- 4335
- MARS - was
there water there? Evidence of ancient
lake sediments at the base of Mars' Jezero crater offer new hope for finding
traces of life in samples collected by NASA's Perseverance rover. What about Venus? Did it have oceans?
-------------------------- 4335
- MARS - was
there water there?
-
- “Perseverance rover” found evidence of
ancient lake sediments at the base of Mars' Jezero Crater offering new hope for
finding traces of life in samples collected.
-
- Perseverance touched down on Feb. 18, 2021
inside the Red Planet's 28-mile-wide Jezero Crater, which is believed to have
once hosted a large lake and river delta. The rover has been scouring the
crater in search of signs of past life and collecting and caching dozens of
samples along the way for a possible future return to Earth.
-
- Using the rover's “Radar Imager for Mars'
Subsurface Experiment” instrument,
researchers from the University of California, Los Angeles and the University
of Oslo revealed new clues about how sediment layers formed over time on the
crater floor.
-
- As Perseverance travels across the surface
of Mars, the RIMFAX instrument sends radar waves downward at 4-inch
(10-centimeter) intervals and measures pulses reflected from depths of about
65.6 feet (20 meters) below the surface to create a subsurface profile of the
crater floor.
-
- The RIMFAX data showed evidence of sediment
deposited by water that once filled the crater. It's possible that microbial
life could have lived in the crater at this time and, if such life existed on
Mars, sediment samples from this area would contain signs of their remains.
-
- Two distinct periods of deposition
occurred, creating layers of sediments on the crater floor that appear regular
and horizontal, much like strata layers seen on Earth. Fluctuations in the
lake's water levels caused some of the sediment deposits to form an enormous
delta, which Perseverance traversed between May and December 2022.
-
- The radar measurements also show an uneven
crater floor below the delta, which is likely due to erosion before sediments
were first deposited. After, as the lake dried up over time, the sediment
layers in the crater were eroded, forming the geologic features visible on the
Martian surface today.
-
- The changes preserved in the rock record
are driven by large-scale changes in the Martian environment.
-
- Looking at the next p;anet in the other
direction we hope to learn why Venus died.
Venus is only slightly smaller than the Earth. But for this planet's heat has betrayed it.
The planet is now wrapped in suffocating layers of a poisonous atmosphere made
of carbon dioxide and sulfuric acid.
-
- The pressures on the surface reach almost
100 times the air pressure at Earth’s sea level. The average temperatures are
over 700 degrees Fahrenheit, more than hot enough to melt lead, while the
deepest valleys see records of over 900 degrees.
-
- Like Mars, we suspect that Venus also once
hosted a thinner, balmier atmosphere and a surface replete with liquid water
oceans. The reasoning here is a little more tenuous than for Mars. The thinking is that both Venus and Earth
formed in a roughly similar fashion, in roughly the same orbits with roughly
the same material. Thus we should have been born with roughly the same amount
of water.
-
- Like Earth, most of that water would have
been chemically bound up in rock, buried deep in the mantle. But some of it may
have leeched to the surface or been delivered by hosts of water-rich comets
shortly after formation, building up a supply on the surface, once again
stabilized by a thick atmosphere.
-
- What doomed Venus was not any fault of its
own, but our own treacherous Sun. As stars age they gradually brighten. Day by
day it’s imperceptible, but over the course of millions of years it completely
changes the character of a star. Billions of years ago our Sun’s habitable zone
was shifted inwards compared to where it rests now, but with increased
brightness comes increased heat, and
that habitable zone steadily creeps outwards over time.
-
- Did Venus ever host life? Temperatures on the surface make exploration
nearly impossible. But it’s likely that it had water and a rich atmosphere, the
basic ingredients were there. But if life did gain a foothold it did not last
long. As our Sun aged, Venus got warmer and warmer. On a warmer planet, more
water exists as vapor in the atmosphere than as liquid on the surface.
-
- Venus reached a tipping point. With too much
water vapor, the atmosphere of Venus became too good at trapping the heat
radiating from the surface. That radiation could not penetrate the haze and
make into space, but instead was ensnared within the atmosphere itself, heating
it up.
-
- Venus entered a feedback loop, dumping more
heat into the atmosphere, which boiled the oceans into more vapor, which
increased the temperatures, and so on. First the shallow lakes and streams were
gone, then came the deeper oceans, until every scrap of water was blowing in
the winds of the atmosphere.
-
- With its proximity to the ever-brightening
Sun, the water vapor did not last long. Solar radiation pummeled it,
disassociating its chemical bonds and sending the oxygen and hydrogen flying
away beyond our solar system.
-
- If Venus had plate tectonics like the Earth,
then this is where that process came to end. With no water to act a lubricant,
the great slow grinding of the plates seized up, locking the crust in place.
This constant churning acts as a natural sink for carbon: the carbon dioxide
binds to rocks which get pulled deep into the mantle, preventing too much
carbon from building up in the atmosphere.
-
- But without the cleansing effect of plate
tectonics, carbon dioxide levels rose to dangerous heights, its own ability to
absorb radiation from the surface choking off any remaining hope for rescuing
the planet. Eventually the atmosphere would pile upon itself until it reached
its present swollen size.
-
- As our Sun aged, Venus strangled
itself. Venus is not alone in sharing
that fate, for the Sun has not yet reached its final days. It continues to
brighten, bringing more warmth to the solar system day by day, its habitable
zone steadily inching outwards with every passing year.
-
- At some point, approximately 500 million
years from now, Venus will not be alone, The Earth’s oceans will boil, our
continents will halt their ancient motion, and we will finally be twins with
our sister: dead, lifeless, and strangling on our own bloated atmosphere. This will definitely end our coffee club.
-
-
January 31, 2023 MARS - was
there water there? 4335
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--- to:
------
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------ “Jim Detrick” -----------
--------------------- --- Wednesday, January 31,
2024
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