's Randall Munroe looked at what would be required to catch up with and return the Voyager I probe, similar in spirit to trying to deaccellerate using rockets on arriving at Pluto. It's not pretty: https://what-if.xkcd.com/38/

For more on delta-v budgets for various destinations: https://en.wikipedia.org/wiki/Delta-v_budget

Slowing down and speeding up are symmetrical, roughly speaking you'd need a rocket similar to the one used to launch New Horizons to put it into orbit around Pluto. So you'd need an enormous rocket to send all of that to Pluto, which is beyond our current technology and budget limits.

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