I did read the answers! In fact, it was from the answers that I chose my guess.

We are looking for a surface feature (#11) on an object in the Solar System (#1) that is not an asteroid or a satellite (#13). Therefore it must be on a planet, a dwarf planet or the Sun. A robotic explorer flew close to it (#12) and so it can’t be the Sun, while #3 rules out all the dwarf planets except Ceres. The feature can’t be seen from Earth with Earth-made optical equipment (#6) so it must be far away – hence it probably isn’t on Ceres. So it’s most likely on one of the planets Jupiter, Saturn, Uranus and Neptune. It’s not Jupiter’s Great Red Spot, which has been known for centuries (#8), while Saturn and Uranus have no prominent surface features that are well known. I therefore concluded that it was something on Neptune – and Voyager 2 discovered Neptune’s Great Dark Spot in 1989.

So it’s the wrong answer. But I did try and make an intelligent guess, not just a stab in the dark.

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You evidently missed this: "#14: No, the feature is not an atmospheric component of one of the four gas giant planets."

#11 ought exclude the gas giants - they don't have "geology" as commonly understood. #10 excludes Mars and #7 probably excludes Earth. #13 exludes moons and asteroids (persumably including Ceres - the IAU has artfully avoided giving an official definition of "asteroid", and the definition of "dwarf planet" doesn't say the body can't simultaneously be an asteroid, leaving one to suppose that Ceres is still one). #3 Excludes the Kuiper belt and all that riff-raff.

This would leave us with Venus, Mercury, or some silly interloper like a short-period comet or a Neptune trojan (arguably asteroids, arguably more like KBO's with orbital pretensions). Such interlopers may indeed have geology (sillyinterloperology?) of a sort, but known features are in desperately short supply. This strongly suggests Venus or Mercury.

#7 Suggests it's on Venus - surface features on Mercury could in principle be viewed by a terrestrial telescope. It just about could be a subsurface object like a masscon, but there can't be a lot of those known on Mercury, and if it were Arneb would probably be more definite regarding the rest of the visual spectrum.

That's about as much cognition I can manage right now. I'll leave it to someone else to ask an actual question.

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Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

Susannah, I didn't mean to be rude or condescending - but AndreasJ precisely laid out why your attempt couldn't possibly be right. I didn't count the question primarily because there are not so many attempts left, and an obviously unhelpful question could ruin any chances left to solve the riddle in time.

AndreasJ, I am totally in agreement with your reasoning reagarding the bodies that are left in the game, except for one point - have a look at the chapter "ground-based telescopic observations of Mercury" in the Mercury Wikipedia article...

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Non sunt multiplicanda entia praeter necessitatem.

Maybe I should have added my reasoning with my guess; then it wouldn’t have looked as if I was deliberately being “unhelpful” (which I assure you was absolutely no intention of mine whatsoever).

Well, I took “geologic feature” in #11 to mean an observable surface feature. And #14 only refers to “atmospheric component of one of the four gas giant planets” – it still does not rule out surface feature of one of the four gas giant planets. Hence I can say that my guess was still consistent with the answers – since the answers did not totally exclude the gas giants.

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Random Fact: Pell’s equation

The great dark spot is atmospheric, so it's excluded by #14 no matter how you interpret #11.


Having read the Wikipedia section Arneb indicated, I must confess I do not understand what he's whistling about.

__________________
Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

I thought the article made it clear that the probable invisibility of a surface feature in a telescope from Earth is not something that would favour Venus over Mercury.

Well, ask the question already!

Susannah - no intention on your part was implied. Promise. "Unhelpful" was only my way of saying your question wouldn't help you towards your goal of a solution.

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Non sunt multiplicanda entia praeter necessitatem.

I have to say I’m beginning find this game too expert-based for an amateur to cope with.

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Random Fact: Pell’s equation

Don't worry. You can't be worse than wrong and what can happen?

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Non sunt multiplicanda entia praeter necessitatem.

Very well. AndreasJ has narrowed it down to something on either Venus or Mercury (more likely the former). We still have 6 lives left. So I believe we can safely use up one of those lives on …

#15 Is it on Venus?

If the answer is “no”, then it must be on Mercury – so whatever happens, we will definitely be spending our last 5 lives on the correct planet.

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Random Fact: Pell’s equation

The I guess I overinterpreted your correction re: visibility from Earth - I took you as saying no visual 'scope could view it from Earth ever ever, not merely that current 'scopes aren't up to the task.

Anyway, Susannah asked a question, so I dont have to.

