Rosetta catches dusty organics | Hacker News Reader

Rosetta catches dusty organics

blogs.esa.int

141 pointsokket35 comments

Just a few days left for Rosetta, you might want to mark the date in your calendar:

  On September 29, a rocket burn will essentially cancel out
  Rosetta's orbital motion around the comet, initiating a
  free fall from an altitude of 20 kilometers. The spacecraft
  will impact the comet at a speed of about 90 centimeters
  per second at 04:20 PDT / 07:20 EDT / 11:20 UTC / 13:20
  CEST, give or take 20 minutes.

http://www.planetary.org/blogs/emily-lakdawalla/2016/0909102...

(The rocket burn is on the 29th, the impact on the 30th, of course.)

See also ESA's FAQ explaining why they decided to end the mission this way.

http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rose...

TL;DR: as it ventures further and further away from Earth, it won't be able to transmit much useful information, and it's unlikely the instruments will survive until the comet comes back again; letting it descend onto the surface while it's still in useful range will give a lot of up-close data.

Is it possible the impact will affect trajectory of the comet?

From the FAQ:

  How fast will Rosetta impact the surface?

  One of the key features of the trajectory design is to
  minimise the spacecraft's relative velocity at impact. The
  current scenario predicts that the impact velocity will be
  around 90 cm/s, around walking pace. It is worth keeping in
  mind that Rosetta was not designed as a lander, and some of
  its appendages including the 32m-wide solar panels will be
  damaged by the impact. This energy dissipation will very
  likely ensure that the escape velocity will not be exceeded
  during any bounce, thus preventing Rosetta from returning
  to orbit after impact with Comet 67P/C-G.

http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rose...

(I read from this that it is highly unlikely that the comet trajectory is affected in a noticeable way by the impact. See also the answer from symmetricsaurus above. This would qualify as a good FAQ, IMHO.)

It's fascinating how brilliant this solution is. Let it slowly bounce on the comet, so that the rebounce velocity is very low, it doesn't affect the comet trajectory in any way, and they're collecting data during the slow descent. Nice.

Rosetta couldn't really affect the comet trajectory in a meaningful way, even if we wanted to. The comet has a mass of nearly 10 trillion kg, the orbiter is <3000 kg, and P = MV. It would need to have insane velocity to impart any meaningful momentum.

No, Rosetta is already in orbit around the comet. By the principle of conservation of momentum the impact will not change the total momentum of the system (comet plus spacecraft).

The changes in trajectory happens when the engines are used on the spacecraft.

Would this still hold true if Rosetta were commanded to slam into the comet hard enough for some of the impact debris to reach escape velocity? (Not trying to nitpick your argument, it certainly holds true for the soft landing case, but I'm curious how strong this axiom is)

Which means that Rosetta already affected the trajectory of the comet - when it entered orbit.

probably the same way a flea getting hit by a fastball affects the trajectory of the pitch

It will. The question is if it will at all be noticeable. Given the low mass and velocity of Rosetta, I'd say not by much.

For those wondering, 90 cm / s = ~ 2mph = 3.24kph

"Impact" seemed to imply a harder hit, but it should be a nice gentle landing.

3 KPH? will it continue working?

No. Not only because the antenna and solar panels will likely break, but Rosetta will receive a self-kill program initiated 10hrs prior to impact, which will shut off all systems on expected impact time. This is in part due to regulations regarding the deep space radio networks.

First time I'm hearing of regulations on deep space radio - is that to prevent SETI interference?

No. As far as I'm aware, there exist no regulations regarding SETI interference (mainly because this is a private endeavour and regulations would need strong international political support).

From the FAQ (http://m.esa.int/Our_Activities/Space_Science/Rosetta/Rosett...):

As soon as Rosetta hits the surface, its main systems will be turned off, including the attitude and control systems, as well as the main transmitter, the latter in order to meet regulations aimed at avoiding interference on deep space network communications channels.

Sorry, I have no further info on what these regulations are.

If Rosetta crashed but remained operational enough to keep an open connection but not enough to receive commands to close it, it would use up incredibly valuable resources on a highly resource-constrained network.

I don't really understand that. DSN antennas are highly directional because they have to be. If they don't aim directly at the asteroid -- and we're talking a tiny fraction of a degree of beamwidth -- they won't hear anything, even if they want to.

There is no conceivable risk of "jamming" the DSN.

I suppose it's not about "jamming" but rather "accidental overlap" with future trajectories, i.e. another mission may pass through the axis between DSN-station and comet and the signals will mix.

Be aware that the beam is conical, so even if the pointing is exact within a few fractions of a degree, the further away you are from the DSN-station, the wider is the coverage area of the beam (and the lesser the signal strength, of course).

https://en.wikipedia.org/wiki/NASA_Deep_Space_Network#Networ...

Can anyone comment on how significant this discovery is? Are we talking unprecedented or has this been hypothesized for a while? Are the conditions on such comets more conducive for organic molecule formation than the surface of a planet or large moon might be?

According to the article, they were expecting it:

From analyses of meteorites and laboratory simulations, the team was also expecting to identify a wide diversity of organic material in Comet 67P/C-G, ranging from very small molecules to heavy (or ‘high molecular weight’) organics.

Organic = https://en.wikipedia.org/wiki/Organic_compound

I doubt anyone would expect to find organically grown veggies on a comet. Not sure what you're trying to say. Isn't it pretty clear that they're referring to molecules containing carbon?

There was a related discussion recently where "organic" in an article was referring to life-forms. So it's good to clarify which organic is being discussed.

Of course, if they found microbes on a comet this would be a much bigger announcement.

I think that for a lot of people organic == life. I suspect he was pre-empting that.

Genuine question: How do we know the organic compounds seen by Rosetta do not come from Earth and were not brought by Rosetta itself?

From https://en.wikipedia.org/wiki/Rosetta_(spacecraft)#Design_an...

  Rosetta was built in a clean room according to COSPAR
  rules, but "sterilisation [was] generally not crucial since
  comets are usually regarded as objects where you can find
  prebiotic molecules, that is, molecules that are precursors
  of life, but not living microorganisms", according to
  Gerhard Schwehm, Rosetta's project scientist.

See also the Committee on Space Research (COSPAR) Target Categories:

https://en.wikipedia.org/wiki/Planetary_protection#Target_ca...

Usually spacecrafts like that are built in clean rooms and care is taken so they are sterilized when sent to space. I have no specific answer, though.

This will be especially true for instruments that are designed to find such compounds. It would be fairly embarrassing to send the probe into space, only to notice that apparently interplanetary space is full of organic compounds no one else has ever seen ...

That blurry something on the inner side of the lens turned out to be an ... ant?

“These particles have remained pristine and untouched for billions of years until they were released in the days or weeks before being ‘caught’ by COSIMA,"

I hope they will release the particles back into the wild once they are done with their analysis.

I'm not against releasing the particle...but any specific reason you hope they release them once back into the wild after?

Anyone could explain briefly what is the "stretch" theory or hypothesis that is mentioned in the heated comments section to the blog post?

I can't - and hell, I barely understand anything they say - but the style reminds me of how Asimov would picture an academic dialogue between two rivals.

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