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Founded January 1970
Julian Date: 24592545.18
2020-2021: LXXXVI
THE DAILY ASTRONOMER
Tuesday, February 9, 2021
Exploratorium XIX: Verona Rupes
*Location *
Verona Rupes on Miranda, a Uranian moon
*Time*
Now
Did you ever hear about Buridan's donkey? It is one of those
philosophical paradoxes that keep profound thinkers deeply engaged and
gainfully employed for decades. The idea is that a donkey that is both
hungry and thirsty is placed midway between a pile of hay and a pail of
water. Being both parched and ravenous, this bewildered beast of burden
should die of hunger and thirst because it is equidistant from both the
food and water and shouldn't be able to decide if it should eat or drink
first. Somehow, though, if someone managed to actually try this
experiment, the donkey would certainly choose either the water first or the
hay, depending if its hunger is of greater or lesser intensity than its
thirst. Or, maybe the donkey would simply walk toward whatever it sees
first. In reality there is always some subtle influence that perturbs any
perfect balance.
The Exploratorium literally has billions of options of how to spend any
given moment. That might seem a sublime state for the time-stuck and
gravity burdened, of course. However, when we make a choice as to how to
spend one minute, we forego innumerable other experiences we could have
otherwise chosen. Like a solitary charged particle trapped in the center
of a perfect circle of opposite charges, we should be suspended ghost -like
within the infinitude of all space-time coordinates, unable to incline
toward anything.
But, we're not suspended at all , because we exist in a virtual state. So,
let'sjump off a cliff. Specifically, we have decided to jump
off Verona Rupes, the highest known cliff (approximately 20 miles) in the
solar system. Don't fret if you've never heard of it. Verona Rupes is not
on Earth, but is instead on Miranda, a bitterly frigid ice moon of Uranus.
That image above imagines future astronauts standing atop Verona Rupes as
they prepare to dive off. Drawn by Erik Wernquist, this portrait is a
lovely, but inaccurate depiction of the first humans to descend down this
sheer ice facade. That will occur in 2287. We are taking the plunge in
2021. The word "plunge" might not be exactly apt, for we shall initially
descend quite lazily down toward the distant surface.
See? We are hardly moving now. One can ascribe this lethargic descent to
Miranda's low surface gravity. Out here, the moon is drawing us down at
an acceleration of 0.079 meters per second squared: (about 0.25 feet per
second squared). If you were to leap off Earth's tallest cliff (on Mount
Thor), you would plummet toward the ground at 9.8 meters per second squared
(or, 32 feet per second per second.) You would rapidly crash to terra
firma with a bone-pulverizing thud. Here, along Verona Rupes, we shall
be trapped in a 12 minute free fall that will eventually send us careening
into the unyielding ice at about 200 km/hour, a wallop that would prove
fatal were we not virtual.
You have certainly noticed that even though our initial descent was almost
comically slow, the acceleration is gradually, but inexorably, increasing
our speed. Notice also that this rugged little ice moon lacks any
atmosphere so we are descending vertically without any of that complex
turbulence one might experience when plunging through Earth's fluid
atmosphere. Falling through a fluid not only makes the free fall math a
complicated mess, but it also impedes the descent. Nothing is impeding
us as we waft gradually down toward the....
Ok, since now this would be the perfect time for a lot of cheap, tawdry
poetic passages pertaining to scintillating ice fields bejeweled by the
Sun's luster. Alas, since the point of this plummet is to discuss
astronomy, we can dispense with the bombast and explain that Miranda does
not resemble Earth's crystalline ice fields or glistening snow shrouds.
Out here around the seventh planet the Sun is quite faint. Remember that
Uranus is about 19 times farther from the Sun than Earth. Light
intensity falls off with the square of the distance. (So, for instance,
the Sun on a planet twice as far from the Sun as Earth would be a quarter
as bright.) Uranus receives about four watts per square meter of energy
from the Sun. Compare this meager portion to Earth's generous 1353 watts
per square meter allotment. We are now moving noticeably faster into a
gaping abyss of shadow.
Mind you, there are consolations! The stars above are exquisite: far
brighter, sharper than they appear on Earth. Again, blame the layers of
atmospheric gases that obscure the incoming star light. Out here I can
watch the behemoth Orion and attendant Canis Major poised like giants over
the distant ice peaks. So crisp are their stars they almost appear
tangible: three dimensional sparks that cast pock mark reflections off the
dark ice. Yes, we can see the same constellations Earth-watchers see
because the stars are so much farther away from us than the planets.
Earth's Orion is Uranus' Orion.
We've fallen far enough so that I must strain to look back and see the
apex I abandoned.
Oh, yes, we certainly can see Uranus! It is not a brilliant blue orb as
one finds when visiting those frauds at the planetarium. It is a mammoth
sphere cast in a subtle tint, reminiscent of a midnight tree canopy
rendered slightly luminous by a remote street light: just switch the color
from yellow to azure. Miranda is locked in a synchronous rotation with
Uranus so it always keeps its same side toward the planet, just as the moon
does toward Earth. Therefore, on our icy little moon, an observer would
either see the parent planet all the time or it would never appear at all.
Looming Gas Giant planet cast against a brilliant array of stars that look
as though they could be plucked from the night hollows like phosphorescent
berries. We are falling faster, ever faster toward the barely discernible
base of this, the solar system's highest cliff. We can see the faint, but
sharp, shadow we cast against the sheer cliff face. We know that within a
few moments, we will snap out of existence only to reemerge somewhere else
at some other time: astride the retreating Voyagers or cast into the star
fields of Andromeda or wherever else the mood might move us...as of now we
are about to crash onto Miranda in a cascade of dispersing virtual
particles...What better way to embrace non-being.
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