__________________
Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

# 1: Yes, it is in the Solar system.
# 2: No, I haven't seen it.
# 3: No, it is not further from the Sun than Neptune
# 4: No, it is not a natural satellite orbiting a planet.
# 5: No, it is not an asteroid.
# 6: I honestly don't know. It seems possible, but I don't know enough details to be sure. To be more helpful, no intrument currently in existence on the Earth could visualize it.
# 7: Yes, I am indeed looking for a portion of a celestial object instead of the entire object.
Jeff - I won't count your question, as I probably mislead you with my answer to # 6. I should correct myself: The object in question cannot be visualized by any visual intrument on the Earth itself (I don't know about other parts of the EM spectrum). The reason has to do with the answer to # 7.
# 8: No, the existence of the object was not known before 1970.
# 9: Yes, it was detected by a robotic explorer.
#10: No, it is not on Mars. (I dare say that with so many possibilities left and just 10 more questions, ticking off solar system bodies one by one may be an inefficient strategy).
#11: Yes, the feature is a geologic feature.
#12: Yes, the robotic explorer was indeed flying through space when it first detected the object.
#13: No the feature is neither on an asteroid nor on a natural satellite.
#14: No, the feature is not an atmospheric component of one of the four gas giant planets. Bonus: And neither is it an atmospheric component of any other planet. Remark: I think this was answered in #11. Geology (or Hermetology, Aphroditology, Areology, Plutology, Charonolgy...) isn't about atmospheres, it it?
#15: No, it is not on Venus.

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Is the feature also not on Mercury?



-- Jeff. in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

# 1: Yes, it is in the Solar system.
# 2: No, I haven't seen it.
# 3: No, it is not further from the Sun than Neptune
# 4: No, it is not a natural satellite orbiting a planet.
# 5: No, it is not an asteroid.
# 6: I honestly don't know. It seems possible, but I don't know enough details to be sure. To be more helpful, no intrument currently in existence on the Earth could visualize it.
# 7: Yes, I am indeed looking for a portion of a celestial object instead of the entire object.
Jeff - I won't count your question, as I probably mislead you with my answer to # 6. I should correct myself: The object in question cannot be visualized by any visual intrument on the Earth itself (I don't know about other parts of the EM spectrum). The reason has to do with the answer to # 7.
# 8: No, the existence of the object was not known before 1970.
# 9: Yes, it was detected by a robotic explorer.
#10: No, it is not on Mars. (I dare say that with so many possibilities left and just 10 more questions, ticking off solar system bodies one by one may be an inefficient strategy).
#11: Yes, the feature is a geologic feature.
#12: Yes, the robotic explorer was indeed flying through space when it first detected the object.
#13: No the feature is neither on an asteroid nor on a natural satellite.
#14: No, the feature is not an atmospheric component of one of the four gas giant planets. Bonus: And neither is it an atmospheric component of any other planet. Remark: I think this was answered in #11. Geology (or Hermetology, Aphroditology, Areology, Plutology, Charonolgy...) isn't about atmospheres, it it?
#15: No, it is not on Venus.
#16: No, it is not not on Mercury - Yes, it is on Mercury...

Jeff, are you content with how things turned out re. ## 6 and 7? Mercury is visible during the next two weeks, but I couldn't be sure if the feature was actually in view (=on the hemisphere facing Earth and illuminated), and anyway, it is quite certainly too small to see from here, much less for an amateur.

__________________
Non sunt multiplicanda entia praeter necessitatem.

Awww, I'm disappointed. I was hoping it was on Earth. You had
not yet ruled out Earth as far as I could tell, but everyone seemed
to be ignoring Earth as a possibility. Even better would have
been something between planets, but the number of geological
features not on planets and not on asteroids is mighty small!

Yes, it looks like your answers are almost all very reasonable. The
one little bit that I think might be excessively misleading was your
parenthetical disclaimer about the feature possibly being detectible
in "other parts of the EM spectrum".

I asked question #6 about whether I would be able to see the
"object" from Minneapolis in the next two weeks because I thought
it might be something on the Moon, but either on the farside or too
small to see. Your answer suggested to me that it might be visible
to a spacecraft but not an observer on Earth either because of the
part of the spectrum it was seen in, or because it was too big to
be seen from close-up, so a view from a height was required.

I asked question #11, whether an average Joe would consider the
thing to be geological because I thought it might be something like
the Van Allen belts, also discovered by a robotic space probe.

As a suggestion to the others-- neither a question nor a guess--
I think it's a pretty good bet that the feature was discovered by
MESSENGER, not by Mariner 10. I'm not at all familiar with the info
recently returned by MESSENGER, so I'll let someone else take it.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

Hey, I did not! I noted that not being visible from Earth made it unlikely to be on Earth. (It's also questionable whether terrestrial features count as "astronomical".)

Now, I'm trying to think of a good question to nail it down ...

__________________
Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

Jeff - I was circumspect about the "rest of the EM spectrum because I couldn't (and frankly, didn't bother to ) exclude radar.

AndreasJ - without wanting to be overly pessimistic or dismissive of y'all's skills, I think that will be next to impossible. So here is an

extension to 25 questions.

That should suffice, given sufficiently evil questions .

__________________
Non sunt multiplicanda entia praeter necessitatem.

#17: Is it a volcano?

__________________
- Learn a lot teaching others.

# 1: Yes, it is in the Solar system.
# 2: No, I haven't seen it.
# 3: No, it is not further from the Sun than Neptune
# 4: No, it is not a natural satellite orbiting a planet.
# 5: No, it is not an asteroid.
# 6: I honestly don't know. It seems possible, but I don't know enough details to be sure. To be more helpful, no intrument currently in existence on the Earth could visualize it.
# 7: Yes, I am indeed looking for a portion of a celestial object instead of the entire object.
Jeff - I won't count your question, as I probably mislead you with my answer to # 6. I should correct myself: The object in question cannot be visualized by any visual intrument on the Earth itself (I don't know about other parts of the EM spectrum). The reason has to do with the answer to # 7.
# 8: No, the existence of the object was not known before 1970.
# 9: Yes, it was detected by a robotic explorer.
#10: No, it is not on Mars. (I dare say that with so many possibilities left and just 10 more questions, ticking off solar system bodies one by one may be an inefficient strategy).
#11: Yes, the feature is a geologic feature.
#12: Yes, the robotic explorer was indeed flying through space when it first detected the object.
#13: No the feature is neither on an asteroid nor on a natural satellite.
#14: No, the feature is not an atmospheric component of one of the four gas giant planets. Bonus: And neither is it an atmospheric component of any other planet. Remark: I think this was answered in #11. Geology (or Hermetology, Aphroditology, Areology, Plutology, Charonolgy...) isn't about atmospheres, it it?
#15: No, it is not on Venus.
#16: No, it is not not on Mercury - Yes, it is on Mercury...
#17: No, it is not a volcano

__________________
Non sunt multiplicanda entia praeter necessitatem.

Is it a crater or other impact structure?

__________________
Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

Andreas,

You would include rays as impact "structures", wouldn't you?

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

But if it was on Earth, it would be in the geography quiz, wouldn’t it? Since it’s in an astronomy quiz, common sense would dictate that the thing in question must be on a non-Terrestrial body.

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Random Fact: Pell’s equation

I would include ejecta rays, yes.

__________________
Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

If yes, this new map may help from here.

__________________
Lighten up! This is a stellar board!

What an awesome range of different crater types in those images!
The multi-ring crater just below 30 deg N near 120 deg E is especially
impressive.

Is the feature one of the 15 craters named on the map George linked?

Edit: I should have waited for the answer to Andreas's question....

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

# 1: Yes, it is in the Solar system.
# 2: No, I haven't seen it.
# 3: No, it is not further from the Sun than Neptune
# 4: No, it is not a natural satellite orbiting a planet.
# 5: No, it is not an asteroid.
# 6: I honestly don't know. It seems possible, but I don't know enough details to be sure. To be more helpful, no intrument currently in existence on the Earth could visualize it.
# 7: Yes, I am indeed looking for a portion of a celestial object instead of the entire object.
Jeff - I won't count your question, as I probably mislead you with my answer to # 6. I should correct myself: The object in question cannot be visualized by any visual intrument on the Earth itself (I don't know about other parts of the EM spectrum). The reason has to do with the answer to # 7.
# 8: No, the existence of the object was not known before 1970.
# 9: Yes, it was detected by a robotic explorer.
#10: No, it is not on Mars. (I dare say that with so many possibilities left and just 10 more questions, ticking off solar system bodies one by one may be an inefficient strategy).
#11: Yes, the feature is a geologic feature.
#12: Yes, the robotic explorer was indeed flying through space when it first detected the object.
#13: No the feature is neither on an asteroid nor on a natural satellite.
#14: No, the feature is not an atmospheric component of one of the four gas giant planets. Bonus: And neither is it an atmospheric component of any other planet. Remark: I think this was answered in #11. Geology (or Hermetology, Aphroditology, Areology, Plutology, Charonolgy...) isn't about atmospheres, it it?
#15: No, it is not on Venus.
#16: No, it is not not on Mercury - Yes, it is on Mercury...
#17: No, it is not a volcano
#18: No, it is not an impact structure (and yes, I would have included rays and ejecta formations in that definition)

Susannah - I wouldn't have felt compelled to exclude objects on the Earth in this quiz, but as you see, I am not that evil.

__________________
Non sunt multiplicanda entia praeter necessitatem.

Is it an escarpment (rupes)?

__________________
Science is like sex. Sometimes something useful comes out, but that is not the reason we are doing it.
-- Richard Feynman

Good one.

I just noticed this one.

__________________
Lighten up! This is a stellar board!

# 1: Yes, it is in the Solar system.
# 2: No, I haven't seen it.
# 3: No, it is not further from the Sun than Neptune
# 4: No, it is not a natural satellite orbiting a planet.
# 5: No, it is not an asteroid.
# 6: I honestly don't know. It seems possible, but I don't know enough details to be sure. To be more helpful, no intrument currently in existence on the Earth could visualize it.
# 7: Yes, I am indeed looking for a portion of a celestial object instead of the entire object.
Jeff - I won't count your question, as I probably mislead you with my answer to # 6. I should correct myself: The object in question cannot be visualized by any visual intrument on the Earth itself (I don't know about other parts of the EM spectrum). The reason has to do with the answer to # 7.
# 8: No, the existence of the object was not known before 1970.
# 9: Yes, it was detected by a robotic explorer.
#10: No, it is not on Mars. (I dare say that with so many possibilities left and just 10 more questions, ticking off solar system bodies one by one may be an inefficient strategy).
#11: Yes, the feature is a geologic feature.
#12: Yes, the robotic explorer was indeed flying through space when it first detected the object.
#13: No the feature is neither on an asteroid nor on a natural satellite.
#14: No, the feature is not an atmospheric component of one of the four gas giant planets. Bonus: And neither is it an atmospheric component of any other planet. Remark: I think this was answered in #11. Geology (or Hermetology, Aphroditology, Areology, Plutology, Charonolgy...) isn't about atmospheres, it it?
#15: No, it is not on Venus.
#16: No, it is not not on Mercury - Yes, it is on Mercury...
#17: No, it is not a volcano
#18: No, it is not an impact structure (and yes, I would have included rays and ejecta formations in that definition)
#19: Yes, it is an escarpment (rupes).

Jeff - I overlooked your question. Really. So let's pretend you didn't ask

__________________
Non sunt multiplicanda entia praeter necessitatem.

#20 Is it named after a ship of Captain Cook?

__________________
 
Did You Know?

Random Fact: Pell’s equation

# 1: Yes, it is in the Solar system.
# 2: No, I haven't seen it.
# 3: No, it is not further from the Sun than Neptune
# 4: No, it is not a natural satellite orbiting a planet.
# 5: No, it is not an asteroid.
# 6: I honestly don't know. It seems possible, but I don't know enough details to be sure. To be more helpful, no intrument currently in existence on the Earth could visualize it.
# 7: Yes, I am indeed looking for a portion of a celestial object instead of the entire object.
Jeff - I won't count your question, as I probably mislead you with my answer to # 6. I should correct myself: The object in question cannot be visualized by any visual intrument on the Earth itself (I don't know about other parts of the EM spectrum). The reason has to do with the answer to # 7.
# 8: No, the existence of the object was not known before 1970.
# 9: Yes, it was detected by a robotic explorer.
#10: No, it is not on Mars. (I dare say that with so many possibilities left and just 10 more questions, ticking off solar system bodies one by one may be an inefficient strategy).
#11: Yes, the feature is a geologic feature.
#12: Yes, the robotic explorer was indeed flying through space when it first detected the object.
#13: No the feature is neither on an asteroid nor on a natural satellite.
#14: No, the feature is not an atmospheric component of one of the four gas giant planets. Bonus: And neither is it an atmospheric component of any other planet. Remark: I think this was answered in #11. Geology (or Hermetology, Aphroditology, Areology, Plutology, Charonolgy...) isn't about atmospheres, it it?
#15: No, it is not on Venus.
#16: No, it is not not on Mercury - Yes, it is on Mercury...
#17: No, it is not a volcano
#18: No, it is not an impact structure (and yes, I would have included rays and ejecta formations in that definition)
#19: Yes, it is an escarpment (rupes).
#20: No, it is not named after a ship by James Cook.

Uh-oh, I feel your hot breath in my neck...

__________________
Non sunt multiplicanda entia praeter necessitatem.